(b)
In the first officer's indicator, control and operation of the synchrotel is like the captain's but the error signal generated is not used.
XA (c) On XA ALL EXCEPT LH and AZ (AEB AF 22-107), the vibrator shown in figure 6 is attached to the instrument frame to reduce any friction or hysteresis errors occuring in the indicated airspeed mechanical linkage.
XA On airplanes AF 101-111; SN ALL; IB ALL, less airplanes
XA incorporating SB 22-2034, auto throttle computer turns the vibrator on whenever the auto throttle system is powered.
EFFECTIVITY
ALL ATG Page 11 Sep 25/9434-13-00
XA On airplanes AF 112-115, 121, 122, 151-199; MD 501-599;
XA GN 601-699; AT 701-750; VM 751-799; plus airplanes
XA incorporating SB 22-2034,
auto throttle computer turns the vibrator on only when the auto throttle system is engaged.
C. Indicated and maximum-allowable-airspeed mechanisms have no controls or operational modes. They are always on and react to whatever pressures are present in the pitot and static systems.
D. Mach number portion of indicators receives 26 volt ac power controlled by circuit breakers in electronic circuit breaker panel P7. Captain's power comes from essential flight instrument bus (115 volt ac) through flight instrument transformer No. 3 and circuit breaker CADC 1, IAS/MACH IND 1 on panel P7. First officer's power comes from flight instrument bus No. 2 through flight instrument transformer No. 6 and circuit breaker CADC 2, IAS/MACH IND 2 on panel P7.
E. Command airspeed portion of indicators requires 28 volt dc and 26 volt ac power which is supplied and controlled by auto throttle system. Refer to 22-31-00, Auto Throttle System.
7. Primary Altitude Indicators (Fig. 1, Sheet 1)
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A. Each altitude indicator displays corrected pressure altitude from -1000 feet to +50,000 feet and barometric correction from 28.1 inches of mercury/950 millibars to 31 inches of mercury/1050 millibars.
(1)
The two altimeters are independent as each instrument depends on a different pressure source and central air data computer for its inputs. Static pressure (coarse drive) controls a two-drum numerical counter reading altitude to the nearest 1000 feet. A servo output from a central air data computer (fine drive) adds corrected pressure altitude to the instrument drive with the accuracy necessary to position a single drum numerical counter reading altitude to the nearest 100 feet and a rotating pointer displaying altitude to the nearest 20 feet. An instrument memory index (IMI) ring is mounted on the indicator bezel.
(2)
Each altimeter contains a barometric correction mechanism. Manual operation of a BARO set knob on the front of the instrument performs a mechanical adjustment to the fine and coarse altitude indicator drives, to offset local variations in barometric pressure. The mechanism displays this manual setting in units of millibars and inches-of-mercury on two four-drum numerical counters. When BARO set is adjusted, the mechanism also positions a coarse and fine synchro control transformer. Through these control transformers, the captain's altimeter provides a barometric correction service for the autopilot/flight director altitude select error signal. AF 121, 122, 157, 161, 183, 184; the first officer's altitude indicator provides a barometric correction service for the altitude alert system.
(3)
A two position mode switch on the front of the altimeter provides manual selection of either normal or standby mode. In standby mode, the altimeter operates at reduced accuracy from coarse pressure drive only. A red STBY flag is visible on the face of the instrument while operating in standby mode.
EFFECTIVITY
ALL ATG Page 12 Sep 25/9434-13-00
B. In each primary altitude indicator, altitude display is accomplished by a mechanical system governing the position of numerical counters and a rotating pointer. Operation of this mechanical system is modified by a manually positioned barometric correction system and refined by a servo repeater system (Fig. 7).
(1)
The mechanical system derives its motion from variations in static pressure acting on an aneroid capsule. These variations are translated into a shaft rotation which drives the counters and pointer.
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