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TCF Alert Envelope
12NM
4NM
15NM
700'
30'
400'
ENHANCED FUNCTIONS:
Envelope
Modulation
060-4241-000 • Rev. E - December 2003
26 MK V & MK VII EGPWS Pilot Guide
In -210-210 and later versions, the TCF alert envelope
and Envelope Bias Factor are improved. The alert
envelope is limited to a minimum of 245 feet AGL
adjacent to the runway as illustrated in the following
diagrams. The Envelope Bias Factor is reduced (moved
closer to the runway) when higher accuracy aircraft
position and runway position information is available.
This is typically 1/3 to 1 nm providing greater protection
against landing short events. With version -218-218 and
later models, the envelope bias factor is reduced to 1/4 nm
if runway and position data is of high integrity.
Also in -210-210 and later versions, runway selection
logic is improved to better identify the destination
runway. Comprehensive aircraft position and navigation
information is used to evaluate proximity runways and
determine the most likely destination runway for all
alerting purposes.
Improved TCF Envelope
Improved TCF Envelope Plan View
Terrain
Clearance
Floor
Continued
060-4241-000 • Rev. E - December 2003
MK V & MK VII EGPWS Pilot Guide 27
Terrain
Look Ahead
Alerting
TCF and RFCF alerts result in illumination of the EGPWS
caution lights and the aural message “TOO LOW TERRAIN”.
The audio message is provided once when initial envelope
penetration occurs and again only for additional 20%
decreases in Radio Altitude. The EGPWS caution lights will
remain on until the TCF envelope is exited.
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.
In -210-210 and later versions, a Runway Field
Clearance Floor feature is included. This is similar to
the TCF feature except that RFCF is based on the current
aircraft position and height above the destination
runway, using Geometric Altitude (in lieu of Radio
Altitude). This provides improved protection at
locations where the runway is significantly higher than
the surrounding terrain as illustrated below.
With version -218-218 and later models, the RFCF envelope
is moved from 1nm to 1/2nm if runway and position data is
of high integrity.
RFCF Alert Envelope
Runway
Field
Clearance
Floor
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28 MK V & MK VII EGPWS Pilot Guide
CAUTION
WARN
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
illustration). These ribbons project down, forward, then up
from the aircraft with a width starting at 1/4 nm and extending
out at ±3º laterally, more if turning. The look-down and up
angles are a function of the aircraft flight path angle, and the
look-down distance a function of the aircraft’s altitude with respect
to the nearest or destination runway. This
relationship prevents undesired 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
TERRAIN, 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 60 seconds ahead of the terrain/obstacle conflict and is
repeated every seven seconds as long as the conflict remains
within the caution area.
When the warning ribbon is intruded (typically 30 seconds
prior to the terrain/obstacle conflict), EGPWS warning lights activate
and the aural message
“TERRAIN, TERRAIN, PULL UP” or “OBSTACLE,
OBSTACLE, PULL UP” is enunciated with “PULL UP”
repeating continuously while the conflict is within the
warning area.
Terrain
Look
Ahead
Alerting
continued
060-4241-000 • Rev. E - December 2003
MK V & MK VII EGPWS Pilot Guide 29
In -210-210 and later versions, the look-ahead alerting
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