You can't do a NPA without the required published
aids, whether those aids are VOR, VOR/DME, NDB,
or GPS with or without the box.
The "what if" principle resolves the question in a
lot of cases.
Vilas - if say the Tawau VOR and DME is out and
you get a NAV ACCUR DOWNGRAD while still in a
rebut putir what you gonna do?