Lecture 10: Traffic alert

and Collision Avoidance System (TCAS)

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Learning Outcomes

• At the end of this lecture, the student should be able to:– Describe the theory of early warning system

including TCAS & GPWS

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Mid-Air Collision

A mid-air collision is an aviation accident in which two or more aircraft come into contact during flight.

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CASE 1: Saudi Arabian Airlines VS Kazakhstan Airlines

• Worst Mid-Air Collision in History

• Mid-air collision occurred on 12 November 1996

• Saudi Arabian Airlines (Boeing 747)from New Delhi, India, to Dhahran, Saudi Arabia.

• Kazakhstan Airlines (Ilyushin Il-76) from Kazakhstan to New Delhi

• Both aircrafts collided at India airspace.

• All 349 people on board both flights were killed, making it the WORST mid-air collision in history

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Causes of Accident

The causes of accident are:

• Failure of the Kazakh pilot to follow ATC instructions.– Commanded by ATC to descend at altitude 15’000ft, but he

descend to altitude 14’500ft.

• Lack of English Language Skills of Kazakh pilot.

• Indira Gandhi International Airport did not have secondary surveillance radar, which produces exact readings of aircraft altitudes; instead the airport had outdated primary radar, which produced approximate readings.

• No TCAS

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Case 2: Bashkirian Airlines collided with DHL

• Bashkirian Airlines (Tupolev Tu-154M) passenger jet en route from Moscow to Barcelona.

• DHL Flight 611 (Boeing 757) cargo jet flying from Bergamo, Italy, to Brussels, Belgium.

• The two aircraft collided in mid-air on 1 July 2002, in Germany airspace killing all 71 aboard both aircraft.

• The Investigation found that the accident had been caused by problems within the air traffic control system and problems with the use of the Traffic alert and Collision Avoidance System (TCAS).

• On 24 February 2004, the ATC who was on duty at the time, was stabbed to death by a man who had lost his wife and two children in the accident.

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Traffic alert and Collision Avoidance System (TCAS)

• TCAS is a special system designed to reduce the incidence of mid-air collisions between aircraft.

• It is also known as ACAS (Airborne Collision Avoidance System)

• TCAS system capable of displaying conflicting traffic and providing resolution advice.

• According to ICAO, TCAS is mandatory for all aircraft with MTOM (maximum take-off mass) over 5700 kg or carry more than 19 passengers

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Traffic alert and Collision Avoidance System (TCAS)

• TCAS monitors the airspace around an aircraft for other aircraft equipped (independent of ATC)

• TCAS warns pilots of the presence of other aircraft (transponder-equipped) which may present a threat of mid-air collision (MAC).

• Intended as a last resort protection against risk of collision.

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HOW TCAS WORKS

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HOW TCAS WORKS

• TCAS works as a back up to the ATC system and the ‘see & avoid’ system.

• TCAS consists of antennas on aircraft body, computer processor & TCAS display inside cockpit.

• TCAS antenna continually surveys the airspace around an aircraft & transmit the signal.

• Other aircraft that also equipped with TCAS in the surrounding area will reply the signal.

• TCAS continuously calculates tracked aircraft position, therefore TCAS display constantly updated and provide real time position information.

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HOW TCAS WORKS

• Targets are displayed on the TCAS screen as different symbols which show level of threat.

• Aircraft relative altitude also will be displayed.– Relative altitude is the targets altitude in

relation to the aircraft. EX: -03↑ depicts a target 300 feet below and climbing.

• TCAS can not display aircraft without TCAS antenna/transponders.

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TCAS

• Determination of the alerts: TA & RA• Traffic Advisory (TA)- help the pilots in the

visual search for the intruder aircraft, and alert them to be ready for a potential resolution advisory. EX: TA “Traffic, Traffic”

• Resolution Advisory (RA)- avoidance maneuvers recommended to the pilot. RA “Climb, Climb”

• Range = 14 NM

• Maximum number of aircraft processed = 30

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TYPICAL TCAS DISPLAY

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TCAS DisplayIn modern glass cockpit aircraft, the TCAS display may be integrated in the Navigation

Display

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TCAS Advantages

• Highly accurate distance measurements, with a one-second refresh rate.

• All threats taken into account

• Detection of all transponding aircraft, including those which are not displayed on the air traffic controller’s screen

• Independent system, which acts as a last resort measure to avoid mid-air collision when other safety precautions fail.

• TCAS reduced the risk of mid-air collision

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TCAS Limitations

• No detection of aircraft without or not operating transponders (e.g. VFRs, military flights)

• No knowledge of the pilot’s intentions and of the ATC separation minima

• Basic display: no identification, no past positions, no speed vector

• Sometime generate unnecessary alerts.