(a)
Drift Angle: -10° (L)
(b)
Ground Speed: 200 Kts
(c)
Inertial Vertical Speed: -600 ft/min
(d)
Magnetic heading: 15°
(e)
Pitch Angle: 5°
(f)
Present Position (Lat, Long): N22° 30', E22° 30'
(g)
Roll Angle: 45° (R)
(h)
True Heading: 10°
(i)
Wind Direction: 30°
(j)
Wind Speed: 100 Kts
(3)
The total time indicator displays accumulated operating time.The IRU has two power sources, one a 115 volt ac source and one a 28 volt dc source. Either source is sufficient for operation but both are required for initial startup.Inside the IRU, the power control circuit automatically switches to a backup source (hot battery bus) when the normal 115 volt ac source is not available. During startup, the control circuit verifies that the battery is connected by switching off the 115 volt ac input. Inputs from the mode select switch controls the power supply switching circuits. The output of the power supply provides control voltage for the IRU and the ISDU and high voltage excitation to the three laser gyros.All IRU input data is routed into the computation circuit. The air data source supplies the ARINC 429 bus input containing air data. Initialization data originates from either the flight management computer or the ISDU. The IRU program pins tell the computation circuits which way the IRU is facing in the airplane.Software does all computations, including compensations, navigational calculations, and coordinate transformations. Gyro and accelerometer outputs are compensated for sensor bias, scale factor, misalignment, and thermal changes. The compensated signals are used in computing airplane pitch, roll and heading relative to the local navigation coordinates. Airplane attitude is used to resolve acceleration into components relative to the local navigation coordinate system. Barometric altitude from an air data computer is used to compensate the vertical speed computations.Three identical ARINC 429 data buses (high speed) provide digital data to navigation, flight management, autoflight, and flight instrument system. A status discrete is applied to the MSU.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
J. Built-in test equipment (BITE) circuits isolate faults to the LRU level. Faults are indicated by the yellow fault ball on the front of the IRU, the amber FAULT light on the MSU, and a status bit on the data buses to the user systems. The user systems may record an inflight fault based upon the fault from the IRU. In addition, status words are stored in a non-volatile memory in the IRU for at least the previous nine flights. Contents of the non-volatile memory can be extracted on the ground for maintenance.
K. Parameters continuously monitored by the BITE include the laser gyros, accelerometer and power supply outputs, computer and memory operation, and temperature. When the IRU is initially turned on, the battery power is tested. The ON DC indication displays during the battery check.
L. The manual test is initiated by pressing the test switch on the IRU or by holding the display selector in TEST position. The test is also performed as part of the IRS BITE from the FMCS CDU. The test can be done in ALIGN mode, or in NAV mode when ground speed is less than 20 knots. It is inhibited in ATT mode.
6. FMCS-CDU IRS Functions______________________
A. Initialization Functions
(1) The IRS is initialized (present position entered) by selecting IRS pages on the FMCS-CDU keyboard. For detailed operation of the FMCS-CDU, refer to 34-62-00. The FMCS-CDU(s) are located in the forward electronics panel, P9.
B. IRS Related CRT Displays
(1)
The POS INIT page is selected to enter the initial reference position for IRS alignment.
(2)
The POS REF 2/2 page displays current position as computed by the FMC and each IRU.
(3)
The MAINTENANCE INDEX provides access to pages of data from which maintenance personnel can check IRU performance data.
7. Digital/Analog Adapter (DAA) (Fig. 11)____________________________
A. The DAA converts digital data inputs to analog outputs and analog data inputs to digital outputs. It serves the FMCS, the IRS and other airplane systems.
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