This article may use the following abbreviations commonly used in civil aviation, and this article will not explain them.
Enhanced ground proximity warning system.
Terrain perception warning system Terrain prompting and warning system
Near earth warning system
Controllable flight into terrain
Faa: Federal Aviation Administration Federal Aviation Administration (USA)
Cfit and Near-Earth Warning System
Before introducing EGPWS enhanced ground proximity warning system, we should know about its predecessor GPWS ground proximity warning system. Why do you need a ground proximity warning system? This should start with cfit (Controlled Collapse). CFIT is an accident in flight, not because of the failure of the aircraft itself or the engine, but because the crew manipulated the aircraft to crash into the mountain, the ground or fly into the water without realizing the danger, resulting in the crash or serious damage of the aircraft, resulting in casualties.
According to the statistics of ICAO, cfit has become the chief culprit of fuselage damage and death accidents of commercial jets. To this end, civil aviation began to install GPWS near-ground warning system on aircraft to avoid similar accidents and increase safety.
1974, FAA began to require the mandatory installation of GPWS on flights flying in American airspace. 1979, ICAO suggested that users install this equipment. Since then, CFIT accidents have been greatly reduced. After 1985, CFIT accidents only occur 1 2 times a year, while before installation, it is mandatory to happen 7 to 8 times a year. At present, almost all commercial jets in the world are equipped with GPWS.
GPWS consists of a ground proximity warning computer, a warning light and a control panel. Its core is the near-ground warning computer. Once unsafe conditions are found, the driver is informed by lights and sounds until the driver takes measures to get rid of the unsafe conditions.
The near-earth early warning system mainly divides the dangerous situation into six ways for early warning:
-The descending speed is too high;
-The approaching speed to the ground is too high;
-When taking off or going around to climb high, the flap is too small;
-The plane is not high enough from the ground;
-When the plane approaches, the glide slope deviates downward;
Wind shear.
The near-ground warning system also gives an audible alarm to the driver through the loudspeaker in the cockpit, and the main indicator light of the warning system gives an alarm instruction and displays warning information on the electronic flight instrument system.
Although GPWS can effectively reduce accidents, CFIT accidents are still the main cause of commercial jet accidents. Accident data shows that GPWS needs to be improved. The current GPWS has the following characteristics and shortcomings.
-I can't understand the situation ahead. It only has the function of "looking down", depends on the radio altitude and cannot reflect the terrain in front of the plane.
-Although we can track past flight information and predict future flight information to assess whether there is danger ahead. When the plane flies to the terrain with large ascending slope, it sends an alarm signal to the pilot. However, if there is a sudden rising terrain, a vertical cliff or a steep cliff ahead, it is impossible to send an alarm signal in time.
-There is a "no warning" factor: when the landing gear and flaps of the aircraft are in landing mode and descending at normal speed, it is impossible to provide terrain warning, because at this time, GPWS thinks that the aircraft will land at the airport, and it is necessary to suppress the warning in order to avoid interference. Facts show that many CFIT accidents occur during the landing phase.
EGPWS Enhanced Near-ground Warning System
The disadvantage of GPWS is that the early warning time is insufficient when flying to steep terrain, and the early warning is insufficient when flying to flat land that is not a runway. These shortcomings can also lead to CFIT accidents. ICAO proposed to install TAWS terrain early warning system to make up for the deficiency of GPWS, so as to avoid similar CFIT accidents. While maintaining the advantages of the original GPWS system, TAWS system has added new functions such as forward-looking terrain warning and terrain display, which can make the flight crew know the terrain around the aircraft more comprehensively, thus further reducing the incidence of CFIT accidents.
At present, there is only one supplier in the world, Honeywell, and their TAWS system is EGPWS enhanced ground proximity warning system. In 1996, the system passed the certification of the Federal Aviation Administration (FAA). As the name implies, it is an improved product of traditional ground proximity warning system (GPWS).
Up to now, there has never been a CFIT accident where EGPWS equipment has been installed in the world.
EGPWS equipment appearance
In order to simplify the connection between the unit and EGPWS and make the unit adapt quickly, the early warning mode of EGPWS is almost the same as that of traditional GPWS, and it also includes the related functions of traditional GPWS. The specific functions and operation modes of GPWS are not introduced here. Compared with traditional GPWS, EGPWS has some new functions and features.
The enhanced ground proximity warning system has the following features:
The enhanced near-ground warning system uses its own global airport location database and terrain database, and uses aircraft position, barometric altitude and flight trajectory information to determine potential collision risks. The airport location database contains all the information of more than 20,000 runways with a length of more than 3,500 feet (65,438+0,067 meters) in the world. The terrain database includes almost all the terrain conditions in the world. In the database, the earth's surface is divided into countless squares, and the grid value in each square is expressed according to the highest terrain point. And these data will be updated regularly. When the plane is in flight and close to an airport, the data of the surrounding environment detected by the plane will be compared with the data stored on the plane in real time. Before the plane enters the dangerous area, the system will warn the crew to avoid the accident that the plane hits the ground or the mountain in bad weather such as rain and fog while the pilot is still effectively controlling the plane. At present, the system has become the standard equipment for new Boeing and Airbus aircraft.
