Garmin G1000 NAV III Line Maintenance Manual page 152

The following are potential causes for failure of the engine run-up test:
a) Excessive flexibility of GRS77 and/or GMU44 mechanical mounting with respect to airframe.
b) Vibrational motion of GRS77 and/or GMU44 caused by neighboring equipment and/or supports.
c) Mounting of GRS77 at a location that is subject to severe vibrations (for example, close to an
engine mount.)
d) Mounting screws and other hardware for GRS77 and/or GMU44 not firmly attached.
e) Absence of mounting supports recommended by the aircraft manufacturer.
f) GRS77 connector not firmly attached to unit.
g) Cabling leading to GRS77 or GMU44 not firmly secured to supporting structure.
h) An engine / propeller that is significantly out of balance.
In some aircraft, attempting the engine run-up test on a day with very strong and/or gusty winds may
cause the test to occasionally fail. However, windy conditions should not be taken as evidence that the
test would pass in calm conditions; an actual pass is required before the installation can be considered
adequate.
5. Press the ENT key on the PFD to conclude this procedure.
With the G1000 in normal mode, the aircraft can now be taxied back and the engine can be shut down for final
testing. When the PFD powers up in normal mode, the AHRS attitude and heading information displayed should
become valid within 1 minute of power-up.
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Rev. L
G1000 Nav III Line Maintenance Manual
190-00352-00