DOC AIRBUS | TSM A320FDisagree between the FMS and the IRS Positions/Excessive drift
TASK 34-14-00-810-926-A
Disagree between the FMS and the IRS Positions/Excessive drift
1. Possible Causes
A. Referenced Information
3. Fault Confirmation
Subtask 34-14-00-710-082-A
Subtask 34-14-00-810-180-A
[Rev.8 from Aug 2018]
2026.04.04 04:32:50 UTC
Disagree between the FMS and the IRS Positions/Excessive drift
1. Possible Causes
- ADIRU
A. Referenced Information
| REFERENCE | DESIGNATION |
|---|---|
| AMM 34-12-34-000-001 | Removal of the ADIRU |
| AMM 34-12-34-400-001 | Installation of the ADIRU |
POSITION MONITOR Page on the MCDUSubtask 34-14-00-710-082-A
A. At the end of the flight, on the MCDU:
(1) If available, make sure that the GPS SELECTED indication is shown on the "SELECTED NAVAIDS" page.
(a) If the indication is not shown:
(3) Get the POSITION MONITOR page
(4) Read each IRS position error shown on line 5 and read the radial position error given on the aircraft log book.
4. Fault Isolation(1) If available, make sure that the GPS SELECTED indication is shown on the "SELECTED NAVAIDS" page.
(a) If the indication is not shown:
- Change the status from DESELECTED to SELECTED.
(3) Get the POSITION MONITOR page
(4) Read each IRS position error shown on line 5 and read the radial position error given on the aircraft log book.
NOTE: The radial position error does not stay in the memory of the MCDU after the aircraft electrical circuits are de-energized.
Subtask 34-14-00-810-180-A
A. Compare the values that you read with the curve shown on the figure.
(1) Calculate the NAV time of the ADIRU as follows:
(3) If the radial position error value is permitted (AREA 1), no maintenance action is necessary.
(4) If the radial position error value is in AREA 2, you must do a check of this value after the subsequent flight.
(a) If after the second check, the radial position error value is in AREA 1, no maintenance action is necessary.
(b) If after the second check, the radial position error value is in AREA 2 or 3, replace the defective ADIRU AMM 34-12-34-000-001 and AMM 34-12-34-400-001.
(1) Calculate the NAV time of the ADIRU as follows:
- record the flight time of the previous flight given in the logbook and add 30 minutes to this time.
NOTE: This 30-minute period is the assumed time interval from the end point of the ADIRU alignment and aircraft door closing before pushback.
(2) If the radial position error value is not permitted (AREA 3), replace the defective ADIRU AMM 34-12-34-000-001 and AMM 34-12-34-400-001. (3) If the radial position error value is permitted (AREA 1), no maintenance action is necessary.
(4) If the radial position error value is in AREA 2, you must do a check of this value after the subsequent flight.
(a) If after the second check, the radial position error value is in AREA 1, no maintenance action is necessary.
(b) If after the second check, the radial position error value is in AREA 2 or 3, replace the defective ADIRU AMM 34-12-34-000-001 and AMM 34-12-34-400-001.