in Airbus A320 by John

Unexpected G/S Mode Armed – A320

Issue:

As the wording suggests, the condition arises when ‘G/S’ is displayed as armed on the FMA despite not being expected. This issue occurs when the following conditions are satisfied within a timeframe of less than 1.5 seconds:
  • AP 1+2 set to OFF
    FD 1+2 set to OFF
  • A/THR set to OFF.

Here, although AP/FDs are OFF and G/S mode is correctly disarmed, a software glitch causes the G/S armed problem to become latched in the system. Now, when the FDs are reengaged, G/S mode armed is displayed on the FMA along with the current vertical mode.

Pilots should be aware of this potential delay and take appropriate actions to ensure the safe conduct of the approach.

Solution:

Issue on ground – If this situation occurs on the ground, i.e., with FDs ON, if G/S is armed, the flight crew shall perform an aircraft power OFF. This will cancel the sequence.

If this issue occurs in flight, arm the approach with APP pb. Check for LOC and G/S on FMA. Now again disarm the approach with APP pb. In most of the cases G/S should no longer be displayed on FMA. This procedure is more significant if LOC only approach is required. In case issue persist, solution is to fly raw data approach.

Note – Most of the temporary abnormal behaviors’ issues are MSN specific. Check your FCOM for list of applicable issues.

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