Say Altitude.

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.

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.

I was not using the GPS for altitude. Always use the altimeter
The altimeter was showing 7000.
ATC was showing 6700
Gps was 7060. However when I changed altitude the gps stayed frozen at 7060.
Hank

"Hankal" wrote in message
...
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.

I was not using the GPS for altitude. Always use the altimeter
The altimeter was showing 7000.
ATC was showing 6700
Gps was 7060. However when I changed altitude the gps stayed frozen at
7060.

Aren't controllers supposed to tell you to turn off your altimeter and go to
VFR when an error that big is detected?

"William W. Plummer" wrote in message news:ctncc.82738
I was not using the GPS for altitude. Always use the altimeter
The altimeter was showing 7000.
ATC was showing 6700
Gps was 7060. However when I changed altitude the gps stayed frozen at
7060.

Aren't controllers supposed to tell you to turn off your altimeter and go to
VFR when an error that big is detected?

They can tell you to stop altitude squawk if they want. They have no business to
tell you to "go VFR"

"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.

I've never been told to turn off my altimeter!

Rich


William W. Plummer wrote:
"Hankal" wrote in message
...


Aren't controllers supposed to tell you to turn off your altimeter and go to
VFR when an error that big is detected?

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.

Ron Natalie wrote:


They can tell you to stop altitude squawk if they want. They have no business to
tell you to "go VFR"

When was the last time you had a controller ask you to turn off your altimeter? ;-)

Rich wrote:

I've never been told to turn off my altimeter!

I would if I could only find the switch.

Aren't controllers supposed to tell you to turn off your altimeter and go to
VFR when an error that big is detected?


The controller requested I turn off mode C.
In 25 miles he asked to turn back on.
Everything went fine from there on.
I could not have accepted VFR since I was in IMC condition.