During an ILS approach, a pilot experiences a glideslope receiver failure before reaching the final approach fix (FAF). The approach plate shows LNAV minimums available. What is the most appropriate action for the pilot?
- AContinue the approach using the localizer for lateral guidance and LNAV minimums for descent.
- BExecute a missed approach immediately.
- CRequest vectors to a different approach with a functioning glideslope.
- DProceed to the alternate airport as a glideslope is essential for all ILS approaches.
Show answer & explanationAnswer & explanation
Correct answer: A. Continue the approach using the localizer for lateral guidance and LNAV minimums for descent.
If the glideslope fails on an ILS approach and LNAV minimums are published, the approach effectively becomes a localizer-only approach. The pilot can continue to use the localizer for lateral guidance and descend to the LNAV Minimum Descent Altitude (MDA) instead of the Decision Altitude (DA) associated with the ILS glideslope. This is often referred to as 'LOC minimums' or 'Localizer (glideslope-out)' minimums.
Why the other options are wrong
- B. A missed approach is not immediately required if alternative minimums (like LNAV/LOC) are available.
- C. While requesting a different approach is an option, continuing the current approach with available minimums is often the most efficient and appropriate first step.
- D. Proceeding to an alternate is unnecessary if the approach can be completed safely using available minimums.
Glideslope Failure on ILS (with LNAV)
If the glideslope fails during an ILS approach and LNAV minimums are published, the approach reverts to a non-precision localizer-only approach, and the pilot uses the LNAV (or LOC) MDA.
- ILS becomes a localizer-only approach.
- Pilot uses published LNAV (or LOC) Minimum Descent Altitude (MDA).
- Decision Altitude (DA) is no longer applicable.
- Lateral guidance is still provided by the localizer.
Memory trick: Glideslope Gone? Go Low, but Stay on the Localizer.