AD 88-11-12

88-11-12 BOEING: Amendment 39-5890. Applies to Model 737 series airplanes listed in Boeing Service Bulletin 737-53-1051, Revision 4, dated July 30, 1987, certificated in any category.

Compliance required as indicated, unless previously accomplished.

To prevent rapid loss of cabin pressure resulting from undetected frame cracking, accomplish the following:

A. Prior to the accumulation of 6,000 landings after June 16, 1986, visually inspect the forward and aft body frames adjacent to the forward lower cargo door for cracks, in accordance with Flight Safety Inspection Program in Boeing Service Bulletin 737-53-1051, Revision 3, dated July 12, 1985. Repeat the inspections at intervals not to exceed 4,000 landings.

B. After the effective date of this AD, if cracks are found, prior to further flight, repair in accordance with Part III.A. or Part III.B., as applicable, of Boeing Service Bulletin 737-53-1051, Revision 4, dated July 30, 1987.

C. For airplanes that have had cracks repaired in accordance with Part III.A. of Boeing Service Bulletin 737-53-1051, initial release, dated June 16, 1978, or later FAA-approved revisions: Prior to the accumulation of 25,000 landings after the repair, and thereafter at intervals not exceed 17,000 landings, visually inspect the frames for cracks in the area of the repair in accordance with Boeing Service Bulletin 737-53-1051, Revision 3. Parts found cracked must be repaired prior to further flight in accordance with an FAA-approved repair method.

D. For airplanes that have had cracks repaired in accordance with Part III.B. of Boeing Service Bulletin 737-53-1051, Revision 3: Prior to the accumulation of 3,000 landings after effective date of this AD, replace the repair parts with new airworthy repair parts in accordance with Boeing Service Bulletin 737-53-1051, Revision 4.

E. For airplanes that have had cracks repaired in accordance with the Boeing Model 737 Structural Repair Manual,Section 51-40-3, or with Part III.B. of Boeing Service Bulletin 737-53-1051, Revision 4, or later FAA-approved revisions, or in accordance with paragraph D., above: Prior to the accumulation of 6,000 landings after the repair and thereafter at intervals not to exceed 4,000 landings, visually inspect the frames for cracks in the area of the repair in accordance with Boeing Service Bulletin 737-53-1051, Revision 4. Parts found cracked must be repaired prior to further flight, in accordance with an FAA-approved repair method.

F. Modification of uncracked frames in accordance with the Preventative Modification of Boeing Service Bulletin 737-53-1051, Revision 3, dated July 12, 1985, constitutes terminating action for the requirements of this AD.

G. Airplanes with cracked frames may be flown unpressurized in accordance with FAR 21.197 and 21.199 to a maintenance base for repairs or replacement required by this AD.

H. For the purposes of complying with this AD, subject to acceptance by the assigned FAA Maintenance Inspector, the number of landings may be determined by dividing each airplane's number of hours time in service by the operator's fleet average time from takeoff to landing for the airplane type.

I. An alternate means of compliance or adjustment of the compliance time, which provide an acceptable level of safety and which has the concurrence of an FAA Principal Maintenance Inspector, may be used when approved by the Manager, Seattle Aircraft Certification Office, FAA Northwest Mountain Region.

All persons affected by this directive who have not already received the appropriate service documents from the manufacturer may obtain copies upon request to the Boeing Commercial Airplane Company, P.O. Box 3707, Seattle, Washington 98124. These documents may be examined at the FAA, Northwest Mountain Region, 17900 Pacific Highway South, Seattle, Washington, or the Seattle Aircraft Certification Office, 9010 East Marginal Way South, Seattle, Washington.

This amendment supersedes AD 86-09-06, Amendment 39-5307.

This amendment, 39-5890, becomes effective June 27, 1988.