Garmin International Inc 0181200 Manuel D’Utilisation

190-01277-00

GRA 5500 Installation Manual

Rev. A

Page 3-17

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 

 for more information) or by activating the “self-test inhibit” command in GIFD 

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 

 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 

 for more information) or by 

activating the “self-test inhibit” command in GIFD installations any time (or always) during 
normal unit operation.

DRAFT