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3.7.3
Zero-Foot Calibration
After the GRA 5500 is configured, but before it may be put into normal flight operation, a one-time zero-
foot calibration procedure must be performed on the unit in order to "zero" the altitude outputs from the
unit for the individual aircraft installation. This procedure removes the altitude offsets associated with
antenna cables, antenna height above ground, etc. This procedure is accomplished via GDU display
interface in Garmin Integrated Flight Deck installations (see
Flight Deck (retrofit) installations this procedure is accomplished via the GRA 5500 Retrofit Installation
Tool (see
Section 3.7.1.2
calibration procedure should be attempted:
1. The entire GRA 5500 must be completely installed and mounted in the final configuration as
representative of normal flight conditions.
2. The installer must perform a visual inspection to verify that the antenna installation meets all the
guidelines of
Section
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. Dual or triple unit installations must be calibrated separately and independently. Thus, the
system(s) not presently being calibrated must be powered down (circuit breaker pulled or circular
connector wiring harness disconnected) so as to prevent interference with the unit presently being
calibrated.
Once the calibration has successfully completed, the GRA 5500 should output "0 feet" from the altitude
outputs with no GRA 5500 faults annunciated in the GDU or Retrofit Installation Tool (depending upon
installation type). For further details on how to accomplish the zero-foot calibration procedure, see
3.7.2.
NOTE
Prior to completing the zero-foot calibration procedure for the first time on an individual
GRA 5500 unit, the status of the GRA 5500 should indicate "fail" and a calibration fault
should be annunciated. This is normal operation and is used to indicate that a valid zero-
foot calibration has not yet occurred.
3.7.4 Built-In Self-Test Functionality
The GRA 5500 contains a full-featured built-in self-test (BIST/BITE) and fault logging functionality
(including automated self-testing and fault detection of the entire internal TX and RX circuitry – see
Section 3.7.4.1
for more information) that occurs every time the unit is powered up and at periodic and
various times during unit operation. The tests in
are displayed and stored in the Assert Log.
NOTE
Faults can be viewed by using the GRA 5500 Retrofit Installation Tool as described in
Section 3.6
and the corresponding Assert Log may be diagnosed by using the Installation
Tool to download and diagnose the unit's Assert Log. Alternatively, the Assert Log file
may be downloaded and send to Garmin for diagnosis.
GRA 5500 Installation Manual
Page 3-16
and
Section
3.7.2). The following conditions must be met before the zero-foot
2.3.3. Also, the visual inspection must verify that the antenna coaxial cables
Table A-3
Section
3.7.1.1). In non-Garmin Integrated
are run on the system and the resulting faults
Section
190-01277-00
Rev. A
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