G300 Installation Manual - Troubleshooting
Page 10-3
190-00921-01
Revision A
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 Input
GSU 73 Output
GSU 73 Mode
GPS data
GMU44 data
Air data data
Heading
Pitch
Roll
Primary
Good
Good
Doesn’t
matter
Valid
Valid
Valid
Reversion No GPS
Bad
Good
Good
Valid
Valid
Valid
Reversion No Mag
Good
Bad or
anomaly
Good
Invalid
Valid
Valid
Reversion No Mag,
No Air
Good
Bad or
anomaly
Bad
Invalid
Valid
Valid
Coast On Gyros
Bad
Either or Both Bad
Invalid
Invalid
Invalid
Output Unreliable
Bad
Either or Both Bad
Invalid
Invalid
Invalid
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
Sensor Inputs Available and Valid
Mode of Operation Entered
Following Initialization
All
Inertials
GPS
Mag
Air Data
(internal)
Bank Limit
in Degrees
Pitch Limit
in Degrees
Primary
YES
YES
YES
NA
± 20.0
± 5.0
Reversion No GPS
YES
NO
YES
YES
± 10.0
± 5.0
Reversion No Mag
YES
YES
NO
YES
± 10.0
± 5.0
Reversion No Mag, No Air
YES
YES
NO
NO
± 10.0
± 5.0
