A Bell UH-1B helicopter that crashed following engine failure on June 22, 2022, was being inspected under less stringent requirements than should have applied, according to the NTSB.
Damage to the T53-L-11D turboshaft engine’s compressor section, gas-producer turbine, and exhaust diffusor rear bearing cover was not detected, and following the engine failure, the helicopter ran into powerlines during an attempted forced landing. All six onboard were killed.
The flight was part of the “7th Annual Huey Reunion” celebration held at Logan County Airport in Logan, West Virginia. During the event, visitors were invited to fly in the helicopter, and one person could pay a “required” donation of $250 to fly from the right seat for 30 minutes with no experience, according to the NTSB.
The helicopter’s operator, Marpat Aviation, held a special airworthiness certificate in the experimental exhibition category issued by the FAA’s Charleston, West Virginia Flight Standards District Office (FSDO). However, Marpat Aviation “did not hold a living history flight experience exemption for the helicopter,” the NTSB explained, “which would have allowed the helicopter to be operated for compensation.”
Marpat also failed to inform the FAA of its plans to fly the helicopter at the Huey Reunion, which it was required to do as part of operating limitations on the helicopter’s special airworthiness certificate. “As a result, the Charleston FSDO was unaware that Marpat Aviation was operating the accident helicopter at that event,” the NTSB wrote.
As part of the special airworthiness certificate, the FSDO had issued operating limitations that included specific inspection standards. These turned out to be the provisions of Appendix D to FAR Part 43. “We found that the inspection standards in Part 43 Appendix D did not have sufficient scope and depth for inspecting former military turbine-powered rotorcraft because the standards comprised generic inspection criteria for aircraft systems and components undergoing annual and 100-hour inspections,” the NTSB wrote.
“We also found that the damage to the engine exhaust diffuser (cracking) and the rear bearing cover (outer flange separation) were significant long-term engine issues that could have been detected if the operator, Marpat Aviation, had used more detailed inspection criteria and more frequent inspection intervals than those in Part 43 Appendix D. The inspection standards in Part 43 Appendix D did not have sufficient scope and depth for inspecting former military turbine-powered rotorcraft, especially given the complex design of typical former military rotorcraft…such a program would be expected to have more comprehensive information than only a listing of inspection criteria," the Safety Board continued. "For example, Appendix D stated that a reciprocating aircraft engine needed to be inspected for proper cylinder compression but did not specify critical turbine engine components for inspection, such as an engine compressor or turbine, and the necessary inspection steps to ensure the continued airworthiness for a complex turbine-powered aircraft.”
The probable cause of the accident “was 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 subsequent loss of control after the helicopter struck powerlines during a forced landing.” The NTSB cited as causal to the accident “the FAA’s inadequate inspection and maintenance standards” for operating former military aircraft under a special airworthiness certificate; the operator using the lesser standards instead of the more rigorous standards, which had been used previously on that helicopter; and inadequate oversight of the operator by the FAA, “which did not detect the inherent risk associated with the operation.”
In the examination of the engine after the accident, NTSB investigators “found static damage in the compressor section; rotational damage in the gas-producer turbine; and additional damage to the exhaust diffuser, rear bearing cover, No. 2 bearing, and two power turbine blades.” Evidence showed that the main rotor blades didn’t show significant impact fragmentation that would be expected if they were being powered, thus there was a partial or total loss of power before impact.
AIN contacted Marpat owner Michael Holbrook, and he responded "no comment" to AIN's inquiry. Marpat Aviation's website is still live and promoting the 2022 Huey Reunion and the company's other services.