Garmin GRA 55 Maintenance Manual - Page 20

System Maintenance Manual GRA 55/5500 Bell 206 STC, Rev. 1,

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3.4.6 Zero-Foot Calibration Anytime the GRA 55/5500 is removed and reinstalled in the helicopter, a one-time zero-foot calibration procedure must be performed on the unit in order to "zero" the altitude outputs from the unit. This procedure removes the altitude offsets associated with antenna cables, antenna height above ground, etc. This procedure is performed via the GRA 55/5500 Retrofit Installation Tool. The following conditions must be met before the zero-foot calibration procedure should be attempted: 1. The entire GRA 55/5500 must be completely installed and mounted in the final configuration as representative of normal flight conditions. 2. A visual inspection must be performed to verify antenna installation and the antenna coaxial cables are installed and connected properly. 3. The zero-foot calibration procedure must be performed outdoors on a hard, flat surface and away from hangars, buildings, or other metal structures that may reflect the radar signal. 4. GRA 55/5500 Retrofit Installation Tool must be connected to the GRA via USB dongle cable. The GRA 55/5500 Retrofit Installation Tool provides an interface button to initiate the zero-foot calibration procedure. Clicking this button will make a series of requests to the connected GRA 55/5500. During the calibration procedure, the GRA 55/5500 Retrofit Installation Tool will report progress updates next to the "Initiate Calibration Procedure" button. Once the calibration procedure has completed, the text will display "Calibration Complete" and the status tab will be updated. If the fault list does not annunciate any faults and the information displayed in the status bar area indicates "0 ft" and "Normal," the unit has been successfully calibrated. 190-01277-A3 Rev. 1 System Maintenance Manual GRA 55/5500 Bell 206 STC Page 3-8

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190-01277-A3
System Maintenance Manual GRA 55/5500 Bell 206 STC
Rev. 1
Page 3-8
3.4.6
Zero-Foot Calibration
Anytime the GRA 55/5500 is removed and reinstalled in the helicopter, a one-time zero-foot calibration
procedure must be performed on the unit in order to “zero” the altitude outputs from the unit. This
procedure removes the altitude offsets associated with antenna cables, antenna height above ground, etc.
This procedure is performed via the GRA 55/5500 Retrofit Installation Tool.
The following conditions must be met before the zero-foot calibration procedure should be attempted:
1.
The entire GRA 55/5500 must be completely installed and mounted in the final configuration as
representative of normal flight conditions.
2.
A visual inspection must be performed to verify antenna installation and the antenna coaxial cables
are installed and connected properly.
3.
The zero-foot calibration procedure must be performed outdoors on a hard, flat surface and away
from hangars, buildings, or other metal structures that may reflect the radar signal.
4.
GRA 55/5500 Retrofit Installation Tool must be connected to the GRA via USB dongle cable.
The GRA 55/5500 Retrofit Installation Tool provides an interface button to initiate the zero-foot
calibration procedure. Clicking this button will make a series of requests to the connected GRA 55/5500.
During the calibration procedure, the GRA 55/5500 Retrofit Installation Tool will report progress updates
next to the “Initiate Calibration Procedure” button. Once the calibration procedure has completed, the text
will display “Calibration Complete” and the status tab will be updated. If the fault list does not annunciate
any faults and the information displayed in the status bar area indicates “0 ft” and “Normal,” the unit has
been successfully calibrated.