AD 85-01-06

85-01-06 BOEING: Amendment 39-4982. Applies to Model 737 series airplanes certificated in all categories listed in Boeing Service Bulletin 737-53A1064, Revision 3, dated November 23, 1983. To prevent sudden loss of cabin pressure resulting from undetected cracking of the frames adjacent to the forward airstair, accomplish the following prior to accumulation of 29,000 landings, or within 90 days from the effective date of this AD, whichever occurs later, unless previously accomplished:

A. Visually inspect for cracks the body station 351.2 and 360 frames in accordance with the Flight Safety Addendum in Boeing Service Bulletin 737-53A1064, Revision 3, or later FAA approved revisions. Repeat the internal visual inspection at intervals not exceeding 3000 landings for Group 1 airplanes without external doublers installed in accordance with Boeing Service Bulletin 737-53-1058. For all other airplanes, repeat the inspection at intervals not exceeding 6000 landings.

B. If cracks are detected, repair before further flight in accordance with Service Bulletin 737-53A1064, Revision 3, or later FAA approved revisions, and continue the repetitive inspections of paragraph A., above.

C. As an alternative to the internal inspections of paragraph A., above, operators may visually inspect the external skin for cracks in the area of the forward airstair door cutout in accordance with Boeing Service Bulletin 737-53A1064, Revision 3, or later FAA approved revisions. Repeat external skin inspections at intervals not exceeding 300 landings until the internal frame inspection of paragraph A. is accomplished within 3000 flight cycles of the initial external visual inspection. Continue inspections in accordance with paragraph A.

D. If skin cracks are detected, unless previously accomplished during the same inspection period, inspect the frames in accordance with paragraph A., above. Repair cracks in accordance with the Structural Repair Manual or Boeing Service Bulletin 737-53-1058, as applicable, and continue the inspections of paragraph A.

E. Airplanes may be flown to a maintenance base for repairs or replacement in accordance with FAR 21.197 and 21.199 with prior approval of the Manager, Seattle Aircraft Certification Office, FAA, Northwest Mountain Region.

F. Modification of airplanes in accordance with the Accomplishment Instructions, Part II of Boeing Service Bulletin 737-53A1064, Revision 3, or later FAA approved revisions, constitutes terminating action for this AD.

G. For 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 time in service by the operator's fleet average time from takeoff to landing for the airplane type.

H. Upon request of the operator, an FAA Maintenance Inspector, subject to prior approval of the Manager, Seattle Aircraft Certification Office, FAA, Northwest Mountain Region, may adjust the repetitive inspection intervals specified in this AD, if the request contains substantiating data to justify the increase for the operator.

I. Alternate means of compliance which provide an equivalent level of safety may be used when approved by the Manager, Seattle Aircraft Certification Office, Northwest Mountain Region, Seattle, Washington.

All persons affected by this directive who have not already received these 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 also be examined at FAA, Seattle Aircraft Certification Office, 9010 East Marginal Way South, Seattle, Washington.

This amendment becomes effective February 25, 1985.