Filter
Top Products
G3X Installation Manual - Troubleshooting Page 9-3
190-01115-01 Revision A
9.3 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 9-1 below for the attitude and
heading outputs the GSU 73 can provide based on the available data inputs.
Table 9-1 – 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 9-2 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 9-2 – 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