C J Campbell wrote:

"Bob Gardner" wrote in message
...
Can't address your problem, but AIM 1-1-20(a)(8) tells us not to use GPS
altitudes. Doesn't say anything about WAAS...yet.

1-1-20's title is "Wide Area Augmentation System (WAAS)." There is no
1-1-20(a)(8). 1-1-20(b) gives guidance and procedures for flying approaches
with vertical guidance from WAAS and says that some installations of WAAS
may be certified for precision approaches as having greater accuracy than
barometric altimeters.

The sections were rearranged but Bob Garder is right; the prohibition still
exists. What the language you cite refers to is LPV. If you have IFR
certified LPV on your aircraft (which I doubt), then you can use LPV from the
PFAF to Decision Altitude, only. There is no authorization to use LPV in any
other manner to determine altitude, nor is there any other provision to use
WAAS-augmented GPS in general to replace the barometric altitmeter for
determining altitude under IFR.