Which mode should be selected to rely on attitude and heading from IR 1 if it is degraded and ATT mode is available?

Which mode should be selected to rely on attitude and heading from IR 1 if it is degraded and ATT mode is available?

• A. NAV
• B. DES
• C. ATT
• D. OFF

Answer: (C)

When one inertial reference system is degraded, you want to keep attitude and heading data available from the remaining healthy source. Selecting ATT makes the system rely on the Attitude Reference, using the available AHRS data to provide attitude and heading to the flight computers and instruments. This keeps the aircraft controllable and allows continued navigation even with the degraded IR1. Choosing NAV would depend on the full integrity of the IRS for navigation data, which isn’t guaranteed with an degraded IR. OFF would remove the attitude reference entirely, leading to loss of attitude information. DES is for degraded navigation scenarios and does not provide the same reliable attitude/heading source as ATT in this situation.

When one inertial reference system is degraded, you want to keep attitude and heading data available from the remaining healthy source. Selecting ATT makes the system rely on the Attitude Reference, using the available AHRS data to provide attitude and heading to the flight computers and instruments. This keeps the aircraft controllable and allows continued navigation even with the degraded IR1.

Choosing NAV would depend on the full integrity of the IRS for navigation data, which isn’t guaranteed with an degraded IR. OFF would remove the attitude reference entirely, leading to loss of attitude information. DES is for degraded navigation scenarios and does not provide the same reliable attitude/heading source as ATT in this situation.