Erroneous Radio-Altimeter Altitudes on Ground Displayed on CAPT and F/O PFDs

TASK 34-42-00-810-846-A
Erroneous Radio-Altimeter Altitudes on Ground Displayed on CAPT and F/O PFDs

1. Possible Causes

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
ESPM 205323
ASM 344201
AMM 34-42-11-615-001	Cleaning of the External Surface of the Radio Altimeter Antennas
AMM 34-42-33-000-001	Removal of the Radio Altimeter Transceiver
AMM 34-42-33-400-001	Installation of the Radio Altimeter Transceiver

3. Fault Confirmation
Subtask 34-42-00-740-117-A

A. Not applicable, the fault is evident.

4. Fault Isolation
Subtask 34-42-00-810-103-A

A. If the fault symptom is identified by the crew observation on a discrepancy of Radio Altitude display on CAPT and F/O PFD on ground:

Make sure that the difference between RA1 and RA2 indications is permanent and more than or equal to 2ft.

(1) If the difference is more than or equal to 2ft:

Make sure that there are no objects (such as towbar) in the area.
Make sure that the area below the Radio Altimeter (RA) antennas has no contamination with fluids (such as water, oil...) or rough substance (snow, grass...).

(a) If the fault continues:

Do the cleaning of the external surface of the radio altimeter antennas AMM 34-42-11-615-001.

1 If the fault continues:

Swap the RA transceiver 1 (2SA1) and the RA transceiver 2 (2SA2) AMM 34-42-33-000-001 and AMM 34-42-33-400-001.

a If the RA1 indication moves from CAPT PFD to F/O PFD and if RA2 indication moves from F/O PFD to CAPT PFD:

Swap back the RA transceivers 1 and 2 and replace the defective RA transceiver XCVR-RA, 1 [2SA1] or XCVR-RA, 2 [2SA2] AMM 34-42-33-000-001 and AMM 34-42-33-400-001.

NOTE: The defective system most likely gives the value farthest from 0ft.

b If the RA1 and RA2 indications do not move:

Swap back tha RA transceivers 1 and 2 AMM 34-42-33-000-001 and AMM 34-42-33-400-001.
Replace the coaxial cables related to the defective system: the coaxial cables between the RA transceiver 1 (2SA1) pins AA/C and AB/C and the radio altimeter antennas or the coaxial cables between the RA transceiver 2 (2SA2) pins AA/C and AB/C and the radio altimeter antennas ESPM 205323 ASM 344201.

(2) If the difference is less than 2ft:

[Rev.8 from Aug 2018] 2026.04.04 04:33:11 UTC