AD 85-16-04

85-16-04 GATES LEARJET: Amendment 39-5110. Applies to Model 35, 35A, 36, and 36A series airplanes modified by Raisbeck Group Supplemental Type Certificate (STC) SA766NW, certificated in any category. The affected airplane serial numbers are:

35-023, 35-034, 35-042, 35-044, 35-047, 35A-068, 35A-073, 35A-075, 35A-076, 35A- 086, 35A-092, 35A-093, 35A-095, 35A-118, 35A-127, 35A-132, 35A-135, 35A-145, 35A- 172, 35A-185, 35A-192, 35A-203, 35A-206, 35A-207, 35A-209, 35A-228, 35A-231, 35A- 244, 35A-245, 36-003, 36-004, 36-017, 36A-028, 36A-029, 36A-031, 36A-038, 36A-043, and 36A-044.

To prevent deterioration of the airplane lateral control characteristics as a result of aileron buffet or buzz accomplish the following, unless previously accomplished.

A. Within the next 200 hours time in service or six months after the effective date of this AD, whichever comes first, accomplish either paragraph 1. or 2., as follows:

1. Reduce MMO by accomplishing the following:a. Submit the FAA approved STC SA766NW Airplane Flight Manual Supplement to the Manager, Flight Test Branch, ANM-160S, Seattle Aircraft Certification Office, FAA, Northwest Mountain Region, 17900 Pacific Highway South, Seattle, Washington 98168, to change the limit Mach number from .83 to .80;

b. Remove the "Mach Overspeed Warning Switch" and have it reset from Mach .83 to .80. Contact the manufacturer PRECISION SENSOR, P.0. Box 509, Milford, Connecticut 06460, telephone number (203) 877-2795, to have the instrument recalibrated. Reidentify the Mach overspeed warning switch by ink stamping "Mach limit .80" adjacent to the part number. Reinstall the "Mach Overspeed Warning Switch" after it has been calibrated; and

c. Remove pilot's and copilot's airspeed indicators and have them modified by changing the "Barber Pole" from Mach number .83 to .80. The instrument must be recalibrated by the instrument manufacturer or a certified repair station. Reidentify the airspeed indicators by ink stamping "Mach limit .80" adjacent to the part number. Reinstall the pilot's and copilot's airspeed indicators after they have been recalibrated.

2. Remove the modifications installed by Raisbeck Group STC SA766NW, and return the aircraft to the original type design configuration or to the Gates Learjet "Softflight" configuration.

B. Airplanes may be ferried to a maintenance base for repair in accordance with FAR 21.197 and 21.199.

C. Alternate means of compliance which provide an acceptable level of safety may be used when approved by the Manager, Seattle Aircraft Certification Office, FAA, Northwest Mountain Region.

All persons affected by this directive who have not already received these documents from the manufacturer may obtain copies upon request to Jet Air Corporation, P.O. Box 245, Bellevue, Washington 98009. These documents may be examined at the FAA, Northwest Mountain Region, 17900 Pacific Highway South, Seattle, Washington, or at 9010 East Marginal Way South, Seattle, Washington.

This amendment becomes effective September 6, 1985.