Accident Recovery: Too Many Shades of Gray Regulatory ambiguity, inadequate oversight lead to preventable tragedy. By David Jack Kenny US civil aviation is a heavily regulated activity. Some of those regulations have details so intricate as to provide endless fodder for would-be “armchair aviation lawyers” to debate in the comfort of their hangars. But actual inconsistencies between different provisions, or frequent, apparently incompatible revisions, can leave operators without needed guidance on questions that may prove crucial. The Event The 7th Annual Huey Reunion was scheduled for Jun. 21–26, 2022, at Logan County Airport (6L4) in Logan, West Virginia. Its sponsor, MARPAT Aviation, offered “all helicopter (especially Huey) enthusiasts … an opportunity to fly/ride in this historical [sic] helicopter.” A series of 30-minute flights was offered between 08:30 and 17:30 each day, subject to weather and maintenance constraints. Participants were offered the opportunity to fly the helicopter from the right seat for a $250 “donation to pay for fuel” or to ride in the cabin for “a small donation.” Prior aviation experience wasn’t required; the event’s website stressed that “You DO NOT need to be a pilot to make a reservation to fly!” A volunteer “safety pilot” in the left seat would serve as pilot in command (PIC) throughout. Different volunteers served in that role during the event. One of those volunteers conducted a preflight inspection at about 08:00 on Jun. 22. After the engine was started for the morning’s first flight, it continued to run all day, including during passenger embarkation and disembarkation and while the helicopter was refueled. The Aircraft The aircraft, N98F, was a UH-1B manufactured by Bell for the US military in 1962. It was flown in Vietnam from 1962 to 1971 before being sold to a civilian operator. Its two-bladed main-rotor system and two-bladed tail rotor were powered by an Ozark Aeroworks T53-L-11D turboshaft engine rated for 1,100 shaft horsepower. (The engine’s type certificate, originally issued to Honeywell, was subsequently registered in the names of AlliedSignal and then Textron Lycoming before being transferred to Ozark on May 6, 2022.) As of Jun. 22, 2022, the engine had been operated for 5,583 hours since new and 583 hours since overhaul. The circle at left indicates the area where the NTSB found pieces of plexiglass, the aft cap of the left skid, a tail-rotor blade segment, and green paint transfer onto a rock. (National Transportation Safety Board Photo) The aircraft’s last annual inspection was completed on Mar. 29, 2022, at an aircraft total time of 9,029 hours and signed off in accordance with the 14 CFR Part 43, Appendix D, annual inspection. It was flown another 14 hours before the 7th Annual Huey Reunion. Both tail-rotor blades had been replaced on Apr. 9, 2013; the replacement components had documented service times of 1,017 and 1,025 hours, respectively. Between the blade replacement and its last annual inspection, the helicopter flew an estimated 237 hours, pushing the components’ service times to 1,254 and 1,262 hours, respectively. The manufacturer’s established life limit for those blades, however, was 1,200 hours. MARPAT Aviation didn’t own the Huey; in April 2003, the helicopter was acquired by “a friend of the owner of MARPAT … not affiliated with the operator.” He registered the aircraft under a special airworthiness certificate in the restricted category for agricultural, forest conservation, and external-load operations. MARPAT held a contract with the State of West Virginia to fly N98F as a firefighting aircraft during wildfire season. Beginning in May 2010, its registration was repeatedly switched between the restricted and experimental exhibition categories, with seven changes in a little over four and a half years (see Table 1). Each registration was accompanied by an FAA statement of special operating limitations acknowledged in writing by the operator. The 2014 registration in the experimental exhibition category remained in effect through June 2022. The Pilots The 53-year-old PIC held a private pilot certificate with helicopter, gyroplane, and single-engine airplane ratings. His logbook showed only 493 hours of flight time, but his son-in-law (a flight instructor) said the PIC didn’t log all his flights, so a “big chunk of time” wasn’t shown. His most recent application for a medical certificate, filed just over a year earlier, listed 1,400 hours of flight experience with 20 in the previous six months. He had documented 21 hours in the UH-1B since 2020, though other volunteer pilots suggested he’d been flying it for four to five years. The PIC had no prior UH-1 experience when he began flying N98F. Another pilot suggested that the PIC’s previous helicopter experience had been in a Robinson R22. Prior to beginning passenger flights, the volunteer pilots made informal refresher flights to “get to know the aircraft again.” The maneuvers practiced included approaches, pedal turns, and hovers; no autorotations, other emergency procedures, or transfers of control from the right-seat passenger were reviewed. The 69-year-old passenger in the right seat held a commercial certificate issued Feb. 15, 1995, with rotorcraft helicopter and instrument helicopter ratings. His last medical certificate was issued in April 1996. Further details of his piloting experience were not provided by the US National Transportation Safety Board (NTSB). The Flight The UH-1B lifted off from 6L4 at about 16:30 on Jun. 22, 2022, on the last flight of the second day of the Huey reunion. In addition to the two pilots, four passengers were seated in the cabin. Fifteen minutes later, the aircraft hit power lines 180 ft. above a two-lane road, struck the adjacent rock face, and crashed onto the road, where it hit a guardrail. The impact ignited a fire that consumed the cockpit and canopy. All six on board perished at the scene. The helicopter wasn’t in radio contact with the airport, and the NTSB was unable to find any witnesses to the accident itself. Someone, however, made a 911 emergency call to