AD 63-03-03 ACTIVE

63-03-03 LOCKHEED: Amdt. 531 Part 507 Federal Register February 2, 1963. Applies to All Model 18 and Learstar Aircraft, Which Incorporate Landing Gear Drag Strut Anchor Fitting, P/N 51101.

Compliance required as indicated.

There have been cases of malfunctioning, due to loose bolts and elongated bolt holes, of the anchor fitting which secures the main landing gear drag strut to the center section on Lockheed Model 18 and Learstar aircraft. As this condition is likely to exist on other such aircraft, accomplish the following:

(a) Within the next 25 landings after the effective date of this AD and thereafter at intervals not to exceed 100 landings, conduct a close visual inspection of anchor fitting, P/N 51101,* which transmits main landing gear drag strut loads to the wing center section main beam and adjacent structure, in order to detect any evidence that the fitting has been moving during applications of load.

(b) If evidence is found to indicate that the fitting has been moving under load, accomplish the following:

(1) Gain access to the anchor fitting by drilling out the attachment rivets and removing the bolts which are used to fasten channels, P/N 51119* and P/N 51061,* in place.

(2) Conduct another close visual inspection of the anchor fitting to determine whether the attachment bolts are loose or to confirm that the fitting has been moving during applications of load.

(3) Any fitting inspected in accordance with (b)(2) and found to have loose bolts, or to have moved under load shall, prior to further flight, be reworked per (b)(4) or modified per (b)(5), as applicable, or replaced with a new anchor fitting, P/N 51101, of the original or modified design presently approved for use in the airplane.

(4) Anchor fittings, P/N 51101, or the structure which mates with the holes in the anchor fitting, which have not been previously modified, as indicated in (b)(5), if found to have elongated or deformed holes, may be returned toservice if the holes are reamed to accommodate steel bushings having a nominal wall thickness of 0.032 inches. The bushing material shall be steel, 4130 or equivalent, heat treated to 125,000-145,000 p.s.i. The dimensions to be maintained are:

Hole Diam.
Bushing O.D.
Bushing I.D.
For 5/16
attachment bolts

0.3758
0.3750

0.3766
0.3761

0.318
0.312
For 3/8
attachment bolts

0.4383
0.4375

0.4391
0.4386

0.381
0.374

Only those holes found elongated or deformed are to be reamed oversize to accommodate the 0.032 inch bushing.

(5) Anchor fittings, P/N 51101, and the structure which mates with the holes in the anchor fitting, which have been previously modified in conjunction with the "Learstar" modification or other gross weight increase programs, if found to have elongated or deformed holes, may be returned to service if modified in a manner approved by the Chief, Engineering and Manufacturing Branch, of the FAA region in which the gross weightmodification for the aircraft was approved.

(6) When new or reworked fittings are installed, new bolts or bolts which have been checked and found to exhibit no evidence of wear shall be used and shall be tightened to the torque values shown in Table 6-1 of Civil Aeronautics Manual 18.

(7) When channels P/N 51119 and P/N 51061 removed per (b)(1) are replaced, NAS 623 screws and appropriate steel washers and steel stop nuts may be substituted for the rivets. This will require reaming out the existing holes in P/N 5-119 channel and mating parts to a push fit for the screws. If rivets are selected, AN 430AD8 and AN 430AD5 type respectively shall be used.

(c) Upon request of the operator, an FAA maintenance inspector, subject to prior approval of the Chief, Engineering and Manufacturing Branch, FAA Western Region, may adjust the repetitive inspection intervals specified in this AD to permit compliance at an established inspection period of the operator if the request containssubstantiating data to justify the increase for such operator.

This directive effective March 5, 1963.

* The landing gear drag strut anchor fitting, P/N 51101, together with channels P/N 51119 and P/N 51061 are illustrated and listed on pages 56 and 57 of "Lockheed Handbook of Instructions for the Structural Repair" for Lockheed 18 Series aircraft.