The IRS mode select panel (IRMP) is used to control the three IRUs. It provides individual mode selection, displays align status, displays fault annunciation for each IRU, and provides a display and keyboard for IRU initialization and data display. The IRMP is located on the pilot's overhead panel.
The IRMP has three rotary switches for selecting the following modes of each IRU.
(a) OFF - IRS is off.
(c) NAV (navigation) - The NAV mode is the normal operating mode for the IRS. In this mode, the IRS performs inertial navigation functions and outputs normal IRS data to be
displayed or used by other systems.
(d) ATT (attitude) - The ATT mode is used when failure or total power loss (AC and DC power) is detected in the NAV mode. In this mode, only attitude data is output to the user systems.
The ALIGN, NAV, ATT, and OFF modes are entered using the following mode sequences. The corresponding IRU operation and ALIGN annunciator status are as follows:
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| MODE SEQUENCE | IRU OPERATION | ALIGN LIGHT |
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|OFF TO ALIGN | REMAINS IN ALIGN MODE AND CONTINUES FINE| REMAINS ON |
| *[1] | LEVELING AND EARTH RATE ESTIMATION. | |
| | | |
|OFF TO ALIGN TO NAV| PERFORMS 10-MINUTE ALIGNMENT AND | ON DURING |
| *[1] *[2] | AUTOMATICALLY SEQUENCES TO NAV MODE. | ALIGNMENT |
| | | |
|OFF OR NAV TO ATT | FULL SUPPORT OF ATTITUDE - RELATED AND | ON FOR 30 |
| | BODY ACCELERATION OUTPUTS IN 30 SECONDS.| SECONDS |
| | | |
|NAV TO ALIGN | SETS VELOCITIES TO ZERO AND CONTINUES | REMAINS ON, |
| *[1] *[3] | TO REFINE LEVELING AND HEADING | FLASHES IF |
| | DETERMINATION (NAV MAY BE RE-ENTERED | MOVEMENT |
| | IN APPROXIMATELY 30 SECONDS). | |
| | | |
|NAV TO ALIGN TO NAV| SETS VELOCITIES TO ZERO. | ON FOR 30 SEC, |
| *[1] *[3] | | FLASHES IF MOV-|
| | | EMENT WHILE ON |
| | | |
|ATT TO NAV OR ALIGN| REMAINS IN ATT MODE UNTIL SWITCHED OFF. | OFF |
| | | |
|ALIGN TO NAV | IF ALIGN TIME GREATER THAN 10 MINUTES, | ON DURING |
| | IRU SEQUENCES TO NAV, HOWEVER, AN ALIGN | ALIGNMENT |
| | TIME OF 17 MINUTES IS REQUIRED ABOVE | |
| | 70 DEGREES NORTH LATITUDE. | |
| | | |
|ATT OR NAV OR ALIGN| 30 SECOND POWER-OFF COUNTDOWN, BITE | ON FOR 30 |
|TO OFF | INFORMATION, PPOS, AND AUTOCAL TRANSFER | SECONDS |
| | TO NVM. | |
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*[1] Details of mode sequences to ALIGN mode are described in Functional Description of IRS Alignment.
*[2] The mode sequence "OFF TO ALIGN TO NAV" should not be used above 70 degrees North latitude. A full 17 minute alignment is required.
*[3] The IRU should not be sequenced out of NAV mode above 70 degrees North latitude. Accuracy updates require a full 17 minute alignment.
Each mode select switch has a detented NAV position which prevents accidental movement of the switch out of the NAV mode. When the switch is in the NAV position, it must first be pulled out of detent before selecting a new position to prevent damage to the switch.
Three sets of four lights provide system status and fault indication. ALIGN (white when lit), ON DC, DC FAIL, and FAULT (amber when lit) lights are provided for each IRU. These lights work as follows:
(a) The ALIGN light denotes that the IRU is in the align mode and is running an initial position determination, is in initial attitude mode, or is powering down.
(b) The ON DC annunciator lights when the IRU has switched to backup battery power.
(c) If battery power fails, the DC FAIL light will come on.
(d) A lit FAULT annunciator indicates that a BITE detected failure has occurred. The FAULT light also comes on if certain alignment tests fail. These tests are covered in detail in the
operation section.
IRMP Keyboard and Display
(a) The SYS DSPL switch selects the IRU, for on-line interface with the IRMP. The IRMP can only display data from the IRU which has been selected by the SYS DSPL switch.
(b) The DSPL SEL switch selects the type of data to be displayed on the IRMP numeric displays. The IRU, as selected by the SYS DSPL switch, supplies the data. The four switch positions and the data displayed for each position is as follows:
1) TK/GS - Track angle (TK) is displayed in the left display and the ground speed (GS) in the right display.
2) PPOS - Latitude is displayed in the left display and the longitude in the right display.
3) WIND - Wind angle is displayed in the left display and the wind velocity in the right display.
4) HDG - True heading is displayed in the left display and the right display remains blank.
