Ground Proximity Warning System
Overview
 


A ground proximity warning system (GPWS) is a system designed to alert pilots if their aircraft is in immediate danger of flying into the ground
Controlled flight into terrain
Controlled flight into terrain describes an accident in which an airworthy aircraft, under pilot control, is unintentionally flown into the ground, a mountain, water, or an obstacle. The term was coined by engineers at Boeing in the late 1970s...

 or an obstacle. The United States Federal Aviation Administration
Federal Aviation Administration
The Federal Aviation Administration is the national aviation authority of the United States. An agency of the United States Department of Transportation, it has authority to regulate and oversee all aspects of civil aviation in the U.S...

 defines GPWS as a type of terrain awareness warning system (TAWS). More advanced systems, introduced in 1996, are known as enhanced ground proximity warning systems (EGPWS), although sometimes confusingly called terrain awareness warning systems.
In the late 1960s, a series of controlled flight into terrain
Controlled flight into terrain
Controlled flight into terrain describes an accident in which an airworthy aircraft, under pilot control, is unintentionally flown into the ground, a mountain, water, or an obstacle. The term was coined by engineers at Boeing in the late 1970s...

 (CFIT) accidents took the lives of hundreds of people.
Encyclopedia


A ground proximity warning system (GPWS) is a system designed to alert pilots if their aircraft is in immediate danger of flying into the ground
Controlled flight into terrain
Controlled flight into terrain describes an accident in which an airworthy aircraft, under pilot control, is unintentionally flown into the ground, a mountain, water, or an obstacle. The term was coined by engineers at Boeing in the late 1970s...

 or an obstacle. The United States Federal Aviation Administration
Federal Aviation Administration
The Federal Aviation Administration is the national aviation authority of the United States. An agency of the United States Department of Transportation, it has authority to regulate and oversee all aspects of civil aviation in the U.S...

 defines GPWS as a type of terrain awareness warning system (TAWS). More advanced systems, introduced in 1996, are known as enhanced ground proximity warning systems (EGPWS), although sometimes confusingly called terrain awareness warning systems.

History

In the late 1960s, a series of controlled flight into terrain
Controlled flight into terrain
Controlled flight into terrain describes an accident in which an airworthy aircraft, under pilot control, is unintentionally flown into the ground, a mountain, water, or an obstacle. The term was coined by engineers at Boeing in the late 1970s...

 (CFIT) accidents took the lives of hundreds of people. (A CFIT accident is one where a properly functioning airplane under the control of a fully qualified and certificated crew is flown into terrain (or water or obstacles) with no apparent awareness on the part of the crew.)

Beginning in the early 1970s, a number of studies looked at the occurrence of CFIT accidents. Findings from these studies indicated that many such accidents could have been avoided if a warning device called a ground proximity warning system (GPWS) had been used. As a result of these studies and recommendations from the U.S. National Transportation Safety Board
National Transportation Safety Board
The National Transportation Safety Board is an independent U.S. government investigative agency responsible for civil transportation accident investigation. In this role, the NTSB investigates and reports on aviation accidents and incidents, certain types of highway crashes, ship and marine...

 (NTSB), in 1974 the FAA required all large turbine and turbojet airplanes to install TSO
Technical Standard Order
A Technical Standard Order is a minimum performance standard issued by the United States Federal Aviation Administration for specified materials, parts, processes, and appliances used on civil aircraft. Articles with TSO design approval are eligible for use on the United States type certificated...

-approved GPWS equipment.

C. Donald Bateman
C. Donald Bateman
Charles Donald Bateman, known as Don Bateman, is the inventor of the Ground Proximity Warning System , a device that is responsible for a marked decline in controlled flight into terrain accidents....

, a Canadian-born engineer, developed and is credited with the invention of GPWS.

In March 2000, the U.S. FAA amended operating rules to require that all U.S. registered turbine-powered airplanes with six or more passenger seats (exclusive of pilot and copilot seating) be equipped with an FAA-approved TAWS. The mandate affects aircraft manufactured after March 29, 2002.

