AD 63-18-03 ACTIVE

63-18-03 LOCKHEED: Amdt. 604 Part 507 Federal Register August 17, 1963. Applies to All Models 188A and 188C Aircraft.

Compliance required as indicated.

Several fuselage stringers have been found cracked at the forward rivet through the "tee" clips attaching these stringers to the forward side of the pressure bulkhead at fuselage Station 1117.0. The following inspections and corrective action shall be accomplished:

(a)(1) On aircraft with more than 4,000 hours' time in service within the next 460 hours' time in service after the effective date of this AD, unless accomplished within the 540 hours' time in service preceding the effective date of this AD; and on aircraft with less than 4,000 hours' time in service, prior to the accumulation of 4,460 hours' time in service, inspect for cracks visually, or by X-ray, or FAA approved equivalent, fuselage stringers below the floor at the front rivet through the "tee" clips attaching these stringers to the forward side of the pressure bulkhead at fuselage Station 1117.0.

(2) On aircraft with more than 4,000 hours' time in service, within the next 920 hours' time in service after the effective date of this AD, unless accomplished within the 3,080 hours' time in service preceding the effective date of this AD; and on aircraft with less than 4,000 hours' time in service, prior to the accumulation of 4,920 hours' time in service, inspect for cracks visually, or by X-ray, or FAA approved equivalent, stringers at or above the floor at the front rivet through the "tee" clips attaching these stringers to the forward side of the pressure bulkhead at fuselage Station 1117.0, and the four longerons at their attachment to the forward side of the pressure bulkhead at fuselage Station 1117.0.

(b) The inspection of (a) shall be repeated for stringers below the floor at intervals not to exceed 1,000 hours' time in service and for stringers at or above the floor at intervals not to exceed 4,000 hours' time in service. These repetitive inspections may be discontinued for cracked stringers if they have been both repaired and reinforced per (c) and (d), and for uncracked stringers reinforced per (d).

(c) If cracks are detected in the stringers during the inspection specified by (a) or (b), the stringer shall be repaired before further flight. Cracks are to be repaired by the following method or by an equivalent method approved by FAA Engineering and Manufacturing Branch, Western Region: Remove approximately 16 inches of the affected stringer, extending from the "tee" clip forward, and replace with a new section made from the same material, with the same heat treat as the original affected stringer, but 1 or 2 gages thicker. Splice this section in accordance with Lockheed Structural Repair Manual, Section 53-2-2, pages 5 and 7. Particular care shall be taken to assure correct alinement of the replacement section to the "tee" clip. Use shims as necessary. Shims 0.050-inch thick or thicker must extend at least 5 inches forward of the "tee" clip. Shims less than 0.050-inch thick are to be terminated at the end of the "tee" clip. Shims extending forward of the "tee" clip shall be attached to the stringer with AD 5 rivets, Hi-Lock fasteners, or equivalent. The assembly of shims and stringers shall be attached to the "tee" clips with DD 6 rivets, Hi-Lock fasteners, or equivalent. Reference Lockheed Structural Repair Manual, Section 51-2-12, page 9, for fastener installation data.

(d) If no cracks are detected in the stringers during the inspection specified by (a) or (b) the stringers may be reinforced as indicated on Lockheed-California Company Drawing 841110B, "Service Mod. Inst.-Str. Attach. Reinforcement, FS.1117", or by an equivalent method approved by FAA Engineering and Manufacturing Branch, Western Region.

(e) If cracks are detected in the longerons during the inspection specified by (a)(2), the longeron shall be repaired before further flight in a manner acceptable to the FAA Engineering and Manufacturing Branch, Western Region.

(f) 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 contains substantiating data to justify the increase for such operator.

(Lockheed telegrams to operators, FS/260650W, dated September 17, 1962, FS/260672W, dated October 19, 1962, and Lockheed Service Bulletin 88/SB-581 cover the same subject.)

This directive effective September 17, 1963.