Ground Proximity Warning System
• A Ground Proximity Warning System (GPWS) is
Previous a type of equipment carried by aircraft to warn
pilots if they are at a dangerously low altitude
and in danger of crashing.
• The main purpose of these systems is to
prevent what is called a Controlled Flight Into
• CFIT is an accident in which an aircraft crashes
into the ground, the water, or an obstacle such
as a mountain or building .
CCFIT= Controlled Flight Into Terrain
Since 1960s, a series of Controlled Flight Into Terrain
(CFIT) accidents killed hundreds of people.
CFIT and GPWS
• CFIT can be the result of factors such as navigation
errors, pilot fatigue or disorientation, or reduced
visibility owing to weather conditions.
• CFIT incidents have been reduced since GPWS entered
widespread use in the 1970s.
• The use of a GPWS in large aircraft is required by law in
• In the late 1990s improvements were made and the
system was renamed "Enhanced Ground Proximity
Warning System“ (EGPWS)
Ground Proximity Warning System (GPWS)
Home • A GPWS monitors the aircraft's altitude with a radar altimeter,
which transmits radio waves downward from the plane to
Previous determine how far away the ground is.
• Most radar altimeters carried by commercial aircraft are short-
range devices with ranges of less than a mile (about 1.6 km).
Help • The information from the radar is monitored and analyzed by a
computer that can identify hazardous situations and trends in the
data, such as
– a dangerously rapid rate of descent,
– dangerously close ground during, or
– unexpected loss of altitude.
• If hazardous conditions are detected, the GPWS gives visual and
audio warning signals to the pilot.
• A radar altimeter or simply RA measures
Previous altitude above the terrain presently beneath an
• This type of altimeter provides the distance
between the plane and the ground directly
below it, as opposed to a barometric altimeter
which provides the distance above sea level.
HOW GPWS WORKS
Home • The heart of the GPWS is a computer processor which
interprets data from a number of sources such as:
– Radar & Navigation Antennas
– Gear and flap indicating system
Help – Roll attitude input sensor
• The computer analyzes a number of parameters such
as, speed, proximity to terrain, and descent rate in
order to issue appropriate warnings.
• The pilots are alerted through visual and audio
warnings by GPWS display inside cockpit.
Audio & Visual Warning
• Audio & Visual Warnings are provided under any of the
– Excessive rate of descend (“sink rate”)
– when closure rate with terrain is too high (“terrain-
– loss of altitude after take-off (don’t sink)
– if the aircraft is too low and slow, with landing gear
retracted (“too low, gear”)
Home • Some typical GPWS warnings are:
– “CLIMB, CLIMB”
– “SINK RATE”
– “TERRAIN, TERRAIN”
– “DON’T SINK”
– “TOO LOW, TERRAIN”
– “TOO LOW GEAR”
– “PULL UP”
• These aural warnings will be accompanied by
illumination of a GPWS display.
• Mode 1: Excessive Descent Rate..
• Mode 2: Excessive Terrain Closure Rate
• Mode 3: Altitude Loss After Take-off
• Mode 4: Unsafe Terrain Clearance
MODE 1: Excessive Descent Rate..
• Warns of excessive descent rate..
• A GPWS warning light will illuminate and “sink
rate, sink rate” will be heard.
• If the situation is not corrected “whoop,
whoop, pull up, pull up” will be heard.
MODE 2: Excessive Terrain Closure Rate
• Warns crew when closure rate with terrain is
• Designed to warn crew when rising terrain is a
• “terrain, terrain”
• “whoop, whoop, pull up, pull up”
• There may be no change in barometric altitude
but the radar altitude is decreasing.
MODE 3: Altitude Loss After Take-off
• Warns of loss of altitude after take-off, or go-
• If the aircraft sinks 10 percent of its radar
altitude “don’t sink” will be heard.
MODE 4: Unsafe Terrain Clearance
• MODE 4a: if the aircraft is too low and slow, with
landing gear retracted.
• “too low, gear”
• If the airspeed is higher the warning will be “too low,
• MODE 4b: When the gear is selected down, but the
flaps are still retracted “too low, flaps”
• This warning can be canceled by the pilot in the event
of a flapless landing.
• Recovery procedure will vary depending on the
Previous type of aircraft, but the general response is:
– Roll level and simultaneously set maximum power.
– Slowly pitch up and maintain Vx.
– Retract gear and flaps.
– Continue climb until clear of terrain.
Enhanced Ground Proximity
• Enhanced Ground Proximity Warning System
Previous • A limitation of GPWS is the fact that with radar
altimeter information only the aircraft is only
capable of seeing terrain directly below.
• In the case of rapidly rising terrain it may not
react quick enough to issue a warning in time.
Enhanced Ground Proximity Warning System
• EGPWS corrects this problem by integrating an aircraft
navigational source into the system.
• GPS position in conjunction with a terrain database is
used to help predict terrain conflict.
Help • Any catalogued man made obstructions are included in
• This type of system can be used to display terrain
profile to the pilot to improve situational awareness.
• Question 2: FAA defines GPWS as a type of
a) Terrain awareness and warning system
b) Aircraft flight control system
c) Controlled flight into terrain
d) Ground proximity warning system
• Question 3: ________
a) American Airlines Flight 191
c) Garuda Fokker F28 crash
d) Air New Zealand Flight 901
• TACA Flight 390Santa Bárbara Airlines Flight
Previous 518Continental Airlines Flight 1404Hewa Bora
Airways Flight 122
• In the late 1990s improvements were made and
Previous the system was renamed "Enhanced Ground
Proximity Warning System" (________/TAWS).
a) Global Positioning System
b) Local Area Augmentation System
c) Ground proximity warning system
d) Global navigation satellite system
• Question 6: The system was now combined
Previous with a worldwide digital terrain database and
relies on Global Positioning System (________)
• Inertial navigation system
• Global Positioning System
• F-15 Eagle