1 Terrain Caution and Warning Envelopes
_ (Ref. Fig. 018)
a Caution Altitude Floor
_ The caution altitude floor (or terrain floor) is computed as a function of aircraft altitude with respect to nearest runway altitude and range to the nearest runway threshold position. This parameter represents a distance below the aircraft. The relationship to the nearest runway threshold location prevents undesired alerts when the aircraft is taking off or landing at an airport. The system is compatible with terrain clearances allowed for by regulatory approach and departure design criteria.
b Caution Look Ahead Distance
_ The caution look ahead distance is computed from aircraft ground speed and turn rate to provide an advanced caution with adequate time for the crew to react safely. Depending on the situation this distance roughly corresponds to between 40 and 60 seconds for advance alerting.
c Warning Altitude Floor
_ The warning altitude floor is set to a fraction of the caution altitude floor, as illustrated in the upper part of this illustration. (Ref. Fig. 018) The warning altitude floor is computed as a function of aircraft altitude with respect to nearest runway altitude and range to the nearest runway threshold position. This parameter represents a distance below the aircraft. The relationship to the nearest runway threshold location prevents undesired alerts when the aircraft is taking off or landing at an airport.
d Warning Look Ahead Distance
_ The warning look ahead distance is a fraction of the caution look ahead distance (computed from aircraft ground speed and turn rate) to provide an advanced warning with adequate time for the crew to react safely.
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D. Enhanced Features
(1) Terrain Awareness alerting and Display (TAD) functions The terrain awareness component of the Enhanced GPWS is divided into functional blocks with an interface to Navigation Display. (Ref. Fig. 016A) The highlighted blocks monitor aircraft position with respect to local terrain data base and provide rapid audio and visual alerts when a terrain threat is detected. Terrain threats are recognized and annunciated when terrain violates specific computed envelope boundaries forward of the aircraft path. The terrain awareness alert lamps and audio outputs behave in the same manner as the standard GPWS mode alerts. A terrain caution alert or terrain warning alert initiates a specific audio alert phrase (Ref. para.D.(1)(d)2_ and D.(1)(d)3_. Complementing the terrain threat alerts, the Enhanced GPWS also maintains a synthetic image of local terrain forward of the aircraft for display on EFIS Navigation Displays (ND). The Enhanced GPWS is configured to automatically de-select the weather display and pop-up a display of the terrain threats when they occur. The logic used provides an external input for predictive windshear alerts that can override a terrain display and revert to the weather display with the corresponding windshear data (if WR/PWS installed). The Enhanced GPWS provides two external display outputs, each with independent range-scaling control in the same fashion as a weather radar on both NDs. Changes of range scaling to one ND do not affect the other display. Each of these two independent outputs may be used to drive more than one display.
(a) Enhanced GPWS input processing and signal selection. (Ref. Fig. 016A) The Enhanced GPWS input processing and signal selection function conditions and formats aircraft data into proper form for use by the Enhanced GPWS while insulating the Enhanced GPWS from variations in aircraft type and configuration.
1_ Aircraft data inputs
Aircraft position latitude and longitude are required for
terrain awareness operation and are received from the Flight
Management System (FMS). The terrain threat detection and
display processing are automatically disabled in some
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particular conditions. This is indicated to the flight crew by an ECAM memo (TERR STBY). (Ref. Fig. 009) Additionally, aircraft ground track and ground speed data are received from the IR portion of the ADIRU 1 (IRS). The aircraft altitude MSL is received from the air data portion of the ADIRU 1. When QNH baro setting is selected on FCU, baro correction altitude (label 204) from ADIRU 1 is used. When STD baro setting is selected on FCU, standard altitude (label 203) from ADIRU 1 is used. When QFE baro setting is selected on FCU (assuming QFE option activated), the altitude is computed:
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during take off, using standard altitude (label 203) from ADIRU 1 and landing elevation,
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