Gsu 73 - Garmin G300 Installation Manual

10.3 GSU 73

GSU 73 ground operation is heavily dependent on GPS data inputs. Be sure to correct any GPS
performance problems (i.e. interference caused by some types of cell phones or anything that transmits in
the area) before troubleshooting the GSU 73/GMU 44. For GPS data to be considered usable, the
receiver must be tracking at least 4 satellites and have a 3D GPS Solution.
GSU 73 AHRS operation needs at least two of the three inputs from; the GPS receiver, the GMU 44, and
the Air data (also part of the GSU 73) for proper operation. See Table 10-1 below for the attitude and
heading outputs the GSU 73 can provide based on the available data inputs.
Table 10-1 – GSU 73 AHRS Operating Mode Table
GSU 73 Mode
Primary
Reversion No GPS
Reversion No Mag
Reversion No Mag,
No Air
Coast On Gyros
Output Unreliable
For complaints concerning GSU 73 realignments performed while in the air (i.e. the pilot feels that the
realignment is taking too long or does not seem to be reinitializing), Table 10-2 shows the pitch and roll
limits that the pilot must maintain for the GSU 73 to realign itself. If the pilot was performing maneuvers
outside these limits, the GSU 73 may not properly reinitialize.
Table 10-2 – GSU 73 AHRS Pitch/Bank Limitations for Cold Start While Airborne
Mode of Operation Entered
Following Initialization
Primary
Reversion No GPS
Reversion No Mag
Reversion No Mag, No Air
G300 Installation Manual - Troubleshooting
190-00921-01
GSU 73 Input
GPS data GMU44 data
Good Good
Bad Good
Bad or
Good
anomaly
Bad or
Good
anomaly
Bad Either or Both Bad
Bad Either or Both Bad
Sensor Inputs Available and Valid
All
GPS
Inertials
YES YES
YES NO
YES YES
YES YES
Air data data Heading
Doesn't
Valid
matter
Good Valid
Good Invalid
Bad Invalid
Invalid
Invalid
Air Data Bank Limit
Mag
(internal) in Degrees
YES NA
YES YES
NO YES
NO NO
GSU 73 Output
Pitch Roll
Valid Valid
Valid Valid
Valid Valid
Valid Valid
Invalid Invalid
Invalid Invalid
Pitch Limit
in Degrees
± 20.0 ± 5.0
± 10.0 ± 5.0
± 10.0 ± 5.0
± 10.0 ± 5.0
Page 10-3
Revision A