(c) There are two numeric displays on the IRMP. When the IRMP is receiving IRU data, the DSPL SEL switch determines the data on the display. When the IRMP keyboard is used to initialize an IRU, the data punched in at the keyboard is shown on the two displays. For invalid data from an IRU, both displays are blanked. A brightness control for the displays is located concentric within the DSPL SEL switch.
(d) The keyboard consists of twelve lighted keys. To change the numeric display from the IRU receive mode to a keyboard display mode, one of the following keys must first be pressed: N(2), S(8), H(5), E(6), or W(4). Any other initial key is ignored.
1) Pressing N(2) or S(8) once will cause a N or S to appear in the left display. These represent north and south and are used to initialize latitude in the IRU.
2) Pressing W(4) or E(6) once will cause a W or E to appear in the right display. These represent west and east and are used to initialize longitude in the IRU.
3) Pressing H(5) once will also switch the IRMP from an IRU receive mode to the keyboard display mode. This is used to enter magnetic heading in the ATT mode.
4) Numeric data can be entered after one of the five letter keys is pressed. It will be appropriately displayed in the numeric display as it is entered.
5) Keys with letters on them, as well as numbers, provide the letter value when they are the first punched key in a program sequence.
6) The ENT key, when pressed, transfers the data in the IRMP to the IRU. Also, when the ENT key is pressed, the display is first blanked and then returned to the IRU receive mode.
7) The CLR key clears the display, then returns the IRMP to the IRU receive mode.
The IRMP also has a Time to NAV (TTN) display and a maintenance fault code display.
(a) The Time to NAV (TTN) feature counts down the minutes to alignment completion.
(b) The IRU must be in the ALIGN mode, the IRMP mode select switch must be set to ALIGN or NAV, and the DSPL SEL switch must be set to HDG. A single digit will appear on the right side of the IRMP display to indicate minutes remaining as follows:
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| MINUTES | NUMBER |
| REMAINING | DISPLAYED |
#########################
| 10 | 7 |
| 9 | 7 |
| 8 | 7 |
| 7 | 7 |
| 6 | 6 |
| 5 | 5 |
| 4 | 4 |
| 3 | 3 |
| 2 | 2 |
| 1 | 1 |
| 0 | 0 |
#########################
1) The TTN zero will not be visible with the mode select switch set to NAV. The display will blank as the IRS sequences to NAV and the ALIGN annunciator goes off.
2) When realign mode is selected, the TTN will display 7 and count toward 0 in 30 seconds.
(d) The maintenance fault code display mode provides access to some IRU faults without external test equipment. Faults are classified as either critical, noncritical, or BITE memory
only. The maintenance fault code display mode will display critical and noncritical faults, but external test equipment is required to read faults stored in BITE memory. Regardless of fault classification, all faults are stored in BITE memory when the IRU is turned off.
1) To enter the maintenance code display mode, first select the desired IRU using the SYS DSPL Select Switch. Next, set the DSPL SEL switch to the HDG position. Enter a 0 on the
keyboard, followed within five seconds by a 1. The highest priority code will be displayed in the two right digits of the IRMP display. Record the code, press CLR to display the next priority code, and repeat to cycle through the remaining codes.
2) If the IRS was navigating, the last displayed value of true heading will be frozen on the display.
3) If TTN display was present, the display will be frozen when the maintenance code is entered. The internal clock will continue to run and a new TTN value will appear after all
maintenance codes are displayed.
4) The following table indicates the corresponding fault for each IRMP code:
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| IRMP CODE AND | |
| PRIORITY | IRU FAULT |
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| 01 | POWER SUPPLY CRITICAL |
| 02 | DIGITAL I/O WRAP-AROUND |
| 03 | RAM/NVM/PROM MEMORY |
| 04 | LSIC |
| 05 | DISCRETE INPUT |
| 06 | PROCESSOR |
| 07 | GYRO |
| 08 | ALIGN/SYSTEM |
| 09 | A/D MUX DATA TRANSFER |
| 11 | POWER SUPPLY |
| 12 | ADC DISCRETE OUT |
| 13 | NOT USED |
| 14 | CALIBRATION PROM |
| 15 | INA/OTA |
| 16 | ANALOG PITCH RATE |
| 17 | GYRO |
| 18 | GYRO CONFIGURATION |
| 19 | TEMPERATURE SENSOR |
| 20 | NOT USED |
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6) Codes 01 thru 09 are critical faults. A critical fault turns on the IRMP FAULT light.
7) Codes 11 thru 20 are noncritical faults and are indicated as follows:
a) During initialization, align, align downmode, or navigate mode, if a non-critical fault is detected on the ground, the IRMP fault annunciator turns on. If a non-critical fault is detected in the air, the IRMP fault annunciator turns on below a set ground speed after touchdown.
b) During attitude mode,no failure indication is given by the IRMP fault annunciator. A fault detected prior to entering
attitude mode is indicated as previously described. Entering attitude mode causes the IRMP fault annunciator to go out.
Here are few pictures, a video of light test and manual keyboard position immission and a video with demonstration of ARINC data feeded to the unit's left channel.
