23. EU ATM - ACAS / TCAS

Question 1

What is TCAS? (2)

Answer 1

TCAS - Traffic & Collision Avoidance System

• Gives Traffic Information about other ‘cooperating’ aircraft which are displayed as various symbols in various colours
• Will tell you how to get out of the way - as long as the other aircraft is ‘cooperating’
• Uses range & Altitude data from transponders to determine possibility of collision
• Presents bearing information of aircraft intruding into your airspace (uses this information on the display only to assist in visual acquisition of an intruder
• When range and altitude of an intruder are computed and a collision risk is predicted, TCAS II will declare the intruder a “threat” and give manoeuvre advice in visual and aural form

Question 2

Transponder types working with TCAS (3)

Answer 2

Mode A/C transponders:
- Give both Traffic Advisory and Resolution Advisory
(only if Mode C available but any manoeuvre may not be in the logical sense)

Mode S transponders:
- ‘communicate’ with each other and ‘agree’ a course of action

No transponder:
- No TCAS alert

Question 3

How does the TCAS system operate? (2)

Answer 3

• A protected volume of airspace surrounds each ACAS II equipped aircraft
• Size of the protected volume depends on the altitude, speed, and heading of the aircraft involved in the encounter

Question 4

What target symbols are displayed on TCAS? (4)

Answer 4

• Hollow cyan (light blue) or white diamond – for other traffic
• Solid cyan (light blue) or white diamond – for proximate traffic
• Solid yellow or amber circle – for intruders (i.e. aircraft which trigger a TA)
• Solid red square – for threats (i.e. aircraft which trigger an RA)

Question 5

When does traffic class as Traffic Advisory (TA)? (3)

Answer 5

• Traffic assumes “threat” status
• 20 – 48 secs before Closest Point of Approach (CPA)
• “Traffic Traffic”

Question 6

When does traffic class as Resolution Advisory (RA)? (3)

Answer 6

• Starts the conflict resolution process 15 to 35 secs before Closest Point of Approach (CPA)
• “Climb, Climb Now”

Question 7

What limitations does TCAS have? (5)

Answer 7

1. Enhanced RA - <1450ft AGL - “Increase Descent”
2. Descend RA <1100ft AGL
3. All RAs - <1000ft AGL
4. All spoken messages - <500ft AGL
5. RAs some terrain avoidance systems or windshear warnings are active

Question 8

What are the actions required from ATC when a RA is notified? (3)

Answer 8

• Do Not Issue Instructions to the Aircraft
• Cease provision of standard separation from affected traffic
• Should not routinely pass traffic information to aircraft conducting RA manoeuvres, or other aircraft affected by such manoeuvres

Question 9

What other systems may be available to the GA community? (2)

Answer 9

• TAS
• FLARM

**THEY DO NOT PROVIDE COLISION AVOIDANCE **

Question 10

What is an Airprox? (1)

Answer 10

A situation in which, in the opinion of the pilot or air traffic services personnel, the distance between aircraft as well as their relative positions and speed have been such that the safety of the aircraft involved may have been compromised

Question 11

What is TAWS? (4)

Answer 11

TAWS - Terrain Awareness and Warning System

• Uses position / terrain database and radar altimeter to generate wide range of alerts and warnings to flight crew
• Uses “Soft” or “Hard” alerts
• Can give Terrain warnings visually (See diagram)