Chapter 7. Navigation and surveillance systems

7.10. Ground Proximity and Warning System

The first Ground Proximity Warning System( GPWS)began in the early 80s. The main functions of GPWS it has warned the pilot about the possibility of collision aircrafts with the earth's surface due to a fast descend.

The development of information technology has contributed of significantly improving basic functions of GPWS [25]. The development of satellite navigation systems made it possible to determine the coordinates of the location, and use precision electronic maps of the earth's surface. All of this led to the emergence of Enhanced Ground Proximity Warning System (EGPWS). Currently, the FAA introduced the designation for this type of systems (Terrain Awareness and Warning System - TAWS) and standardized three main classes of TAWS [61].

TAWS Class B

TAWS equipment shall to signal when:
-Reducing the distance to the earth's surface;
- Explicit future collision;
- Rapid descend;
- Insufficient rate of climb after take-off;
- Descend of aircraft below 500 feet above the ground .As the TAWS application can display a map of the underlying surface on a special display.

TAWS Class A

TAWS of this class must include a warning in all cases of class B and provide an alarm in case of:
- Exceeding the maximum acceptable speed of convergence;
- Flying near the ground with unreleased landing gears;
- Excessive glideslope deviation from the line during landingof aircraft.

In addition, TAWS of class A must display a map of the underlying surface or position of the aircraft regarding the terrain in the vertical plane. Class C. To the TAWS of this class of requirements is considerably lower and include only the most necessary warning functions. TAWS of class C designed for aircrafts of light aviation, the number of seats less than six.

In general Ground Proximity Warning System is intended for timely issuance for aircraft crew of warning language and visual alarm in the event of such situations in flight, the development of which can lead to unintended collisionof aircraft with the earth's surface, and to increase awareness of the crew of aircraft about components of surface and location of artificial obstacles are in database system and represent a potential danger to its actual or projected path.

In addition, the system provides the issuance of:
- Voice messages during the specified fixed heights;
- Alarm in case of exceeding unacceptable value of roll;
- Warning alarm in case of early descend during the landing approach.

Relationship between Ground Proximity Warning System and other aircraft systems shown in Fig. 104. Ground Proximity Warning System equipment continuously analyzes the current flight parameters of aircraft, flaps and landing gear position , relief of underlying surface and the presence of artificial obstacles on the surface. In case of detection in the direction of flight of a potentially dangerous situation proactively alerts the pilot with visual and voice messages. An early warning of the possibility of collision allows the pilot to navigate and begin to perform a maneuver to avoid a collision of aircrafts, without violating the rules of piloting.

There are three main functions of Ground Proximity Warning System:
– The function of Ground Proximity Warning System( GPWS);
– The function of Enhanced Ground Proximity Warning System (EGPWS) including alarm about the early descend;
– Formation warning voice messages.

Fig. 104. Interconection of Ground Proximity Warning System

Functions GPWS provide the issuance of warning messages in the event of certain flight parameters for valid values:
– The rate of descend exceeded the limit;
– Speed Ground Proximity exceeded the limit;
– Loss of altitude on takeoff or out in the second round;
– Flight below the allowable height of not landing configuration;
– Deviation down from the glide path to landing by radio means landing, which significantly exceeds the established limits;
– The threshold differences between the relative barometric height and the true height.

In the GPWS the Ground Proximity Warning System based on database of relief underlying surface ,current coordinates whereabouts of aircraft, flight parameters and air quality, tactical and technical characteristics of the type of aircrafts, international rules on minimum acceptable clearance above the earth's surface and obstacles to it, and generally accepted rules of piloting system that creates a workspace of two zones alarm - alarm and emergency. Getting the underlying surface in the appropriate zone lead a warning or an alarm in the form of language and picture messages.

To raise awareness of the crew of the aircraft on the ground situation, the system issues on the electronic display system information of the underlying terrain. In addition, in the event activation the warning alarm the system identifies on screen display of bright yellow of area underlying surface that caused activation of the warning alarm. In case of activation the alarm the system identifies on screen indicator corresponding section of bright red color (Fig. 105).

Basic functions of GPWS:
- Early warning of insufficient height over an obstacle in the direction of flight;
- Prevention of early descend during the landing approach;

Issue on the screen of the display device the visual environment of the underlying terrain in the area of review and artificial obstacles.

Fig. 105. Ground Proximity Warning System terrain indication (Crimean mountains) on EFIS]

During the descend of aircraft in algorithm of Ground Proximity Warning System lies the possibility issuing voice messages passing of aircraft predetermined fixed height above the underlying surface in case of:
- Crossing decision height;
- Achieving a height of 150 m in the descend;
- Passing a number of specified fixed heights;
- Exceeding the established limit value of roll.

Typical voice messages of Ground Proximity Warning System

  • Pull up
  • Terrаin
  • Too Low terrain
  • Too Low Gear
  • Too Low Flaps
  • Minimum-minimum
  • Sink rate
  • Don’t sink
  • Glides lope
  • Obstacle Ahead
  • Terrain Ahead
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Ostroumov IvanOSTROUMOV Ivan, PhD
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