A previous question concludes that it is legal to fly an aircraft in the US with only an IFR-approved GPS/WAAS system and no other navigation equipment on an IFR flight plan. My question is about how the pilot is then allowed to navigate.
Specifically, must a pilot fly on GPS (T and Q) Routes? FAA Advisory Circular 90-108 discusses using RNAV systems on conventional routes, so it seems that a pilot could also fly on VOR airways, for instance. In fact, 90-108 specifies exactly what a pilot can use their RNAV system for:
- Determine aircraft position relative to or distance from a VOR, ... DME fix, ...
- Navigate to or from a VOR, TACAN, NDB, or compass locator.
- Hold over a VOR, TACAN, NDB, compass locator, or DME fix.
- Fly an arc based upon DME.
Navigating on a VOR airway involves navigating to and from VORs, which is covered by point 2. However, the list does not include navigating to a DME/radial fix off a VOR. After taking off IFR the departure controller may clear an aircraft direct to a fix on the airway e.g. "cleared direct BOONE". Could a pilot legally use only GPS/WAAS to fly to BOONE or any other VOR radial/DME point?