The incidence and prevalence of firearm-related homicide in the United States make headlines daily. As a result, an epidemic of penetrating injuries is on the rise. Specifically, foreign bodies such as bullets and shrapnel are usually left inside the human body due to penetrating injuries, unless they are in close proximity to vital structures. We present a case of a bullet within the right atrial chamber of the heart, which was successfully removed by a minimally invasive endovascular approach. According to the Organization for Economic Cooperation and Development, homicide rates are seven times higher in the United States compared to other high-income countries, driven by a firearm-related homicide rate that is 25.2 times higher than the next leading country . In 2016As gun violence has become an expanding and alarming issue in the United States, the management of gunshot-induced trauma has also become a common scenario for physicians. Likewise, the increasing amount of gunshot-induced trauma has allowed for unique case-dependent scenarios, leading to specifically tailored management of these patients as dictated by their clinical presentations. The following case will demonstrate the minimally invasive interventional management of a gunshot-induced trauma that was necessary for avoiding damage to the patient’s vital surrounding structures.We present the case of a 27-year-old African American male who was shot with a 9 mm handgun during an attempted home invasion and burglary. An initial axial non-contrast computed tomography (CT) of the chest and abdomen was done that showed a bullet found anterior to the abdominal midline. The bullet had ricocheted off of the T12 vertebral body and penetrated the inferior vena cava (IVC) . The interventional radiology team agreed to proceed with the extraction, and the patient was brought to special procedures. The patient’s right neck was prepared and draped in a sterile fashion to initiate venous access into the IJV. Using ultrasound guidance, access was obtained into the right IJV using a micropuncture kit. Through the micropuncture sheath, a Benson wire was advanced into the right IJV, superior vena cava (SVC), and ultimately the IVC. A 10 cm by 11 cm bright tip sheath was then advanced over the Benson wire, into the right IJV. A 12 mm by 20 mm snare device was advanced over a 6 French sheath into the right atrium. Ultimately, the bullet was snared with tension placed on the ensnare device, which lassoed the bullet against the guiding sheath Figure .The serrated edges of the bullet made the removal difficult once snared, and numerous attempts to reposition the bullet were made to allow for preservation of the surrounding structures. The bullet was then retrieved once it was certain to have a clear path for removal out of the right atrium, SVC, and right IJV Figure .A venogram of the proximal-most aspect of the right IJV as shown in Figure Surgical incision and cut down of the right IJV inferior to the percutaneous access site was conducted in order to provide a controlled exit site for the bullet. Vessel loops were placed around the right IJV superior and inferior to the incision. After the surgical incision, control of bleeding, and evacuation of blood, the bullet was identified Figure .The snare device and vascular sheath were removed, and a multi-layer surgical closure of the right IJV was performed.The rise of firearm-related homicide in the United States has led to the increased management of gunshot wound traumas. Furthermore, the patient presented represents an age group population for which firearm-related injury is highly prevalent. From patient-to-patient, gunshot trauma is managed based on the case scenario. It is not uncommon for penetrating injury to be managed by surgical intervention, especially if the patient is hemodynamically unstable . HoweverThere have been documented cases of peripheral bullet embolization from the extremities to the right heart that have resulted from penetrating gunshot wound traumas . The litIn this case, an intuitive surgical intervention was initially indicated for gunshot trauma, leading to the clamping of the IVC. The bullet was not indicated for removal, as doing so would have caused further damage to the surrounding structures and possible decompensation of the patient. However, the post-surgical chest x-ray and CT confirmed that the bullet had migrated from the patient’s IVC to the right atrium, requiring further discussion of management from the surgical teams. In an attempt to remove the bullet embolus, interventional radiology used a method for extraction which also preserved the patient’s myocardial tissue and prevented any other damage to the surrounding structures.Penetrating gunshot trauma is on the rise with the increasing amount of firearm-related homicide in the United States. Gunshot-related trauma affects certain age groups more prolifically than others. This case demonstrates a successful minimally invasive method for extraction of a bullet embolism that migrated from the patient’s IVC to the right atrium. Snare extraction of a bullet embolus found in the right atrium preserves the patient’s myocardial tissue and surrounding structures by avoiding invasive surgical intervention.


The last quartile of maintenance-related accidents occurred after 60 flight-hours following maintenance and inspection. We then examined the “physics of failures” underlying maintenance-related accidents and analyzed the prevalence of different types of maintenance errors in helicopter accidents. We found, for instance, that the improper or incomplete (re)assembly or installation of a part category accounted for the majority of maintenance errors with 57% of such cases, and within this category, the incorrect torquing of the B-nut and incomplete assembly of critical linkages were the most prevalent maintenance errors. We also found that within the failure to perform a required preventive maintenance and inspection task category, the majority of the maintenance programs were not executed in compliance with federal regulations, nor with the manufacturer maintenance plan. Maintenance-related accidents are particularly hurtful for the rotorcraft community, and they can be eliminated. This is a reachable objective when technical competence meets organizational proficiency and the collective will of all the stakeholders in this community. We conclude with a set of recommendations based on our findings, which borrow from the ideas underlying the defense-in-depth safety principle to address this disquieting problem.In this work, we establish that maintenance and inspection are a risk factor in helicopter accidents. Between 2005 and 2015, flawed maintenance and inspection were causal factors in 14% to 21% of helicopter accidents in the U.S. civil fleet. For these maintenance-related accidents, we examined the incubation time from when the maintenance error was committed to the time when it resulted in an accident. We found a significant clustering of maintenance accidents within a short number of flight-hours after maintenance was performed. Of these accidents, 31% of these accidents occurred within the first 10 flight-hours. This is reminiscent of infant mortality in reliability engineering, and we characterized it as  As a result, unlike the situation with fixed-wing aircraft, lift generation is not contingent on the forward motion of the vehicle. The consequence of this is that several new flight regimes are enabled by this particular design choice, including hovering, vertical flight, and translational flight in directions  that are beyond the flight envelope of fixed wings. These flight regimes have made the helicopter indispensable for many civilian and military applications, from medical evacuation to law enforcement and close air support to mention a few.The fundamental feature of a helicopter’s design, a rotating the wing raises a host of design and operational challenges and complexities, including issues related to vibrations and wear-out of a variety of components on the helicopter. The consequence of this is that maintenance and inspection are particularly crucial for helicopters for their continued airworthiness. In this work, we examine helicopter maintenance and inspection and their association with helicopter accidents. To place this work in proper context, some background is warranted.By the same token however, Helicopters have a poor safety track record and little progress has been recorded in the last decade, at least in their fatal accident rates. The present work is part of a larger effort that focuses on the epidemiology of helicopter accidents. Its aim is to provide a better understanding of helicopter accidents and to identify possible blind spots and important areas for different stakeholders to focus their attention and resources for accident prevention. The end-objective is to contribute toward improving the safety track record of helicopters, and ultimately to reduce the burden of injuries, fatalities, and financial losses due to helicopter accidents. In a previous work, we examined trends, rates, and factors associated with helicopters accidents . We contAt an aggregate level, we found that the fatal accident rate of U.S. civil helicopters has averaged 0.7 fatal accidents per 100,000 flight-hours since 2005, and no statistically significant improvement has occurred since then. Similarly, we found that the total accident rate has averaged about 4.8 accidents per 100,000 flight-hours;Helicopters have a 17.3 times or 1,730% the risk of fatal accidents of passenger cars in the U.S. (based on the size of the respective fleets). This is a staggering result and it provides a benchmark for appreciating the safety record of helicopters;Helicopter accident rates vary by number of main rotor blades, by engine type, and by number of engines (when controlling for each of the other factors). For instance, the 2-bladed (2B) reciprocating helicopters have an accident rate 1.31 times that of the 2B turboshaft. This risk ratio increases to 1.56 when comparing the 3B reciprocating with the 3B turboshaft helicopters;We noted that these findings deserve careful attention and can help operators and regulators better target their prevention efforts for more effective safety interventions. Additional details can be found in .pilot errors, and most of the rest—unknown causes excluded—to airworthiness causes, which include failure through fatigue, corrosion, or wear of components such as the power plant, rotor, or transmission .Part 43, which is referenced in §91.405(d), provides a detailed discussion of maintenance and inspection requirements for specific equipment and aircraft parts. Within Subpart E of Part 91, §91.409 entitled “Inspections” covers some of the main issues of interest to this work.