AD 91-07-04

91-07-04 BOEING: Amendment 39-6933. Docket No. 90-NM-116-AD.

Applicability: Model 737 series airplanes, line numbers 001 through 519, certificated in any category.

Compliance: Required as indicated, unless previously accomplished.

To prevent rapid decompression of the airplane, accomplish the following:

A. Within the next 3,000 cycles after the effective date of this AD, unless previously accomplished within the last 3,000 cycles, and thereafter at intervals not to exceed 6,000 cycles, perform an ultrasonic inspection for delamination of the window belt skin doubler from the fuselage skin, in accordance with Boeing Service Bulletin 737-53-1078, Revision 1, dated September 25, 1986, or Revision 2, dated April 19, 1990.

B. If delamination is found as a result of the inspections required by paragraph A. of this AD, prior to further flight, conduct a high frequency eddy current (HFEC) inspection for cracks of the skin around the countersunk fasteners in thearea of delamination and common to the window forging, in accordance with Boeing Model 737 Non-destructive Test (NDT) Manual Document D6-37239, Part 6, Subject 53-30-05, and repeat thereafter at intervals not to exceed 6,000 cycles.

C. If cracks are detected as a result of the inspection required by paragraph B. of this AD, prior to further flight, repair cracking and delamination in accordance with Boeing Service Bulletin 737-53-1078, Revision 1, dated September 25, 1986, or Revision 2, dated April 19, 1990. Further HFEC inspections for cracks under the repairs are not required.

D. If delamination is found as a result of the inspection required by paragraph A. of this AD, perform the terminating modification in accordance with Boeing Service Bulletin 737- 53-1078, Revision 1, dated September 25, 1986, or Revision 2, dated April 19, 1990, prior to the accumulation of 40,000 cycles or within the next 24 months, whichever occurs later, after discovery of the delamination. Accomplishment of this modification constitutes terminating action for the inspections required by paragraphs A. and B. of this AD.

E. An alternative method of compliance or adjustment of the compliance time, which provides an acceptable level of safety, may be used when approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate.

NOTE: The request should be forwarded through an FAA Principal Maintenance Inspector, who may concur or comment and then send it to the Manager, Seattle ACO.

F. Special flight permits may be issued in accordance with FAR 21.197 and 21.199 to operate airplanes to a base in order to comply with the requirements of this AD.

All persons affected by this directive who have not already received the appropriate service documents from the manufacturer may obtain copies upon request to Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124. These documents may be examined at the FAA, Northwest Mountain Region, Transport Airplane Directorate, 1601 Lind Avenue S.W., Renton, Washington.

Airworthiness Directive 91-07-04 supersedes AD 89-15-05, Amendment 39-6264.

This amendment (39-6933, AD 91-07-04) becomes effective on April 15, 1991.