On September 9, 2005, the FAA issued a final rule airworthiness directive (AD) that requires the inspection of the propeller blades and other critical propeller parts. The AD resulted from two incidents where "Z-shank" blades failed and separated. Teardown inspections detected corrosion in the blade bores. The AD affects some 1,200 airplanes in the U.S. registry that may include the Cessna 172, 175, 190, 195, and 421; the Piper PA-23, PA-24, and PA-25; and several other models from Beechcraft, Aero Commander, Grumman, and Mooney.
Undetected corrosion and mechanical damage in the propeller assembly could result in propeller blade failure and subsequent loss of aircraft control. To mitigate this possibility, the FAA issued AD 2005-18-12, which requires inspection of the propeller assembly for corrosion and mechanical damage if the propeller assembly has more than 10 years time-since-overhaul (TSO) on the effective date of this AD, or if the TSO is unknown, or if the propeller has not complied with Hartzell Service Bulletin (SB) No. HC-SB-61-136, Revision I, H, or G. The FAA has established a compliance schedule for completing the inspections, ranging from 12 to 36 months.
The AD does not require further action on the aircraft owner if the propeller TSO is 10 years or less on the AD's effective date, or the propeller assembly was inspected in accordance with one of the previously referenced Hartzell SBs.
AOPA agrees that, in this particular situation, the possibility for blade failure caused by corrosion in the blade bore, and possible subsequent in-flight propeller blade separation, warrants airworthiness action. The AD is reasonable in that it only requires a one-time inspection ranging from 12 to 36 months from the AD's effective date to comply. Affected owners may request an alternate means of compliance from the FAA.