1. Lecture 9: Traffic alert and Collision Avoidance System (TCAS)

2. Exercises
Explain how Traffic alert and Collision Avoidance System (TCAS) work?
Explain how Ground Proximity Warning System (GPWS) work?

3. Traffic alert and Collision Avoidance System (TCAS)
TCAS is a special system designed to reduce the incidence of mid-air collisions between aircraft. 3

4. Mid-Air Collision

5. Worst Mid-Air Collision in History Saudi Arabian Airlines VS Kazakhstan Airlines
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

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not have secondary surveillance radar, which produces exact readings of aircraft altitudes; instead the airport had outdated primary radar, which produced approximate readings.

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. 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.

9. TYPICAL TCAS DISPLAY 9

10. TCAS Display
In modern glass cockpit aircraft, the TCAS display may be integrated in the Multifunction Display (MFD)

12. 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. 12

13. 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. 13

15. 15

16. 16

18. CAUTIONS
TCAS is designed as a tool to improve situational awareness and as a last resort measure to avoid mid-air collision when other safety precautions fail.
An intimate understanding of each specific system is required in order to accurately interpret the displayed information.
The visual information displayed to the pilot is limited and can be misleading, caution is advised.

19. Ground Proximity Warning System (GPWS)

20. Ground Proximity Warning System (GPWS)
Since 1960s, a series of Controlled Flight Into Terrain (CFIT) accidents killed hundreds of people.
Thus, a device called a ground proximity warning system (GPWS) had been used to overcome CFIT problem.

21. Controlled Flight Into Terrain
CFIT describes about aircraft collision, under pilot control, inadvertently flies into terrain, an obstacle, or water.
The pilots are generally unaware of the danger until it is too late.
Controlled flight into terrain.
Prior to the widespread implementation of GPWS, CFIT was an all too common occurrence.
CFIT accidents involve a normally operating aircraft which contacts the ground due to loss of situational awareness, or other pilot error.
GPWS has greatly reduced the number of these incidents. 21

22. Korean Airlines Boeing 747: CFIT while attempting to land in heavy rain: 228 of 254 killed (Aug. 6, 1997)

23. Ground Proximity Warning System (GPWS)
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.
GPWS has greatly reduced the number of CFIT incidents.

24. HOW GPWS WORKS
The heart of the GPWS is a computer processor which interprets data from a number of sources such as radar, gear and flap indicating system & roll attitude input sensor.
The computer analyzes a number of parameters including aircraft configuration, speed, proximity to terrain, and descent rate in order to issue appropriate warnings.
The pilots are alerted through aural & visual warnings by GPWS display inside cockpit.

25. Aural & Visual Warning
Aural & Visual Warnings are provided under any of the following conditions:
Excessive rate of descend
when closure rate with terrain is too high.
loss of altitude after take-off
if the aircraft is too low and slow, with landing gear retracted.

26. AURAL WARNINGS Some typical GPWS warnings are: “DESCENT,DESCENT”
“CLIMB, CLIMB”
“SINK RATE”
“TERRAIN, TERRAIN”
“DON’T SINK”
“TOO LOW, TERRAIN”
“TOO LOW GEAR”
“PULL UP”
These aural warnings will be accompanied by illumination of a GPWS display.

28. MODE 1 Warns of excessive descent rate..
A GPWS warning light will illuminate and “sink rate, sink rate” will be heard.
If the situation is not corrected “whoop, whoop, pull up, pull up” will be heard.

29. MODE 2 Warns crew when closure rate with terrain is too high.
Designed to warn crew when rising terrain is a threat.
“terrain, terrain”
“whoop, whoop, pull up, pull up”
There may be no change in barometric altitude but the radar altitude is decreasing.

30. MODE 3 Warns of loss of altitude after take-off, or go-around.
If the aircraft sinks 10 percent of its radar altitude “don’t sink” will be heard.

31. MODE 4
MODE 4a: if the aircraft is too low and slow, with landing gear retracted.
“too low, gear”
If the airspeed is higher the warning will be “too low, terrain”
MODE 4b: When the gear is selected down, but the flaps are still retracted “too low, flaps”
This warning can be canceled by the pilot in the event of a flapless landing.

32. MODE 5 Warns the crew of glideslope deviations.
When the aircraft receives a valid glideslope and sinks two dots below “glideslope” will be heard.
The warning will continue with increasing intensity if the problem is not corrected.
This warning may be canceled by the pilot.

33. RECOVERY PROCEDURE
Recovery procedure will vary depending on the type of aircraft, but the general response is:
Roll level and simultaneously set maximum power.
Slowly pitch up and maintain Vx.
Retract gear and flaps.
Continue climb until clear of terrain.
NOTE: in VMC conditions terrain may be avoided visually.

34. ADVISORY CALLOUTS
GPWS is capable of advisory callouts as an aid to normal operations:
“GLIDESLOPE” two dots below glideslope
“FIVE HUNDRED” 500 AGL on non-precision approach
“MINIMUMS, MINIMUMS” upon reaching radar altimeter selected decision height.

35. Enhanced Ground Proximity Warning System
A limitation of GPWS is the fact that with radar altimeter information only the aircraft is only capable of seeing terrain directly below.
In the case of rapidly rising terrain it may not react quick enough to issue a warning in time.

36. Enhanced Ground Proximity Warning System
EGPWS corrects this problem by integrating an aircraft navigational source into the system.
GPS position in conjunction with a terrain database is used to help predict terrain conflict.
Any catalogued man made obstructions are included in the database.
This type of system can be used to display terrain profile to the pilot to improve situational awareness.