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3.7.4.1 Automated and Manually-Initiated Altitude Self-Test and Self-Test Inhibit
Functionality
The GRA 5500 includes an advanced altitude self-test functionality which provides the ability to detect
and log faults within the entire internal transmitter and receiver circuitry and processing chain at various
internally simulated altitudes. The altitude self-test functionality is completely automated (and can be
inhibited), but it also may be run manually if desired. See below for more information applicable to both
forms of altitude self-test:
Automated Altitude Self-Test
•
Functionality is completely transparent to the pilot or any user of radar altitude data from the GRA
5500.
•
Runs every time the unit is powered up and subsequently every 1 minute during normal unit
operation at calculated altitudes above 250 ft AGL or during "No Computed Data" conditions
(such as at actual altitudes above 2550 ft AGL, during excess pitch or roll maneuvering, or
anytime the ground reflection is poor enough to cause "No Computed Data" to appear on the
altitude outputs).
•
Other than during initial unit power up, the automated altitude self-test functionality is never
initiated at calculated altitudes of 250 ft AGL or below.
•
Other than during initial unit power up, the automated altitude self-test functionality can be
completely disabled (inhibited) by grounding the SELF TEST INHIBIT* active-low discrete input
(see
Section 4.4.1
installations any time (or always) during normal unit operation.
Manually Initiated Altitude Self-Test
•
Performs the same physical functionality as the automated altitude self-test, but may be manually
initiated at any time during normal unit operation (including at altitudes below 250 ft AGL).
•
During manually initiated altitude self-test, the status of all altitude outputs from the GRA 5500
are set to "Test" and an altitude of 40 ft is output. Unlike the automated altitude self-test, this
functionality is intentionally not transparent to the pilot or any user of radar altitude data from the
GRA 5500 in order to be useful to the pilot or crew and not provide misleading data.
•
May be initiated by grounding the SELF TEST SELECT* active-low discrete input (see
4.4.1
for more information) or by activating the "self-test" command via GDU in GIFD
installations.
•
Activation of manually initiated altitude self-test may be disabled (inhibited) by grounding the
SELF TEST INHIBIT* active-low discrete input (see
activating the "self-test inhibit" command in GIFD installations any time (or always) during
normal unit operation.
NOTE
The manually initiated altitude self-test is completely optional for installation and use. It
does not provide any additional safety enhancements or fault monitoring capabilities
beyond the automated altitude self-test other than allowing the pilot or users of the GRA
5500 data to see feedback (a displayed test altitude) during any stage of GRA 5500
operation.
190-01277-00
Rev. A
for more information) or by activating the "self-test inhibit" command in GIFD
Section 4.4.1
for more information) or by
GRA 5500 Installation Manual
Section
Page 3-17
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