Remarks: The compliance of this AD must be recorded in Aircraft Logbook, where applicable the requirements of this AD must be integrated into Aircraft Technical Documentation. Address inquiries concerning this AD to: Civil Aviation Authority, Airworthiness Division, Ruzyne Airport, 160 08 Prague 6, Czech Republic, tel: 420 2 33320922, fax: 420 2 20562270.

2000-07-06 BOEING: Amendment 39-11660. Docket 99-NM-81-AD.

Applicability: All Model 737-100, -200, -200C, -300, -400, and -500 series airplanes; certificated in any category.

NOTE 1: This AD applies to each airplane identified in the preceding applicability provision, regardless of whether it has been modified, altered, or repaired in the area subject to the requirements of this AD. For airplanes that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must request approval for an alternative method of compliance in accordance with paragraph (e) of this AD. The request should include an assessment of the effect of the modification, alteration, or repair on the unsafe condition addressed by this AD; and, if the unsafe condition has not been eliminated, the request should include specific proposed actions to address it.

Compliance: Required as indicated, unless accomplished previously.

To prevent fatigue cracking of the lower corners of the door frame and cross beam of the forward cargo door, which could result in rapid depressurization of the airplane, accomplish the following:

(a) Within 1 year or 4,500 flight cycles after the effective date of this AD, whichever occurs later, perform a high frequency eddy current (HFEC) inspection to detect cracking of the lower corners (forward and aft) of the door frame of the forward cargo door in accordance with Boeing 737 Nondestructive Test Manual, Part 6, Section 51-00-00, Figure 4 or Figure 23.

(1) If no cracking is detected, repeat the HFEC inspection thereafter at intervals not to exceed 4,500 flight cycles, until the requirements of paragraph (c) of this AD have been accomplished.

(2) If any cracking is detected during any inspection required by paragraph (a) of this AD, prior to further flight, accomplish the requirements of paragraphs (a)(2)(i) AND (a)(2)(ii) of this AD, which constitute terminating action for the repetitive inspections required by paragraph (a)(1) of this AD.

(b) Within 1 year or 4,500 flight cycles after the effective date of this AD, whichever occurs later, perform a detailed visual inspection to detect cracking of the cross beam (i.e., upper and lower chord and web sections) of the forward cargo door in accordance with Boeing Service Bulletin 737-52-1100, Revision 2, dated March 31, 1994.

NOTE 2: For the purposes of this AD, a detailed inspection is defined as: "An intensive visual examination of a specific structural area, system, installation or assembly to detect damage, failure or irregularity. Available lighting is normally supplemented with a direct source of good lighting at intensity deemed appropriate by the inspector. Inspection aids such as mirror, magnifying lenses, etc. may be used. Surface cleaning and elaborate access procedures may be required."

(1) If no cracking is detected, repeat the inspection thereafter at intervals not to exceed 4,500 flight cycles until the requirements of paragraph (c) of this AD have been accomplished.

(2) If any cracking is detected on the lower chord section of the cross beam during any inspection required by paragraph (b) of this AD, prior to further flight, repair in accordance with a method approved by the Manager, Seattle ACO, or in accordance with data meeting the type certification basis of the airplane approved by a Boeing Company DER who has been authorized by the Manager, Seattle ACO, to make such findings.

(3) If any cracking is detected on any area excluding the lower chord section of the cross beam (i.e., upper chord and web section) during any inspection required by paragraph (b) of this AD, prior to further flight, accomplish the requirements of paragraph (b)(3)(i) or (b)(3)(ii), as applicable, of this AD, which constitute terminating action for the repetitive inspections required by paragraph (b)(1) of this AD.

NOTE 3: Due to implications and consequences associated with cracking, this AD does not allow the option of replacing the door frame as an alternative method of compliance to installing the preventative modification.

(c) Within 4 years or 12,000 flight cycles after the effective date of this AD, whichever occurs later: Install the preventative modification of the outboard radius of the lower corners (forward and aft) of the door frame and the reinforcement modification of the cross beam of the forward cargo door in accordance with paragraph (c)(1) or (c)(2) of this AD, as applicable. Accomplishment of paragraph (c)(1) or (c)(2) of this AD, as applicable, constitutes terminating action for the repetitive inspections required by paragraphs (a)(1) and (b)(1) of this AD.

(1) For airplanes with line numbers 1 through 1231: Accomplish the preventative modification and the reinforcement modification in accordance with Boeing Service Bulletin 737-52-1100, Revision 2, dated March 31, 1994.

(2) For airplanes with line numbers 1232 and subsequent: Accomplish the preventative modification and the reinforcement modification in accordance with a method approved by the Manager, Seattle ACO or in accordance with data meeting the type certification basis of the airplane approved by a Boeing Company DER who has been authorized by the Manager, Seattle ACO, to make such findings.

(d) For all airplanes on which modifications of the forward lower corner of the door frame and the cross beam of the forward cargo door were accomplished in accordance with Boeing Service Bulletin 737-52-1100, dated August 25, 1988, or Revision 1, dated July 20, 1989, or in accordance with the requirements of AD 90-06-02, amendment 39-6489: Within 4 years or 12,000 flight cycles after the effective date of this AD, whichever occurs later, install the reinforcement modification of the aft corner of the door frame of the forward cargo door in accordance with Boeing Service Bulletin 737-52-1100, Revision 2, dated March 31, 1994. Accomplishment of such modification constitutes terminating action for the repetitive inspections required by this AD.

NOTE 4: Accomplishment of Boeing Service Bulletin 737-52-1100, Revision 2, dated March 31, 1994, does not supersede the requirements of AD 90-06-02, amendment 39-6489.

(e) An alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used if approved by the Manager, Seattle ACO. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Seattle ACO.

NOTE 5: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Seattle ACO.

(f) Special flight permits may be issued in accordance with sections 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the airplane to a location where the requirements of this AD can be accomplished.

(g) Except as provided by paragraphs (a)(2)(i)(A), (a)(2)(ii), (b)(2), (b)(3)(ii), and (c)(2) of this AD; the actions shall be done in accordance with Boeing Service Bulletin 737-52-1100, Revision 2, dated March 31, 1994; and Boeing 737 Nondestructive Test (NDT) Manual, D6-37239, Part 6, Section 51-00-00, Figure 4 or Figure 23, dated August 5, 1997; as applicable. Boeing 737 NDT Manual contains the following list of effective pages:

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 98134-2207. Copies may be inspected at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

(h) This amendment becomes effective on May 16, 2000.

FOR FURTHER INFORMATION CONTACT:
Nenita Odesa, Aerospace Engineer, Airframe Branch, ANM-120S, FAA, Transport Airplane Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 227-2557; fax (425) 227-1181.

Issued in Renton, Washington, on March 31, 2000.
Donald L. Riggin, Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.