A pilot is selecting an alternate airport for an IFR flight plan. The only published instrument approach procedure at the intended alternate is an RNAV (GPS) approach, and the aircraft is equipped with a non-WAAS IFR-approved GPS receiver. According to FAA guidance, what limitation applies to using this airport as an alternate?
- AThe airport cannot be used as an alternate at all if only a GPS approach is published
- BThe pilot may plan to use the RNAV (GPS) approach at the alternate only if the approach can be flown to LNAV or circling minimums, since WAAS-specific minimums (LPV/LNAV VNAV) cannot be used for alternate planning with a non-WAAS receiver
- CThe pilot must instead select a VOR approach even if none is published at that airport
- DThe pilot may use any published minima including LPV as long as the GPS is IFR-approved
Show answer & explanationAnswer & explanation
Correct answer: B. The pilot may plan to use the RNAV (GPS) approach at the alternate only if the approach can be flown to LNAV or circling minimums, since WAAS-specific minimums (LPV/LNAV VNAV) cannot be used for alternate planning with a non-WAAS receiver
FAA guidance (AIM 1-1-19 and related Notices) specifies that when using GPS for alternate airport planning, a non-WAAS GPS receiver may only be used to fly the approach to LNAV or circling minimums; WAAS-dependent minima such as LPV or LNAV/VNAV cannot be used for alternate planning purposes if the aircraft lacks WAAS capability, since those vertical guidance minima are not guaranteed to be available without WAAS.
Why the other options are wrong
- A. GPS-only approaches can be used for alternates; they are not automatically disqualified.
- C. There's no requirement to have a VOR approach if RNAV(GPS) is properly usable to LNAV minimums.
- D. Using LPV minimums requires WAAS capability, which this aircraft lacks.
GPS Alternate Airport Limitation
A non-WAAS IFR GPS may be used for alternate planning only to LNAV or circling minimums; WAAS-only minima like LPV or LNAV/VNAV cannot be relied upon for alternate planning without WAAS avionics.
- Non-WAAS GPS limited to LNAV/circling minimums for alternates
- WAAS-equipped aircraft may use LPV/LNAV VNAV for alternate planning
- This distinction affects flight planning, not enroute nav which may still be fine
Memory trick: 'No WAAS? No vertical guidance for your alternate.'