Piper Aircraft has opposed an FAA Notice of Proposed Rulemaking (NPRM) that would require wing spar inspections for a significant number of Piper PA28 and PA32 aircraft.
The NPRM–issued at the beginning of October–relates to a proposed Airworthiness Directive (AD) that would require calculating service hours for each main wing spar; repetitively inspecting the lower main wing spar bolt holes for cracks and "non-crack damage" and taking corrective actions as needed, and "replacing or modifying main wing spars at a specified time".
The FAA is basing the need for inspections on two accidents with PA28-181 aircraft in 1987 and 1993, and one with an Arrow in 2018. In all three cases, fatigue cracks were found in the outboard bolt holes of the main wing spar.
If the AD is published as proposed, it is almost certain it would be adopted by CASA as written, requiring hundreds of Australia's ageing Warrior, Archer, Arrow, Pathfinder/Dakota, Lance/Saratoga and Cherokee Six fleet to be inspected.
Piper Aircraft has lodged feedback with the FAA pointing out that the regulator rescinded a similar AD issued in 1989 because the mandated inspection could more damage to the wing mounting hardware, resulting in fatigue failures. Piper says it believes that same thing can happen now.
"The FAA accurately recognized that more frequent inspections lead to increased damage, potentially resulting in fatigue failures caused by the inspections themselves," the company says.
"As inspection intervals shorten, mechanical damage will escalate, leading to premature fatigue failures. This creates a self-perpetuating cycle that will only worsen as damage accumulates and the need for inspections intensifies."
The company also points out that the wing spar in the NPRM was manufactured from 1961 to 2023 and fitted to 40,000 airframes, of which 20,000 are thought to be still airworthy in the USA alone.
Piper believes the wing spars are still in airworthy condition on many aircraft despite their constant use as primary trainers.
"The fleet of aircraft with 19,000 plus hours TIS [Time in Service] and no cracks has increased significantly in the last 35 years," their submission to the FAA states. "Likewise the overall fleet age with no cracks continues to increase.
"One operator reports a fleet of 11 PA-28-181 Archer II’s ranging in age from 22-47 years old, with no cracks, operated in a flight training environment, with four aircraft over 23,000 hours TIS and one aircraft with a max time of over 41,000 hours with no cracks."
Piper has estimated the cost of inspecting the US fleet at $US214.5 million, with correction and replacement costs reaching as high as $US 1.5 billion if all wings had to be replaced.
"This proposed rule will disproportionately affect the training fleet, imposing significant maintenance costs and requirements that will permanently burden future flight students," Piper says.
"Lower-cost pre-owned aircraft that are popular and needed in today’s flight training environment, such as the PA-28-151, PA-28-161, and PA28-181, will be significantly impacted.
"The installation time for the wing spar kit will ground many of these aircraft, straining flight schools and potentially forcing several to cease operations."
The company noted that existing date suggests that cracks are likely caused by the way the aircraft are operated rather than materials and manufacture, and that failures aren't likely if the aircraft is operated within the Pilots Operating Handbook (POH) limitations.
Piper has recommended the AD reflect Piper Aircraft Service Bulletin SB 1372 released in April this year, which addresses the same issues as the FAA NPRM.
More information on the NPRM and Piper's response is on the US government regulations website.