PROPELLER BULLETIN

Sensenich Propeller

SERVICE BULLETIN #R-12A
FEBRUARY 6, 1967

TO:

FAA APPROVED PROPELLER REPAIR STATIONS, SENSENICH DISTRIBUTORS; BEECH MUSKETEER OWNERS

PROPELLER MODELS AFFECTED:

ALL SENSENICH FIXED-PITCH METAL PROPELLERS WITH WATER-SOLUBLE MID-BLADE DECALS INCLUDING MODELS M74DC AND M74DM WITH BEECH MID-BLADE DECALS, BUT EXCLUDING THOSE PROPELLERS WHICH HAVE ALREADY BEEN SERVICED OR REPLACED IN ACCORDANCE WITH SENSENICH BULLETINS R-11 AND R-12 AND FEDERAL AVIATION AGENCY AIRWORTHINESS DIRECTIVES 66-11-3 AND 66-23-2

COMPLIANCE DATE:

NOT LATER THAN THE NEXT TWENTY HOURS OF OPERATION

SUBJECT:

REMOVAL OF MID-BLADE DECALS AND INSPECTION OF MID- BLADE AREA FOR CORROSION PITS AND CRACKS

Sensenich Propeller Bulletin Number R-11 dated March 1,1966 and FAA Airworthiness Directive 66-11-3 dealt with the problem of corrosion pits found in the area of the mid-blade propeller decal. Instances of corrosion pits under and in the immediate area of the mid-blade decal have been discovered in M74DC and M74DM propellers carrying Beech decals and other models of Sensenich fixed-pitch metal propellers with Sensenich decals attached by a water-soluble adhesive. The Sensenich decals can be identified by their black border (sketch #1). Later Sensenich epoxy-adhesive decals (with a narrow gold border outside the black, sketch #2 ) are satisfactory. Water-soluble decals must not be re-installed.
These decals must be removed by soaking with paint remover and rubbing off with a rag; they must not be scraped or sanded off. The mid-blade area must be thoroughly inspected with a glass of at least 3 power. If a crack or corrosion pits deeper than .015 inch are found, the propeller must be replaced before further flight. If corrosion pits (tiny black dots) are discovered, they must be removed within the next twenty hours of operation. They can be removed in the following manner: (1) Sand the area with 220 grit wet-or-dry abrasive paper and polish with 320 grit or finer. (2) Clean the area thoroughly and apply a dye penetrant. (3) Inspect with a low-power glass; it is very important that the bottom of the pits be completely removed. If the pits re-appear, repeat the operations. (4) When the pits are completely removed, spray the area with a clear lacquer.
Owners who wish to do so may return their propellers to the factory for reconditioning or exchange for a factory reconditioned propeller.

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