During an ILS approach in IMC, the pilot receives a glideslope flag indicating the glideslope has failed shortly after passing the outer marker. According to standard procedure, what must the pilot do?
- ADescend to the LOC MDA immediately upon losing the glideslope, regardless of current position on the approach
- BTransition to the localizer-only (LOC) minimums, which use a higher MDA and different visibility requirement than the ILS DA
- CImmediately execute the missed approach because glideslope failure invalidates the entire approach
- DContinue the approach using the ILS DA, since the localizer alone still provides adequate vertical guidance
Show answer & explanationAnswer & explanation
Correct answer: B. Transition to the localizer-only (LOC) minimums, which use a higher MDA and different visibility requirement than the ILS DA
When the glideslope becomes unusable, the ILS approach reverts to a nonprecision localizer approach. The pilot must use the LOC-only minimums published on the same chart, which typically have a higher MDA (rather than a DA) and may require a different visibility minimum, and continue the approach in level flight at the appropriate step-down altitudes to the MAP.
Why the other options are wrong
- A. Incorrect — the pilot must not descend below applicable step-down altitudes prematurely; descent must be flown per the LOC procedure, not immediately upon glideslope loss
- C. Incorrect — a missed approach is not automatically required; LOC-only minimums can be used
- D. Incorrect — without glideslope, there is no vertical guidance for the ILS DA
Glideslope Inoperative Procedure
If the ILS glideslope fails during an approach, the pilot flies the approach to the localizer-only (LOC) minimums published on the same approach chart, which use an MDA instead of a DA.
- LOC-only minimums are always higher (or equal) than ILS DA minimums
- Approach becomes nonprecision; stepdown fixes and MDA apply
- Chart typically lists both S-ILS and S-LOC minima lines
Memory trick: No glide? Slide to LOC minimums, not below.