(a) Except as provided in paragraph (c) of this section, no person may operate an aircraft unless, within the preceding 12 calendar months, it has had -(1) An annual inspection in accordance with part 43 of this chapter and has been approved for return to service by a person authorized by § 43.7 of this chapter; or(2) An inspection for the issuance of an airworthiness certificate in accordance with part 21 of this chapter […](b) Except as provided in paragraph (c) of this section, no person may operate an aircraft carrying any person […] unless within the preceding 100 hours of time in service the aircraft has received an annual or 100-hour inspection and been approved for return to service in accordance with part 43 of this chapter […].Some exceptions apply, as alluded to in the opening sentence of §91.409. Their details are outside the scope of our work . However, one exception to the entries (a) and (b) is important to note. It relates to the possible substitution of the Annual and 100-hour inspections by Progressive Inspection, described next:(d) Progressive inspection. Each registered owner or operator of an aircraft desiring to use a progressive inspection program […] shall provide -(1) A certificated mechanic holding an inspection authorization, a certificated airframe repair station, or the manufacturer of the aircraft to supervise or conduct the progressive inspection;(2) A current inspection procedures manual available and readily understandable to pilot and maintenance personnel containing, in detail -(i) An explanation of the progressive inspection, including the continuity of inspection responsibility, the making of reports, and the keeping of records and technical reference material;(ii) An inspection schedule, specifying the intervals in hours or days when routine and detailed inspections will be performed and including instructions for exceeding an inspection interval by not more than 10 hours while en route and for changing an inspection interval because of service experience; […];The frequency and detail of the progressive inspection shall provide for the complete inspection of the aircraft within each 12 calendar months and be consistent with the manufacturer's recommendations, field service experience, and the kind of operation in which the aircraft is engaged. […].(1) the 100-hour, (2) the Annual, and two types of progressive programs: (3) the progressive also known as the Approved Aircraft Inspection Program (AAIP), and (4) the Continuous Airworthiness Maintenance Program (CAMP). There is little difference between the 100-hour and the Annual, except that the latter requires a technician with an Inspection Authority (IA) to conduct. Whereas the 100-hour can be conducted by any qualified technician, typically an Airframe and Powerplant (A&P) mechanic. An AAIP can be done in lieu of the 100-hour and the Annual, and it contains the same inspection procedures, the only difference being that they are spread over time to minimize downtime given the utilization profile of the rotorcraft  suddenly descend rapidly into a densely populated residential area. Descent rates […] were consistent with an autorotation. A post-impact fire consumed the cabin and main fuselage of the helicopter.Immediate cause: External examination of the engine at the accident site revealed that the fuel inlet union that connected to the fuel injection manifold and provided fuel from the hydro-mechanical unit to the combustion section had become detached from the boss on the compressor case. The two attachment bolts and associated nuts were not present on the union flange nor were they located within the helicopter wreckage debris. Separation of the fuel inlet union from the fuel injection manifold interrupted the supply of fuel to the engine and resulted in a loss of engine power. Post-accident engine runs performed with an exemplar engine showed that, with loose attachment bolts and nuts, the union initially remained installed and fuel would not immediately leak. As the engine continued to operate, the loose nuts would progressively unscrew themselves from the bolts. With the bolts removed, the union would ultimately eject from the boss, and the engine would lose power due to fuel starvation.Maintenance and inspection: The repair station technician disassembled [the accident engine], replaced the fuel injection manifold, and then reassembled the engine. This work required that the fuel inlet union be removed and reinstalled. It is likely that the technician did not tighten the bolts and nuts securing the union with a torque wrench and only finger tightened them. […]. The repair station technician was serving as both mechanic and inspector, and he inspected his own work.Conclusion: The National Transportation Safety Board determines the probable cause(s) of this accident as follows: The repair station technician did not properly install the fuel inlet union during reassembly of the engine; the operator’s maintenance personnel did not adequately inspect the technician's work; and the pilot who performed the post-maintenance check flight did not follow the helicopter manufacturer's procedures. Also causal were the lack of requirements by the Federal Aviation Administration, the operator, and the repair station for an independent inspection of the work performed by the technician.This case brings out a host of important issues, from the regulatory and organizational shortcomings in the causal chain of this accident to the technical, immediate factor leading to it, that is, the improper installation and torquing of the fuel inlet nuts, which in turn led to fuel starvation and loss of engine power. This case clarifies one such failure mechanism: in the vibrating environment of the helicopter in operation, the loose nuts progressively unscrewed themselves. The incubation time in this case, one flight-hour, was therefore contingent on several stochastic factors, the extent to which the nuts were improperly torqued and the intensity of vibration in this particular helicopter.This accident occurred on January 1, 2014 in Boulder City, NV, less than one flight-hour after maintenance and inspection were performed on the helicopter (Eurocopter EC 130 B4). No fatalities resulted from this accident. We provide next a brief description of the accident.Phenomenology of the accident: During a post-maintenance operational check flight and while on final approach for landing, the fuel pressure indicator light illuminated, and the engine “flamed out.” The pilot lowered the collective to initiate an autorotation; however, due to the low altitude and airspeed, the helicopter subsequently landed hard and rolled over.Maintenance and inspection: During a post-accident examination of the wreckage, a main fuel supply line B-nut fitting was found without the safety wire, and the nut was loose when turned by hand. Before the accident flight, the line had been disconnected during a task to replace the bidirectional suspension cross-bar assembly, and the accident flight was the first flight since the task was performed. According to the non-certificated maintenance technician who performed the task, the line was removed to defuel the fuel tank, which was contrary to manufacturer’s maintenance manual instructions.Conclusion: A loss of engine power due to fuel starvation as a result of the non-certificated maintenance technician’s failure to properly tighten and safety wire a B-nut fitting. Contributing to the accident was the maintenance technician’s failure to follow the manufacturer’s maintenance manual instructions.This accident is similar to the previous one. It highlights three violations as well as significantly poor training and lack of oversight: a non-certified maintenance individual performing this critical task, non-compliance with the manufacturer’s instruction for de-fueling, and most importantly the incorrect and incomplete installation of the B-nut. This reflects a considerably poor safety culture at all levels in this organization. The B-nut is standard terminology for nuts used to connect fluid lines. It is a simple component, but it provides a critical function as a reliable seal in plumbing systems on aircraft and rotorcraft. It is sometimes connected and disconnected during maintenance and inspection on helicopters, and perhaps its simplicity lulls some individuals into handling it casually, “finger tightening it” instead of properly torquing it (at the manufacturer’s specification) and wire-securing it. We have found this to be a recurrent failure mechanism in maintenance accidents.The accident occurred on November 9, 2013 in Shreveport, LA, less than one flight-hour after maintenance and inspection were performed on the helicopter . Three individuals were injured in the accident. The following are short snippets from the accident report:Phenomenology of the accident: The helicopter departed on a local maintenance test flight to perform a hover test. The pilot flew the helicopter toward a nearby field to perform the test and then heard a “pop,” and the helicopter subsequently began to spin. The pilot attempted to regain control of the helicopter using the anti-torque pedals, but they were ineffective. […]. The helicopter landed hard and rolled on its right side.Immediate cause: Examination of the wreckage found that the anti-torque pedals had separated from the anti-torque levers. The attachment hardware was not located in the wreckage or the surrounding area. Neither the anti-torque pedals nor the lever attachment holes displayed elongation, which is consistent with the hardware bolts not being in place at the time of impact.Maintenance and inspection: A review of maintenance logbooks revealed that a mechanic had conducted maintenance on the anti-torque pedals before the accident flight. After the accident, a parts bag containing bolts similar to the bolts needed to secure the anti-torque pedals was found in the maintenance facility where the maintenance was performed. Based on the evidence, it is likely that the mechanic reinstalled the anti-torque pedals without the required attachment hardware, which allowed the anti-torque pedals to separate from the anti-torque levers during flight and led to the loss of helicopter control.Conclusion: The National Transportation Safety Board determines the probable cause(s) of this accident as follows: The mechanic's improper installation of the anti-torque pedals, which resulted in an in-flight loss of helicopter control.This accident highlights a functionally different failure mechanism than the previous two cases, namely the loss of (yaw) control of the helicopter instead of loss of engine power leading to the accident. As the pilot activated the anti-torque pedals, his action had no effect on the tail rotor pitch link since the mechanic failed to connect the pedals to the anti-torque levers. Underlying the maintenance error however is the same problem as in the previous cases, namely the incorrect/incomplete reassembly of a critical part.The accident occurred on March 27, 2007 in Ponte Verde Beach, FL, one flight-hour after maintenance and inspection were performed on the helicopter (Robinson R44 II). Two individuals were killed in the accident. The following are short snippets from the accident report.Phenomenology of the accident: Several witnesses observed the helicopter approximately 200–500 feet above ground level in cruise flight along the coastline […]. One witness, a former pilot and mechanic, reported he observed the helicopter in straight and level flight, then heard a change in "rotor noise, followed by a bang/pop/twang sound." The helicopter then "snap-rolled" to the left and descended into the terrain in a nose low attitude.Immediate cause: Examination of the helicopter's flight control system revealed that the right forward servo to swash-plate push-pull tube joint was disconnected and the attach hardware  was missing. […]. Material analysis of the components revealed that only one of the two nuts for the left and right connections were installed, and then only finger tight. The nut on right servo connection rotated off during flight which allowed the bolt to extract itself and disconnect the servo from the push-pull tube.Maintenance and inspection: Prior to the accident flight, an inspection, which required the push-pull tubes to servo connections to be disassembled, was performed on the helicopter […]. The mechanic who preformed the inspection, stated