AD 91-09-05

91-09-05 BOEING: Amendment 39-6969. Docket No. 90-NM-188-AD.

Applicability: All Model 737-300 series airplanes, and 737-400 series, and 737-500 series airplanes, prior to line position 2000, certificated in any category.

Also applies to Model 707 series airplanes with the following serial numbers, certificated in any category: 20474, 20669, 20830, 20831, 20832, 20833, 20834, 20835, 21081, 21092, 21103, 21104, 21123, 21124, 21125, 21126, 21127, 21128, 21129, 21228, 21261, 21334, 21367, 21368, 21396, 21428, 21475, 21956.

Also applies to Model 727 series airplanes with the following serial numbers, certificated in any category: 21040, 21080, 21091, 21229, 21230, 21347, 21348, 21349, 21426, 21427, 21458, 21459, 21460, 21595, 21636, 21844, 21845, 21846, 21847, 21945, 21946, 21947, 21948, 22268, 22359, 22360, 22361, 22362, 22763, 22968.

Also applies to Model 737-200 series airplanes with the following serial numbers, certificated in any category: 21667, 21613, 21957, 22431, 22620, 22628, 22777, 22778, 22779.

Compliance: Required within the next 180 days after the effective date of this AD, unless previously accomplished.

To prevent damage to the circuits contained within the Flight Instrument Accessory Unit, Integrated Flight Systems Accessory Unit, or Inertial Navigation System Battery Monitor Module, and to surrounding equipment, accomplish the following:

A. For Model 707 series airplanes: Install a modification to add a 2-ampere thermal circuit breaker electrically located between the crew call horn drive circuitry, located on printed circuit card assembly (part number 69-66423-11) contained within the Flight Instrument Accessory Unit or contained in the Inertial Navigation System Battery Monitor Module (part number 65-38292-192), as applicable, and the crew call horn. The modification must be approved by the Manager, Seattle Aircraft Certification Office, FAA, Transport Airplane Directorate.

B. For Model 727 series airplanes: Install a modification to add a 2-ampere thermal circuit breaker electrically located between the crew call horn drive circuitry and the crew call horn in accordance with Boeing Service Bulletin 727-23-0052, dated January 31, 1991.

C. For Model 737 series airplanes: Install a modification to add a 2-ampere thermal circuit breaker electrically located between the crew call horn drive circuitry and the crew call horn in accordance with Boeing Service Bulletin 737-23-1059, dated January 31, 1991.

D. 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 (PMI), who may concur or comment and then send it to the Manager, Seattle ACO.

E. 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 SW., Renton, Washington.

This amendment (39-6969, AD 91-09-05) becomes effective on May 28, 1991.