(1)
Indicated airspeed (IAS) is derived directly from pitot and static pressures without any correction for static pressure source error. The indicators use independent pressure sources. A pneumatically actuated mechanism rotates a solid color pointer over a fixed airspeed scale. An instrument memory index (IMI) ring is mounted on the indicator bezel. It has four manually positioned markers which are set wherever desired on the periphery of the fixed airspeed scale.
(2)
Maximum operating airspeed is derived directly from static pressure (no correction, and independent pressure sources). A second pneumatic mechanism rotates a diagonally striped pointer over the fixed airspeed scale.
(3)
Mach number is derived from pitot and static pressure by the central air data computers which correct for static pressure source error. Each airspeed indicator displays an independently computed mach number on a three-drum numerical counter located on the instrument face. The counters are actuated by synchro transmitters in the central air data computers. Yellow warning flags cover the numerical counters in case of failure.
(4)
Command airspeed is displayed by orange reference markers moving along each fixed airspeed scale periphery. This portion of the captain's airspeed indicator serves the auto throttle system (Ref 22-31-00) by providing a display of the command airspeed that the auto throttle system desires to maintain and by generating the error signal required by the auto throttle computer to maintain a commanded airspeed. The first officer's airspeed indicator contains the same system but the generated error signal is not connected to the auto throttle computer. On both indicators, the peripheral reference markers display command airspeed from 98 |2 knots to 400 |5 knots.
B. Each airspeed indicator contains two pneumatically controlled rotating pointer readout systems, a servo driven counter readout, and a servo-mechanical system providing error signal generation.
(1)
The indicated airspeed pointer is controlled, through mechanical linkage, by expansion or contraction of a capsule sensitive to the differential between pitot and static pressure. Pointer rotation with respect to airspeed is linear between 60 and 250 knots, nonlinear between 250 and 470 knots and mechanically limited at 0 and 470 knots.
(2)
The maximum operating airspeed pointer (striped) is controlled, through mechanical linkage, by expansion or contraction of a capsule sensitive to changes in static pressure. The pointer rotates on a shaft concentric with indicated airspeed shaft. Internal adjustments to mechanical linkage positions the pointer to read airspeed as a function of a predetermined limit speed curve.
EFFECTIVITY
ALL 03 Page 10 Apr 25/8234-13-00
On indicators with AUX FUEL/NORM mode, in the normal mode of operation, the pointer will indicate increasing values until an altitude of 23,311 feet (switchover point) is reached. In the auxiliary fuel mode, the pointer will indicate 310 knots IAS until an altitude of 35,148 feet is reached. Above these altitudes the pointer will move in a decreasing direction following a predetermined limit speed curve. On airplanes incorporating SB 34-2186, the maximum Vmo pointer will indicate 342 knots IAS, until an altitude of 30,692 feet is reached. Above these altitudes the pointer will move in a decreasing direction.
(3)
Mach number numerical counter is mechanically coupled to a servo repeater circuit. The servo repeater is controlled by a synchro signal representing computed airspeed (Fig. 5). This input signal originates in computed airspeed module of central air data computer 1 or 2. Counter readout indicates mach number from 0.200 to 0.999 with a maximum error of | 0.002 mach. A failure monitor system covers numerical counter with a yellow OFF flag if:
(a)
Indicator power is lost.
(b)
Flag signal from central air data computer indicates a failure.
(c)
Loss of synchro transmitter input from computer.
(d)
Excessive null occurs in servo repeater loop.
(4)
On ALL XA EXCEPT LH 011-030, 051-070, 082-099, AF 121, 122, 152-199; MD 501-599; GN 601-699; AT 701-750; IB 406-499; VM 751-799, in the command airspeed subsystem, a servo repeater follows the synchro position transmitter input from the auto throttle speed select system in the autopilot/flight director mode select panel (Fig. 6).
(5)
On LH 011-099; AF 121, 122, 152-199; MD 501-599; GN 601-699; AT 701-750; IB 406-499; VM 751-799, in the command airspeed subsystem, a servo repeater follows a linear DC signal input from the auto throttle select system in the auto throttle computer (Fig. 6).
(a) 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：747飞机维护手册AMM CHAPTER 34 - NAVIGATION 第34章导航1(78)
