A pilot is flying an ILS approach. The approach plate indicates that the ILS frequency for Runway 27 is 110.3 MHz, and the associated DME is on Channel 40. During the approach, the pilot notices the DME display indicates 'HOLD' and the distance is not updating. What is the most likely reason for this indication?
- AThe ground-based DME facility associated with the ILS is inoperative or unmonitored.
- BThe aircraft is outside the service volume of the DME facility.
- CThe aircraft's DME unit has failed and requires maintenance.
- DThe pilot has tuned the DME to an incorrect frequency or channel.
Show answer & explanationAnswer & explanation
Correct answer: A. The ground-based DME facility associated with the ILS is inoperative or unmonitored.
A DME display indicating 'HOLD' or a non-updating distance, especially when tuned to the correct frequency/channel and within expected service volume, is a strong indication that the ground-based DME facility itself is either inoperative, unmonitored, or experiencing issues. DME systems are paired with localizer frequencies, so if the ILS is working, but DME isn't, the ground DME is the likely culprit, not the aircraft's internal unit or tuning.
Why the other options are wrong
- B. If outside the service volume, the DME would typically show a blank display, 'NO ID', or 'OFF', rather than 'HOLD', which implies a temporary or unreliable signal reception from a potentially active but faulty station.
- C. While possible, a 'HOLD' indication is more often associated with a ground facility issue or being outside service volume rather than an internal unit failure which might show a flag or blank display.
- D. The question implies the pilot has tuned correctly by stating 'the associated DME is on Channel 40,' which is paired with 110.3 MHz (typically), so incorrect tuning is less likely if the ILS itself is working.
DME 'HOLD' Indication
A 'HOLD' indication on an aircraft's DME display, especially when tuned to the correct frequency and within expected service volume, usually signifies that the ground-based DME facility is inoperative, unmonitored, or experiencing intermittent signal issues.
- DME 'HOLD' means no valid ground signal received.
- Indicates ground facility issue (inoperative, unmonitored).
- Not typically caused by aircraft unit failure or tuning error (if ILS is working).
- Requires pilot to rely on other navigation or execute missed approach if critical.
Memory trick: DME Holds? Ground Control's Cold.