he forgot to properly secure the hardware for the left and right servo connections. The mechanic stated the reasons for the error were the following: 1. He was pulled," in all directions" by company personnel since his arrival at that facility; 2. The "reassembly was not opposite of the disassembly," which was a personal maintenance practice he used to eliminate errors; 3. Two nights prior to the completion of the inspection and the maintenance test flight, the apprentice providing assistance, wanted to stay late to finish with the mechanic a certain section of the inspection. As a result, the mechanic forgot to go back and secure the hardware connecting the two push-pull tube to servo joints; 4. The company was understaffed with maintenance personnel.Conclusion: The National Transportation Safety Board determines the probable cause(s) of this accident as follows: the mechanic's improper installation of the attachment hardware for the servo to swash-plate push-pull tube joint which resulted in a disconnection, subsequent loss of control, and impact with terrain. Contributing factors were the company management's inadequate surveillance and enforcement of maintenance procedures, [and] the excessive maintenance workload due to inadequate staffing of maintenance personnel, […].It is difficult not to be affected by this (preventable) accident and the reasons provided, especially since two individuals lost their lives. The failure mechanism in this case is a loss of cyclic control, which resulted from an incomplete reassembly of a most critical system on a helicopter, the swash-plate (and associated links). The organizational factors in this accident are also considerable, and there appears to be a significantly poor safety culture at all levels in this organization.In all these cases, the maintenance error offered no grace period and transformed almost immediately into accidents. Next, we examine a few select cases in which the incubation time was much longer and maintenance errors turned into accidents after more than 60 flight-hours. We include shorter selections from accident reports than the previous cases.The accident occurred on January 1, 2012 in Lohn, TX, 68 flight-hour after maintenance and inspection were performed on the helicopter . Two individuals were seriously injured in the accident. The following is a short snippet from the accident report.A post-accident examination of the wreckage revealed that the tail rotor gearbox did not operate when it was rotated. […]. Examination of the ring and pinion gears revealed thatthe teeth on the pinion gear were deformed and worn almost down to the tooth root in some locations. Wear was observed on the top land and drive faces of the ring gear. Wear patterns were noted on the coast faces of the ring and pinion gear teeth. The observation of wear on the coast faces of the gear teeth is most probably an indication thatthe spacing between the gears was too tight as a result of improper alignment during installation, causing accelerated wear. A logbook entry showed that the helicopter’s last annual inspection was completed before the accident during which the tail rotor gearbox was overhauled and installed. The National Transportation Safety Board determines the probable cause(s) of this accident as follows: The improper installation of the tail rotor gearbox by maintenance personnel, which led to accelerated wear of the ring and pinion gears, resulting in the loss of tail rotor effectiveness and subsequent forced landing.This case highlights another failure mechanism, also prevalent in our sample, namely the misalignment of rotating parts during reassembly, which in turn leads to excessive wear and tear, and ultimately loss of control  or loss of engine power . The incubation time in this case, from maintenance error to accident, was a long 68 flight-hours. It was contingent on the extent of misalignment during the reinstallation of the part. A more (or less) egregious misalignment would likely result in an accident in a shorter (longer) period of flight-time. There are examples in our dataset of both situations, from a short 3 flight-hours, e.g., the accident identification WPR14TA236, to 99 flight-hours, e.g., LAX05FA264. This again highlights the stochastic nature of the factors affecting the incubation time from maintenance errors to accident.The accident occurred on March 13, 2015 in Anchorage, AK, 141 flight-hour after maintenance and inspection were performed on the helicopter (Airbus AS350 B2). Three individuals on-board survived unscathed. The following is a short snippet from the accident report.The pilot reported that, while the helicopter was in cruise flight […] he felt a “clunk” in the tail rotor control pedals. Immediately thereafter, the helicopter began to yaw left. The pilot attempted to counteract the yaw by pressing the right tail rotor control pedal up to its forward stop, but the helicopter did not respond. The pilot […] executed an emergency run-on landing. […]. An examination of the helicopter revealed that the tail rotor pitch change spider assembly had fractured into two pieces with rotational scarring present along the fractured surfaces; […]. Further examination revealed that the spider assembly failure was consistent withbearing seizure . It is characterized by stoppage of motion and can be particularly disruptive, especially if high RPM or high inertia are involved. Different failure mechanisms (or physics of failure) can lead to bearing seizure, the most prevalent is oil starvation or improper lubrication. See for example Wang, 1997). No evidence of [lubrication] grease was found on the bearing surfaces or the bearing housing. A review of maintenance records revealed that, about 13 months before the accident, the pitch change spider assembly was overhauled by a certified repair station, during which the original ball bearing was replaced. According to the helicopter manufacturer’s spider assembly overhaul procedures, grease was to be applied during the installation of the new bearing. […]. The National Transportation Safety Board determines the probable cause(s) of this accident as follows: the failure of the ball bearing within the pitch change spider assembly due to its operation with no grease within the bearing, which resulted in the subsequent fracture of the spider assembly and a loss of tail rotor control authority. Also causal to the accident werethe overhaul facility’s failure to follow the helicopter manufacturer’s spider assembly overhaul procedures, which resulted in the assembly leaving the facility with no grease in the bearing, andthe mechanic’s failure to complete all of the tasks on the inspection checklist, which led to the lack of grease in the bearing going undetected.This case highlights yet another failure mechanism in maintenance accidents. Unlike the previous examples of the improper or incomplete assembly of critical equipment for example, tasks performed incorrectly, this example identifies a “task not performed” when it was required as the maintenance error. The incubation time in this case, from maintenance error to accident, was a long 144 flight-hours. It is perhaps to the credit of the safety margin in the design of the bearing/spider assembly that the system operated for this long before failing.There are other examples in our dataset in which failure to apply lubrication when required was a causal factor in the accidents, and the corresponding incubation times significantly shorter than the one previously discussed, for example the ERA12FA563 case in which the maintenance personnel applied a corrosion-inhibiting material on critical rotating parts but thinking it was a lubricant (it was not). The maintenance error in this case offered no grace period and resulted in a fatal accident within one flight-hour. As with some of the previous examples, there was non-compliance with helicopter manufacturer's maintenance manual in this case as well as failures at several levels in the organizations, which allowed a non-lubricant to be assessed, purchased, and used (inadvertently) instead of a lubricant for critical parts on the helicopter.For all the maintenance accidents, we examined the maintenance and inspection type that preceded each accident. Given our sample and data filters, recall we are concerned with four types: (1) the 100-hour, (2) the Annual, and two types of progressive programs, (3) the progressive also known as the Approved Aircraft Inspection Program (AAIP), and (4) the Continuous Airworthiness Maintenance Program (CAMP). The results are provided in Caution is advised when considering these results. They cannot be interpreted to mean that one type of maintenance and inspection is associated with more or fewer accidents, since as noted previously, we do not know the extent (percentage) of helicopters in the U.S that are operating under any of these maintenance and inspection regimes. As a result, given this lack of measure of exposure, we cannot establish rates or a hazard index to compare the risks associated with each type of maintenance and inspection leading to an accident. If the progressive maintenance programs (AAIP and CAMP) were in the minority, the results in A commonly used error classification scheme is the Human Factors Analysis and Classification System, or HFACS, developed in a series of articles by Shappel and Wiegmann –30 and bIn our sample, the majority of the maintenance errors were skill errors (77%) and very few decision errors (12%). We found no perceptual errors, and the accident narrative was not descriptive enough to assign a particular error type for the remaining errors (11%).We did not adopt or further pursue the HFACS framework in our work for two reasons. First, except in rare cases, there was no discussion of organizational influences or the pre-conditions for unsafe acts in the accident reports (Level 1 and 3 in HFACS). Furthermore, in the vast majority of cases, poor inspection was at fault (Level 2). Second, more importantly, we found repeated patterns of maintenance errors (by function and location on a helicopter), which the HFACS unsafe acts classification was blind to. We propose the following classification (based on ) and hieThe results are shown in Improper or incomplete (re)assembly or installation of a part. This accounted for the majority of maintenance errors with 57% of such cases;Failure to perform a required preventive maintenance and inspection task: 35%;Use or installation of the wrong part: 3%;Other. This category accounted for situations we either could not resolve or for which there was only a single occurrence.Improper or incomplete (re)assembly or installation of a part. We found for example that:We further decomposed these categories when enough data was available in the accident reports. For example, the following sub-categories clearly emerged under the 1.1 Incorrect torquing or incomplete assembly of nuts, bolts, cutter pins, or safety wires was the most prevalent sub-category in (1), accounting for 57% of the maintenance errors under this category (1);1.2 Misalignment of shafting components after maintenance accounted for 11% of this category;1.3 The incorrect assembly of the fuel control unit and mixture control accounted for another 11% of this category;1.4 The incorrect assembly of the gearbox accounted for 9% of the maintenance errors in this category.A further sub-classification of (1.1) yielded the following results see :1.1.1 The B-nut was involved in 33% of the cases of incorrect torquing or incomplete assembly of nuts, bolts, cutter pins, or safety wires;1.1.2 The swash plate and pitch control links (main rotor) were also involved in 33% of these cases;1.1.3 The tail rotor pitch control links were involved in 11% of these cases.Failure to perform a required preventive maintenance and inspection task, with the parts to which the preventive maintenance was meant to be applied and for which there was enough data. The results show:Going back to It is important to clarify that this means that the maintenance program was not executed in compliance with federal regulations, nor with the manufacturer maintenance plan or service bulletins. In some of these cases, the parts were overflown past their service life by several hundred hours;2.1 A prevalence of structural parts  not properly inspected or maintained, 34%. 