1. Lecture 10: Traffic alert and Collision Avoidance System (TCAS)

2. Learning Outcomes
At the end of this lecture, the student should be able to:
Describe the theory of early warning system including TCAS & GPWS

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

4. 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
TCAS is a special system designed to reduce the incidence of mid-air collisions between aircraft.

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not have secondary surveillance radar, which produces exact readings of aircraft altitudes; instead the airport had outdated primary radar, which produced approximate readings.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

6. 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.

7. 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
The Traffic alert and Collision Avoidance System (or TCAS) is an aircraft collision avoidance system designed to reduce the incidence of mid-air collisions between aircraft. It monitors the airspace around an aircraft for other aircraft equipped with a corresponding active transponder, independent of air traffic control, and warns pilots of the presence of other transponder-equipped aircraft which may present a threat of mid-air collision (MAC). It is an implementation of the Airborne Collision Avoidance System mandated by International Civil Aviation Organization to be fitted to all aircraft with MTOM (maximum take-off mass) over 5700 kg (12,586 lbs) or authorized to carry more than 19 passengers.
Official definition from PANS-ATM (Nov 2007): ACAS / TCAS is an aircraft system based on secondary surveillance radar (SSR) transponder signals which operates independently of ground-based equipment to provide advice to the pilot on potential conflicting aircraft that are equipped with SSR transponders.
In modern glass cockpit aircraft, the TCAS display may be integrated in the Navigation Display (ND); in older glass cockpit aircraft and those with mechanical instrumentation, such an integrated TCAS display may replace the mechanical Vertical Speed Indicator (which indicates the rate with which the aircraft is descending or climbing). 7

8. 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.
Does not warn of loss of separation
􀁺Sometime generate unnecessary (nuisance) alerts
􀁺Sense of RAs coordinated between ACAS equipped aircraft
􀁺Complying with RAs can result in deviation from clearance

9. HOW TCAS WORKS

10. 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. 10

11. 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. 11

13. 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

14. TYPICAL TCAS DISPLAY

15. TCAS Display
In modern glass cockpit aircraft, the TCAS display may be integrated in the Navigation Display

16. 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

17. 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.