51-21-02 PIPER: Applies to All Model PA-12 Airplanes.
Compliance required not later than October 15, 1951, and each 100 hours of operation thereafter unless reinforcements are installed.
Carefully inspect aileron hinge brackets to false spar attachment fittings, P/N N10931, (3 per wing), for cracks at the bend between the channel and flat portions of the fittings. If cracked fittings are found, add reinforcement bracket P/N 12047. With reinforcement brackets P/N 12047 installed, special inspections may be discontinued.
(Piper Service Bulletin No. 107, dated September 24, 1948, covers this same subject.)