Effects and statistics

Prior to the development of GPWS, large passenger aircraft were involved in 3.5 fatal CFIT accidents per year, falling to 2 per year in the mid-1970s. Since 1974, when the U.S. Federal Aviation Administration
Federal Aviation Administration
The Federal Aviation Administration is the national aviation authority of the United States. An agency of the United States Department of Transportation, it has authority to regulate and oversee all aspects of civil aviation in the U.S...

 made it a requirement for large aircraft to carry such equipment, there has not been a single passenger fatality in a CFIT crash by a large jet in U.S. airspace.

After 1974, there were still some CFIT accidents which GPWS was unable to help prevent, due to the blind spot of those early GPWS systems. More advanced systems were developed.

Older TAWS systems, or deactivation of the EGPWS system, or ignoring its warnings when airport is not in its database still leave aircraft vulnerable to possible CFIT incidents. In April 2010, a Polish Air Force Tupolev Tu-154M aircraft crashed near
2010 Polish Air Force Tu-154 crash
The 2010 Polish Air Force Tu-154 crash occurred on 10 April 2010, when a Tupolev Tu-154M aircraft of the Polish Air Force crashed near the city of Smolensk, Russia, killing all 96 people on board...

 Smolensk, Russia, in a possible CFIT accident killing all passengers and crew. The aircraft was equipped with TAWS made by Universal Avionics Systems of Tucson. According to the Russian Interstate Aviation Committee TAWS was turned on. However, the airport where the aircraft was going to land (Smolensk (XUBS)) is not in the TAWS database. In January 2008 a Polish Air Force Casa C-295M crashed in a CFIT accident near Mirosławiec, Poland, despite being equipped with EGPWS; the EGPWS warning sounds had been disabled, and the pilot-in-command was not properly trained with EGPWS.

Commercial aircraft

The system monitors an aircraft's height above ground as determined by a radio altimeter. A computer then keeps track of these readings, calculates trends, and will warn the captain with visual and audio messages if the aircraft is in certain defined flying configurations ("modes").

The modes are:
  1. Excessive descent rate ("SINK RATE" "PULL UP")
  2. Excessive terrain closure rate ("TERRAIN" "PULL UP")
  3. Altitude loss after take off or with a high power setting ("DON'T SINK")
  4. Unsafe terrain clearance ("TOO LOW – TERRAIN" "TOO LOW – GEAR" "TOO LOW – FLAPS")
  5. Excessive deviation below glideslope ("GLIDESLOPE")
  6. Excessively steep bank angle ("BANK ANGLE")
  7. Windshear protection ("WINDSHEAR")


Traditional GPWS does have a blind spot. Since it can only gather data from directly below the aircraft, it must predict future terrain features. If there is a dramatic change in terrain, such as a steep slope, GPWS will not detect the aircraft closure rate until it is too late for evasive action.

In the late 1990s improvements were made and the system was renamed "Enhanced Ground Proximity Warning System" (EGPWS/TAWS). The system was now combined with a worldwide digital terrain database and relies on Global Positioning System
Global Positioning System
The Global Positioning System is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites...

 (GPS) technology. On-board computers compared its current location with a database of the Earth's terrain. The Terrain Display now gave pilots a visual orientation to high and low points nearby the aircraft.

EGPWS software improvements were focused on solving two common problems; no warning at all, and late or improper response.

No warning

The primary cause of CFIT occurrences with no GPWS warning is landing short. When the landing gear is down and landing flaps are deployed, the GPWS expects the airplane to land and therefore, issues no warning. EGPWS introduces the Terrain Clearance Floor (TCF) function, which provides GPWS protection even in the landing configuration.

Late warning or improper response

The occurrence of a GPWS alert typically happens at a time of high workload and nearly always surprises the flight crew. Almost certainly, the aircraft is not where the pilot thinks it should be, and the response to a GPWS warning can be late in these circumstances. Warning time can also be short if the aircraft is flying into steep terrain since the downward looking radio altimeter is the primary sensor used for the warning calculation. The EGPWS improves terrain awareness and warning times by introducing the Terrain Display and the Terrain Data Base Look Ahead protection.

