The FAA's proposed airworthiness directive (AD) for McCauley C406 and C409 propellers seems unfounded, since there are no accidents attributed to the malfunction of these propellers, AOPA says. The association has requested that the FAA withdraw the proposal or make public the test data the AD is based on and seek more user input.
The proposed AD would affect nearly 1,000 Beechcraft Bonanza, T-34, and Navion aircraft and is intended to prevent blade or hub failure that could result in the separation of a propeller blade. However, AOPA has not been able to find data to substantiate that claim.
"The proposed AD appears to be based entirely on the test data supplied by McCauley with no input from the user community or validation of the safety issue," wrote Luis Gutierrez, AOPA director of regulatory and certification policy, in formal comments to the FAA. "The FAA must supply the test data before the GA community can make a fair assessment of the safety of these propellers."
The AD would prohibit continuous propeller operation between 2,350 and 2,450 rpm at 24 inches Hg and higher manifold pressure, which is a common setting extensively used for normal operation.
"AOPA questions the justification for this restriction given that C406/C409 propellers have been safely operating for almost 30 years with no identified safety issues in this engine operating range," Gutierrez said. "Plus, AOPA could not find any accidents or incidents attributable to propeller blade or hub failure."
It also would remove from service all C406 and C409 propellers with unknown time in service (TIS) and set a 10,000-hour life limit on the propellers, which could affect the value of higher-time Bonanzas, T-34s, and Navions.
AOPA also faulted the FAA for neglecting to follow the airworthiness concern process, an agreed upon process that benefits the FAA and GA community by reducing the number of potential ADs based on actual field activity and providing for realistic alternative methods of compliance.
"The FAA instead chose to circumvent the agreed upon process and proceed to develop and issue this NPRM unilaterally without any input other than the manufacturer," Gutierrez said. "The FAA should follow the agreed upon process for dealing with airworthiness concerns that benefits the entire GA community."
January 19, 2006