Introduction to the use of EGPWS:
In order to display the terrain and provide terrain warning, EGPWS's computer is connected with other systems of the aircraft. The navigation system of the aircraft provides the current position of the aircraft, which can tell the computer which part of the terrain database to refer to, and the altimeter of the aircraft can tell the computer the current flying height, so that it can determine where the terrain height will cause danger.
How to display terrain:
The terrain display function of EGPWS can be turned on manually by the crew, or it can be automatically displayed when warning or warning is started according to the current flight conditions. Terrains below 2000 feet and above the altitude of the aircraft can be displayed on the electronic flight instrument system EHSI, nd or weather radar display or screen of the aircraft. The terrain displayed on the display is dotted red, yellow and green spots, and the density of color spots increases with the height of the terrain. With reference to the figure below, a brief introduction is as follows:
Red light spot: indicates the terrain obviously higher than the flight altitude of the aircraft, and the terrain threat is 2000 feet (6 10/0m) higher than the current altitude of the aircraft;
Yellow (amber) light spot: indicates the terrain equivalent to the aircraft altitude, and there is a terrain conflict between the range of 2000 feet (6 10/0m) higher than the current altitude of the aircraft and the range of 500 feet (152m) lower than the current altitude;
Green light spot: indicates that the terrain height is lower than the flight height of the aircraft, and there is a terrain interval of 500 feet (152 meters) to 2,000 feet (6 10 meters) lower than the current altitude of the aircraft;
Magenta light spot: indicates the unrecognizable area in the terrain database.
In order to reduce the display confusion and avoid unnecessary interference, any terrain below the current altitude of the aircraft is not displayed, and only a black background is used instead.
How to issue a warning:
EGPWS can provide alarm level or warning level information to the unit. When the EGPWS alert or warning is started due to the current flight conditions, the topographic map will be automatically displayed on the flight instrument, regardless of whether the crew selects it or not.
Because of the use of terrain database, EGPWS can send out early warning signals earlier than GPWS. In EGPWS, the computer keeps searching the database along the scheduled flight path of the aircraft, which can make the system have virtual forward-looking ability.
Early warning can be used for direct flight, level flight or maneuvering flight. If the plane is descending, the computer will search along the descending trajectory; If the plane is turning, search along the turning trajectory.
If EGPWS thinks that the flight path of the plane is too close to a certain terrain, it will send out an audio-visual early warning signal more than one minute in advance, and if the computer thinks that the time needs to be advanced, it will send out an early warning time.
As shown in the left figure, when the EGPWS system gives an alarm, it will be emphasized by a colored fixed square on the flight instrument, indicating the terrain that will cause danger, accompanied by the corresponding sound alarm.
The fixed red square indicates that the terrain is within the flight time range of 30 seconds, and the crew is required to immediately execute the maneuver procedure to avoid the terrain;
The fixed yellow square indicates that the terrain is within the flight time range of about 30 to 60 seconds, and the crew is required to check the flight trajectory immediately and correct it as needed, and execute the corresponding terrain maneuver program.
Installation of EGPWS on China Civil Aviation Aircraft
According to the requirements of the Civil Aviation Administration of China, from June 5438+1 October1day, 2005, all turbine-engine aircraft with the maximum authorized takeoff weight exceeding 15000 kg or with more than 30 passengers will be equipped with EGPWS system. It's going well so far.
As early as 1997, we began to pay attention to and track the international requirements for the near-earth early warning system, and have been paying attention to the progress of the TAWS system installation policy. At the same time, the main problems that originally restricted the application of the system in China have made breakthroughs in management and technology, such as the effectiveness of the database, the error elimination of the difference of the earth coordinate system, and the compensation for the insufficient coverage of terrestrial radio navigation. All these make it possible to install the system in China's fleet. From 1998 to 1999, the FAA of the United States began to solicit opinions on the installation policy and airworthiness requirements of TAWS system, and officially promulgated the installation policy of this system on 1999. At that time, we began to consider the relevant requirements of our country, conducted a general survey on the installation of more than 600 aircraft in our existing fleet, made a concrete investigation on the feasibility of installation, analyzed the policy requirements of FAA, JAA and ICAO, and considered it feasible and necessary to install this system in our country. In June 2002, the Airworthiness Department of CAAC held a seminar after formulating the draft policy to learn more and get feedback from airlines. In September 2002, the Civil Aviation Administration of China officially issued the TAWS installation policy. According to the document issued by the Civil Aviation Administration of China in September 2002, by the end of 2004, domestic airlines will install enhanced ground proximity warning systems on all passenger planes with more than 30 seats.