ATTITUDE REFERENCE SYSTEMS - DESCRIPTION AND OPERATION
EFFECTIVITY
GJ ALL EXCEPT B-2509 and B-2510

1. General
A.  The attitude reference system is designed primarily to furnish the captain and first officer with information concerning the airplane's attitude in both pitch and roll axes at all times during flight. It also provides pitch and roll displacement signals to the autopilot, flight director systems, comparator and weather radar antenna stabilization system. Two systems are installed; system No. 1 feeding information to the captain's ADI, flight director steering computer No. 1, flight recorder and autopilot; while system No. 2 feeds information to the F/O ADI, flight director steering computer No. 2, and weather radar.
B.  Each system consists of the following components; vertical gyro, roll servo-amplifier, pitch servo-amplifier, warning flag logic circuit, and attitude director indicator. The amplifiers, plus an excitation transformer for the servo circuits are contained in the instrument amplifier unit, and the location of all components is shown in Fig. 1.
C.  Power to withdraw the warning flag from view in each ADI is generated in the warning flag logic circuit for that system. The warning flag will appear when power is lost to the instrument amplifier, or if the flag logic circuit loses its reference from the vertical gyro fail logic, or in the event of a malfunction in either pitch or roll servo-amplifier circuits.
D.  The VERTICAL GYRO transfer switch operates a transfer relay that connects the captain's ADI to either gyro reference. With the transfer switch in NORMAL position, the captain's ADI is referenced to vertical gyro No. 1 and the F/O's ADI is referenced to vertical gyro No. 2. With the transfer switch in BOTH ON 1 position, both ADI's are referenced to vertical gyro No. 1. With the transfer switch in BOTH ON 2 position, both ADI's are referenced to vertical gyro No. 2.
2.  Vertical Gyro
A.  The gyro has 360 degrees of freedom about the roll axis, and 士 85 degrees of freedom about the pitch axis. Initial erection of the gyro is accomplished by internal circuits, and no manual caging device is used. The erection system maintains verticality within 1/4 degree during unaccelerated flight and within 1 degree during maneuvers; or in turbulent air.
5C8
Jun 20/85 34-22-0 Page 1
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.

K77827
Attitude Reference System Component Location  5D8 
34-22-0  Figure 1  Jun 20/86 
Page 2 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

3.  Flight Instrument Amplifier Rack
A.  The roll and pitch servo-amplifiers and the warning flag amplifiers are all plug-in type units which plug into the appropriate amplifier rack.
4.  Attitude Director Indicator (ADI)
A.  Each artificial horizon (contained in the ADI) consists of a moving tape assembly which displays the horizon line, pitch scale and roll index. The tape assembly is coupled to the rotors of the roll and pitch synchros and to the roll and pitch servomotors. When the servomotors turn, the synchros and the tape assembly are positioned simultaneously. Airplane attitude in roll is read from the roll index against the roll scale, and airplane attitude in pitch is read from the pitch scale against the miniature airplane symbol. Adjustment of the tape in pitch is provided for, through the pitch trim adjuster at the lower left corner of the indicator.
B.  A gyro warning flag is provided in each ADI to indicate loss of power, or malfunction of the gyro or of either servo-amplifier circuit in the system.
5.  Operation
A.  Both systems are made operational by closing the system circuit breakers. After a brief period of time the gyros will erect and each ADI should indicate a level condition in both pitch and roll axes.
B.  Each system operates as follows: when the airplane is displaced in the roll plane, the gyro will transmit an ac signal which is not only related in amplitude to the degree of displacement, but also phase oriented to differentiate between left and right roll. The signal is passed to the roll servo-amplifier where it is amplified to drive the servomotor, which in turn drives the horizon tape. This ac signal is fed via the roll synchro on the roll motor shaft to ensure that the motor stops as soon as it has turned sufficiently to null out the error signal. Pitch displacement signals are handled in a similar way, and the electromechanical design is such that the horizon tape is able to respond to both pitch and roll signals simultaneously (Fig. 2).
C.  The operation of the transfer switch and relays is illustrated in Fig. 3 and 4. Figure 3 shows how the relay coils are connected with the ground through the relay contacts. The switch is shown in its NORMAL setting. Assume that the transfer switch is now set to BOTH ON 2. This switch puts a ground on the lower end of latching relay coil A via contacts B2 and A1; and since the other end of that coil is connected to 28 volts dc, it will now latch over to the alternate set of contacts and remain there until energized once more. Note that the ground is removed from the coil by the transfer of contacts at A1. In order to ground the coil once more and switch the relay back again, it will be necessary to return the switch to NORMAL. The switching to BOTH ON -1 is carried out in a similar way.
　
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