A aviation & planes forum. AviationBanter

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.

Go Back   Home » AviationBanter forum » rec.aviation newsgroups » Instrument Flight Rules
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

Altimeter inaccurate



 
 
Thread Tools Display Modes
  #11  
Old May 4th 04, 02:04 AM
Ron Rosenfeld
external usenet poster
 
Posts: n/a
Default

On Mon, 03 May 2004 20:34:22 GMT, "John R. Copeland"
wrote:

Along that line, perhaps you've noticed that the new VNAV approaches
typically carry a note to the effect that Baro-VNAV is not authorized
at temperatures below some limiting number.
---JRC---


Yes, I have. The RNAV (GPS) Z RWY 1 at KPQI states Baro-VNAV not
authorized below -16°C (4°F).


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)
  #12  
Old May 4th 04, 03:06 AM
David Megginson
external usenet poster
 
Posts: n/a
Default

Ron Rosenfeld wrote:

It is my understanding that in Canada there is a requirement to alter
minimums for certain approaches in very cold weather. No such requirement
exists (Part 91, at least) in the US.

I don't believe there have been any accidents in the US due to this
phenomenon.


You're correct about the Canadian regs, though I don't know how many
Canadian pilots remember to apply them. In any case, many parts of the
northern U.S. can see temperatures down to -35 degC or -40 degC just as much
as Canada can; when you combine that with the allowed +/-50 ft altimeter
error, you could be down below 100 ft when you think you're at 200 ft DH.

A more likely problem, though, would be early in an IAP, when you're still a
few thousand feet above the station elevation and have to clear a mountain
or a tower on a hill.


All the best,


David
  #13  
Old May 4th 04, 03:10 AM
David Megginson
external usenet poster
 
Posts: n/a
Default

Bob Gardner wrote:

AIM 1-1-20 (a)(8) tells us not to rely upon GPS to determine aircraft
altitude.


Right -- ATC counts on the altimeter's temperature errors for traffic
separation (since every plane in the same area will share the same errors).
Our altimeters are pretty inaccurate at cruising altitudes, but as long as
we're all inaccurate in the same way, the system works.

In any case, I don't think that the poster was using his GPS for altitude --
he was just concerned that his altimeter might be wrong. I expect that this
will be a FAQ now that a lot of people have WAAS-enabled GPS's (they used to
think that the altimeter was right and the GPS altitude wildly inaccurate).


All the best,


David
  #14  
Old May 8th 04, 02:49 AM
AJNOKC
external usenet poster
 
Posts: n/a
Default

SOURCE DOD FLIGHT INFORMATION HANDBOOK
(https://164.214.2.62/dafif/dafif_0404_ed6/plan/fih.pdf)

3. TEMPERATURE ERRORS (AFFSA/AFFSA LTR)
a. Pressure altimeteres are calibrated to indicate true altitudes under
International
Standard Atmospheric (ISA) conditions. Any deviation from these
standard conditions will result in
an erroneous reading on the altimeter. This error becomes important
when considering obstacle
clearances in temperatures lower than standard since the aircraft’s
altitude is below the figure
indicated by the altimeter.
b. The error is proportional to the difference between actual and ISA
temperature and the
height of the aircraft above the altimeter setting source. Height
above altimeter source is
considered to be published HAT or HAA for the approach. The amount of
error is approximately 4
feet per thousand feet for each degree Celsius of difference.
c. Corrections will only be made for Decision Heights (DHs), Minimum
Descent Altitudes
(MDAs), and other altitudes inside, but not including, the Final
Approach Fix (FAF). The same
correction made to DHs and MDAs can be applied to the other altitudes
inside the FAF.

TEMPERATURE CORRECTION CHART (FEET)
AIRPORT
TEMP °C
0 0 20 20 20 40 40 40 40 60 80 90 110 120 140 180 240
300
-5 10 20 30 30 50 50 60 60 80 110 120 150 160 180 240 320
400
-10 20 20 40 40 60 60 80 80 100 130 150 180 200 230 300
400 500
-15 20 30 50 50 70 80 90 100 120 160 180 220 240 280 360
480 600
-20 20 40 60 60 80 100 100 120 140 180 210 250 280 320 420
560 700
-25 30 50 60 70 90 110 120 140 160 210 240 290 320 370 480
640 800
-30 40 60 60 80 100 120 140 160 180 240 270 330 360 410 540
720 900
-35 40 60 70 90 110 130 150 180 200 260 300 360 400 460 600
800 1000
-40 40 60 80 100 120 140 160 200 220 290 330 400 440 510 660
880 1100
-45 50 70 90 110 140 160 180 210 240 310 360 430 480 550 720
960 1200
-50 60 80 100 120 160 180 200 220 260 340 390 470 520 600 780
1040 1300
200 300 400 500 600 700 800 900 1000 1300 1500 1800 2000 2300 3000 4000
5000
HAT/HAA
NOTE: Must round interpoldated values to nearest 10 feet.



On Sun, 2 May 2004 13:50:02 -0500, smf wrote:

My Altimeter is accurate when on the ground or at lower alt. When I
climb up
to 7k and above and check it against GPS and approach controls read out
it
is about 300+ feet off.

Is it the altimeter I'm having problems with?


Steve


--
Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
encoding altimeter pinout? Bill Chernoff Home Built 3 July 15th 04 04:34 PM
Inaccurate airspeed indicator Wyatt Emmerich Instrument Flight Rules 20 April 20th 04 12:08 AM
Adjustment of Altimeter Ron Home Built 5 April 5th 04 03:12 AM
GPS Altitude with WAAS Phil Verghese Instrument Flight Rules 42 October 5th 03 12:39 AM
Recommendation for Radio, transponder and Altimeter Ron Natalie Home Built 0 July 8th 03 03:40 PM


All times are GMT +1. The time now is 01:38 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 AviationBanter.
The comments are property of their posters.