A failed HSI could cause loss of VOR and TACAN, as well as heading and course deviation information.
In the event that the compass card freezes or displays erroneous information, obtain heading information
from the ADI and cross-check the standby compass.
Figure 42 shows one of the possible indications of a failed HSI. Remember that the OFF flag does not
have to be present for the indicator to give false readings because it only indicates the status of electrical
power and SAHRS validity signals.
The procedure for dealing with a HSI failure is:
1. Determine the nature of the malfunction.
2. Use backup navigation instruments as
3. Report the failure to ATC.
4. Maintain VFR conditions, if possible.
5. Land as soon as practicable.
Figure 42: FAILED HSI