2.2 The landing gear was surprisingly involved in 17% cases of maintenance errors in this category. In this sub-category, the maintenance error led to ground resonance, and the consequence was dire: as one (un)lucky pilot was quoted in the accident report, “in a matter of seconds, the helicopter shook itself apart”;2.3 The non-application of grease or lubricant when required was involved in 14% of the cases in this category. The failure mechanism in these cases typically involved thermal damage, which led to structural failure.failure to perform a required preventive maintenance and inspection task, can be classified either under errors or under violations. In a couple of cases, the accident reports specify this was the result of poor record keeping and oversight. For the majority of cases however, no such information is available, and it is understandably difficult to ascertain. Although it is unlikely that there were any willful violations of safety-critical preventive maintenance tasks, our classification avoids this dichotomy in the HFACS classification at Level 4.Furthermore, breakdown of these or other (sub-)categories was either impossible or not meaningful at the present and given our sample. It is worth acknowledging that within the HFACS framework, our second category, improper or incomplete (re)assembly, and failure to perform…. As a result it does not appear in Two final comments: the magneto was involved in two cases, each one under a different category, In this section, we propose a set of recommendations for addressing maintenance errors, which are based on the findings in the previous section on the one hand, and which borrow from the ideas underlying the defense-in-depth safety principle on the other hand. First, a brief discussion of this principle is provided.Defense-in-depth is a fundamental safety principle that is widely adopted in different industries, sometimes under different names but with the same underlying basis , 36. It Multiple lines of defenses or safety barriers should be placed along potential accident sequences;Safety should not rely on a single defensive element ;The successive barriers should be diverse in nature and include technical, operational, and organizational safety barriers. In other words, defense-in-depth should not be conceived of as implemented only through physical or technical defenses.prevention function, a second set of safety defenses should be in place to block further escalation of the accident sequence. Finally, the third line of defenses is designed and put in place to minimize or mitigate the consequences of the accident should the previous barriers fail in their function. Lifeboats are one illustration of this third line of defense. Crash-resistant fuel systems are another example of this third line of defense for helicopter . The various safety barriers have different objectives and perform different functions. The first set of barriers, or line of defense, is meant to prevent an accident sequence from initiating. Should this first line of defense fail in its The following recommendations, as noted previously, are based on our examinations of the maintenance accidents, and they are informed by the safety principle of defense-in-depth. They include technical, operational, and organizational recommendations. At a high level, the fundamental recommendation is to develop a strong safety culture among individuals and organizations who deal with helicopter maintenance. This was clearly lacking in the majority of accidents examined. Some ways for achieving this given our findings are discussed next.R1. Provide better training and certification: Our results provide a clear indication that better training of maintainers and inspectors would be beneficial. Figs critical hot spots conducive to maintenance errors. These are specifically the tasks and areas that deserve more emphasis for proper training and certification. For example, the repeated improper torquing or incomplete assembly of nuts, bolts, and cutter pins should not be accepted as a common risk in helicopter maintenance; it is easily preventable with better training and a dedicated module to these assemblies , and some form of verification that these critical skills have been properly retained.R2. Develop checklists and emphasize compliance: Except in rare cases when documentation was lacking or not clear, most maintenance accidents in our sample could have been avoided if the work was done in compliance with federal regulation and manufacturer’s maintenance plan or service bulletins. It is important that operators and regulators repeatedly emphasize the importance of compliance with official documentation, that usable checklists be developed, and that maintenance processes and execution be occasionally audited.R3. Strongly communicate the importance and safety-critical nature of maintenance and inspection tasks: helicopter maintenance is a momentous responsibility, and it cannot be treated with the same attitude as the maintenance of a pedestrian item such as an HVAC or a dishwasher. In several of the cases we examined, it appears that maintenance and inspection were treated with a casual level of attention and without an appreciation for the serious potential consequences down the road. The community would be well served if helicopter operators, regulators, and professional societies developed a communication and outreach campaign to emphasize the safety-critical nature of the work of maintainers and inspectors.The three previous recommendations operate at the prevention level within a defense-in-depth framework, that is, striving to avoid the initiating event or maintenance error from being committed in the first place. But should this prevention function fail, another set of safety barriers should be in place to catch these accident pathogens and block an accident sequence from further escalating. The following address this part.R4. Organize for, and execute careful inspection and quality assurance of all maintenance work: in the vast majority of cases, poor inspection of maintenance work was noted as a failure to catch the maintenance error assembly or installation of a part). Furthermore, in some cases, either no inspection was conducted to verify the quality of the maintenance work, or the same person who performed the maintenance inspected their own work as well. The pilot was also noted on several occasions to have failed to notice the problems during pre-flight checks. We strongly recommend that operators develop a formal process  and assign dedicated quality assurance personnel if they can afford it, to inspect all maintenance work, especially those involving critical bolts and nuts. This need not be a time-consuming activity, even if done thoroughly. Incorrect torquing and assembly of critical bolts and linkages for example, which is responsible for the largest proportion of maintenance accidents, can be easily caught with proper inspection, and this opportunity should not be forfeited for accident prevention.R5. Re-examine the conduct of post-maintenance flight check? This is not a recommendation per se since there was no data in the accident reports to inform it. However, we raise the fact that some accidents occurred immediately after maintenance was performed (in some instances within the first flight-hour). Fatalities also occurred on these flight. As a result, we invite the rotorcraft community, especially pilots and maintainers, to reflect on the following question: are there ways to (re-)design post-maintenance flight checks to tease out some of the maintenance errors we see in Figs There was anecdotal evidence in some accident reports that organizational issues were contributing factors to the accident. We propose the following tentative recommendation and recognize the difficulty of operationalizing it. However, we believe this deserves careful consideration, and it may be adopted in different forms given the particular circumstances of each operator.R6. Isolate (excessive) flight pressure from maintainers, and carefully manage workload of maintenance personnel. In some of the accident cases, there was clear maintenance work overload, the maintainer “felt pulled in all directions”, and perhaps thoroughness was sacrificed for availability. Mechanic’s fatigue and long working hours were also noted in the NTSB documents discussed previously as contributing factors to accidents [ccidents , 21. It We conclude with a final recommendation specifically addressed to the Federal Aviation Administration. We urge the FAA to establish a multi-stakeholder taskforce, which would include helicopter manufacturers, operators, pilots, and maintenance personnel to bring their collective wisdom to bear on these issues and devise targeted recommendations and effective safety interventions to address this disquieting problem.maintenance accidents per year. The histograms for the other categories of accidents can be found in the appendix in In this work, we first established that maintenance and inspection were a risk factor in helicopter accidents. Between 2005 and 2015, we found that flawed maintenance and inspection were causal factors in 14% of helicopter accidents in the U.S. civil fleet, excluding homebuilt and experimental helicopters. We argued that this figure constitutes in all likelihood a lower bound, and that the actual extent is closer to 21%. With a rough average of about 150 helicopter accidents per year over the time period here considered, this represents about 20 to 30 helicopter maintenance error infant mortality. Equally important however was the finding that the “time signature” of maintenance accidents is not confined to the immediate temporal vicinity following maintenance and inspection. We found for example that about half of the maintenance accidents occurred after 20 flight-hours, and that the last quartile of such accidents occurred after 60 flight-hours following maintenance and inspection.For these maintenance accidents, we then examined the incubation time or duration (flight-hours) from when the maintenance error was committed to the time when it resulted in an accident. We found a significant clustering of maintenance accidents within a short number of flight-hours after maintenance and inspection were performed. For example, 31% of these accidents occurred within the first 10 flight-hours. We also found that the conversion of maintenance errors into accidents decreases with time, which is reminiscent of infant mortality in reliability engineering, and we characterized it as improper or incomplete (re)assembly or installation of a part category accounted for the majority of maintenance errors with 57% of such cases, and within this category, the incorrect torquing of the B-nut or incomplete assembly of critical linkages was the most prevalent maintenance errors. We also found that within the failure to perform a