AD 80-26-02

80-26-02 GATES LEARJET: Amendment 39-4015. Applies to 23, 24, 25, 28 and 29 series airplanes certificated in all categories.

COMPLIANCE: Required as indicated, unless previously accomplished in accordance with AD 80-22-10.

A) Before further flight:

1. Deactivate the pitch function of the FC-110 Automatic Flight Control System (AFCS) or Automatic Flight Control Stability System (AFC/SS), as indicated below, by pulling the AFCS Pitch DC Circuit Breaker to the off position, banding it to prevent use of this function and checking to assure this function is the only deactivated circuit or control:

SERIES SERIAL NUMBERS LOCATION 23 003 thru 014 015 thru 099 Pilot's Switch Panel Pilot's Sub Panel 24 100 thru 139 (except 131, 132, & 134) 131, 132, & 134 140 thru 229

230 and up Pilot's Sub Panel

Pilot's circuit breaker panel Autopilot computer rack (under pilot's seat) Pilot's circuit breaker panel 25 003 thru 069 (except 032) 032070 and up Autopilot computer rack (under pilot's seat) Pilot's Sub Panel Pilot's circuit breaker panel 28 001 and up Pilot's circuit breaker panel 29 001 and up Pilot's circuit breaker panel

2. Install a locally fabricated placard on or near the autopilot control head in clear view of the crew, using letters at least 3/32 inch high, which reads:

AUTOPILOT PITCH AXIS INOPERATIVE

OBSERVE APPROPRIATE AFM AIRSPEED LIMITATIONS FOR INOPERATIVE AUTOPILOT and operate the airplane in accordance with this placard.

3. Insert in the appropriate section of the existing Airplane Flight Manual (AFM) the FAA approved temporary Airplane Flight Manual Change dated October 22, 1980, pertaining to emergency procedures for pitch axis malfunction.

B) On or before April 1, 1981, accomplish all of the following at a Gates Learjet authorized service center holding appropriate FAA repair station ratings.

1. Visually inspect the elevator control system to assurethat Pitch Axis Servo (D.C. Torquer), P/N 6600163-( ) is installed.

a) If installed, modify the airplane by incorporating autopilot pitch trim monitor test switch in accordance with Gates Learjet Airplane Modification Kit AMK 80- 16B, Change 2.

b) If not installed, modify the airplane by replacing the pitch servo actuator and capstan and incorporating autopilot pitch trim monitor test switch in accordance with Gates Learjet Airplane Modification Kits AMK 80-3, Change 4, and AMK 80-16B, Change 2, respectively.

2. Insert in the appropriate sections of the existing Airplane Flight Manual (AFM) the FAA approved temporary Airplane Flight Manual changes dated October 22, 1980, for autopilot trim monitor.

C) When paragraph B of this AD has been accomplished, the requirements of paragraphs A)1. and 2. of this AD are no longer applicable.

D) Airplanes may be flown in accordance with FAR 21.197 to a location where the requirements of this AD can be accomplished provided the autopilot is not operative during that flight.

E) Any equivalent method of compliance with this AD must be approved by the Chief, Aircraft Certification Program, FAA, Central Region, Room 238, Terminal Building No. 2299, Mid-Continent Airport, Wichita, Kansas 67209.

This AD supersedes AD 80-22-10.

This amendment becomes effective on January 15, 1981, to all persons except those to whom it has already been made effective by an airmail letter from the FAA dated December 11, 1980, and is identified as AD 80-26-02.