Enhanced Functions; Envelope Modulation; Terrain Clearance Floor - Honeywell MK VI Pilot's Manual

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ENHANCED FUNCTIONS:

Envelope
Modulation
Terrain
Clearance
Floor
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effective Radio Altitude height (and rate of change) resulting in
some biasing of the actual callout altitude and bank angle limit.
When the Autopilot is engaged, the 20% increases and process
reset principles are applied to the reduced limit in the same
manner.
NOTE: Envelope Modulation is not available and active in
the initial version of the MK VI and MK VIII EGPWS (-001 part
numbered units). This feature is incorporated in later ver-
sions (-003 and later part numbered units) and is provided
in this guide for informational purposes only for initial ver-
sion applicability.
Due to terrain features at or near certain specific airports around
the world, normal operations have resulted in nuisance or
missed alerts at these locations in the past. With the introduction
of accurate position information and a terrain and airport data-
base, it is possible to identify these areas and adjust the normal
alerting process to compensate for the condition.
The EGPWS Envelope Modulation feature provides improved alert
protection and expanded alerting margins at identified locations
throughout the world. This feature is automatic and requires no
flight crew action.
Modes 4, 5, and 6 are expanded at certain locations to provide
alerting protection consistent with normal approaches. Modes 1,
2, and 4 are desensitized at other locations to prevent nuisance
alerts that result from unusual terrain or approach procedures.
In all cases, very specific information is used to correlate the
aircraft position and phase of flight prior to modulating the en-
velopes.
The Terrain Clearance Floor (TCF) function (enabled with TAD)
enhances the basic GPWS Modes by alerting the pilot of descent
below a defined "Terrain Clearance Floor" regardless of the air-
craft configuration. The TCF alert is a function of the aircraft's
Radio Altitude and distance (calculated from latitude/longitude
position) relative to the center of the nearest or destination run-
way included in the database. The TCF envelope is defined for
all runways as illustrated below and extends to infinity, or until it
meets the envelope of another runway.
060-4314-000 • Rev. C - May 2004
MK VI & MK VIII EGPWS Pilot Guide