Citing ongoing failures and risk of fire after years of model-specific airworthiness directives, the FAA published an AD that requires inspection and possible replacement of all spot-welded, multi-segment exhaust pipe v-band couplings installed between tailpipe and turbocharger, or up to two years of periodic inspections until replacement parts are available.
AD 2023-09-09, published June 12 in the Federal Register, is effective July 17, and seeks to resolve an issue with a decadeslong history of causing or contributing to accidents and incidents, some fatal, involving aircraft with turbocharged engines including in-flight fire that can result from the exhaust pipe separating from the turbocharger and venting hot gas into the engine compartment. The FAA noted in the AD that failures of v-band couplings attaching the tailpipe exhaust to the turbocharger “have resulted in a significant number of accidents (fatal and non-fatal) on both airplanes and helicopters.” The AD is specific to the spot-welded v-band multi-segmented coupling, which connects the tailpipe to the turbocharger, and establishes a life limit and inspection requirements. The AD does not reference part numbers produced by various manufacturers. The AD does not apply to couplings that are not spot-welded.
The new AD does not apply to aircraft that have complied with certain previous ADs, and/or to aircraft with riveted v-band turbocharger exhaust couplings installed, but there are no other exceptions: The new directive applies to “turbocharged, reciprocating engine-powered airplanes and helicopters and turbocharged, reciprocating engines with a certain v-band coupling installed.”
In 2018, a General Aviation Joint Steering Committee working group concluded that spot welds used instead of rivets to secure the segments (two or three) to the outer band of the clamp become prone to fail after a certain period of time in service (TIS). “Although multi-segment exhaust tailpipe couplings can also be riveted, the riveted couplings do not create an unsafe condition,” the FAA noted.
The FAA proposed the new AD in 2022, drawing support from the NTSB though not all 35 public comments on the proposed directive were supportive. The AD is substantially unchanged in its final form.
“Because these [spot-welded] v-band couplings are widely used by many design approval holders on various models (engines and aircraft), several Aircraft Certification Office Branches were involved in the decision to propose a single AD. The FAA also determined that the corrective actions recommended in the final report were appropriate to address this unsafe condition,” the agency wrote. “This condition, if not addressed, could lead to failure of the spot-welded, multi-segment exhaust tailpipe v-band coupling, leading to detachment of the exhaust tailpipe from the turbocharger and allowing high-temperature exhaust gases to enter the engine compartment. This could result in smoke in the cockpit, in-flight fire, and loss of control of the aircraft. The FAA is issuing this AD to address the unsafe condition on these products.”
The AD establishes a 500-hour life limit on spot-welded v-band couplings, allowing 50 hours of TIS to replace v-band couplings known to be at or beyond 500 hours, or of an unknown TIS. The FAA does offer an alternative to immediate replacement of these v-band couplings: “Do the initial inspections at the time the v-band coupling would have been removed from service and thereafter at intervals not to exceed 6 months or 100 hours TIS, whichever occurs first, for a period not to exceed 2 years after the effective date of this AD.”
Parts availability—particularly in light of the demand driven by imposition of a 500-hour TIS limit on the part in question—is expected to be a more impactful problem for owners than the cost of replacing the part. The FAA notes that the paragraph allowing up to two years of periodic inspections (every six months or 100 hours, whichever comes first) "was provided to allow compliance with the requirements of this AD with regards to hardware availability."
The FAA estimates 41,058 aircraft will require a records review (estimated to cost $42.50, or one-half hour of shop time), with additional costs of $570 to replace the affected part on a single-engine aircraft, or $1,140 for twin-engine aircraft. Periodic inspection of the couplings without removal and replacement is estimated to cost a half-hour of work per engine. AOPA does not agree with the cost estimates that the FAA used in the AD, including labor cost based on an hourly rate of $85. Members have reported significantly higher labor rates, up to $180 per hour. AOPA will address this issue with the FAA.
The AD includes detailed specifications and instructions for inspecting spot-welded v-band couplings.