AF 121-199; AZ 221-299; AND GN 601-699 AIRPLANES  CONFIG 1 WITHOUT PMS  10 Page 1
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34-15-00

COMPUTER
FAILURE
LIGHT

MODE PANEL FAILURE LIGHT
TEST SWITCH
TAT SIGNAL FAILURE LIGHT
TAT/N1 LIMIT COMPUTER

ASPIRATED TOTAL AIR TEMPERATURE PROBE NO.1
FWD
MAIN ELECTRONIC EQUIPMENT CENTER
Total Air Temperature/N1 Limit Indicating System - Component Location Figure 1 (Sheet 2)
T33624
EFFECTIVITY
LH 011-030, 051-070, 082-099;

AF 121-199; AZ 221-299; AND CONFIG 1 GN 601-699 799 Page 3AIRPLANES WITHOUT PMS Apr 25/95
34-15-00
 B.  The computer receives input analog signals of altitude and mach from CADC No. 1, total air temperature from TAT probe No. 1 via the TAT/N1 limit indicator, and engine select and mode from the mode selector panel. The computer also utilizes additional discrete inputs of nacelle anti-ice, wing anti-ice, CADC valid, and test. The computed N1 limit is compensated for engine bleed air for anti-ice and the effects of air conditioning and pressurization air extraction requirements for normal operation (three air conditioning packs operating). Valid mach and altitude signals from the CADC system are routed to the TAT/N1 limit computer as a CADC valid signal. Engine N1 limit, total air temperature and computer valid signals are provided to the auto throttle system. An auxiliary output is also provided for driving the command counters on the engine N1 limit indicators via the auto throttle computer. The computer provides discrete signals to engine rating I and II indicator lights on the pilots' center instrument panel for annunciation of the rating select switches on the A/T-TAT N1 limit mode selector panel.
 C.  The computer has the ability to fault isolate a malfunction in the system to a line replaceable unit (LRU). Three fault isolation lamps labeled CMPTR, MODE PANEL, and TAT SIGNAL are located on the front of the computer. When a malfunction occurs in an LRU or in the TAT circuit between the computer and indicator, the appropriate lamp or lamps come on. A press-to-test switch is also provided on the front of the computer to test the fault isolation lamps. Actuation of the press-to-test switch will cause all three lamps to come on independent of the fault isolation circuits.
 3.  A/T-TAT/N1 Limit Mode Selector Panel (Fig. 1)
____________________________________
 A.  The auto throttle-total air temperature/N1 limit (A/T-TAT/N1) mode selector panel is an electromechanical device with lighted push switches and rotary switches to select engine N1 limit modes, auto throttle modes, alternate engine rating limits, derated engine N1 limits, and test modes. Also on the panel is a derate display to indicate the amount of derate selected.
 B.  The N1 limit mode rotary selector switch positions are take-off dry (TOD), maximum continuous (CON) maximum climb (CLB), maximum cruise (CRZ) and go-around (GA). These modes select the maximum N1 engine speed as computed by the TAT/N1 computer. The switch is solenoid held and will return to GA mode whenever GA mode is armed by the A/P-F/D system or auto throttle system. The mode switch will return to GA mode with or without auto throttle engaged.
 C.  The rating selector pushbutton switches permits selection of alternate N1 limit program in the TAT/N1 computer. This permits programmed maximum engine speed reduction for different engine characteristics. The respective switch illuminates green when selected. A second push of the switch disengages the rating selection. Rating selection must be accomplished prior to auto throttle engagement when in takeoff N1 mode.
 EFFECTIVITY
 LH 011-030,051-070,082-099;

 AF 121-199; AZ 221-299; AND GN 601-699 AIRPLANES  CONFIG 1 WITHOUT PMS  16 Page 4
   Sep 25/94

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 D.  The derate switch permits selection of incremental reduction of N1 limit whether the auto throttle is engaged or not. A switch is used to select the desired derate which is displayed on digital panel readouts. Derate increments are 0.5% N1 with a maximum selection of 5.0% N1. The derate is automatically reset to 0.0 when a rating select is engaged. The derate automatically resets to 0.0 when auto throttle is engaged in any mode except TOD N1; when a new auto throttle mode is selected with the auto throttle engaged or when auto throttle go-around mode is activated. After go-around arm, derate may be selected and will not reset when go-around (N1 mode) is engaged.
 E.  The auto throttle mode pushbutton switches labeled N1, MACH and SPEED are interlocked to permit selection of one mode only. The desired auto throttle mode must be selected before the auto throttle can be engaged. The respective mode switch illuminates green when the mode is selected. Mode selection is cancelled when the auto throttle is disengaged. When the airplane is on the ground and TOD is selected on the N1 limit mode switch the mach and speed modes are inhibited allowing selection of N1 mode only (Ref 22-31-00 for the Auto Throttle System).
　
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