It may not be a done deal yet, but the NTSB has presented a compelling case to the FAA for an Airworthiness Directive on the vintage Piper PA-12 Super Cruiser, the PA-14 Family Cruiser and potentially the PA-18 Super Cub, due to metal fatigue issues with the steel that forms the rudder post.
Last month after a two-year study, the Board cited two accidents in Alaska to support its recommendation for an AD, focused on Piper part number 40622 which is made of AISI 1025 carbon steel. The NTSB noted that the accident aircraft were produced between 1946-1948 and that Piper Aircraft, Inc. no longer owns the type certificates for the PA-12 and PA-14.
The NTSB studied at least five failed rudders, including one from a 1969 Super Cub, and findings suggested that fractures will occur due to fatigue “under normal service conditions,” exacerbated by scratches or other surface “features” on the steel. In its recommendation to the FAA, the Board specified that a rudder post made of updated AISI 4130 steel should address any unsafe condition. Rudders made of the updated steel appear to have been available on the Piper parts market for many decades.
At least one eagle-eyed airplane owner voiced concern that all the failed rudders in the NTSB airworthiness concern sheet are to be from Pipers running larger 150-180 hp engines versus the original 104-115 hp Lycoming O-235 powerplant on PA-12 and PA-14 models. While the Board made no mention of this in its recommendations, it will be interesting to see if the FAA acts solely on models with upgraded engines, or if it will blanket all 1,329 PA-12 and -14 models remaining on the Registry for inspection.
If the FAA decides to involve the Super Cub, which began production in 1949 and saw north of 10,300 units produced, we can begin to imagine a long waiting line to obtain updated rudders with fresh fabric, dope and paint.