CAA-AD-1-006/98

98-02-0l BOEING: Amendment 39-10283. Docket 97-NM-45-AD.

Applicability: All Model 737-100, -200, -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 (c) 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 sudden uncommanded yawing of the airplane due to potential failures within the yaw damper system, and consequent injury to passengers and crewmembers, accomplish the following:

(a) Remove the yaw damper coupler, replace the internal rate gyroscope with a new or overhauled unit, and perform a test to verify the integrity of the yaw damper coupler, all in accordance with a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate, at the applicable time specified in paragraph (a)(1) or (a)(2) of this AD.

( 1 ) For airplanes on which the yaw damper coupler has accumulated less than 12, 000 hours time-in-service since its last maintenance activity as of the effective date of this AD: Perform the actions within 6,000 hours time-in-service after the effective date of this AD; and thereafter at intervals not to exceed 9,000 hours time-in-service.

( 2 ) For airplanes on which the yaw damper coupler has accumulated 12,000 or more hours time-in-service since its last maintenance activity as of the effective date of this AD: Perform the actions within 3,000 hours time-in-service after the effective date of this AD; and thereafter at intervals not to exceed 9,000 hours time-in-service.

(b) If the yaw damper coupler fails the test required by paragraph (a) of this AD, prior to further flight, repair the coupler in accordance with a method approved by the Manager, Seattle ACQ.

(c) 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 2: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Seattle ACO.

(d) 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.

(e) This amendment becomes effective on February 17,1998.

FOR FURTHER INFORMATION CONTACT:

T. Tin Truong, Aerospace Engineer, Systems and Equipment Branch, ANM-1305, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 227-2552; fax (425) 227-1181.