47-50-13 DOWNER (BELLANCA and UNIVERSAL (Stinson): Applies Only to Aircraft Equipped With Koppers Model Aeromatic F200 Propellers.
Compliance required no later than the next 25-hour propeller lubrication and at 25 hours of operation thereafter.
Inspect propeller hub as follows:
Remove balancing band from both ends of hub barrel after index marking each to facilitate proper reassembly. Examine the other surfaces of the hub completely for indications of line cracks or fractures. The areas of primary concern are (1) those beneath the balancing bands, (2) the weld joint where hub barrel and mounting tube meet, and (3) the weld joint where mounting tube and mounting flange meet.
Defective hubs should be removed from service.
(Koppers Service Bulletin No. 12, dated October 9, 1947, covers this same subject.)