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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
C. Mach number indication is presented on a two drum digital readout through the range .40 to .99 mach. Below .40 mach the readout is covered by a black mask. The indicator computes mach from inputs of airspeed and altitude signals from the air data computer. Upon power failure, or loss of 28 volts dc from the air data computer a red and white OFF flag will appear to cover the digital mach readout.
D. The colored pointer on the indicator shows maximum operating speed of the airplane as a function of corrected altitude and airspeed from the air data computer. The speed reference marker (target bug) is electrically fed from the AFCS system. The "INOP" flag indicates the absence of an operational AFCS system and the target bug will store at 440 knots. Pulling the bug set knob out will place the target bug in manual mode and will retract "INOP" flag. When operating in the manual mode, an "M" flag will appear in view at top of indicator. White peripheral pointers may be set manually to any desired airspeeds.
E. The indicator generates a VMO signal for controlling the maximum operating airspeed pointer mechanism in the indicator. The indicator also provides an output signal to actuate an aural warning when maximum operating speed is exceeded.
F. The air data computers provide a valid signal to the indicators. Monitoring within the indicator of the maximum operating airspeed display output signal and the maximum operating airspeed function switch is capable of detecting the following conditions; 1) absence of the altitude valid signal from the air data computer, 2) loss of electrical power to the indicator, 3) failure of indicator power supply, 4) open circuit in interlocks. When a fault condition is detected, a VMO flag in the indicator will come into view and the maximum operating airspeed switch will be inhibited from producing an airspeed warning.
G. The indicators have a self-test capability for the maximum operating airspeed switch. Operation of the mach airspeed warning test switch results in an overspeed aural warning unless failure monitoring within the indicator detects a fault condition. The aural warning input is switched to external ground through the indicator airspeed switch. Power to the indicators is 26 volts ac through circuits breakers located on circuit breaker panel P18 for the captain's indicator and P6 for the first officer's indicator.
3. Electric Altimeter (Fig. 1 and 4)__________________
A. Electric altimeters are provided for the pilots. Each altimeter is an electric drum-pointer type that recieves altitude information from the air data computer. The altitude is displayed in 1000-feet, 100-feet, and 20-foot increments on counters and in 100- and 20-foot increments by a pointer which reads against a fixed scale. The range of the altimeter if from -1000 to 50,000 feet with altitudes below sea level displayed by the rotating pointer and a NEG flag covering the counter. A warning flag will cover the counter drums in the event of a failure. The failure monitor will show the flag in the event of the following: loss of electrical power to the indicator, loss of flag signal from the DADC, excessive servo null voltage, loss of input synchro signal and internal indicator malfunction. A barometric pressure setting knob is provided to adjust the pressure setting which is displayed in both millibars and inches of mercury (Fig. 1).
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
B. The altimeters provide a barometric corrected resolver altitude signal to the DADC's and a barometric corrected potentiometer signal to the cabin pressurization system (Chapter 21-31-00).
4. Standby Airspeed/Altimeter Indicator____________________________________
A. The standby airspeed/altimeter indicator is a combination of two flight instruments which presents an integrated display of indicated airspeed and altitude (Ref Fig. 1).
B. The standby pneumatic airspeed indicator gives indicated airspeed 60 to 450 knots. A diaphragm within the instrument case is actuated by differential pressure from the airplane pitot static system. The diaphragm expands or contracts in proportion to the difference between the pressure around it and the pressure in it. The information is transferred from the diaphragm to the drum counter through mechanical linkage. The pointer shows indicated airspeed on a drum graduated in knots.
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