D. Independent Position Determining This part of the navigation system, which is basically independent of ground installations, provides data on the position of the aircraft. It comprises :
(1) Weather radar system The weather radar system is a X-band system which can be capable of the Predictive Windshear function. This system enables:
-detection and localization of the atmospheric disturbances in the area defined by the antenna scanning with visual display of their intensity
-presentation of terrain mapping information by the combination of the orientation of the radar beam and of the receiver gain
-detection and presentation of windshear events in the area defined by the antenna scanning (if the Predictive Windshear function is operative).
NOTE : The Electronic Flight Instrumental System (EFIS) controls the
____ operation and superimposes the weather picture on the Navigation Display.
This system is made up of the following components : - one or two transceivers (transceiver 2 is optional)
-
a control unit
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a flat plate antenna and its drive unit. More explanations are given in the W/R system (Ref. 34-41).
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(2) Radio altimeter The function of the radio altimeter is to determine precisely and continuously, the height of the aircraft from 0 to 2500 ft above the terrain independently of the atmospheric pressure. The Height and Decision Height data are displayed on the PFD. The selection and reading of Decision Height are performed on the Multipurpose Control and Display unit (MCDU). The radio altimeter system is composed of:
-two transceivers
-four identical antennas, one for transmission and one for reception
for each transceiver.
More explanations are given in the RA system (Ref. 34-42).
(3)
Traffic Collision Avoidance System (TCAS) (optional system) The TCAS is designed to protect a volume of airspace around the TCAS equipped aircraft. The function of the TCAS II is to determine the range, altitude and bearing of other aircraft equipped with ATC transponders. The system monitors the trajectory of the other aircraft for the purpose of determining if any of them constitute a potential collision hazard. If a potential conflict exists, the system provides the pilots with aural and visual advisories which indicate the vertical avoidance maneuvers. The aircraft is equipped with :
-a TCAS computer unit
-two TCAS antennas.
The system exchanges data with the Air Traffic Control (ATC) System.
Traffic advisories are shown on the EFIS displays.
More explanations are given in the TCAS system (Ref. 34-43).
(4)
Gound Proximity Warning System (GPWS) This system is used to inform the crew if the aircraft is in a dangerous configuration when approaching the ground in a non-predetermined manner.
(a)
The GPWS generates aural and visual warnings if the aircraft adopts a potentially hazardous condition with respect to:
-
Mode 1 - Excessive rate of descent
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Mode 2 - Excessive closure rate with terrain
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Mode 3 - Descent after takeoff and minimum terrain clearance
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Mode 4 - Unsafe terrain clearance
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Mode 5 - Descent below glide slope.
The system is operative between 30ft and 2450ft radio altitude.
(b)
Enhanced Ground Proximity Warning System (Enhanced GPWS) (optional system) The purpose of the Enhanced GPWS is to alert the flight crew of potentially hazardous conditions with respect to the terrain.
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The following Enhanced features have been added to existing basic Ground Proximity Warning Modes 1 to 5 which are the backbone of the system:
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Terrain Clearance Floor (TCF) function. It creates an increasing terrain clearance envelope around the intended airport runway directly related to the distance from the runway. The TCF function generates aural and visual alerts.
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Terrain Awareness alerting and Display (TAD) function. This function uses aircraft geographic position, aircraft altitude and a terrain data base to predict potential conflicts between the aircraft flight path and the terrain, and to provide graphic displays of the conflicting terrain on the NDs. The terrain awareness alerting algorithms continuously compute terrain clearance envelopes ahead of the aircraft.
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