required preventive maintenance and inspection task category, the majority of the maintenance programs were not executed in compliance with federal regulations, nor with the manufacturer maintenance plan or service bulletins.We also examined some of the “physics of failures” underlying maintenance accidents. We then proposed a classification of maintenance errors and analyzed their prevalence in helicopter accidents. We found for instance that the Finally, we provided a set of recommendations based on our findings and which borrow from the ideas underlying the defense-in-depth safety principle.We indicated throughout this work a number of fruitful venues for future work such as, for example, expanding the scope of the analysis to include helicopter incidents from the NTSB database, not just accidents as we have done in this study. This has the potential to yield additional insights, identify precursors to helicopter accidents, and further strengthen our present findings. We also discussed the importance of examining in future work the prevalence of different types of maintenance programs (AAIP and CAMP) and analyzing “maintenance accident rates” associated with each type. These topics, however, are of little significance when compared with what we consider the most important future work, namely the planning and execution of safety interventions to address this problem. Every year, dozens of helicopter accident occurs in which maintenance errors are causal factors, and more individuals are killed or injured in the process. These are preventable accidents, and this heavy cost in lives and limbs need to be paid. We reiterate our most important recommendation, that the FAA establish a multi-stakeholder taskforce, which would include helicopter manufacturers, operators, pilots, and maintenance personnel to bring their collective wisdom to bear on these maintenance issues and devise targeted recommendations and effective safety interventions to eliminate this disquieting problem.We conclude this work with a paradoxical statement, that helicopter maintenance and inspection are highly reliable. How do we reconcile this statement with the previous analyses? We examined in this work the likelihood that an accident has a maintenance contribution, given that an accident has occurred. The 14% quoted previously is the estimate of the following conditional probability, maintenance accidents per year noted previously, this give an average reliability of the maintenance and inspection intervention of 99.94% to 99.96%, or 4 to 6 in 10,000 intervention lead to an accident.There are roughly 12,000 helicopters in the U.S. fleet, their average flight-hours per year is about 300 hours (these are not uniformly distributed across different types of helicopters). Assuming 90% of helicopters operate under the 100-hour and annual inspection regime, this results in et al [−5 to 10−6 of unreliability per unit of exposure in a healtchare context (blood transfusion and anesthesiology) and in civil aviation (per departure) for example. This represents about 2 to 3 orders of magnitude better reliability than that of helicopter maintenance and inspection. The rotorcraft community deserves and can do better.Our comment that helicopter maintenance and inspection are highly reliable is related to this estimate. It is nevertheless worthwhile to reflect on whether this is a good reliability achievement to be content with or not. If banks for example had a similar reliability per transaction, the result would likely be financial mayhem and riots. Amalberti et al  benchmar


Previous research has mainly dealt with the physiological and psychological restorative effects of the forest environment. However, comparatively few studies have focused on how the traits and attributes of individuals  affect the restorative effects of the forest environment. In this study, we examined the relationships between the psychological restorative effects offered by perceived restorativeness of outdoor settings and the individual traits. Then, we investigated the relationships between the restorative indicators that are useful in examining the restorative properties ; seven indicators in total), the psychological restorative effect (Profile of Mood States (POMS), Restorative Outcome Scale (ROS), positive and negative affect schedule (PANAS), and Subjective Vitality Scale (SVS); 10 indicators in total), and the individual trait indicators that could be used to investigate individual traits , and Sukemune-Hiew Resilience test for resilience; 28 indicators in total) in forest and urban settings. Respondents consisted of 46 male students in their twenties. A short-term experiment was conducted using the same method in both environmental settings. We then analyzed the intrinsic restorative properties and the restorative effects of the settings and referred to prior research to determine the restorative effects. Furthermore, we analyzed the relationship between the restorative indicators and the individual trait indicators by correlation analysis and multiple regression (step-wise) analysis. These new findings were obtained: (1) the forest setting was a restorative environment with a higher restorative effect than the urban setting; (2) although the forest setting had a higher restorative effect than the urban setting, and the influence of individual traits was small; (3) in the forest setting, the relationship between the restorative indicators and individual traits indicators were arranged; (4) distancing (Stress coping), psychological health (QOL), and satisfaction with living environment (QOL) were likely important indicators that are related to the restorative effects in the forest setting. With urban life in the modern world, people experience many stressors, which increasingly drive them to seek some form of stress reduction. In the recently urbanized environments and societies, chronic and intense stress, and a deficiency in restoration from stress are well recognized as increasing problems that have long-term negative effects on health ,2,3. PooDue to the social problems caused by urban stress, there is an increasing focus on the potentially restorative effects of the natural environment. Lots of evidence on the positive effect of the natural environment on health and happiness has already been published. As a principle, the physiologist Miyazaki advocated using Miyazaki’s Nature Therapy Theory to improve health, which was based on an evolutionary anthropological perspective . For exaThe Attention Restoration Theory (ART) proposed by Kaplan and Kaplan 1989) [89 [19] hIt has been previously mentioned that there may be influences from inter-individual differences on the restorative effect of forest bathing. For example, using on-site experiments, Koyama et al.  found thWe also agree that it is desirable to provide the most effective choice in consideration of the user’s traits, even in future studies aiming to further demonstrate the health and recreational benefits of the forest environment. Therefore, in this study, to clarify whether individual traits affect the restorative effects of the forest setting and to elucidate which indicators of individual traits affect the restorative effects, we attempt to identify the properties of the forest setting that are considered to have high restorative effects using prior research. Then, we also discuss the relationships between the representative individual traits and the restorative effects of the forest setting.The experiments were carried out in four municipalities. The characteristics of each municipality, forest, and urban sites are presented in We controlled for the variation between respondents to avoid the influence of differences in attributes, such as age or gender, by selecting 46 young male undergraduate and graduate university students as respondents . We askeThe experiment was conducted over a period of 2 days. The respondents were gathered at a meeting point on the morning of the first day. They were then taken to the meeting room for an orientation where they received an explanation of the experimental procedures. They were required to sign a consent form. After the orientation, the respondents were randomly divided into two groups, each with five to six respondents. On the first day, the respondents in one of the groups were taken to the forest sites, while the respondents in another group were taken to the urban sites. On the second day, the same respondents were taken to the other opposite setting  to avoid order bias. In a waiting room, we administered four questionnaires, α, β, γ, and δ . These wIn this study, we tested the hypothesis that the traits of each individual had an influence on the restorative effects received from both settings. As a part of investigating the restorative effects of the forest and the urban setting, it is also important to investigate the restorative properties via the perception of the respondents. Thus, we compared the perception of the respondents with the results obtained from the restorative properties. We measured the data based on three categories: the restorative property of environment , the restorative effect from the environment , and the personality traits .We used the Perceived Restorativeness Scale (PRS) and requested all respondents to complete the questionnaire to investigate the restorative properties of the forest and urban settings. The PRS was developed by Hartig  and was The POMS is a well-established, analytically-derived factor-based measure of psychological distress. Its validity and reliability are well documented . We usedIn some cases, it was difficult to distinguish between traits and attributes from the indicators of the individual traits consisting of the four items. Here it was not critical to distinguish between these in a strict sense; therefore, we interpreted the meanings of the individual traits more broadly. Even if the original meaning of the term contained elements of the attribute, we defined the term in relation to the individual traits. Our investigation focused on four major psychological aspects: health and lifestyle habits, quality of life, stress coping, and resilience . The useAfter categorizing the survey results of the PRS, we compared the restorative effects between the forest and urban settings for each of the seven indicators mentioned above. We used paired t-test and Bonferroni’s correction to avoid Type-I errors . The resIn the comparison between forest and urban sites using the PRS score, significant differences were found in all indicators except for “Fascination” and “Coherence.” “Being away,” “Scope,” “Compatibility” and “Preference” were significantly higher in the forest sites, and only "Familiarity" was significantly higher in the urban sites. As for “Fascination” and “Coherence,” there was little difference in the scores among the two different sites and no significant difference between the two sites could be confirmed .To investigate the overall trend of the relationship between the restorative effects and individual traits for each environmental setting, correlation analyses were performed for all indicators . The resWe conducted multiple regression analyses  to investigate further how the indicators of individual traits influenced the restorative effect. In the forest setting, there were significant relationships in 5 out of 280 cases. On the other hand, in the urban setting 12 out of 280 relationships were significant. We assessed the restorative properties of the forest and urban settings and the psychological restorative effects. First, the scores related to daily life, Being