AD 92-14-07

92-14-07 BOEING: Amendment 39-8289. Docket No. 92-NM-29-AD. Supersedes AD 91-08-06, Amendment 39-6960.

Applicability: Model 747 series airplanes equipped with General Electric CF6-80C2 engines; as listed in Boeing Alert Service Bulletin 747-26A2179, dated February 28, 1991, and Revision 2, dated December 18, 1991; certificated in any category.

Compliance: Required as indicated, unless accomplished previously.

To prevent inadequate fire extinguishing agent concentration levels within the engine fire zone following engine fire system discharge, accomplish the following:

(a) For airplanes listed in Boeing Alert Service Bulletin 747-26A2179, dated February 28, 1991: Within 10 days after April 19, 1991 (the effective date of AD 91-08-06, Amendment 39-6960), accomplish the procedures specified in subparagraphs (a)(1), (a)(2), and (a)(3) of this AD in accordance with that service bulletin; or Revision 1, dated August 6, 1991; or Revision 2, dated December 18, 1991.(1) Visually inspect the engine number two and number three fire extinguishing tubes and specified tube clamps within the engine strut.

(2) If damage is detected, prior to further flight, replace or repair the damaged engine fire extinguishing tubes, as applicable, in accordance with Boeing Alert Service Bulletin 747-26A2179, dated February 28, 1991; or Revision 1, dated August 6, 1991; or Revision 2, dated December 18, 1991. (The service bulletins specify three repair procedures, depending upon the amount of chafing damage to the tube.)

(3) Remove the specified tube clamp from the fixed strut structure (the clamp should remain attached to the tube), and reinstall the tube clamp to orient the legs away from any structure.

(b) For airplanes listed in Boeing Alert Service Bulletin 747-26A2179, Revision 2, dated December 18, 1991, and not subject to paragraph (a) of this AD: Within 20 days after the effective date of this AD, accomplish the procedures specified in subparagraphs (b)(1), (b)(2), and (b)(3) of this AD in accordance with "Part I - Inspection" of that service bulletin.

(1) Visually inspect the engine number two and number three fire extinguishing tubes and specified tube clamps within the engine strut.

(2) If damage is detected, prior to further flight, replace or repair the damaged engine fire extinguishing tubes, as applicable, in accordance with the Boeing Alert Service Bulletin 747-26A2179, Revision 2, dated December 18, 1991. (The service bulletin specifies three repair procedures, depending upon the amount of chafing damage to the tube.)

(3) Remove the specified tube clamp from the fixed strut structure (the clamp should remain attached to the tube), and reinstall the tube clamp to orient the legs away from any structure.

(c) Repeat the inspection required by paragraphs (a) or (b) of this AD at the interval specified in subparagraph (c)(1) or (c)(2) below, as applicable:

(1) For airplanes that have not used the extinguishing tube patch repair procedures to repair the tube in accordance with paragraph (a) or (b) of this AD: Repeat the inspection at intervals not to exceed 100 flight cycles or 400 hours time-in-service, whichever occurs first.

(2) For airplanes that have used the extinguishing tube patch repair procedures to repair the tube in accordance with paragraphs (a) or (b) of this AD: Repeat the inspection at intervals not to exceed 50 flight cycles or 175 hours time-in-service, whichever occurs first.

(d) For airplanes listed in Boeing Alert Service Bulletin 747-26A2179, Revision 2, dated December 18, 1991: Within 6 months after the effective date of this AD, accomplish the modification specified in "Part II - Terminating Action" of the service bulletin. Accomplishment of this modification constitutes terminating action for the repetitive inspections required by paragraphs (c) 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. The request shall be forwarded through an FAA Principal Maintenance Inspector, who may concur or comment and then send it to the Manager, Seattle ACO.

NOTE: Information concerning the existence of approved alternative methods of compliance with this airworthiness directive, if any, may be obtained from the Seattle ACO.

(f) Special flight permits may be issued in accordance with FAR 21.197 and 21.199 to operate the airplane to a location where the requirements of this AD can be accomplished.

(g) The inspections, repairs, replacement, and modification shall be done in accordance with Boeing Alert Service Bulletin 747-26A2179, dated February 28, 1991 (the date of this document appears only on page 1 of the document); or Boeing Alert Service Bulletin 747-26A2179, Revision 1, dated August 6, 1991 (the revisionlevel and date of this document appear only on page 1 of the document); or Boeing Alert Service Bulletin 747-26A2179, Revision 2, dated December 18, 1991. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR Part 51. Copies may be obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124. Copies may be inspected at the FAA, Transport Airplane Directorate, 1601 Lind Avenue SW., Renton, Washington; or at the Office of the Federal Register, 1100 L Street NW., Room 8401, Washington, DC.

(h) This amendment becomes effective on August 20, 1992.