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T.O. GR1F16CJ1 156 At 1.4 mach and greater, the minimum thrust level is near MIL even though the throttle may be retarded below MIL. Typically, the minimum thrust level decreases with mach number between 1.41.1 mach. At IDLE and while decelerating through 1.1 mach, the engine decelerates to normal inflight idle thrust. Reduced speed excursion (RSE) logic is activated during engine deceleration to idle speed above 0.6 mach. RSE results in a higher inflight idle rpm offset by a greater nozzle opening than normal inflight idle. Idle thrust changes from inflight idle to approach idle between 0.50.6 mach, resulting in an engine rpm change of approximately 10 percent. Slightly more time is required to accelerate the engine from approach
idle thrust when airspeed is below 0.5 mach. Idle thrust changes from approach idle to ground idle between 8090 knots and results in reduced engine rpm of approximately 2 percent. This change occurs during the landing roll to achieve desired ground idle thrust levels for taxi. While VSV reset is active, idle rpm is 23 percent higher than normal. A high frequency vibration may be felt through the cockpit floor, ejection seat, and/or rudder pedals as a result of aircraft structural response to normal engine operation. The vibration is most noticeable with the aircraft in a clean configuration with reduced fuel loads at lower airspeeds when the engine is operating near MIL thrust or above. This vibration has no adverse effect on the engine or aircraft. AB Operation 129 GE Refer to figure 117 for AB operational characteris tics. During AB operation, FTIT, rpm, and oil pressure vary with altitude and airspeed. NOZ POS indications during minimum AB operation should be between 717 percent open and for MAX AB operation, between 4070 percent open. The engine has a reduced AB region of operation (at high altitudes and low airspeeds) and commands a decrease in AB fuel flow to prevent AB instabilities. The NOZ POS indicator indicates approximately 3050 percent open during this reduced AB operation. When AB operation is first initiated, the exhaust nozzle preopens up to 10 percent more than MIL exhaust nozzle position to increase stall margin during AB lightoff. Fuel flow and exhaust nozzle area are held at minimum AB levels until the flame detector determines that lightoff (within 5 seconds (greater than 40 _ F) or 10 seconds (40 _ F or less) of AB selection) has occurred. Once AB lightoff occurs, fuel flow and exhaust nozzle area increase to the requested AB level with a corresponding increase in thrust. If AB blowout occurs, the autorelight feature attempts to reinitiate AB without throttle movement. During AB operation at or above 45,000 feet, a mild AB rumble may be felt through the pilot seat. The rumble does not impact engine operation and should not be considered abnormal. Inlet Thump 129 GE An inlet thump is an airflowrelated phenomenon which may occur occasionally during PRI operation below 25,000 feet and below 500 knots when the throttle is retarded from MIL. The thump is the result of airflow changes within the aircraft inlet. A thump can be heard or can be felt through the cockpit floor, ejection seat, and/or rudder pedals. The intensity can vary greatly, ranging from a barely perceptible sound or impulse to a louder and/or harder occurrence which may be quite noticeable. Thumps do not affect engine or aircraft operation. SEC Operation 129 GE The engine can automatically transfer to SEC when a DEC failure occurs. It can manually be transferred to SEC by placing the ENG CONT switch to SEC. Transfer is indicated by the illumination of the SEC caution light; rpm may also initially decrease (up to 10 percent rpm) and then recover to a level slightly below that for PRI. When operating in SEC, the nozzle is closed. Refer to ENGINE LIMITATIONS, Section V for throttle restrictions while operating in SEC. Movement of the throttle to MAX AB is permitted; however, since the AB is inhibited, maximum available thrust in SEC is attained at MIL. The thrust level at MIL during SEC operation is 7095 percent of that available during PRI operation at the same throttle position. Idle thrust in SEC is higher than idle thrust in PRI because the exhaust nozzle is closed. VSV reset is not active in SEC. |