AD 51-27-01

51-27-01 BELL: Applies to All Model 47 Helicopters Incorporating Engine Mount Assembly P/N 47-612-111-1 or -5.

Compliance required as indicated.

1. Compliance required daily after first 300-hour inspection.

(a) Remove paint from welds in tube cluster at mount housing at both sides of mount assembly. Use solvent to remove paint.

(b) With the engine mount under load, either by operating the engine with maximum collective pitch without becoming airborne, or by placing equivalent pilot and passenger weights in the seat and hoisting helicopter until wheels are clear of ground (or any equivalent loading means), inspect the outboard surface of welds with at least a 10-power magnifying glass and the inboard surfaces of welds with an inspection mirror (use magnifying if available). Give particular attention to forward tube in left cluster (from top of mount to housing) and aft tube in right cluster. Oil appearing on surface of weld or tube after cleaning is evidenceof a crack and must be examined carefully. Replace mount if crack is found.

(c) Clean welds in upper forward tube (under collective pitch disc bracket) with a cloth. Carefully inspect welds under disc bracket for cracks using a flashlight and mirror. Give particular attention to weld which joins diagonal tube (right side) to forward tube. Replace mount immediately if a crack is found in these areas. Apply grease or other corrosion preventive on areas where paint has been removed.

2. Compliance required at each 600 hours of engine mount service.

Replace engine mount assembly after 600 hours of operation have been accumulated. (Bell Service Bulletin No. 74, revised February 2, 1953, covers this same subject.) This supersedes AD 51-23-02.