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‘‘That’s one small step for man, one giant leap for mankind.’’ Neil Armstrong
1. OBJECTIVES. To ensure all the small but
important aspects of flight have been tested and
found reliable.
a. The Magnetic Compass. The magnetic
compass should have been checked for accuracy
prior to the first flight. However, the addition and
removal of equipment, changing of wire bundle routing,
and other airframe modifications may have
affected the accuracy of the instrument. The following
recommendations are offered:
(1) The magnetic compass can be checked
for accuracy by using a compass rose located on
an airport, or using a hand held ‘‘master compass.’’
The master compass is a reverse reading compass
with a gun-sight mounted on the top of it. With the
aircraft facing north and the pilot running the engine
at 1,000 rpm, a second individual standing 30 feet
away facing due south ‘‘shoots,’’ or aligns, the master
compass with the aircraft’s centerline. Using hand
signals, the pilot aligns the aircraft with the master
compass. The pilot then runs the aircraft engine up
to approximately 1,700 rpm to duplicate the aircraft’s
magnetic field and reads the compass.
NOTE: Conventional gear aircraft builders
will have to position the magnetic compass
in a straight and level position for this test.
Raise the tail or mount the compass level
with the horizon.
(2) If the aircraft compass is not in alignment
with the master compass (start at north), correct
the error by adjusting the north/south brass adjustment
screw with a non-metallic screwdriver (can be
made out of stainless steel welding rod, brass stock,
or plastic) until the compass reads correctly. Go to
the reciprocal heading (south) and remove half the
error. On the east/west headings, use the other brass
adjustment screw to make the corrections using the
same procedures that was used to correct the north/
south errors.
(3) Check again for errors at each cardinal
heading. Record the last readings and prepare a compass
correction card. The maximum deviation (positive
or negative) is 10 degrees on any one heading.
60
AC 90-89A 5/24/95
(4) If the compass cannot be adjusted to
meet this requirement, install another one. If the new
compass is not available, try a different location in
the cockpit, away from all ferrous metals and electrical
bundles.
NOTE: A common error that affects the
compass’s accuracy is the mounting of magnetic
compass on/in the instrument panel
with steel machine screws and nuts rather
than brass.
(5) If the aircraft has an electrical system
it is recommended that two complete compass checks
be made, one with all electrical accessories on (e.g.,
radios/nav lights), and one with all electrical accessories
off. If the deviation in level flight is more
than 10 degrees on any heading with the accessories
on, make up a separate compass correction card that
shows the magnetic heading with the equipment on.
(6) Record the findings in the aircraft’s
flight manual and create a compass correction card,
mounting it near the magnetic compass in the cockpit.
Make two cards; one with radios on and one
with radios and non essential electrical accessories
off.
b. Very High Frequency (VHF) Omni-directional
Radio Range (VOR) Check. The best guide
to check the accuracy of the VOR on board equipment
is the VOR Receiver Check found in the Airman’s
Information Manual (AIM), available from the
Superintendent of Documents. The following is an
abbreviated summary of the VOR procedure in the
AIM.
(1) For a ground test of the VOR, a VOR
Test Facility (VOT) must be used. To use the VOT
service, tune in the VOT frequency on the VOR
receiver. It is normally 108 Mhz. With the Course
Deviation Indicator (CDI) centered, the omni-bearing
selector should read 0 degrees with the to/from
indicator showing ‘‘from,’’ or the omni-bearing
selector should read 180 degrees with the to/from
indicator showing ‘‘to.’’ The maximum bearing error
should never be more than four degrees.
NOTE: The VOT facilities closest to the
flight test location can be found in the Airport/
Facility Directory. It is available by
subscription from NOAA Distribution
Branch N/CG33, National Ocean Service,
Riverdale, MD 20737, or contact the nearest
FAA FSS.
(2) For the airborne test, select a prominent
ground point along the selected radial, preferably
　
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