AD 58-23-02

58-23-02 DOUGLAS: Applies to All Model DC-6 Series Aircraft Prior to Fuselage Number 221, Except Number 214.

Compliance required as indicated.

Numerous cases have been reported wherein cracks have occurred in the vertical stabilizer front spar fittings, P/N 3344473, at Station 1033 bulkhead. Unless already accomplished, the following inspection must be made on all DC-6 Series airplanes indicated above which have in excess of 10,000 hours total flight time:

1. Within the next 25 hours flying time, inspect the above fittings for cracks occurring through the stabilizer attachment bolt holes and boss of the fitting and which propagate into either or both longitudinal flanges of the part. Cracks in one leg only should not exceed 3 1/2 inches in length. Cracks in both legs should not exceed 2 inches each. Cracks shall not be less than 3/4 inch from the edge of the leg and their length should be measured from the face of the counter bore on the lower side of the stabilizer attach bolt hole.

2. If cracks do not exceed the above limits, the parts may be continued in service for a maximum of 150 hours of flying time before replacement with the new part P/N 3406332, provided they are: (1) Stop drilled using a No. 10 drill and, (2) they are inspected at periods not to exceed 25 hours of flying time.

3. Fittings having cracks in excess of the above limits or cracks which extend across the leg of the fitting, must be replaced with new part, P/N 3406332, prior to next flight.

4. Fittings found to have no cracks at the time of inspection, per 1. must be accorded a repetitive inspection at each block overhaul period or at periods not to exceed 3,500 hours, until new fitting, P/N 3406332, is installed.

(Douglas Alert Service Bulletin No. A-796, dated August 15, 1958, and Service Bulletin No. 796, dated September 2, 1958, cover this same subject.)