away, Scope and Compatibility were statistically higher in the forest setting than in the urban setting . This reOverall the four forest sites are restorative environments with higher restorative effects in contrast to the four urban sites. The higher psychologically restorative effect may be because of the highly restorative properties of the forest acting as a stimulus to the respondents.There was a significant correlation between the composite index of the 10 restorative effects and the index of 28 individual traits. More specifically, in the forest setting there were significant correlations between Vigor (POMS) and Distancing (Stress coping), Fatigue (POMS) and Environment (QOL), Confusion (POMS) and Meal , Confusion (POMS) and Environment (QOL), SVS and Distancing (Stress coping), and Emotion-focused (Stress coping) and Psychological health QOL; . In otheFurthermore, the distancing type of stress coping had a negative relationship with Vigor  and SVS (−0.295). The environmental area of QOL had a negative relationship with Fatigue  and Confusion . In addition, we found that the psychological state was affected by more individual traits from staying in the urban setting than in the forest setting. The urban setting was not a restorative environment compared to the forest, and a restorative effect was not expected either. However, in the urban setting, as a strong stimulus was scattered (in contrast to the forest setting), it was necessary for each person to pay more attention to sufficiently adapt to their environment. For this reason, we considered that many more individual traits were related to the stay in the urban setting rather than in the forest setting.When the results for the forest and urban settings were compared, both correlation and multiple regression analyses revealed many significant relationships in the urban setting . On the other hand, fewer significant relationships were revealed in the forest setting . As previously discussed, a forest setting has a higher restorative effect than an urban setting  because In the present study, we investigated and analyzed the relationships between individual traits  and the restorative effects from a short stay in a forest setting. The following findings were obtained.The forest setting is a restorative environment with a higher restorative effect than the urban setting.Although the forest setting had a higher restorative effect than the urban setting, the influence of differences in individual traits was minimal.The relationships between restorative indicators of the forest environment and individual traits indicators were elucidated.Distancing (stress coping), psychological health (QOL), and satisfaction with the living environment (QOL) were potentially important indicators related to the restorative effects in the forest setting.The above results were obtained even though the time the respondents spent in the forest settings was relatively short. Therefore, regardless of individual traits, people can experience a psychological restorative effect by simply spending time in a forest setting for a relatively short period (approximately 30 minutes to 1 hour). Several studies explored the effects of individual differences on the effect of staying in the forest setting, such as Takayama  and TakaFurthermore, we chose young men in their 20s as respondents to control for the respondent’s attributes. The effects of gender and age would require further exploration in the future. The relationships between cognitive differences in individual respondents  and differences in restorative effects between forest and urban settings , or the relationship between cognitive differences and individual traits have not been studied previously. Exploring such dynamics is important for establishing the overall relationships among individual traits and restorativeness, which should be elucidated further in future studies. Although a well-managed forest environment is highly beneficial to users regardless of individual differences, further research could focus on developing optimal forest management and forest experience programs, while taking into account differences among individual users.The present study had some limitations. First, with regard to correlation and multiple regression analysis, it may be necessary to consider the potential of the presence of type-I errors. Therefore, readers should be careful when they consider the results of the present study. In addition, the urban setting was used as a control and compared with the forest setting, referring to many previous studies ,41,42,43


Age-related macular degeneration (AMD) is a degenerative ocular disease that develops by the formation of drusen in the macula region leading to blindness. This condition can be detected automatically by automated image processing techniques applied in spectral domain optical coherence tomography (SD-OCT) volumes. The most common approach is the individualized analysis of each slice (B-Scan) of the SD-OCT volumes. However, it ends up losing the correlation between pixels of neighboring slices. The retina representation by topographic maps reveals the similarity of these structures with geographic relief maps, which can be represented by geostatistical descriptors. In this paper, we present a methodology based on geostatistical functions for the automatic diagnosis of AMD in SD-OCT.The proposed methodology is based on the construction of a topographic map of the macular region. Over the topographic map, we compute geostatistical features using semivariogram and semimadogram functions as texture descriptors. The extracted descriptors are then used as input for a Support Vector Machine classifier.For training of the classifier and tests, a database composed of 384 OCT exams (269 volumes of eyes exhibiting AMD and 115 control volumes) with layers segmented and validated by specialists were used. The best classification model, validated with cross-validation k-fold, achieved an accuracy of 95.2% and an AUROC of 0.989.The presented methodology exclusively uses geostatistical descriptors for the diagnosis of AMD in SD-OCT images of the macular region. The results are promising and the methodology is competitive considering previous results published in literature. Age-related macular degeneration (AMD) is a progressive chronic disease of the central retina and a leading cause of vision loss worldwide . Its devIt is estimated that AMD is the cause of 8.7% of cases of blindness worldwide, with a higher incidence in developed countries and people over 60 years of age. For 2020, the global projected number of cases is of 196 million and this estimation reaches 288 million for the year 2040 .Recent advances in retinal imaging technology have allowed the handling of age-related macular degeneration through the creation of spectral domain optical coherence tomography (SD-OCT). It is a noncontact, noninvasive, three-dimensional imaging technique that obtains images representing a sectional view of retina at micrometer resolution .This examination modality reconstructs the tomographic image by measuring the optical backscattering of tissues. This technique has gained space as a diagnostic tool for AMD, mainly due to its quickness to acquire images and dispenses the use of contrasts and thus the risks involved.The evaluation of AMD by SD-OCT occurs through the analysis of successive sectional cuts in search of morphological changes caused by the disease. SD-OCT acquisition generates a large number of sectional images, which requires that the expert visualize and evaluate a large number of volume slices seeking for changes, especially if they are minimal and sparse in the early stages of pathology .A typical SD-OCT examination produces about 100 images with a resolution of Accordingly, the development of computer aided diagnostic methods (CADx) can collaborate with the specialist for the detection of AMD by taking advantage of the ability to evaluate the large amount of data that the SD-OCT examination can provide. Even in its variations, a large amount of anatomical retinal information is available to characterize the disease .Typically, we have two main approaches for automated AMD diagnosis based on SD-OCT. One of the approaches involves the following steps to be effectively addressed: (a) obtaining relevant biomedical characteristics for the differentiation between healthy and compromised retinas; (b) use of classifiers to accurately determine the presence or absence of the disease; and (c) validation of the method for generating reliable results from a properly classified image database , 5, 7–13Another approach is based on the use of deep neural networks techniques  to identIn general, these methods use the reflectance values of retinal pixels. They use simple segmentation techniques based on the elimination of the background , a warpiThe main related works are compared in Table Most described methods are based on the individual analysis of the SD-OCT volumes’ B-Scans, not considering the correlation between successive slices as seen in , 15, 21.The main disadvantage of methods that analyze individual B-scans is to disregard the correlation between pixels of successive slices. Moreover, after the step of detecting characteristics that indicate the presence of AMD per slice, a new classification is necessary to indicate the presence of the disease by volume.The approach presented in  differs From this point, they generate mean thickness maps and determine superior and inferior limits for the classification of retinas compromised or not by AMD. Despite this work presenting good results (AUROC = 0.991), we believe it is very dependent on the mean thickness measures and does not analyze how the local variation of thickness occurs along the RPEDC surface. So, we realize it is possible to propose a new approach for describing RPEDC conditions with local thickness variation analysis. Submitting these features to a classification method allows us to develop a methodology for the detection of AMD in human eyes.Given the similarity of the generated retinal topographic maps with geological investigation maps like soil analysis and remote sensing , we propThese geostatistical functions have already been used with success in biomedical contexts such as lung nodule detection  and breaThe main advantage of using geostatistical functions over topographic maps is that they allow a representation of the volume as a whole, not limiting the analysis by individual slices  and providing a local analysis of thickness variation along the RPEDC in macular region.In this work, we used the topographic map proposed by  but, innTo describe the macular region texture we propose the use of the semivariogram and semimadogram functions that we believe can describe the layers thickness variations of the total retina, NSR, e RPEDC. Thus, the complete methodology is innovative in itself, as it is the use of geostatistical functions to discriminate against the texture of the topographic map. This is a way to represent the retina globally.Our approach is innovative in the sense that it uses the analysis of local variation of the thickness as a texture map, based on the assumption that druse formation modifies these measures. This gives us a way to evaluate thickness information with their spatial location building a robust method for AMD detection.The occurrence of druses interferes in the retinal layers morphology, deforming them which reflects on generated topographic maps. Thus, our method of AMD diagnosis is based on the evaluation of the retinal layers thickness alterations. The topographic