A320 INSTRUCTOR SUPPORT
NORMAL OPERATION
DATE: JAN 2001 Page 147 UDY0102
27 - EGPWS AND GPWS
! Technical Background
The Enhanced GPWS incorporates the functions of the basic GPWS with the following added features:
➔ Terrain Clearance Floor (TCF),
➔ Terrain Look Ahead Alerting and
➔ Terrain Awareness Display (TAD).
The purpose of the Enhanced GPWS functions is to provide a better situational awareness to the crew through the
TAD, and to give earlier CAUTION and WARNING to the pilot to initiate a safe recovery maneuver.
The computer incorporates a world wide TERRAIN DATA BASE with varying degrees of resolution. It has also an
airport data base (coordinates of runway center point of all hard surface runway longer than 3500 ft). The earth is
divided into grid sets with the record of the highest terrain altitude in each element of the grid. The resolution of the
data base is a function of the geographic location. It is a HIGH RESOLUTION GRID around an airport, and SMALL
RESOLUTION GRID away from airport. There are 5 levels of resolution (from 15 arc sec. to 5 mn arc or 5 NM).
Having an FMS (and possibly a GPS) on board, the EGPWS determines present position, track and ground speed,
which will be used to advise the crew of any potential conflict with terrain. When the terrain violates specific computed
boundaries on the projected flight path of the A/C, the associated threats will be announced to the crew.
a.) Terrain Clearance Floor (TCF)
The TCF alert function adds an additional element of protection to the standard GPWS by alerting the pilot of
possible premature descent, (for example for NPAs), regardless of aircraft configuration.
It creates an increasing terrain clearance altitude envelope around an airport, directly related to the distance
from the runway. When the aircraft enters this envelope, an alert is triggered.
The alert is a function of A/C position, of the nearest airport location and of current Radio Altitude measure
(R/A). It protects the A/C against an attempt to land on "no airfield".
The TCF is available in ALL FLIGHT PHASES and is a complement to the basic GPWS mode 4.
➔ AURAL MSG -
TOO LOW TERRAIN
(2)
➔
➔➔
➔ GPWS red light illuminates (see note in § b).
NOTE:
As a reminder, the GPWS mode 4 TOO LOW TERRAIN alert is inhibited with the landing gear down.
TCF Alert Envelope
To Next Page
Loading...
Need help?
General
