In a conventional ADI, if a negative DH is entered in EADI or EHSI and RA remains unchanged, what happens to DH?

• A. DH becomes blank
• B. DH doubles
• C. DH decreases
• D. DH increases

Answer: (A)

The DH readout on EADI/EHSI represents a height reference used for decision height. A negative DH isn’t a meaningful value in this context, and if the altitude reference (RA) isn’t changing to produce a valid result, the instrument’s input validation clears the field. So the DH display goes blank to indicate an invalid or unusable input rather than showing a nonsensical negative value. The other possible behaviors would require the system to perform a transformation on a valid value, which isn’t how this input scenario is handled.