AD 58-20-03 ACTIVE

58-20-03 LOCKHEED: Applies to Models 049, 149, 649, 649A, 749, and 749A Aircraft; Serial Numbers 1963 Through 1980; 2021 Through 2088; 2501 Through 2631; 2633 Through 2638 and 2640.

Compliance required as indicated.

A recent in-flight failure of an aft pressure bulkhead has been determined to have resulted from severe corrosion in the area of the lavatories.

The following must be accomplished on all aircraft which have accumulated 6,000 or more flight hours. Items 1. and 2. are not applicable to any of the aircraft which have been inspected in accordance with 2. and repaired as necessary per 3., within the past 4,000 hours. All affected aircraft will be limited to 2 p.s.i. cabin pressure differential until 1. and 2. have been accomplished.

1. Unless already accomplished per Lockheed wire FS/228233W or FS/228562W, within next 50 flight hours thoroughly examine the aft side of the pressure bulkhead (Station 1037) and adjacent shell structure between stringers 24 and 48. Clean and apply concentrated pressure with a device, which will not scratch good metal, to detect any indication of corrosion which may have developed on the forward side. If even slight indication of corrosion is found, conduct inspection 2. immediately.

2. Unless already accomplished per Lockheed wire FS/228233W or FS/228562W, within next 200 flight hours remove toilets, trim, plywood, insulation, paint, sealant, etc., to expose all bulkhead, bulkhead ring and shell structure, both forward and aft side of Station 1037, below the seat level and between stringers 24 and 48 and thoroughly inspect both sides of the pressure bulkhead and ring. Particularly close inspection shall be made to detect any evidence of corrosion at the periphery of faying surfaces at the pressure diaphragm attachment to the bulkhead ring, the elevator-rudder cable pulley bracket attachment on the lower left side and the Cannon plug attachment.

3. Replace any material or parts which show evidence ofcorrosion damage and thoroughly clean entire area, apply inhibitor, reseal, and paint in accordance with standard maintenance procedure. (See also 5.)

4. Inspect as in 2. and repair as in 3. at each block overhaul or at periods not to exceed 4,000 hours. This time may be increased to 8,000 hours on those airplanes in which sealing and drainage provisions equivalent to those outlined in Lockheed Service Bulletin No. SB-597 are incorporated.

5. If corrosion is found, flight operations shall be restricted, pending repairs, as follows:

(a) No flight is permissible with significant corrosion damage to bulkhead ring, web, control brackets or shell structure.

(b) Unpressurized flight is permissible if damage in confined strictly to the pressure diaphragm.

(Lockheed wire FS/228562W, dated September 30, 1958, covers the same subject.)

(Lockheed Structural Repair Manual, Report No. 5886, covers acceptable repair methods.)