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Part Four: Section 3
HTAWS Alerts
NOTE:
HTAWS Caution Alerts are displayed as constant
black text on a yellow background; HTAWS Warning
Alerts are displayed as constant white text on a red back-
ground.
Forward Looking Terrain Avoidance
The unit will issue terrain alerts not only when the
aircraft altitude is below the terrain elevation but
also when the aircraft is projected to come within
minimum clearance values of the terrain. This
alerting, called Forward Looking Terrain Avoidance
(FLTA), is also provided for obstacles.
The FLTA functionality looks ahead of the aircraft
using GPS position information and the terrain
and obstacle databases to provide alerts when the
predicted flight path does not clear the terrain or
obstacle by the required clearance. The amount
of clearance required varies depending on position
relative to airports and heliports, in order to reduce
the occurrence of nuisance alerting.
Any potential impact points are depicted on the
display. There are 2 levels of severity for FLTA alerts.
They are cautionary (amber) and warning (red) in
nature and are described in further detail below.
FLTA CAUTION—Estimated potential impact in approximately
30 seconds after a caution pop-up alert and annunciation. FLTA
caution alerts are accompanied by the aural message “
Caution
Terrain; Caution Terrain
” OR “
Terrain Ahead; Terrain Ahead
”.
Similarly, a
“Caution Obstacle; Caution Obstacle”
or
“Obstacle
Ahead; Obstacle Ahead”
alert is also provided. The time to an
alert can vary with conditions, therefore there is no guarantee
of a 30 second caution alert being issued.
FLTA WARNING— Warning pop-up alerts are issued 15 seconds
prior to an estimated potential impact in normal mode and
approximately 10 seconds in RP Mode. FLTA warning alerts are
accompanied by the aural message “
Warning - Terrain, Terrain
” .
Similarly, a “
Warning - Obstacle, Obstacle
” alert is also provided.
The time to an alert can vary with conditions, therefore there is
no guarantee of a 15/10 second warning alert being issued.
The alerts are annunciated visually through the
annunciator status bar, a pop-up alert box, and the red
and yellow X’s on the NAV - HTAWS page map. The
alerts are annunciated aurally through a voice message
indicating the potential threat, such as “Caution - Ter-
rain, Terrain” or “Warning - Obstacle, Obstacle”.
Voice Call Out Aural Alert
The purpose of the Voice Call Out aural alert mes-
sages are to provide an advisory alert to the pilot that
the aircraft is between 500 feet and 100 feet above ter-
rain in 100 foot increments. When the aircraft descends
within the selected distance from the terrain, the aural
message for the selected distance is generated. There are
no display annunciations or pop-up alerts that accom-
pany the aural message.
190-00356-30 Rev H
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