Airworthiness Concern Issued for Comanche Stabilator Horn Cracks
February 2, 2011 —The FAA has issued an Airworthiness Concern Sheet (ACS) to alert owners and operators of Piper PA-24 Comanche series aircraft about in-service stress corrosion cracking in the stabilator horn. If undetected, this could result in a potential safety of flight hazard such as loss of pitch control. The issue was discovered during inspection and replacement of the stabilator torque tubes. The root cause is stress corrosion cracking, according to the National Institute for Aviation Research (NIAR). In addition, an informal survey of PA-24, PA-30, and PA-39 operators by the International Comanche Society (ICS) found 15 positive findings, all on single-engine Comanches. No in-flight failures related to this problem have been reported.
A Piper Service Bulletin (SB 1189) instructs owners to replace and/or repetitively inspect the horns on all single-engine (PA-24) and twin (PA-30, PA-39) Comanches. Stabilator torque tubes must be replaced when a new stabilator horn is installed.
The FAA is seeking additional information from associations and type clubs regarding service problems, proposed alternate inspection/repair procedures, cost impact, etc. Those with such information should mail it to Gregory K. (“Keith”) Noles, Aerospace Engineer, Atlanta ACO, 1701 Columbia Ave., College Park, GA 30337, or send an e-mail. (All comments or replies need to be as detailed as possible and include specific examples to illustrate the comments/concerns.)
The FAA has not made a determination of what type of corrective action (if any) should be taken. The resolution of this airworthiness concern could involve an Airworthiness Directive (AD) action or an SAIB, or the FAA could determine that no action is needed at this time. The initial risk assessment for this concern indicates that an AD would be considered. The FAA's final determination will depend in part on the information received in response to this ACS.