allowable compass error...

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