* THESE VALUES CAN BE READ ON INSTRUMENTS AND/OR ISDU
1 BITS 11,13,16 AND 17 ARE SET FOR 2 SECONDS AT START OF TEST
IRS Self Test Values
Figure 23
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737-300/400/500MAINTENANCE MANUAL
INERTIAL REFERENCE SYSTEM - TROUBLE SHOOTING
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General
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A. There are two procedures to identify malfunctions or failures of the IRS system. One procedure is a continuous monitoring in the IRS that shows failures as malfunction codes. The other procedure is the BITE (Built-In Test Equipment).
IRS Ground Crew Call Horn - Activation and Deactivation
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A. The inertial reference system (IRS) activates the ground crew call horn when one of these conditions occur:
(1)
Equipment Cooling (all of these conditions must occur)
(a)
Airplane on the ground
(b)
No cooling on the IRU's
(c)
IRS AC circuit breaker is closed
(d)
IRS is on
(2)
IRS on DC power (all of these conditions must occur)
(a)
Airplane on the ground
(b)
IRS AC circuit breaker open or loss of IRS AC power, and DC circuit breaker is closed
(c)
IRS is on
Accidental IRU Self-test after You Apply Static Inverter Power
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A. AIRPLANES WITH DAA P/N 10-62042-301-01; there is an undetectable failure that starts the IRS self-test during standby power tests.
B. A self-test may be initiated if these conditions occur:
(1)
The STANDBY POWER switch on the P5 Overhead panel is moved from the AUTO position to the OFF position.
(2)
The switch remains in the OFF position for a short time.
(3)
The switch is then moved to the BAT position.
C. AIRPLANES WITH DAA P/N 10-62042-301-01; Some of these units are susceptible to slow voltage rises in static inverter power. This slow voltage rise may casue a signal to be sent to the IRU which starts the IRS self-test. This condition occurs when the DAA has its power fully removed and the static inverter power is applied.
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D. The IRU self-test is inhibited when the ground speed is larger than 20 knots. Therefore, this problem will not cause irregular flight compartment indications during flight operation.
4. IRS Alignment - Warning, Restoration Procedure
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A. Figure 101 lists recommended steps that you should follow when the IRS MSU ALIGN light flashes or if the IRS is in the ATT mode but you want the NAV mode. The recommended steps (shown on the figure) should be followed to restore the alignment process.
(1)
Make sure the two ALIGN lights on the IRS MSU are on before you input the present position.
(2)
To correct a flashing ALIGN light problem, the present position may be input through the Flight Management Computer (FMC) Control Display Unit (CDU).
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