Jabiru J450 Constructors Manual
Testing>Flight testing
Tuesday, April 6, 2010
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Compass swing
While you are out in the run-up area and provided that the ground run has gone well, this
would be a good time for a compass swing before you start the actual test flying.
You will need assistance to turn the aircraft accurately onto headings and your ground crew
can help you with this. You'll need a small, brass, non-magnetic screwdriver and ideally an
airport with a compass rose: a compass rose is a pattern painted on the ground, which
accurately depicts magnetic headings. If your local airport doesn‟t have one you can make
your own using the known magnetic orientation of the runways at an airport or a „known
good‟ hand held reference compass with an alignment sight.
Be careful with this approach though, just because a runway is marked "14" doesn‟t mean it is
oriented at 140º, it might actually be oriented 144º or 138º. Check with your local airport
operator to get the precise orientation. A hand held reference compass is usually preferable.
Remove all metal objects from your person and the aircraft before you start and make sure
that the selected area has no nearby metal structures that could affect the magnetic compass.
For the test the aircraft should be configured as it would be for flight, with the engine running
and all avionics and Nav and strobe lights turned on. Try some test transmissions with your
VHF comms to see if transmissions affect the compass in any way.
Under the compass‟ display window are 2 screws that are used to compensate for instrument
errors, one for North South adjustments and the other for East West adjustments.
Position the aircraft at a known North heading using a compass rose or a reference compass.
1.
With the aircraft oriented North, the engine running, and all radios switched on, adjust
the N-S adjusting screw until the compass reads due North, or 0º.
2.
Rotate the aircraft to a known East heading, and use the E-W adjusting screw to make
the compass read due East, or 90º.
3.
Rotate the aircraft to a known South heading. Note how many degrees off South the
compass reads. Turn the N-S adjusting screw to remove one half of the error.
4.
Rotate the aircraft to a known West heading. Note how many degrees off West the
compass reads. Adjust the E-W adjusting screw to remove one half of the error.
5.
Rotate the aircraft through the N, E, S and W headings again, confirming that the
errors for North and South are the same, and the errors for East and West are the same.
You may want to repeat steps 1-4 to fine-tune the corrections.
6.
Now rotate the aircraft from North, stopping at each 30º point on the compass rose or
reference compass (e.g., 030, 060, 090, 120, 150, 180, 210, 240, 270, 300, and 330
degrees) and make a note of the actual aircraft compass reading compared to the
compass rose or reference compass at each point, then complete the compass
calibration card that was packed with your compass, which you should then mount in
the holder on the front of the compass for reference.
If you cannot get a usable set of readings you will need to locate any sources of magnetic
interference. Look for steel screws, washers or other components near the compass. You
should also experiment with aircraft electrical systems (lights, for example), to see whether
activation of that equipment causes the compass to misbehave.
The compass should be re-swung after any significant changes to the panel or engine bay and
at least once every 2 years.