Garmin GTN 650Xi Series Pilot's Manual page 443

ALTITUDE VOICE CALL OUT (VCO)
TAWS-A provides aural advisory alerts as the aircraft descends, beginning at 500 feet
above the terrain, as determined by the radar altimeter (if greater than 5 NM from
the nearest airport) or 500 feet above the nearest runway threshold elevation (if less
than 5 NM from the nearest airport). Upon descent to this altitude, TAWS-A issues
the aural alert message "Five-hundred."
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.
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 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 3D 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, a plus-sign will be present next to the annunciation. The
display of each annunciation will alternate with each being displayed for
approximately five seconds.
190-02327-03 Rev. C Pilot's Guide
Hazard Awareness
5-135