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Introduction about EGPWS


EGPWS Also known as the Enhanced Ground Proximity Warning System reduces the risk of controlled flight into the terrain by providing flight crews with timely, accurate information about terrain and obstacles in the area.

The system predicts and warns flight crews of potential collisions with obstacles or terrain using various aircraft inputs and an internal database.

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 or an obstacle.

The United States Federal Aviation Administration (FAA) defines GPWS as a terrain awareness warning system (TAWS) type. Enhance ground proximity warning systems (EGPWS), a more modern variation of TAWS, were introduced in 1996 and are considered more advanced systems.

A terrain awareness and warning system (TAWS) is an onboard system designed to prevent unintentional impacts with the ground, also known as “controlled flight into terrain” accidents, or CFIT.

The ground proximity warning system (GPWS) and the enhanced ground proximity warning system are the specific systems currently in use (EGPWS). The Federal Aviation Administration (FAA) of the United States coined the term TAWS to refer to all terrain-avoidance systems that meet FAA standards, which include GPWS, EGPWS, and any future system that may replace them.

History Of Warning System

Hundreds of people lost their lives as a result of a series of controlled flight into terrain (CFIT) accidents in the late 1960s. A CFIT accident occurs when a properly functioning airplane is flown into terrain, water, or obstacles by a fully qualified and certified crew with no apparent awareness on the part of the crew.

Numerous studies that started in the early 1970s looked into the frequency of CFIT accidents. According to the findings of these studies, many such accidents could have been avoided if a warning device known as a ground proximity warning system (GPWS) had been used.

Due to these investigations and the National Transportation Safety Board‘s (NTSB) recommendations, the FAA mandated installing TSO-approved GPWS equipment on all large turbine and turbojet aircraft in 1974.

The U.S. FAA amended its operating regulations in March 2000 to mandate that all turbine-powered aircraft registered in the country and having six or more passenger seats (excluding seats for the pilot and co-pilot) be fitted with an FAA-approved TAWS.


In accordance with the level of system sophistication, TAWS equipment is categorized as Class A or Class B. Class A systems are required for all commercial air transport aircraft except the smallest, while Class B systems are required for larger General Aviation (GA) aircraft and recommended for smaller commercial or GA aircraft.

The following functions must be provided by TAWS equipment:

  • FLTA (forward-looking terrain avoidance) feature. The FLTA function scans ahead and below the aircraft’s lateral and vertical flight paths, alerting the pilot if a potential CFIT threat exists.
  • PDA (Premature Descent Alert) function. The DA function of the TAWS determines whether the aircraft is dangerously below the average (typically 3-degree) approach path for the nearest runway as defined by the alerting algorithm by using the aircraft’s current position and flight path information as determined from a suitable navigation source and airport database.
  • A suitable visual and audible discrete signal for both caution and warning alerts.

TWAS – Class A:

TAWS equipment provides warnings of imminent ground contact under the following conditions:

  1. Excessive Descent Rates.
  2. Excessive Terrain Closure Rate.
  3. Negative Climb Rate or Altitude Loss After Take-off.
  4. Flight Into Terrain When Not in Landing Configuration.
  5. Excessive downward deviation from the glideslope of an Instrument Landing System (ILS), Localizer Performance and Vertical Guidance (LPV), or Global Navigation Satellite System (GNSS) Landing System (GLS).
  6. Voice callout “Five Hundred” when the airplane descends to 500 feet above the terrain or nearest runway elevation.

Taws – Class B:

the equipment provides indications of close contact with the ground during the following aircraft operations:

  1. Excessive Rates of Descent.
  2. Negative Climb Rate or Altitude Loss After Takeoff.
  3. A voice callout “Five Hundred” when the airplane descends to 500 feet above the nearest runway elevation.