Spar inspection results raise FAA concern

The final AD, published February 13 and effective March 20, was proposed in May 2021 following the in-flight breakup of a Cessna 210M in Australia in 2019. An FAA-estimated 3,421 U.S.-registered aircraft were to be subject to visual and eddy current inspections of the lower wing spar carrythrough cap. The final AD cites the same number of aircraft, and continues to require one-time visual and eddy current inspection of the same wing spar components.

The FAA estimates that required inspections will cost $3,108 per aircraft, up to $3,788 if oxygen and air conditioning must be removed for inspection access. On-condition costs, including additional eddy current inspection and, in the worst case, wing spar replacement, are far higher: up to $40,200 to replace the spar of a Cessna 177, though that is a theoretical number since the parts are out of production.

Comments on the proposed AD noted that no Cessna 177 wing has failed in flight, and that service difficulty reports did not support the inclusion of that model in the AD. The FAA disagreed, citing the failure rate of Cessna 177 wing spar inspections to date:

“Out of the 211 Model 177-series reports received by the FAA as of January 13, 2023, 120 have reported corrosion,” the agency wrote in the final AD. “Of those, at least 14 were removed from service due to corrosion or damage.”

The 14 Cessna 177 spars taken out of service following inspections to date have not likely been replaced with new parts. The FAA noted that Textron Aviation is still working to develop a replacement spar for those aircraft, long out of production.

None of the later-model Cessna 210s inspected to date had spars taken out of service due to corrosion too severe to grind down and leave enough structure to remain in service, the FAA noted, though two Cessna 210 spars were removed from service due to damage. Just under 7 percent of the newer 210s had any corrosion found on inspection. Among the older Cessna 210s, the rate of corrosion discovery was much higher—47 percent. The FAA noted, however, that while the rate of corrosion discovery was lower, the newer Cessna 210 models are more susceptible to spar failure if the structure becomes compromised:

“Analysis completed by Textron revealed that later Model 210-series airplanes, due to their weight and configuration, demonstrate higher stress levels in operation when compared to earlier Model 210-series airplanes. Therefore, the critical crack length—the length at which the crack reduces the capability of the structure below that provided in the certification basis—is smaller in the later Model 210-series airplanes.”

While the FAA did not entirely close the door on alternative methods of compliance, it rejected arguments that the AD should mirror a 2020 AD issued to address spar corrosion in Piper Aircraft PA–28 and PA–32 models.

“The unsafe condition on the Model 210-and 177-series airplanes addressed by this AD involves both corrosion and cracking,” the agency wrote. “The FAA cannot use an evaluation similar to the one used for the Piper airplanes to draw the same conclusions or correlations to the unsafe condition addressed by this AD, as the unsafe condition associated with AD 2020-26-16 [applicable to Piper airplanes] is primarily associated with fatigue cracking concerns.”

AOPA continues to monitor the effects of age and corrosion across the general aviation fleet, and encourages owners to remain engaged in the process. Information that aircraft owners provide to AOPA (in addition to the reports required by the FAA) will help bolster future advocacy on behalf of aircraft owners against mandating inspections and other measures not supported by data indicating they are needed in the interest of safety.