Say Altitude.

"Bob Gardner" wrote in message
news:R0hcc.78998$K91.171081@attbi_s02...
You're right. AIM 1-1-20(a)(8) tells us that we should not use GPS
altitude.
When WAAS is in common use this will probably change.

The altitude error is part of the WGS-84 model and is not a WAAS issue any
longer. The CNX-80 provides VNAV capability through the use of pressure
altitude from a transponder source and the pilot's baro correction input;
married to a partial TAWS data base. GPS/WAAS is not likely to become an
acceptable substitute for pressure altitude. Larger airplanes use air data
derived pressure altitude in conjunction with GPS for improved RNP
capability.

I think the whole WAAS thing is in flux. The AIM gets wordier and more
difficult to interpret with each change to its discussion of GPS. IMHO,
until there are a whole lot of WAAS capable boxes flying in the system we
will be flailing about in the dark.

Did you see the change to the AIM with regard to a reversed W on approach
plates? Doesn't create much confidence in the system.

Bob Gardner

"Tarver Engineering" wrote in message
...

"Bob Gardner" wrote in message
news:R0hcc.78998$K91.171081@attbi_s02...
You're right. AIM 1-1-20(a)(8) tells us that we should not use GPS
altitude.
When WAAS is in common use this will probably change.

The altitude error is part of the WGS-84 model and is not a WAAS issue any
longer. The CNX-80 provides VNAV capability through the use of pressure
altitude from a transponder source and the pilot's baro correction input;
married to a partial TAWS data base. GPS/WAAS is not likely to become an
acceptable substitute for pressure altitude. Larger airplanes use air
data
derived pressure altitude in conjunction with GPS for improved RNP
capability.

"Bob Gardner" wrote in message
news:%Glcc.191812$_w.1879080@attbi_s53...
I think the whole WAAS thing is in flux. The AIM gets wordier and more
difficult to interpret with each change to its discussion of GPS. IMHO,
until there are a whole lot of WAAS capable boxes flying in the system we
will be flailing about in the dark.

I believe that VDL will be more of a factor moving forward than WAAS will
be. FAA has spent a lot of money on space based WAAS while being in
posession of a lot of underused VHF bandwidth.

"Tarver Engineering" wrote in message
...

"Bob Gardner" wrote in message
news:R0hcc.78998$K91.171081@attbi_s02...
You're right. AIM 1-1-20(a)(8) tells us that we should not use GPS
altitude.
When WAAS is in common use this will probably change.

The altitude error is part of the WGS-84 model and is not a WAAS issue
any
longer. The CNX-80 provides VNAV capability through the use of pressure
altitude from a transponder source and the pilot's baro correction
input;
married to a partial TAWS data base. GPS/WAAS is not likely to become
an
acceptable substitute for pressure altitude. Larger airplanes use air
data
derived pressure altitude in conjunction with GPS for improved RNP
capability.

Bob Gardner wrote:

I think the whole WAAS thing is in flux. The AIM gets wordier and more
difficult to interpret with each change to its discussion of GPS. IMHO,
until there are a whole lot of WAAS capable boxes flying in the system we
will be flailing about in the dark.

You're right on. And, in an effort to sell LPV (WAAS) minimums, the friendlies
"tweaked" the VNAV missed approach criteria so that VNAV minimums will increase,
all to make WAAS look better.

wrote in message ...


Bob Gardner wrote:

I think the whole WAAS thing is in flux. The AIM gets wordier and more
difficult to interpret with each change to its discussion of GPS. IMHO,
until there are a whole lot of WAAS capable boxes flying in the system
we
will be flailing about in the dark.

You're right on. And, in an effort to sell LPV (WAAS) minimums, the
friendlies
"tweaked" the VNAV missed approach criteria so that VNAV minimums will
increase,
all to make WAAS look better.

Just like selective availability.