FAA Instrument Rating Airplane (IRA)Navigation SystemsHard
A commercial pilot is conducting an RNAV (GPS) approach in an aircraft equipped with a GPS receiver that has WAAS. During the final approach segment, the pilot observes a 'GPS Integrity' alert, and the annunciator indicates a degradation from LPV to LNAV minima. What action is required?
- AContinue the approach to LPV minima, as the system will re-acquire integrity.
- BSwitch to VOR navigation and continue the approach if a VOR approach is available.
- CContinue the approach to LNAV minima, using the higher LNAV decision altitude (DA) or minimum descent altitude (MDA).
- DImmediately execute a missed approach, as GPS integrity is compromised.
Show answer & explanationAnswer & explanation
Correct answer: C. Continue the approach to LNAV minima, using the higher LNAV decision altitude (DA) or minimum descent altitude (MDA).
If a WAAS-equipped GPS downgrades from LPV to LNAV minima during an approach, the pilot must immediately utilize the LNAV minima, including the higher LNAV DA/MDA. A missed approach is only required if the integrity is lost below LNAV, or if LNAV minima are unavailable/unacceptable.
Why the other options are wrong
- A. Continuing to LPV minima is unsafe and not permitted as integrity for LPV is lost.
- B. Switching to VOR is an option if the GPS integrity is completely lost or if the LNAV minima are not acceptable, but the immediate action is to use the valid LNAV minima.
- D. A missed approach is only required if the integrity drops below LNAV, or if LNAV minima are not suitable/available.
WAAS Integrity Downgrade
A situation where a WAAS-equipped GPS receiver detects a loss of integrity for a higher service level (e.g., LPV) and automatically reverts to a lower service level (e.g., LNAV).
- Requires immediate adherence to the new, lower minima.
- Pilot must use the corresponding, usually higher, DA/MDA.
- A missed approach is required if integrity falls below the lowest available minima or if the pilot cannot meet the requirements for the new minima.
Memory trick: When the floor drops, use the next highest floor.