10-72
GTN 625/635/650 Pilot’s Guide
190-01004-03 Rev. P
Terrain
10.8.7 TAWS-A System Status
During power-up, TAWS-A conducts a self-test of its aural and visual
annunciations. The system test can also be manually initiated. An aural alert
is issued at test completion. TAWS-A System Testing is disabled when ground
speed exceeds 30 knots.
10.8.8 TAWS-A Abnormal Operations
TAWS-A continually monitors several system-critical items such as database
validity, flap and landing gear position, radar altimeter input, and GPS status.
If the GTN does not contain Terrain, Airport Terrain, and Obstacle databases
(or the databases are invalid), the aural message
“
TAWS System Failure
”
is
generated along with the “TAWS FAIL” alert annunciation.
TAWS-A requires a 3-D GPS navigation solution along with specific vertical
accuracy minimums. Should the navigation solution become degraded or if
the aircraft is out of the database coverage area, the annunciation “TAWS N/A”
is generated in the annunciation window and on the TAWS-A page, the aural
message
“
TAWS Not Available
”
is generated if airborne, some TAWS-A terrain
alerts will not be issued, and GPWS alerting (which are not dependent on GPS
position) will continue to operate. When the GPS signal is re-established and the
aircraft is within the database coverage area, the aural message “TAWS Available”
is generated.
TAWS-A also requires radar altimeter input. Should the radar altimeter input
fail or become degraded, the annunciation “GPWS FAIL” is generated in the
annunciation window and on the TAWS-A Page. The aural message
“
GPWS
System Failure
”
is also generated. The “GPWS FAIL” annunciation will also occur
if both GPS altitude and barometric altitude are unavailable. If only the GPWS
system has failed, GPWS-based alerts will not be available, while other TAWS-A
alerting remains unaffected.
Multiple TAWS or GPWS annunciations cannot be displayed at the same
time. When multiple annunciations exist, an asterisk will be present next to the
annunciation. The display of each annunciation will alternate with each being
displayed for approximately five seconds.
Summary of Contents for GTN 625
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