AF 121-199; AZ 221-299; AND GN 601-699 AIRPLANES CONFIG 1 WITHOUT PMS 02 Page 16
Sep 25/94
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TOTAL AIR TEMPERATURE/ENGINE PRESSURE RATIO LIMIT -
___________________________________________________ DESCRIPTION AND OPERATION
_________________________
1. General_______
A. The total air temperature/engine pressure ratio limit (TAT/EPRL) indicating system computes input data from the CADC, anti-ice, air conditioning and total air temperature systems. The output of the system is a display of total air temperature and maximum EPR limit, allowable under existing conditions. Outputs of EPR limit, mode total air temperature, and computer valid signals are also provided to the auto throttle system (22-31-00). An output is also provided to the EPR command indicators via the auto throttle computer. The system uses inputs of mach number, coarse and line altitude from central air data computer No. 1 an input of total air temperature from total air temperature probe No. 1 and inputs from the anti-ice and air conditioning systems.
B. The TAT/EPRL indicating system consists of three components; a computer, an indicator and a combined auto throttle-TAT/EPRL mode selector panel (Component location is shown in Fig. 1).
C. The A/T-TAT/EPRL mode selector panel allows selection of any one operating mode ranging from takeoff to cruise, alternate EPR limit ratings, EPR derating selection and display and selection of auto throttle operating modes. The computer uses inputs from the CADC and the mode panel to compute the maximum attainable EPR (thrust) available for the engines at any given time. The indicator displays total air temperature and the computed EPRL in the form of analog readouts.
D. The TAT/EPRL system has two sources of power. The computer receives 115-volt ac power from essential flight instrument bus and the indicator receives 26-volt ac power from autotransformer No. 3. The system is energized from circuit breakers on panel P7.
2. TAT/EPRL Computer (Fig. 1)_________________
A. The TAT/EPRL computer is a 3/8 ATR short case and is held in place by a standard cam-lock handle. The computer monitors various analog inputs and automatically calculates the EPRL for current flight conditions. This constantly updated EPRL value is then displayed on the TAT/EPRL indicator and the EPR command indicators.
EFFECTIVITY
AT ALL; MD ALL; VM ALL; CONFIG 2 IB 406-499 10 Page 1 Apr 25/85
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COMPUTER FAILURE LIGHT
MODE PANEL FAILURE LIGHT
TEST SWITCH
TAT SIGNAL FAILURE LIGHT
TAT/EPRL COMPUTER
ASPIRATED TOTAL AIR TEMPERATURE PROBE NO.1
FWD
MAIN ELECTRONIC EQUIPMENT CENTER
Total Air Temperature/Engine Pressure Ratio Limit - Component Location Figure 1 (Sheet 2)
T33671
EFFECTIVITY
CONFIG 2 AT ALL; MD ALL; VM ALL;799 Page 3IB 406-499 Apr 25/85
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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/EPRL 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 EPRL 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/EPRL computer as a CADC valid signal. Engine EPR limit and mode, total air temperature and computer valid signals are provided to the auto throttle system. An auxiliary output is also provided for driving the command counter on the engine EPR indicators via the auto throttle computer. The TAT/EPRL 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/EPRL 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.
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