report the crash just minutes later, at 16:49. The accident site was about 2 miles beyond the easternmost section of the planned tour route. The reason for the diversion was never explained. The Investigation The debris path stretched 542 ft. from a group of three power cables, two of which had been severed. Bits of plexiglass, the aft cap of the left skid, and part of one tail-rotor blade were found on a ledge about 40 ft. above the main wreckage. Green paint transfer marks were also found on a rock there. Both main-rotor blades remained installed on the main gearbox, which had separated from the airframe. Examination of them found no evidence that they’d been turning under power at impact, suggesting that a total or at least partial loss of engine power had precipitated the crash. On-site examination of the engine’s power turbine blades as seen through the exhaust diffuser showed that two had fractured near their roots and were missing; an intact blade remained between those two locations. The engine was taken to Ozark Aeroworks’ facility for a teardown examination. Engine stoppage before impact was confirmed by static impact marks that the impeller airfoils’ leading edges made on the impeller compressor housing, with no material transfer or significant rub damage. All compressor blades “were present and intact, with no rub, impact, or ingestion damage.” The rollers in the No. 2 bearing, which supported the aft end of the gas turbine’s compressor shaft, were flattened, and the outer race “exhibited considerable material transfer.” The roller cage remained in good condition. Rub marks left by the power turbine blades indicated contact with the power turbine inner support and outer ring support, and damage to its front shaft was consistent with contact with the rear compressor stub shaft. Metallurgic analysis of the two fractured blades confirmed that both failed from excess stress. Multiple cracks were found on each inner strut support flange for the exhaust diffuser’s outer cone; one inner strut had separated from the bearing housing. Extensive rubbing damage suggested the strut had separated before the accident and had been “operating in that condition for a considerable amount of time.” These findings led investigators to reconstruct the failure sequence as follows: Fatigue cracks in the spot welds attaching the inner cone to the exhaust diffuser’s bearing-housing support progressed around the cone’s circumference. The preexisting separation in the outer flange of the rear bearing cover reduced load transfer to the inner cone, increasing stresses that led to cracks in the inner and outer flanges of the exhaust diffuser’s inner struts. The diffuser cracks reduced support for the No. 3 and No. 4 bearings, causing misalignment of the power turbine shaft, rubbing on the blade shrouds, and ultimately an imbalance of the power turbine rotor assembly. This in turn caused additional cracking in the exhaust diffuser and rubbing with the rear compressor stub shaft. Frictional heating of the stub shaft caused the failure of the No. 2 bearing, bringing the engine to a stop. The evidence that damage to the exhaust diffuser likely preceded the accident raised the question of why it hadn’t been detected in previous inspections—a key point in the NTSB’s exploration of the multiple and potentially ambiguous regulations governing restricted and experimental exhibition category aircraft and the operation of “living history” flights. The Regulations The foundational requirements for inspection and maintenance of US-registered civilian aircraft are, of course, contained in Title 14 of the Code of Federal Regulations (CFR). Part 43.15(c)(1) of Title 14 requires that “each person performing an annual or 100-hour inspection shall use a checklist” but allows that “the checklist may be of the person’s own design”—necessary in the case of both experimental amateur-built aircraft and orphaned historic models for which no manufacturer’s checklists are known to exist. Appendix D to Part 43 outlines a generic inspection checklist, listing types of components to be examined in each “group” of aircraft structures (“cockpit and cabin,” “engine and nacelles,” etc.). In the case of the Bell UH-1 series, however, model-specific procedures were indeed published in US Army technical manuals (TMs)—TM 55-1520-219-10, issued in January 1969, and TM 55-1520-219-20, dated Jun. 30, 1972. The operating limitations attached to N98F’s initial special airworthiness certificates in both the restricted and experimental exhibition categories specifically required that the aircraft “must be operated and maintained” in accordance with those references. Additional army manuals provided checklists for daily, intermediate, and periodic preventive maintenance. MARPAT Aviation had copies of these, and the checklist it developed for its annual and 100-hour inspections while the aircraft was registered in the restricted category closely tracked the army manuals. Items 9 and 10 of the engine section of the daily checklist (relaxed to every 10 hours or 14 days in civilian service) mandated inspection of the exhaust diffuser, support cone, and second-stage turbine blades. Post-accident, each of these components were found to have incurred progressive damage preceding the eventual engine failure. The operating limitations of the aircraft’s last reregistration in the experimental exhibition category in December 2014 required only that it had to be inspected “in accordance with the scope and detail of 14 CFR § 43, Appendix D, and found to be in a condition for safe operation.” The NTSB noted that the work orders from the aircraft’s two most recent annual inspections referred only to Part 43, Appendix D, and found no evidence that the helicopter had been prepared for long periods of inactivity as stipulated in TM 55-1520-219-20, an oversight that likely contributed to “the extensive corrosion observed within the engine.” The operator likewise didn’t conduct the inspection of the power turbine blades and exhaust diffuser called for in the army’s daily inspection manual and the Interagency