Incidents

In Commercial and Airline operations there are legally mandated procedures that must be followed should an EGPWS caution or warning occur. Both pilots must respond and act accordingly once the alert has been issued. An Indonesian captain has been charged with manslaughter for not adhering to these procedures.

The other sample of incident of plane with EGPWS/TAWS is 2010 Polish Air Force Tu-154 crash
2010 Polish Air Force Tu-154 crash
The 2010 Polish Air Force Tu-154 crash occurred on 10 April 2010, when a Tupolev Tu-154M aircraft of the Polish Air Force crashed near the city of Smolensk, Russia, killing all 96 people on board...

 where all 96 people onboard (including then President of Republic of Poland) died.

General aviation

TAWS equipment is not required by the U.S. FAA in piston-engined aircraft, but optional equipment categorized as TAWS Type C may be installed. Depending on the type of operation, TAWS is only required to be installed into turbine-powered aircraft with six or more passenger seats.

A smaller and less expensive version of EGPWS was developed by AlliedSignal
AlliedSignal
AlliedSignal was an aerospace, automotive and engineering company that acquired and merged with Honeywell for $15 billion in 1999, after which the new group adopted the Honeywell name.AlliedSignal was created through a 1985 merger of Allied Corp...

 (now merged with Honeywell
Honeywell
Honeywell International, Inc. is a major conglomerate company that produces a variety of consumer products, engineering services, and aerospace systems for a wide variety of customers, from private consumers to major corporations and governments....

) for general aviation and private aircraft.

Military fast jet

For military fast-jets, the high speed and low altitude which may frequently be flown, make traditional GPWS systems unsuitable as the blind spot becomes the critical part. Thus an enhanced system is required, taking inputs not only from the radar altimeter
Radar altimeter
A radar altimeter, radio altimeter, low range radio altimeter or simply RA measures altitude above the terrain presently beneath an aircraft or spacecraft...

 but also from inertial navigation system
Inertial navigation system
An inertial navigation system is a navigation aid that uses a computer, motion sensors and rotation sensors to continuously calculate via dead reckoning the position, orientation, and velocity of a moving object without the need for external references...

 (INS), Global Positioning System
Global Positioning System
The Global Positioning System is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites...

 (GPS), and flight control system (FCS), and using these to accurately predict the flight path of the aircraft up to 4 to 5 mi (6.4 to 8 ) ahead. Digital maps
Digital mapping
Digital mapping is the process by which a collection of data is compiled and formatted into a virtual image. The primary function of this technology is to produce maps that give accurate representations of a particular area, detailing major road arteries and other points of interest...

 of terrain and obstacle features are then used to determine whether a collision is likely if the aircraft does not pull up at a given pre-set g-level
G-force
The g-force associated with an object is its acceleration relative to free-fall. This acceleration experienced by an object is due to the vector sum of non-gravitational forces acting on an object free to move. The accelerations that are not produced by gravity are termed proper accelerations, and...

. If a collision is predicted a cockpit warning may be provided. This is the type of system deployed on such aircraft as the Eurofighter Typhoon
Eurofighter Typhoon
The Eurofighter Typhoon is a twin-engine, canard-delta wing, multirole combat aircraft, designed and built by a consortium of three companies: EADS, Alenia Aeronautica and BAE Systems; working through a holding company, Eurofighter GmbH, which was formed in 1986...

. The U.S. FAA has also conducted a study about civilizing 3D military thrust vectoring to recover jetliners from catastrophes.

See also

  • Acronyms and abbreviations in avionics
    Acronyms and abbreviations in avionics
    -A:*ACARS: Aircraft Communications Addressing and Reporting System.*ACAS: Airborne Collision Avoidance System.*ACP: Audio Control Panel.*ACS: Audio Control System.*ADAHRS: Air Data and Attitude Heading Reference System.*ADC: Air Data Computer....

