Terrain Alerting And Display - Honeywell MK VI Pilot's Manual

Terrain
Alerting
and Display
060-4314-000 • Rev. C - May 2004
MK VI & MK VIII EGPWS Pilot Guide
Another enhancement provided by the internal terrain database,
is the ability to look ahead of the aircraft and detect terrain or
obstacle conflicts with greater alerting time. This is accomplished
(when enabled) based on aircraft position, flight path angle,
track, and speed relative to the terrain database image forward
the aircraft.
Through sophisticated look ahead algorithms, both caution and
warning alerts are generated if terrain or an obstacle conflict with
"ribbons" projected forward of the aircraft (see following illustra-
tion). These ribbons project down, forward, then up from the
aircraft with a width starting at 1/4 nm and extending out at 3
degrees laterally, more if turning. The lookdown and up angles
are a function of the aircraft flight path angle, and the lookdown
distance a function of the aircraft's altitude with respect to the
nearest or destination runway. This relationship prevents unde-
sired alerts when taking off or landing. The look-ahead distance
is a function of the aircraft's speed, and distance to the nearest
runway.
A terrain conflict intruding into the caution ribbon activates
EGPWS caution lights and the aural message "CAUTION TER-
RAIN, CAUTION TERRAIN" or "TERRAIN AHEAD, TERRAIN
AHEAD". An obstacle conflict provides a "CAUTION OBSTACLE,
CAUTION OBSTACLE" or "OBSTACLE AHEAD, OBSTACLE
AHEAD" message. The caution alert is given typically 40-60 sec-
onds ahead of the terrain/obstacle conflict and is repeated every
seven seconds as long as the conflict remains within the caution
area.
W ARN
CAUTION
29