Committee for Aviation Policy’s UH-1 Series Inspection Planning Guide (developed when the government began civilian sales of surplus Hueys). The NTSB report also goes into considerable detail about a series of revisions in FAA Order 8130.2, which “establishes policies and procedures for issuing airworthiness certificates for aircraft.” Version G, issued in August 2010, placed the UH-1B in the category of turbine-powered aircraft with maximum gross takeoff weights less than 12,500 lb. Rotorcraft in this group operated under experimental exhibition certificates were required to follow “a current inspection program recommended by the manufacturer” or “any other inspection program … approved by the Administrator.” However, a memorandum of deviation issued in December 2011 relaxed this requirement to the standards of Part 43, Appendix D. Operations in the restricted category still required compliance with the standards of the army technical manuals, reflected in the operating limitations of N98F’s final registration under that classification. Version H of Order 8130.2 required former military turbine-powered helicopters operated under experimental exhibition certificates to be maintained “under an inspection program recommended by the helicopter manufacturer or a NATO military service.” It was issued on Feb. 4, 2015, two months after N98F’s last reregistration. The accident helicopter was therefore not subject to either this or the subsequent Version J, which advised FAA inspectors that Appendix D was “not sufficient to mitigate every safety risk you might encounter with a particular aircraft of operation” and recommended that they “prescribe additional operating limitations … based on inspections and assessments of potential safety hazards.” FAA Oversight FAA surveillance of experimental exhibition aircraft follows only the general procedures for all Part 91 operations, which don’t involve any formal inspection schedules. Specifically, FAA inspectors aren’t required to monitor adherence to the operating limitations of those certificates. The investigation determined that MARPAT Aviation didn’t routinely comply with limitation No. 4, which required submission of annual program letters to the responsible Flight Standards District Office (FSDO) listing the “events at which the aircraft will be exhibited.” The FAA plans its surveillance on the basis of these program letters. MARPAT’s owner suggested that events at the aircraft’s base didn’t have to be reported, but no such provision appeared in the operating limitations. The Charleston, West Virginia, FSDO’s principal maintenance inspector (PMI) confirmed that the FSDO should have been notified of the Huey reunions. Carriage of passengers for compensation or hire is generally subject to CFR 14 Part 119. Exceptions are available for charitable events, defined as those raising funds to benefit organizations qualified as “charitable” under US Treasury Department regulations. No such organization was associated with either MARPAT Aviation or the Huey reunion specifically. In the mid-1990s, the FAA also established the Living History Flight Experience (LHFE) policy “to provide a means for private owners and operators of historically significant … military aircraft to conduct limited passenger-carrying flights for compensation to generate funds for maintaining and preserving such historically significant aircraft.” Participation requires obtaining an exemption from the FAA; in 2022, 21 owners or operators, including 6 operating UH-1 helicopters, held LHFE exemptions. MARPAT Aviation didn’t, and the operator hadn’t applied for any other exemptions to charge for flights in an experimental exhibition category helicopter. The Takeaway Not surprisingly, the NTSB found the probable cause of the accident to be “the operator’s failure to adequately inspect the former military turbine-powered helicopter, which allowed an engine issue to progress and result in a loss of engine power and a subsequent loss of control after the helicopter struck power lines during a forced landing.” Unlike its typical practice of also citing “contributing” factors, the NTSB held that “also causal to the accident were the following: • The FAA’s inadequate inspection and maintenance standards for former military turbine-powered aircraft operating with an experimental exhibition airworthiness certificate • The operator’s use of those standards instead of more rigorous standards, which were readily available to the operator and previously used to inspect and maintain the helicopter • The FAA’s inadequate oversight of the operator, which did not detect the inherent risk associated with the operation.” It’s a safe bet that no operator wants to risk the destruction of equipment, much less the loss of lives. Knowing the risk of impending engine failure would have been ample reason to cancel the Huey reunion, or at least leave the helicopter on static display. And from the beginning of any aviation career, it’s deeply ingrained that compliance with the Code of Federal Regulations is the first defense against trouble—not just legal, but physical, as well. But what happens when the regulations themselves are confusing, ambiguous, or repeatedly changed in ways that don’t seem to make sense? Faced with requirements that seemed to shift almost at random, not only from year to year but between different registration categories, the operator had to make decisions. The most conservative approach would have been to maintain the inspection criteria of the army technical manuals, recognizing that they were more specific to the aircraft as well as more rigorous. The FAA’s willingness to accept the general provisions of Part 43, Appendix D, on the other hand, could be taken as official assurance that those generic standards were good enough, as well as easier and less expensive to implement. The NTSB makes a case that those regulatory gray areas and lack of specific oversight opened enough of a gap for the unfortunate occupants of N98F to fall through. David Jack Kenny is a fixed-wing ATP with commercial privileges for helicopter.