  • Aeroperu Flight 603
    AeroPeru Flight 603
    Aeroperú Flight 603 was a scheduled flight from Jorge Chávez International Airport in Lima, Peru , to Comodoro Arturo Merino Benítez International Airport in Santiago, Chile , which crashed on October 2, 1996....

  • Air New Zealand Flight 901
    Air New Zealand Flight 901
    Air New Zealand Flight 901 was a scheduled Air New Zealand Antarctic sightseeing flight that operated between 1977 and 1979, from Auckland Airport to Antarctica and return via Christchurch...

  • Aircraft collision avoidance systems
  • Airport Movement Area Safety System
    Airport Movement Area Safety System
    The Airport Movement Area Safety System visually and aurally prompts tower controllers to respond to situations which potentially compromise safety. AMASS is an add-on enhancement to the host ASDE-3 radar that will provide automated alerts and warnings to potential runway incursions and other...

     (AMASS)
  • ASDE-X
    ASDE-X
    Airport Surface Detection Equipment, Model X, or ASDE-X, is a runway-safety tool that enables air traffic controllers to detect potential runway conflicts by providing detailed coverage of movement on runways and taxiways...

    —Airport Surface Detection Equipment, Model X
  • American Airlines Flight 965
    American Airlines Flight 965
    American Airlines Flight 965, a Boeing 757 registered , was a scheduled flight from Miami International Airport in Miami, Florida to Alfonso Bonilla Aragón International Airport in Cali, Colombia, which crashed into a mountain in Buga, Colombia on December 20, 1995, killing 151 passengers and 8...

  • Ansett New Zealand Flight 703
    Ansett New Zealand Flight 703
    Ansett New Zealand Flight 703 was an Ansett New Zealand scheduled passenger transport flight from Auckland Airport to Palmerston North. On 9 June 1995, the Dash 8 aircraft flying this route crashed west of the Tararua Ranges and 16 km east of Palmerston North airport, during an instrument...

    , a CFIT accident associated with GPWS malfunction
  • "Bitching Betty
    Bitching betty
    Bitching Betty is the slang term some pilots and crew use when referring to the voice warnings used by some aircraft systems....

    "
  • Fly by wire#Fly-by-wire control systems
  • Santa Barbara Airlines Flight 518
    Santa Bárbara Airlines Flight 518
    Santa Bárbara Airlines Flight 518 was an ATR 42-300 twin-turboprop aircraft, registration YV1449, operating as a scheduled domestic flight from Mérida, Venezuela to Caracas that crashed into the side of a mountain on 21 February 2008, shortly after takeoff. There were 43 passengers on board, with a...

  • South African Airways Flight 228
    South African Airways Flight 228
    South African Airways Flight 228 was a scheduled flight from Jan Smuts International Airport in Johannesburg, South Africa to London Heathrow International Airport that flew into the ground soon after take-off after a scheduled stopover in Windhoek, South West Africa . Five passengers survived...

  • TERPROM
    TERPROM
    TERPROM is a military navigation Ground Proximity Warning System employed on aircraft and missiles, which uses stored digital elevation data combined with navigation system and radar altimeter inputs to compute the location of an aircraft or missile above the surface of the earth...

  • Traffic Collision Avoidance System
    Traffic Collision Avoidance System
    A traffic collision avoidance system or traffic alert and collision avoidance system is an aircraft collision avoidance system designed to reduce the incidence of mid-air collisions between aircraft...

     (TCAS)
  • TWA Flight 514
    TWA Flight 514
    TWA Flight 514, registration N54328, was a Boeing 727-231 en route from Indianapolis, Indiana, and Columbus, Ohio, to Washington Dulles International that crashed into Mount Weather, Virginia, on December 1, 1974. All 85 passengers and 7 crew members were killed.The flight was originally destined...

  • Japan Airlines Flight 123
    Japan Airlines Flight 123
    Japan Airlines Flight 123 was a Japan Airlines domestic flight from Tokyo International Airport to Osaka International Airport on August 12, 1985. The Boeing 747-146SR that made this route, registered , suffered mechanical failures 12 minutes into the flight and 32 minutes later crashed into two...


External links

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