The test switch starts a self-test.
The light emitting diode (LED) status indicators on the front panel show for these conditions:
· LRU STATUS (green), if there are no LRU failures
· LRU STATUS (red), if there is an LRU failure
· ANTENNA TOP FAIL, if the top antenna fails
· ANTENNA BOT FAIL, if the bottom antenna fails
· ALTITUDE FAIL, if the altitude input from the ADIRU fails
· CONTROL FAIL, if the control panel input fails.