-----------------------------------------------------------------------------| SELECTED KEY | DESCRIPTION | |------------------|--------------------------------------------------------| | | required. | |------------------|--------------------------------------------------------| | MIN ALTITUDE | REQUIRES VALID CORRECTED ALTITUDE (QFE OR QNH) TO BE | | SELECTED | GREATER THAN SELECTED VALUE | |------------------|--------------------------------------------------------| | SNAPSHOT SELECTED| REQUIRES SNAPSHOT DETECTED | -----------------------------------------------------------------------------
SNAPSHOT KEYS
-----------------------------------------------------------------------------| SELECTED KEY | DESCRIPTION | |------------------|--------------------------------------------------------| | SNAPSHOT AREA | REQUIRES VALID LATITUDE AND LONGITUDE TO BE WITHIN | | | DEFINED AREA | |------------------|--------------------------------------------------------| | HDG SELECTED | REQUIRES VALID HEADING WITHIN +/- 30 DEG OF SELECTED | | | VALUE | |------------------|--------------------------------------------------------| | MINIMUM RADIO | REQUIRES VALID RADIO ALTITUDE TO BE GREATER THAN | | ALTITUDE | SELECTED VALUE | |------------------|--------------------------------------------------------| | TERRAIN ELEVATION| REQUIRES TERRAIN ELEVATION (QFE OR QNH) TO BE WITHIN | | | A SPECIFIC TOLERANCE OF THE SELECTED VALUE | |------------------|--------------------------------------------------------| | MAXIMUM TIME | MAXIMUM TIME PERMITTED TO SATISFY ALL ENVELOPE | | | MODULATION KEYS AFTER LEAVING THE SNAPSHOT | |__________________|________________________________________________________|
All of the "keys", either by virtue of not being selected, or by being selected and satisfied, are required to enable envelope modulation. Envelope modulation parameters are either within the selected values if the "keys" fit, or defaulted to normal values if the "keys" do not fit. These parameters are used as inputs to the warning modes and thereby provide the mechanism for envelope modulation.
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R **ON A/C 401-499,
R D. Enhanced Features
R (1) Terrain Awareness alerting and Display (TAD) functions
R The terrain awareness component of the Enhanced GPWS is divided into
R functional blocks with an interface to Navigation Display.
R (Ref. Fig. 016A)
R The highlighted blocks monitor aircraft position with respect to
R local terrain data base and provide rapid audio and visual alerts
R when a terrain threat is detected. Terrain threats are recognized and
R annunciated when terrain violates specific computed envelope
R boundaries forward of the aircraft path.
R The terrain awareness alert lamps and audio outputs behave in the
R same manner as the standard GPWS mode alerts. A terrain caution alert
R or terrain warning alert initiates a specific audio alert phrase
R (Ref. para.D.(1)(d)2_ and D.(1)(d)3_.
R Complementing the terrain threat alerts, the Enhanced GPWS also
R maintains a synthetic image of local terrain forward of the aircraft
R for display on EFIS Navigation Displays (ND).
R The Enhanced GPWS is configured to automatically de-select the
R weather display and pop-up a display of the terrain threats when they
R occur. The logic used provides an external input for predictive
R windshear alerts that can override a terrain display and revert to
R the weather display with the corresponding windshear data (if WR/PWS
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