Altimeter accuracy

On Tue, 08 May 2007 03:38:30 GMT, "Jim Carter"
wrote:

Isn't a radar altimeter required equipment for CAT II and CAT III work? We
were trying to get an aircraft and aircrew certified for CAT II in Seattle
many years ago and I thought that was the reason they had the RA installed.

It is definitely not required for Category A aircraft flying under Part 91
for CAT II. I don't know about other categories.

There was a period of time when I and my Mooney were CAT II qualified and
certified.

The inner marker can substitute for a radio altimeter for 100' DH. The RA
is not necessary at all for the 150 DH. The altimeter and static system
has to have had the IFR check within the past 12 months; and altimeter
correction data must be available to the pilot, including both the scale
error and, wheel height correction if the wheel to instrument height is
greater than 10 feet.

There are a very few CAT II approaches that require a RA for use of the
100' DH, because of absent or siting problems with the IM.

I don't know of any guidance for Category A Part 91 a/c under CAT III, or
if any authorizations have ever been issued for that.
--ron

"Ron Rosenfeld" wrote in message
...
On Tue, 08 May 2007 03:38:30 GMT, "Jim Carter"
wrote:

Isn't a radar altimeter required equipment for CAT II and CAT III work? We
were trying to get an aircraft and aircrew certified for CAT II in Seattle
many years ago and I thought that was the reason they had the RA
installed.

It is definitely not required for Category A aircraft flying under Part 91
for CAT II. I don't know about other categories.

There was a period of time when I and my Mooney were CAT II qualified and
certified.

The inner marker can substitute for a radio altimeter for 100' DH. The RA
is not necessary at all for the 150 DH. The altimeter and static system
has to have had the IFR check within the past 12 months; and altimeter
correction data must be available to the pilot, including both the scale
error and, wheel height correction if the wheel to instrument height is
greater than 10 feet.

There are a very few CAT II approaches that require a RA for use of the
100' DH, because of absent or siting problems with the IM.

I don't know of any guidance for Category A Part 91 a/c under CAT III, or
if any authorizations have ever been issued for that.
--ron

Ron is correct. We once had a 182 and pilot approved for the 150' DH for
fog seeding.

Al G

dave wrote:
I read somewhere on the web that your A&P can adjust your altimeter by
removing a pin or a screw that allows the barometric pressure to be set
independently from the altitude. Once it's set correctly, the pin or

It's under warranty and the dealer says his A&P
can't break the seal.


screw is replaced.
Dave


Jim Stewart wrote:
How close should an altimeter be to field elevation
when set to the pressure indicated by the field's
AWOS? I'm seeing a 50' error.

On May 7, 2:41 pm, "Jim Carter" wrote:
I think what you've cited is for bench testing during certification. Once
installed in the aircraft then comparison against the pressure as recorded
by the official weather observation is +/- 75'.

The installed altimeter should give the same reading error
on the ground as it did on the bench unless the static system is way
out of whack, in which case the airplane shouldn't be flown. The
Canadian specs for scale error are he
http://www.tc.gc.ca/civilaviation/Re...ds/t571s02.htm


Dan

On Tue, 8 May 2007 09:03:07 -0700, "Al G" wrote:

We once had a 182 and pilot approved for the 150' DH for
fog seeding.

That wouldn't happen to have been in Medford, OR?
--ron

"Ron Rosenfeld" wrote in message
...
On Tue, 8 May 2007 09:03:07 -0700, "Al G" wrote:

We once had a 182 and pilot approved for the 150' DH for
fog seeding.

That wouldn't happen to have been in Medford, OR?
--ron

*Ding*, We have a winner!

It was indeed. United Airlines hired us to "Clear it up". $15/hr for
Night/Single Engine/IFR below minimums. My wife later bought me some "Small
Flowers" from Wal-Mart, so I would always have "Mini-Mums".

Al G

On Wed, 9 May 2007 09:45:04 -0700, "Al G" wrote:


"Ron Rosenfeld" wrote in message
.. .
On Tue, 8 May 2007 09:03:07 -0700, "Al G" wrote:

We once had a 182 and pilot approved for the 150' DH for
fog seeding.

That wouldn't happen to have been in Medford, OR?
--ron

*Ding*, We have a winner!

It was indeed. United Airlines hired us to "Clear it up". $15/hr for
Night/Single Engine/IFR below minimums. My wife later bought me some "Small
Flowers" from Wal-Mart, so I would always have "Mini-Mums".

Al G


I have waited many an early morning for the fog to clear. (Our kids used
to live in Ashland). Once or twice I noted the Cessna taking off, when the
commercial jets couldn't land.
--ron

"Ron Rosenfeld" wrote in message
...
On Wed, 9 May 2007 09:45:04 -0700, "Al G" wrote:


"Ron Rosenfeld" wrote in message
. ..
On Tue, 8 May 2007 09:03:07 -0700, "Al G"
wrote:

We once had a 182 and pilot approved for the 150' DH for
fog seeding.

That wouldn't happen to have been in Medford, OR?
--ron

*Ding*, We have a winner!

It was indeed. United Airlines hired us to "Clear it up". $15/hr for
Night/Single Engine/IFR below minimums. My wife later bought me some
"Small
Flowers" from Wal-Mart, so I would always have "Mini-Mums".

Al G


I have waited many an early morning for the fog to clear. (Our kids used
to live in Ashland). Once or twice I noted the Cessna taking off, when
the
commercial jets couldn't land.
--ron

The conditions had to be just right. 25-31 degrees F, and the heavier
the fog the better. We would fly a 150' pass, and dribble about a 1/2 pound
of crushed dry ice over the centerline, making several passes. Within 5
minutes, it was snowing. Within 15-20, most of the fog was on the ground,
and RVR's went from -600 to 6000. The 182 would build ice while doing the
low passes, but the normal 90-270 was done above pattern altitude where it
was 40 F and the ice would leave. We had an "Unofficial" backcourse/Loc only
with a 150' DH as well. The Loc/Dme was at the far end of MFR's 14 ILS, so
it gave us a distance to the approach end of our backcourse. We figured if
the engine went, we would just keep the energy up and shoot one of the
approaches. We actually did this under the hood for practice, and I once did
it with the GADO inspector who authorized me, on board. Sounds pretty dumb
now. At the time it was just like going out for touch & go's, except you
couldn't see anything outside.

Al G

"dave" wrote in message
. ..
I read somewhere on the web that your A&P can adjust your altimeter by
removing a pin or a screw that allows the barometric pressure to be set
independently from the altitude. Once it's set correctly, the pin or
screw is replaced.
Dave

Not legally. Adjustment of an altimeter in this manner is considered a
calibration. Calibration of instruments is considered a major repair and A&P
mechanics are prohibited from performing repairs (minor or major) to
instruments. In addition, the data correspondance between the altimeter and
encoder (if equipped) would be nullified and require retesting by an
appropriately-rated repair station.

Mike