AD 55-23-03

55-23-03 LOCKHEED: Applies to Models 49, 149, 649, 749 and 1049 Aircraft, Serial Numbers 1963 Through 1980, 2021 Through 2088, 2503 Through 2590, 2610, 2611, and 2614 Through 2677, 4001 Through 4024, 4163 Through 4166, 4501 Through 4581, 4583 Through 4594, 4602 Through 4604, and 4613 Through 4615.

Compliance required as indicated.

1. As soon as possible, but not later than next 250 hours conduct magnetic particle or magnaglow inspections on main landing gear downlock spring cylinder assembly rod end P/N 295168 for cracks in the threaded portion. If cracks are found replace the part immediately. Repeat inspection, magnetic particle or 20-power magnifying glass at 300-hour intervals until replacement in accordance with paragraph 2 is accomplished.

2. Replace downlock spring cylinder assembly P/N 270104 with new assembly P/N 475211 as soon as practical but not later than the next progressive or base overhaul period approximately 2,500 hours. Concurrently with this replacement, line ream the lugs on the downlock strut assembly to (0.3770 inch-0.3780 inch) diameter and replace the spacer P/N 268225-2 with bushing P/N LS3859-4-1094 and replace bolt AN 23-21 with AN 23-22 attaching the lower end of the spring cylinder assembly to the downlock strut.

(Lockheed Service Bulletins 49/860 and 1049/2709 also cover this subject.)