A pilot is flying an RNAV (GPS) approach with LNAV/VNAV minimums. The aircraft is equipped with a WAAS-capable GPS receiver. As the aircraft approaches the final approach segment, the display indicates 'LNAV+V'. What does this indication signify?
- AThe system is providing LNAV lateral guidance and advisory vertical guidance, but not certified for LNAV/VNAV minimums.
- BThe system is providing glideslope guidance from a ground-based NAVAID, augmenting the GPS.
- CThe system has reverted to LNAV-only guidance due to a WAAS signal degradation.
- DThe system is providing full LNAV lateral and VNAV vertical guidance, certified for LNAV/VNAV minimums.
Show answer & explanationAnswer & explanation
Correct answer: A. The system is providing LNAV lateral guidance and advisory vertical guidance, but not certified for LNAV/VNAV minimums.
LNAV+V indicates that the WAAS-capable GPS receiver is providing LNAV (lateral navigation) guidance and advisory vertical guidance. While it provides vertical guidance, it is not considered precision approach guidance and does not meet the requirements for LNAV/VNAV minimums. It's advisory vertical guidance, typically used when LNAV/VNAV or LPV are unavailable or not selected, but still offers a helpful descent path.
Why the other options are wrong
- B. LNAV+V is derived from GPS/WAAS data, not ground-based glideslope NAVAIDs.
- C. While WAAS degradation can lead to lower service levels, 'LNAV+V' itself is a specific advisory mode, not necessarily a reversion from LNAV/VNAV.
- D. 'LNAV/VNAV' or 'LPV' would be indicated for certified lateral and vertical guidance to LNAV/VNAV minimums.
LNAV+V Indication
An 'LNAV+V' indication on a WAAS-capable GPS receiver signifies LNAV lateral guidance with advisory vertical guidance, which is not certified for LNAV/VNAV minimums.
- Provides a computed vertical path based on WAAS data.
- Considered advisory vertical guidance, not precision.
- Does not meet the stringent integrity and accuracy requirements for LNAV/VNAV or LPV minimums.
- Still provides a useful vertical path to assist pilot workload.
Memory trick: LNAV+V: Lateral, plus a V-path, but not VNAV's class.