AIR DATA PRESSURE INSTRUMENTS - DESCRIPTION AND OPERATION
EFFECTIVITY
GJ ALL EXCEPT B-2509 thru B-2510 and B-2524
1. General
A. Air data pressure instruments are those which derive their inputs from the pitot static air pressure system and the air data computer system (Ref 34-11-0, Pitot Static System). The air data pressure instruments are two airspeed/mach indicators, two instantaneous vertical speed/rate of climb indicators, two altimeters, and one air data computer.
B. Indicated airspeed and mach number are conventionally displayed as a function of differential pitot and static air pressures on mach/airspeed combined instrument indicators. Mach inputs to this indicator will come from the air data computer and static and pitot air pressures.
C. Instantaneous vertical speed/rate of climb, through a range of 0 to 6000 feet per minute, is indicated according to accelerometer and static air pressure information.
D. Altitude throughout the range of 1000 feet below mean sea level to 50,000 feet above mean sea level may conventionally be indicated on both captain's and first officer's indicators from static air pressure information, and by fine altitude signals from the air data computer to the captain's altimeter.
E. The air data computer system electrically integrates and computes from pitot static pressures, the corrected altitude, mach number, and airspeed signals. This data is sent to the ATC transponder, autopilot, flight director, mach trim, and other systems shown in Fig. 6. Power to operate the computer is obtained from circuit breaker panel P18. Provisions are included for the installation of a second air data computer system.
5C8
Feb 20/89 34-12-0 Page 1
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
H23873
Air Data Pressure Instrument System Component Location 505
34-12-0 Figure 1 Nov 15/67
Page 2
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
2. Airspeed/Mach Indicators
A. Pneumatic Instruments
(1)
The airspeed/mach indicator is a combination of two flight instruments which presents an integrated display of indicated a airspeed and mach number (Fig. 2).
(2)
Indicated airspeed is displayed through the range of 60 to 420 knots. The indicator dial scale is calibrated linearly in 2-knot increments between 60 and 160 knots, and logarithmically in 10-knot increments between 160 and 420 knots. A pointer, rotated by a mechanically connected pressure diaphragm, indicates the airspeed range through a single revolution. Two reference pointers (bugs) are provided on the bezel for pilot convenience in presetting airspeed reminders, such as V1 and V2.
(3)
The mach mechanism is actuated by an evacuated capsule whose linkage is such that it rotates a subdial at an angular rate which varies linearly with the logarithm of the static pressure. This subdial is graduated in increments of 0.02 mach and reads from 0.5 to 1.0 mach.
(4)
The airspeed dial and mach subdial scale factors are selected so that the single pointer shows airspeed on the outer perimeter of the dial and mach number on the subdial scale through a cutout in the main dial adjacent to the high airspeed markings.
(5)
A manually operated airspeed command knob rotates the airspeed command index around the outer periphery of the main dial. When the auto throttle system is installed, the airspeed command knob is used to set the airspeed to be maintained (Ref 22-31-0). The VMO pointer locates and accents the maximum operating airspeed of the airplane as a function of altitude.
B. Servoed Instruments
(1)
The airspeed/mach indicator is a combination of two flight instruments presenting an integrated display of computed airspeed and mach number (Fig. 2). The central air data system is designed to utilize a combined instrument in which the altitude assembly, the airspeed assembly and the mach number assembly are operated from air data computer processed information.
(2)
Computed airspeed derived from the air data computer, which is corrected for static pressure source error, drives the airspeed pointer from 60- thru 450-knot range of airspeed. The mechanism produces linear rotation of the pointer in two knot calibration increments between 60 and 160 knots, and logarithmically in 10-knot increments between 160 and 450 knots. An airspeed valid signal from the air data computer is also provided to the A/S flag.
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