allowable compass error...

I had a thought, what do you think? If you are tracking a radial on a VOR
couldn't you compare the radial to the compass heading and get a good idea of
the compass error?


On Mon, 19 Jun 2006 14:17:23 GMT, "Casey Wilson" N2310D @ gmail.com wrote:

Thanks, I know about compass roses and swinging the compass. What I'm
looking for is an indication that the compass needs swinging. That's why my
hypothetical scenario stated that the runway alignment is correct. That does
happen, by the way, even if the odds are against it.

GeorgeC

I've got no problem with that George, as a general indication of
discrepancy. On the other hand, I sure that some of the nitpickers in our
RAP community would want to immediately toss in the VOR calibration and
accuracy, crab angle caused by crosswind drift relative to the actual course
versus heading, yadda, yadda...

What my question really is, is how much difference (for discussion I'll
agree that the method described is acceptable) between that compass heading
and the VOR radial is tolerable before the airplane should be grounded and
the compass readjusted, repaired, or replaced? Secondly, what is the
applicable reference for that?


"GeorgeC" wrote in message
...
I had a thought, what do you think? If you are tracking a radial on a VOR
couldn't you compare the radial to the compass heading and get a good idea
of
the compass error?


On Mon, 19 Jun 2006 14:17:23 GMT, "Casey Wilson" N2310D @ gmail.com
wrote:

Thanks, I know about compass roses and swinging the compass. What I'm
looking for is an indication that the compass needs swinging. That's why
my
hypothetical scenario stated that the runway alignment is correct. That
does
happen, by the way, even if the odds are against it.

GeorgeC

A 100 KIAS with a 50 knot 90 degree crosswind can be flown
without any compass at all, you just need a stable heading
reference, but it is so far from being close to any easy
reference, it tells you nothing about the compass accuracy.

You need an accurate compass/heading reference for ADF
tracking and it does help with getting and staying on course
with radio navigation.

The question is not how bad can it be, but how good can it
be.



--
James H. Macklin
ATP,CFI,A&P

"Casey Wilson" N2310D @ gmail.com wrote in message
news:Y3Flg.22377$YI2.20622@trnddc01...
| I've got no problem with that George, as a general
indication of
| discrepancy. On the other hand, I sure that some of the
nitpickers in our
| RAP community would want to immediately toss in the VOR
calibration and
| accuracy, crab angle caused by crosswind drift relative to
the actual course
| versus heading, yadda, yadda...
|
| What my question really is, is how much difference (for
discussion I'll
| agree that the method described is acceptable) between
that compass heading
| and the VOR radial is tolerable before the airplane should
be grounded and
| the compass readjusted, repaired, or replaced? Secondly,
what is the
| applicable reference for that?
|
|
| "GeorgeC" wrote in message
| ...
| I had a thought, what do you think? If you are tracking
a radial on a VOR
| couldn't you compare the radial to the compass heading
and get a good idea
| of
| the compass error?
|
|
| On Mon, 19 Jun 2006 14:17:23 GMT, "Casey Wilson" N2310D
@ gmail.com
| wrote:
|
| Thanks, I know about compass roses and swinging the
compass. What I'm
| looking for is an indication that the compass needs
swinging. That's why
| my
| hypothetical scenario stated that the runway alignment
is correct. That
| does
| happen, by the way, even if the odds are against it.
|
| GeorgeC
|
|

I misread read your post. I "read" that you wanted to check to see if your
compass was out of tolerance, but your question was what were the tolerances.
Which I see James answered.

On Mon, 19 Jun 2006 21:56:08 GMT, "Casey Wilson" N2310D @ gmail.com wrote:


What my question really is, is how much difference (for discussion I'll
agree that the method described is acceptable) between that compass heading
and the VOR radial is tolerable before the airplane should be grounded and
the compass readjusted, repaired, or replaced? Secondly, what is the
applicable reference for that?

GeorgeC

No, the radial can be flown on any heading. What you can do
in parts of the country that have been laid out with section
line grids of roads and highways, is fly a heading along a
road and not correct for drift. These roads were laid out
to true north/south/east and west. You can apply the local
variation to get the magnetic of that road. You manually
set your heading indicator and then turn to magnetic north,
etc, and check the compass. You can thus swing the compass
in-flight on every 30 degree heading and write down the
observed error. You should probably do this with various
combinations of configuration.

I remember a twin that had a compass error of 30 degrees if
the left alternator was off-line. I seem to remember that
the problems was in the right alternator, the compass would
point to the right engine.

You're probably most concerned about compass errors when the
compass is all you have, so I'd check with alt/gen off,
radios off as well as with all systems on-line. Make a grid
and fill in the blanks. Check the heading indicator on each
true road to be sure that you have compensated for gyro
drift. If you have a remote compass, manually set the
heading to check at least the four headings on the road.


If you find any errors greater than 10 degrees on any
heading, you will need some professional assistance to
determine why and fix the problem. It can be electrical
leakage, or some local magnetic item, even a lightening
strike could have magnetized the engine mount or other steel
parts of the airplane.


--
James H. Macklin
ATP,CFI,A&P

"GeorgeC" wrote in message
...
|I had a thought, what do you think? If you are tracking a
radial on a VOR
| couldn't you compare the radial to the compass heading and
get a good idea of
| the compass error?
|
|
| On Mon, 19 Jun 2006 14:17:23 GMT, "Casey Wilson" N2310D @
gmail.com wrote:
|
| Thanks, I know about compass roses and swinging the
compass. What I'm
| looking for is an indication that the compass needs
swinging. That's why my
| hypothetical scenario stated that the runway alignment is
correct. That does
| happen, by the way, even if the odds are against it.
|
| GeorgeC

If you are tracking a radial on a VOR
couldn't you compare the radial to the compass heading and get a good idea of
the compass error?

Only with no crosswind.

Jose
--
The monkey turns the crank and thinks he's making the music.
for Email, make the obvious change in the address.