INDEPENDENT POS DETERMINING SYS PRES. OF AIRBUS
GENERAL
The Independent Position determining systems include:
- Enhanced Ground Proximity Warning System (EGPWS) or Traffic and
Terrain Collision Avoidance System (T2CAS) as option,
- Radio Altimeters (RAs),
- Weather Radar (WXR) and Predictive Windshear (PWS).
These systems do not rely on external sources to give to the flight crew
the position determination.
EGPWS
The function of the EGPWS is to launch aural and visual warnings if the
A/C adopts a potentially hazardous configuration of Controlled Flight
Into Terrain (CFIT).
This system has five basic Enhanced Ground Proximity Warning System
(EGPWS) modes and has 2 TERRAIN modes called TERRAIN Clearance
Function (TCF) and the TERRAIN Awareness and Display (TAD).
As an option, the T2CAS can replace the EGPWS.
EGPWS (continued)
SYSTEM ARCHITECTURE
The EGPWS computer (or T2CAS computer as an option) processes
the data from:
- RA 1,
- Air Data/Inertial Reference Unit (ADIRU) 1,
- Multi-Mode Receiver (MMR) 1 (Instrument Landing System (ILS)
part),
- Flight Management and Guidance Computer (FMGC) 1,
- Landing Gear Control and Interface Unit (LGCIU) 1,
- WXR/PWS (for ND image source selection between both systems).
The Traffic Collision avoidance System (TCAS) part of the T2CAS
is the part that carries out the TCAS functions.
The Terrain Awareness and Warning System (TAWS) of the T2CAS
is the part of the T2CAS that carries out the EGPWS functions such
as:
- basic TAWS modes base on Radio Altitude (RA),
- predictive TAWS modes: Collision Prediction and Alerting (CPA)
function and Terrain Hazard Display (THD) which gives a
forward-looking terrain alerting capability.
EGPWS (continued)
GPWS PANEL
The GPWS/T2CAS control panel is installed on the overhead panel
and enables the deactivation of:
- TERRAIN mode,
- complete or partial basic EGPWS mode in specific approach
configuration.
EGPWS (continued)
CONTROL AND INDICATING
EGPWS and T2CAS have the same visual warnings that are shown
on the instrument panels. Pressing either of the PULL UP/GPWS
P/BSW starts the systems test.
In addition, two loudspeakers installed on each lower side of the main
panel broadcast EGPWS/T2CAS aural warnings, even if loudspeaker
knobs are turned off.
Terrain information will be automatically displayed on the ND if there
is any danger within the proximity of the A/C. The terrain elevation
surrounding the A/C is color-coded. The TERRain ON ND P/B is
used to display the terrain information on the ND all the time on
request.
RADIO ALTIMETER
The RAs supply accurate measurement of the A/C height above the
ground during initial climb, landing and approach phases.
RADIO ALTIMETER (continued)
CONTROL AND INDICATING
RA data is supplied to several users and is displayed on both PFDs at
all times below 2500 feet Above Ground Level (AGL).
In normal operation, the RA 1 height is displayed on the CAPT PFD
and RA 2 height on the F/O PFD.
WXR/PWS
WXR is installed to detect precipitation. The displayed returns are shown
on the ND.
The weather radar supplies PWS detection. A wind shear event is a sudden
change of wind speed and/or direction over a short distance with a
downwards and/or upwards movement of a very dangerous air during
take off and approach phases.
WXR/PWS (continued)
WXR/PWS PANEL
The WXR control panel is installed on the center pedestal. The
information is displayed on the CAPT or F/O ND.
WARNING: when the WXR is "ON":
- personnel should not be within 5 meters of the radome,
CAUTION: when the WXR is "ON":
- no metallic obstacle should be within 5 meters,
- no refueling within 60 meters
- to avoid damage to the A/C
The multiscan is a radar function that displays all significant weather
at all ranges, at all aircraft altitudes, and at all times on a display that
is essentially clutter-free, without the need for pilot to input tilt or
gain settings. The multiscan function optimizes weather detection and
minimizes ground clutter.
The weather radar can operate in autotilt mode (automatic tilt angle):
the use of the automatic tilt function is recommended in WX and
TURB modes. The autotilt function uses the terrain altitude
information of the EGPWS. Based on the aircraft altitude above the
terrain and on terrain conditions in the area, the EGPWS determines
the optimum tilt angle for the radar
Automatic tilt is selected by setting the MULTISCAN SW to AUTO
on the weather radar control unit.
- switch to AUTO: Tilt setting for weather scans is automatic,
- switch to MAN: Tilt is controlled with the manual tilt control knob.
COMPONENT LOCATION
Here is the location of the:
- EGPWS computer or T2CAS computer,
- WXR computer.
The RAs are installed in the aft cargo compartment.
The various antennae are installed on the lower portion of the fuselage.
The WXR antenna is installed in the radome.
MAINTENANCE/TEST FACILITIES
All navigation systems can be tested from the MCDUs.
SAFETY PRECAUTIONS
When you work on the A/C, make sure that you obey all the Aircraft
Maintenance Manual (AMM) procedures. This will prevent injury to
persons and/or damage to the A/C.
Make sure that:
- all persons are more than 5 meters (16.4 feet) away from the antenna,
nobody is in the area made by an arc of 135 degrees on each side of the
A/C centerline.
- all objects and obstacles are more than 5 meters away from the antenna
in the area made by an arc of 90 degrees on each side of the A/C
centerline.
- Stop the fuel tanker 60 meters from the A/C nose while the weather
radar is operating.
Do not operate the fuel tanker/pump until you stop the operation of the
weather radar.
Make sure that there is no sign of corrosion or damage and no foreign
objects in the test equipment.
