79-12-05\tLEARJET: 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: \n\n\nMODELS\nSERIAL NUMBERS \n24, 24A\n24-100 through 24-180 \n24B, 24B-A\n24-181 through 24-217, 24-219 through 24-229 \n24C, 24D, 24D-A\n24-218, 24-230 through 24-328 \n24E, 24F, 24F-A\n24-329 through 24-357 \n25, 25A\n25-003 through 25-060 \n\n25-062 through 25-066 \n25B, 25C\n25-061, 25-067 through 25-201, 25-204, 25-205 \n25D, 25F\n25-206 through 25-278 \n\nCOMPLIANCE: Required as indicated, unless already accomplished. \n\nA)\tEffective immediately, temporarily insert the following information in the FAA-Approved Airplane Flight Manual and operate the airplane in accordance with these insertions: \n\n1.\tIn Section I, adjacent to the heading STALL WARNING SYSTEM Limitation, add the following: \n\nBoth 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: \n\nNOTE: Warning lights for both stall warning systems are inoperative when the generator and battery switches \n\nTo 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. \n\n2.\tIn Section II, under the heading BEFORE LANDING, add the following: \n\tLANDING APPROACH IN TURBULENCE: \n\tLanding Approach Speed - Computed and bug set. Refer to Section IV.\n\nNOTE: 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. \n\n3.\tIn Section II, under the heading ANTI-ICE SYSTEM, add the following: \n\tANTI-ICE SYSTEM NORMAL OPERATIONS \n\tObserve Airplane Flight Manual's recommendations for normal use of all anti-ice systems.\tWARNING: Even small accumulations of ice on the wing leading edges can cause aerodynamic stall prior to activation of the stick shaker and/or pusher. \n\n4.\tIn Section II, under the heading AFTER TAKEOFF, add the following: \n\tSTALL WARNING SYSTEMS COMPARISON CHECK \nAs a final step in the AFTER TAKEOFF procedures, the following stall warning system comparison shall be observed: \nANGLE-OF-ATTACK Indicators - Cross-check pilot's and copilot's indicators for agreement. \n\n5.\tIn Section II, adjacent to the ICE DETECTION procedures, add the following: \n\tVISUAL ICE DETECTION \n\tA visual inspection may be used to check for ice accumulations on the wing leading edges. \n\nFor 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. \n\nIf 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. \n\n6.\tIn Section III, under the heading ANTI-ICE SYSTEM FAILURE, add the following: \n\tAPPROACH AND LANDING WITH ICE ON WING LEADING EDGES \n\tWARNING: 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: \n\n1.\tFinal Approach Speed - 15 knots above normal \n\n2.\tTouchdown Speed - 15 knots above normal \n\n3.\tLanding distance - Increase by 20% Anti-Skid ON or OFF. \n\n7.\tIn Section IV, adjacent to the heading TAKEOFF DISTANCE, FLAPS 8 DEGREES add the following: \n\tIncrease all chart Takeoff Distances by: \n\tModel 24 with Century III wings + 4% \n\tModel 25 with Century III wings + 6% \n\n8.\tIn 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: \n\tIncrease all chart V1, VR and V2 speeds by: \n\tModel 24 with Century III wings + 2 KNOTS INDICATED AIRSPEED \n\tModel 25 with Century III wings + 3 KNOTS INDICATED AIRSPEED \n\n9.\tIn Section IV, adjacent to the LANDING APPROACH SPEEDS chart, add the following: \n\tIncrease all chart Landing Approach Speeds (V REF) by: \n\t+ 6 KNOTS INDICATED AIRSPEED \n\n10.\tIn Section IV, adjacent to the LANDING DISTANCE chart add the following: \n\tIncrease all Chart Actual and Scheduled and Alternate Stops Field Lengths by: +8% \n\n11.\tIn Section IV in place of the current STALL SPEEDS file the following charts: \n\nNOTE: 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. \n\nB)\tWithin 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. \n\nC)\tWhen 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. \n\nD)\tAny equivalent method of compliance with this AD must be approved by the Chief, Engineering and Manufacturing Branch, FAA, Central Region. \n\nAmendment 39-3488 became effective June 18, 1979. \nThis Amendment 39-3614 becomes effective November 6, 1979.