The FAA has updated its policies for filing alternate airports for pilots who use an IFR-approved GPS.
According to the new policy, which will added to future versions of the AIM, advisory circulars, and other documents, pilots with non-WAAS GPS navigators can now file an alternate airport that is served only by GPS-based instrument approaches, provided the original destination airport has ground-based procedures, or vice-versa.
Pilots flying WAAS-equipped aircraft with baro-VNAV capability (typically only business jets and airliners) can now use the LNAV/VNAV decision altitude for applicable alternate airport weather minimums.
Pilots without baro-aided LNAV/VNAV capability must still meet the requirements of 14 CFR § 91.169, which specifies alternate airport weather minima for non-precision approach procedures. In other words, at the estimated time of arrival at the alternate airport, the forecast weather at the alternate must call for a ceiling of at least 800 feet and visibility of at least 2 statute miles.
The new NOTAM, issued April 4, explains that:
The FAA [has] also studied the availability of GPS and Wide Area Augmentation System (WAAS) for GPS and WAAS-based instrument approaches at destination and alternate airports. As a result, the FAA has updated the policy and provided clarification to enable additional flexibility for users while maintaining safety in the National Airspace System (NAS).
For pilots who fly with IFR-approved GPS navigators without WAAS capabilities, the NOTAM explains that:
The current alternate airport planning policy allows users equipped with non-WAAS navigators…to plan for GPS-based instrument approach procedures (IAP) at their destination but not at their alternate airport.
The FAA has updated this policy to allow an option to flight plan for use of a GPS-based IAP at either the destination or the alternate airport, but not at both locations. At the alternate airport, pilots may plan for applicable alternate airport weather minimums using:
1. Lateral navigation (LNAV) or circling minimum descent altitude (MDA);
2. LNAV/vertical navigation (LNAV/VNAV) decision altitude (DA) if equipped with and using approved barometric vertical navigation (baro-VNAV);
3. RNP 0.3 DA on an RNAV (RNP) IAP if specifically authorized with approved baro-VNAV equipment.
…The FAA based this policy clarification on the facts that GPS-based lateral guidance is the same for LNAV, LNAV/VNAV and RNP 0.3 DA and approved barometric vertical navigation equipment does not rely on GPS information. Therefore, a loss of GPS vertical would not affect these WAAS users navigating vertically with baro-VNAV.
The change in policy for WAAS users does not affect most pilots who fly light GA aircraft with IFR-approved WAAS navigators. According to the NOTAM:
The current alternate airport planning policy explicitly prohibits TSO-C145() and TSO-C146() equipped users (WAAS users) from planning to use WAAS vertical guidance at their alternate airport.
There are some WAAS integrations that use baro-VNAV for vertical guidance. WAAS users should consult their flight manuals for this information. This policy clarification allows properly trained and approved, as required, WAAS users equipped with and using approved baro-VNAV equipment to plan for applicable alternate airport weather minimums using:
1. LNAV/VNAV DA at an alternate airport.
2. RNP 0.3 DA on an RNAV (RNP) IAP at the alternate airport if specifically authorized.
The FAA based this policy clarification on the facts that GPS-based lateral guidance is the same for LNAV, LNAV/VNAV and RNP 0.3 DA and approved barometric vertical navigation equipment does not rely on GPS information. Therefore, a loss of GPS vertical would not affect these WAAS users navigating vertically with baro-VNAV.