AD 79-12-05

79-12-05 LEARJET: Amendment 39-3488 as amended by Amendment 39-3614. Applies to the following (1) model and serial number airplanes on which "reduced approach speed system kit" AAK 76-4 has been installed and, (2) model and serial number 24E, 24F, 24F-A, 25D and 25F airplanes, certificated in all categories:

MODELS SERIAL NUMBERS 24, 24A 24-100 through 24-180 24B, 24B-A 24-181 through 24-217, 24-219 through 24-229 24C, 24D, 24D-A 24-218, 24-230 through 24-328 24E, 24F, 24F-A 24-329 through 24-357 25, 25A 25-003 through 25-060

25-062 through 25-066 25B, 25C 25-061, 25-067 through 25-201, 25-204, 25-205 25D, 25F 25-206 through 25-278

COMPLIANCE: Required as indicated, unless already accomplished.

A) Effective immediately, temporarily insert the following information in the FAA-Approved Airplane Flight Manual and operate the airplane in accordance with these insertions:

1. In Section I, adjacent to the heading STALL WARNING SYSTEM Limitation, add the following:

Both stall warning systems must be ON and operating for all Normal Flight Operations. The systems may be turned off for Emergency Operations per Airplane Flight Manual Section III Procedures and for stall warning system maintenance per the Maintenance Manual Procedures:

NOTE: Warning lights for both stall warning systems are inoperative when the generator and battery switches

To assure proper stall warning system operation, the BEFORE STARTING and AFTER TAKEOFF stall warning system operational and comparison checks in Section II of this Airplane Flight Manual must be completed on each flight. are OFF.

2. In Section II, under the heading BEFORE LANDING, add the following: LANDING APPROACH IN TURBULENCE: Landing Approach Speed - Computed and bug set. Refer to Section IV.

NOTE: It is recommended that if turbulence is anticipated due to gusty winds, wake turbulence, or wind shear, the approach speed be increased. For gusty wind conditions,an increase in approach speed of one-half of the gust factor is recommended.

3. In Section II, under the heading ANTI-ICE SYSTEM, add the following: ANTI-ICE SYSTEM NORMAL OPERATIONS Observe Airplane Flight Manual's recommendations for normal use of all anti-ice systems. WARNING: Even small accumulations of ice on the wing leading edges can cause aerodynamic stall prior to activation of the stick shaker and/or pusher.

4. In Section II, under the heading AFTER TAKEOFF, add the following: STALL WARNING SYSTEMS COMPARISON CHECK As a final step in the AFTER TAKEOFF procedures, the following stall warning system comparison shall be observed: ANGLE-OF-ATTACK Indicators - Cross-check pilot's and copilot's indicators for agreement.

5. In Section II, adjacent to the ICE DETECTION procedures, add the following: VISUAL ICE DETECTION A visual inspection may be used to check for ice accumulations on the wing leading edges.

For night operation, the optional wing inspection light located on the right side of the fuselage may be turned on by setting the WING INSPECTION switch ON and checking for ice accumulations on the wing. It should be noted that the wing inspection light in itself is inadequate for detecting the presence of ice near the wing tips.

If the presence of wing leading edge ice is suspected during operations at night, in atmospheric conditions conducive to icing, the normal approach speeds must be increased per the APPROACH AND LANDING WITH ICE ON WING LEADING EDGES procedures of Section III of the Airplane's Flight Manual.

6. In Section III, under the heading ANTI-ICE SYSTEM FAILURE, add the following: APPROACH AND LANDING WITH ICE ON WING LEADING EDGES WARNING: Even small accumulations of ice on the wing leading edges can cause aerodynamic stall prior to activation of the stick shaker and/or pusher. If approach and landing must be made with any ice (or suspected ice during night operations) on the wing leading edges:

1. Final Approach Speed - 15 knots above normal

2. Touchdown Speed - 15 knots above normal

3. Landing distance - Increase by 20% Anti-Skid ON or OFF.

7. In Section IV, adjacent to the heading TAKEOFF DISTANCE, FLAPS 8 DEGREES add the following: Increase all chart Takeoff Distances by: Model 24 with Century III wings + 4% Model 25 with Century III wings + 6%

8. In Section IV, adjacent to the heading CRITICAL ENGINE FAILURE SPEED, V1, FLAPS - 8 DEGREES; ROTATION SPEED, VR, FLAPS - T.O. -8 DEGREES; AND ENGINE OUT SAFETY SPEED V2 FLAPS - T.O. - 8 DEGREES charts, add the following: Increase all chart V1, VR and V2 speeds by: Model 24 with Century III wings + 2 KNOTS INDICATED AIRSPEED Model 25 with Century III wings + 3 KNOTS INDICATED AIRSPEED

9. In Section IV, adjacent to the LANDING APPROACH SPEEDS chart, add the following: Increase all chart Landing Approach Speeds (V REF) by: + 6 KNOTS INDICATED AIRSPEED

10. In Section IV, adjacent to the LANDING DISTANCE chart add the following: Increase all Chart Actual and Scheduled and Alternate Stops Field Lengths by: +8%

11. In Section IV in place of the current STALL SPEEDS file the following charts:

NOTE: In order to comply with the requirements of paragraph A) of this AD, this airworthiness directive, or a duplicate thereof, may be used as a temporary amendment to the Airplane Flight Manual and carried in the aircraft as part of the Airplane Flight Manual until replaced by the permanent revisions to the Airplane Flight Manual provided by the manufacturer and approved by the FAA.

B) Within the next 300 hours time-in-service after the effective date of this AD, or December 15, 1979, whichever occurs first, adjust the stall warning system and inspect the systems and components that may affect aircraft stall speed in accordance with the procedures provided by Gates Learjet Service Bulletin SB 24/25- 294 dated May 25, 1979.

C) When Gates Learjet Airplane Accessory Kit Number AAK 79-10A (including insertion of the applicable Airplane Flight Manual changes in FAA Approved Airplane Flight Manual) is installed, paragraphs A)7. through A)11. and paragraph B) of this AD are no longer applicable.

D) Any equivalent method of compliance with this AD must be approved by the Chief, Engineering and Manufacturing Branch, FAA, Central Region.

Amendment 39-3488 became effective June 18, 1979. This Amendment 39-3614 becomes effective November 6, 1979.