maps describe how their thickness is varying along the macular region. So it is an appropriate tool to be used in automatic methods. We developed a way to describe these variations based on the assumption that the texture representation of this maps will be a strong indication of healthy and unhealthy patients.So, we believe this methodology may be useful to more robustly distinguish impairment cases and let us develop a computer-based method for automatic diagnosis of AMD impairment. Such a system can offer a second opinion, to provide more information to the specialist, supporting their clinical decision. Processing that data through machine learning methods can allow rapid studies, facilitating population screening, remote diagnosis and even early detection of the disease. The problem addressed in this research will be research on a methodology for the automatic diagnosis of AMD by using SD-OCT exams.The methodology proposed in this work for the development of a CADx architecture is based on the following stages: 1) image acquisition, (2) image representation, (3) features extraction and (4) classification. The flow chart of the proposed methodology is shown in Fig.  image acen face of the SD-OCT volumes. The third step is the central part of the proposed methodology where we extract geostatistical features on the topographic maps obtained from SD-OCT volumes. Finally, in the fourth stage, we submit the extracted features to a classifier method to determine if an SD-OCT volume is whether or not affected by AMD. We detail each step below.In the first step, the images are acquired from the database provided by  which coThe image set used for the validation of the proposed methodology belongs to the database provided by . It is aThe main population characteristics of the AREDS2 trials are: Mean age, 74 years; 57% female; 97% white; 7% current smokers; 19% with prior cardiovascular disease; and 44% and 50% taking statin-class cholesterol-lowering drugs and aspirin, respectively. Ocular characteristics include 59% with large bilateral drusen, 32% with advanced AMD in 1 eye and mean visual acuity of 20/32 in eyes without advanced AMD .The SD-OCT examinations were captured at four clinics using SD-OCT scanners manufactured by Bioptigen, Inc . The volumes were acquired in the rectangular region of The subset provided by   that were segmented altogether with the border of the retinal pigment epithelium. This segmentation was initially performed automatically by the software DOCTRAP, developed by Duke University, and subjected to careful review and adjustments by certified specialists from Duke Advanced Research in Spectral Domain OCT Imaging Laboratory. We present a single B-Scan of an SD-OCT volume in Fig. After segmentation, the specialists manually marked the center point of the fovea. From this marking, they delimited a cylinder centered at this point as the area of interest of each volume. For tests and validation of this step, we utilized all 384 provided volumes and its layers boundaries marks.In spite of the existence of automated segmentation techniques, at the moment, we use the segmentation provided with the base due to it being reviewed by specialists. This gives us greater security for validation of the proposed method since segmentation errors may impact its accuracy.en face for each SD-OCT 3D volume of the image set. Topographic maps represent the thickness of the retina (as well as the neurosensory layer and the RPEDC) for each point on its surface. The reconstruction en face generates images that correspond to the reflectance values of the SD-OCT on the border of the RPE. The image set used represents borders reviewed by specialists as surfaces In this step, we generated two-dimensional representations based on topographic maps and reconstruction x, y) in a substructure of the retina. This is done by summing the amount of voxels existing between the two borders, or simply calculating From the surfaces defining the borders of the layers, we generated three two-dimensional surfaces The first topographic map generated  between samples  can be measured by semivariance. It analyzes the variance between pairs of data points over a range of distances. Its magnitude is directly proportional to the distance between the points, so the larger the distance, the larger the semivariance value.lag is the distance between the pairs of points located in i and j where i and j. N(h) is the number of points separated by h.The semivariance values as a function of distance between pair of points is called semivariogram and can be written as :2\documesill.The semivariogram usually displays a characteristic curve Fig.  in whichrange. At this point, the semivariance is equal to the variance of the data of the sample considered, meaning that there is no relation between the pairs of observations considered at this distance [h is very small, the compared points are very similar to each other, which implies very low values of semivariance for these initial distances, hence the value of the semivariogram will start with very low values nugget effect, or simply nugget.The distance at which the sill is reached is called distance . On the pixels.Some parameters are used for the calculation of the semivariogram: the direction, the measurement (or lag distance), the maximum bandwidth, the lag tolerance and the angular tolerance. Setting these values limits which pixels will be considered for the calculation. Figure h is the lag, pixels of an image separated by h. N(h) is the number of pairs from the distance h.Similar to the semivariogram, the semimadogram is another function also used to measure spatial dependence . It is gen face of the border of the RPE. The calculations were performed in four directions   which isSVM is a proven effective method for general classification tasks. In spite of other classifiers that require large amounts of data, such as deep learning , SVM is TN, is true-negative, FN is false-negative, FP is false-positive, and TP is true-positive.For evaluating the performance of the classifier, we used the measures of sensitivity, specificity, accuracy, AUROC and Cohen’s kappa . SensitiTo evaluate the performance of the proposed methodology, we run an experiment with the 383 SD-OCT volumes provided by . The misen face (semivariogram) and (8) RPEDC en face (semimadogram).The semivariogram and semimadogram for different topographic maps were calculated by generating eight different arrangements of maps/geostatistical functions to be evaluated for the ability to distinguish examination affected by AMD from those considered healthy. The arrangements are: (1) total retina (semivariogram), (2) total retina (semimadogram), (3) neurosensorial retina (semivariogram), (4) neurosensorial retina (semimadogram), (5) RPEDC (semivariogram), (6) RPEDC (semivariogram), (7) RPEDC For each arrangement, the geostatistical functions provide values that show local spatial dependency of the chosen maps. In Fig. The validation tests were performed using the k-fold technique with repetitions. For training, we divided the data into 5 folds with 100 repetitions, setting a ratio of 80% for training and 20% for tests in each interaction. Using a large number of repetitions increases the reliability of the results given the fact that it decreases the contribution of folds that present overfitting to the overall result. We calculated the mean values, standard deviations for each test .On the other hand, the semivariogram an semimadogram functions applied on RPE’s reconstruction For a visual comparison, in Fig. We further compare the performance of our best method (semivariogram over RPEDC) to the classical texture descriptors  , 33 and The results of these experiments Table  show thaTable When using the topographic map of the neurosensory retina, the kappa index of 0.724 indicates a substantial agreement. Notwithstanding, these values are still slightly below the results found in the literature. The main difference between the results obtained by the maps of the total retina and the neurosensory retina is that the last map is calculated from the upper border of the RPE, a layer that is directly deformed from the accumulation of drusen.The best results (semivariogram on the RPEDC) achieved an AUROC of 0.989, a result very close to that achieved by . The valen face of the RPE, which solely considered the reflectance of points in the upper border of this layer, did not demonstrate expressive ability to differentiate the control tests of the examinations affected by AMD. Especially the semivariogram, which resulted in an average AUROC of 0.505, which is a result too similar to a random classifier. A slightly better AUROC (0.778) was achieved when using the semimadogram for this reconstruction. However, a lower kappa value (0.347) indicates that the generated model is biased and tends to present a high number of mismatched classifications.On the other hand, the semivariogram applied on the reconstruction The poorest performance of this last test against the promising results obtained with the topographic map of the RPEDC is due to the fact that the AMD does not cause significant changes in the reflectance of points on the border of the RPE as with the map of thickness. These variations are best observed when evaluating the deformations caused in this layer by the appearance of drusen and possibly choroidal neovascularization. In future work, we can take into consideration not only the border, but also an axial integration of the pixels of the RPE and thus identify whether reflectance changes in this layer are significant for the detection of AMD.en face of the RPE. The values, in turn, become well differentiated when applied on the topographic map of RPEDC, congruent with the best generated model.In Fig. Considering the results achieved, we verified that the best model generated for the diagnosis of AMD using topographic maps is arrangement 5 (RPEDC/Semivariogram). We noticed that the performance of the proposed model is greater than various works that are based in reflectance values. A comparison with related works is presented in Table Some works have presented slightly higher accuracy, however they use smaller image sets for validation, and other ones have used individualized B-Scans. They do not perform an overall evaluation of the retina, which makes it difficult to compare the work directly. It is also important to note that the performance information is not presented in some papers.Among the works that make use of the same SD-OCT volumes base , 11 alonWith the direct comparison between AUROC values, we can see that the results are really promising. The work of   of the macular region together with the reconstruction We exclusively applied geostatistical texture descriptors for the detection of AMD in optical coherence tomography images base. This is done by a texture classification of the topographic map of human retina layers and this method can be used as a disease screening tool or follow-up in studies of new treatments and prevention methods.Considering that the main objective of this work was to demonstrate that these descriptors are effective for the diagnosis of AMD, we believe that we have achieved this goal with assuredly promising results. The best performed model presented an AUROC of 0.989. The validation of this model demonstrates that the proposed methodology can distinguish with excellent accuracy AMD from unafflicted eyes. Nevertheless, it is advisable to test with a larger database with larger varieties of thickness and even try the method with other pathologies that may affect the retina.


