Gdc 74A Field Calibration Utility - Garmin CIRRUS PERSPECTIVE SR20 Line Maintenance Manual

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5.11 GDC 74A Field Calibration Utility
Field calibration of GDC 74A units requires a pressure control system with
altitude accuracy equal to or better than ±5 feet at sea level, ±15 feet at
30,000 feet, and ±15 feet at 41,000 feet. For calibration of the GDC 74A, the
pressure control system must control altitude automatically.
Purpose
The GDC 74(X) Field Calibration utility (P/N T06‐A0156‐00) is designed to adjust the calibration
of GDC 74A units that have failed the 14 CFR Part 43 Appendix E tests due to altitude drift.
Limitations
These procedures should be performed on the bench (not in the aircraft) at room
•
temperature.
The GDC 74(X) Field Calibration utility should only be used to correct errors due to
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altitude drift.
If the drift is greater than the limits defined in the GDC 74(X) Field Calibration utility at
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any of the test points, the utility will not allow the calibration to continue and the
GDC 74A unit must be returned to Garmin.
If the GDC 74A unit does not pass 14 CFR Part 43 Appendix E after the calibration utility
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has been run, the GDC 74A unit should be returned to Garmin.
Requirements
GDC 74A unit.
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Power supply (14/28V, 500mA).
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PC with a Serial Port or serial port adapter.
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Pressure control system capable of generating the correct static pressures for 0 feet,
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11,000 feet, 30,000 feet, and 41,000 feet.
Fabricate a cable built to interface a GDC 74A to a PC Serial Port (see Figure 5‐10). The
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cable is not available from Garmin.
Cirrus Perspective™ Line Maintenance Manual
190-00920-00
NOTE
Figure 5‐10. GDC 74A ‐ PC Interface Cable
Page 5-75
Rev. E