In this study feature extraction of force signals detected during robot-assisted polishing processes was carried out to estimate the surface roughness during the process. The purpose was to collect significant features from the signal that allow the determination of the end point of the polishing process based on surface roughness. For this objective, dry polishing turning tests were performed on a Robot-Assisted Polishing (RAP) machine (STRECON NanoRAP 200) during three polishing sessions, using the same polishing conditions. Along the tests, force signals were acquired and offline surface roughness measurements were taken at the end of each polishing session. As a main conclusion, it can be affirmed, regarding the force signal, that features extracted from both time and frequency domains are valuable data for the estimation of surface roughness. These days, finishing processes such as polishing are not yet fully automated in manufacturing industries. Traditionally, polishing has largely been a manual operation that is very labor-intensive, highly skill-dependent, inefficient due to long processing times, high-cost, error-prone, and hazardous due to abrasive dust . For thiDue to the fact that polishing is not performed by position control but by pressure control, efforts towards automated polishing have mainly focused on the identification and the execution of the motions involved in manual polishing techniques, performing under a desired contact force exerted on the tool . This isThe automated polishing systems developed until now can employ a conventional machine tool structure or an articulated robot arm to hold the finishing tool. For both configurations, force control methods have been designed and can be broadly classified as active and passive force controls. Active force control systems measure and correct the force applied on the workpiece, independently of the tool path, and passive control systems rely on compliance in the tool itself to maintain a nominal contact force or rely on magnetic force to achieve this ,5,6,7.Also, the polishing tool-path has been controlled by the integration of intelligent network systems, using multiple vision sensors to capture images of the polished surface as input collected data . FurtherApart from the approaches made towards the tool-path planning for automated polishing processes, there are other studies focused on endpoint detection; this occurs when a certain target surface roughness value is reached, or it is required to replace the tool with another one with finer grain size and/or implement other polishing conditions. As a result, the polishing sequence can be improved. For this purpose, signals from different sensors have been employed to monitor the surface roughness obtained by polishing. In this scheme, signals from AE, motor current, and light sensors have been employed for the development of expert systems integrated with the data collected during the polishing process ,6,12.In this study, feature extraction of force signals detected during robot-assisted polishing processes was carried out to estimate the surface roughness during the process. The purpose was to collect significant features from the signal that allow the determination of the end point of the polishing process based on surface roughness. For this objective, dry polishing turning tests were performed on a Robot-Assisted Polishing (RAP) machine (STRECON NanoRAP 200) during three polishing sessions, using the same polishing conditions. During the tests, force signals were acquired and offline surface roughness measurements were taken at the end of each polishing session.The experimental procedure of this study as follows.The polishing tests were performed by a Robot-Assisted Polishing (RAP) system  fitted with a robotic arm in which interchangeable polishing tools are mounted. Four cutting parameters can be set up by the integration of a control module in the robotic arm: cutting speed, feed rate, the contact force between the tool and workpiece, and the tool pulsation in the feed direction. Three sessions of polishing tests (60 polishing passes each one) were carried out on a cylindrical probe of alloy steel (UNS G52986) with a length of 75 mm and diameter of 30 mm . The samA gauge was employed to detect the force signal during the polishing tests. First of all, a calibration process was made to establish a relationship between the voltage signal generated on the gauge device and the corresponding force. At this point, it is important to remark that the signal force plotted on the different figures along the present paper is expressed in volts; the objective is to show a trend of the values of forces rather than calculating their absolute values.i, zi) of the surface geometry workpiece were registered for the determination of the arithmetical average roughness parameter, Ra. According to ISO 4288  [R, and is expressed mathematically by means of Equation (1):Five offline surface roughness measurements were taken on the workpiece (on one of its generatrix) at the end of the each polishing session, using a roughness MahrSurf XD1  tester equipped with a radius tip of 2 µm. The cut-off selected was 0.25 mm and the evaluation length was 1.25 mm. In the measurement process, data   standardRow force signal data arrays, each with 16,384 values, are stored and analyzed by Matlab software . Different features were calculated from both the time and frequency domains. In the time domain, a preliminary analysis was made. Different statistical features were calculated from the 2790 signal acquisitions and plotted for each feature. For those feature plots in which a trend can be clearly observed, the average and variance were also determined for each polishing session at the last three passes.FFT (Fast Fourier Transform) power spectral graphics at different polishing time were plotted. The objective is to select a range or ranges of frequencies in which the amplitudes of certain peaks shown in their corresponding FFT power spectral plots may change over time, just as the AE (Acoustic Emission) signal detected during polishing has been processed in previous studies [In the frequency domain,  studies ,16,17.Once the range of frequencies was selected, the maximum amplitude was calculated from all the force signal acquisitions registered. Afterwards, the average and variance were also calculated for each polishing session at the last three passes.Finally, an analysis of the features extracted from the time and frequency was carried out to identify a possible trend and a correlation with the surface roughness.Ra calculated for each polishing session, together with the surface roughness measured before polishing, is represented in the The resultant Ra decreased with the number of passes. In a first step (1st polishing session) the decrease is more accentuated due to the higher quantity of material removed in the first stage of polishing. Hereafter, the analysis of the different features extracted from the force signal is shown and discussed. At time domain, among all the statistical features calculated from the row force signal, only average and variance follow a trend with polishing time, designated in this study as averageF and varianceF. This can be observed in As was expected, Ra hardly decreased during the last session (3rd polishing session), from 0.068 to 0.061 µm, indicates that endpoint detection was almost reached. Also, this can be expected as the force signal in the last session presents a periodical form that does not vary with time  decreases with the polishing passes. This parameter also has a direct relationship with the contact force according to the following expression [k is a constant avgr, the average size of the grain tool, F the contact force, s, the rotational speed, f, the feed rate, wH, the workpiece hardness, and A the contact area between the tool and the workpiece. In spite of the fact that, for all the polishing tests, a constant contact force was applied, contact force and its variations detected along the tests, represented by the parameter averageFa,, follow the same trend that the Ra values obtained. Regarding the rest of the parameters calculated, averageFv,, varianceFa, and varianceFv,, it can be seen that their tendency is inversely proportional to Ra MRR=2al to Ra .FFT power spectral representations, the range selected was between 100 and 1000 Hz. Maximum amplitudes calculated from each acquisition along the three polishing sessions are plotted in From the analysis on frequency domain, according to the peaks shown in the FFT power spectral was calculated for each polishing session and shown in Ra is inverse  measured at the end of three polishing sessions. The main conclusions extracted from the results obtained in this study can be summarized as follows:-After 180 polishing passes under the polishing conditions used in this study, the endpoint detection is almost reached; this is after 45 min of polishing under the cutting conditions employed in this study.-In spite of the fact that for the all the polishing tests a constant contact force between the tool and the workpiece was applied, different features extracted from the signal force detected during the process can be considered valuable data for the indirect evaluation of surface roughness.-averageFa,, averageFv,, varianceFa, and varianceFv,. This makes their relationship with the surface roughness, in the case of averageFa,, proportional, and in the case of averageFv,, varianceFa, and varianceFv,, inversely proportional.In the time domain, average and variance were calculated for each acquisition of force signal and from these signals a feature per polishing session (average and variance) was extracted to compare with the surface roughness, designated in this study by -Ra in polishing processes.In the frequency domain, within the range of frequencies between 100 and 1000 Hz a feature was calculated. This is the maximum amplitude of the peak reached in the range of frequencies for each acquisition of force signal. The average calculated per polishing session is inversely proportional to the surface roughness, so it is a valuable feature for the estimation of -Finally, for future research it is proposed to collect valuable data from the force signal (concretely average feature according to this study) during polishing processes, together with features extracted from other sensors, to further develop polishing systems.In this work, an evaluation of the signal forces detected during Robot-Assisted Polishing (RAP) by a STRECON NanoRAP 200machine was studied. Dry polishing turning tests, under the same cutting conditions, were performed on a cylindrical probe of alloy (UNS G52986) using a tool with a grit number of 800. This semiautomatic polishing system allows the setting of not only conventional polishing parameters such as cutting speed and feed rate, but also the contact force between the tool and workpiece and the tool pulsation in the feed direction. It obtained the trends of different features from the force signal and the surface roughness along the polishing processes to evaluate whether the mentioned features are valuable data for the estimation of