Course 6 - Section 18 - Airborne Collision Avoidance Systems

Question 1

TCAS Overview

Answer 1

• The purpose of TCAS is to provide collision avoidance capabilities to pilots using airborne equipment
• TCAS equipment is carried entirely on board the aircraft and does not depend on any ground-based systems
• The ICAO uses the term Airborne Collision Avoidance System (ACAS). TCAS is used in North America

Question 2

TCAS Function By (Overview, list)

Answer 2

• Interrogating Transponders in the aircraft’s vicinity
• Receiving and analyzing replies
• Determining if any aircraft represent a potential collision hazard
• Providing advisory information to the flight crew

Question 3

The requirement to have TCAS

Answer 3

• The majority of commercial aircraft in Canada are required to have TCAS
• The requirement is based on how the aircraft is used, its weight category, and the class of airspace it will fly in
• There are currently no Canadian Aviation Regulations (CARs) requiring private operators to be equipped with TCAS

Question 4

What does TCAS stand for?

Answer 4

Traffic Alert and Collision Avoidance System

Question 5

The development of which technology marked a turning point for TCAS?

Answer 5

• Airborne transponders with altitude encoding
• Mode S transponders

Question 6

What are the types of TCAS? (List)

Answer 6

Type I
Type II

Question 7

The level of protection provided by TCAS depends on:

Answer 7

• The TCAS version the aircraft is carrying
• The type of transponder on board the aircraft
• TCAS OFFERS NO PROTECTION FROM INTRUDER AIRCRAFT NOT EQUIPPED WITH AN OPERABLE TRANSPONDER

Question 8

TCAS I

Answer 8

TCAS I includes a computer and a pilot display. It is capable of providing TAs to help the pilot visually acquire the intruder aircraft and avoid potential collision

TCAS I DOES NOT PROVIDE RAs

Question 9

TCAS II

Answer 9

TCAS II includes a computer, pilot display, and a Mode S transponder. It is capable of providing both TAs and RAs

Question 10

RAs Overview

Answer 10

Resolution Advisory

RAs include a means of avoiding the conflict vertically, by either increasing or maintaining existing vertical separation between aircraft

NOTE: There is currently no TCAS equipment capable of providing lateral RAs (by having aircraft turn left or right)

Question 11

TAs

Answer 11

Traffic Advisory

If the intruder aircraft has a Mode C or S transponder AND A COLLISION IS PREDICTED TO OCCUR WITHIN THE NEXT 20 to 48 SECONDS (depending on altitude), TCAS issues a TA in the cockpit

TRAFFIC, TRAFFIC

Question 12

TCAS II System Components (LIST)

Answer 12

• Transponder
• Computer
• Display
• Speaker

Question 13

Transponder (Overview)

Answer 13

A transponder is an aircraft receiver-transmitter that sends a coded signal to ground-based equipment and aircraft TCAS equipment

This allows pilots to view traffic on TCAS displays with varying levels of info depending on the mode of transponder

To receive a TA or an RA, both aircraft must be equipped with operating transponders

Question 14

Transponder Modes. List them and briefly describe each

Answer 14

Mode A - Squawk code only. Allows surveillance equipment, but not TCAS, to display a target (without altitude information)

Mode C - transmits the same information as Mode A, plus aircraft altitude, for display on both surveillance and TCAS equipment

Mode S - Mode S transmits the same information as Mode C, plus it permits data exchange between aircraft

Question 15

TCAS Computer

Answer 15

The TCAS computer unit performs airspace surveillance, threat detection and resolution. It also keeps track of its own (interrogation aircraft) position as well as that of the intruder aircraft

Question 16

TCAS Display

Answer 16

TCAS display components provide two primary pieces of information in the event of a conflict situation

TA Display
- Shows the position of the traffic relative to the TCAS aircraft to assist the pilot in visually acquiring the intruder aircraft. It may be a dedicated display or part of the weather radar display

RA Display
- Indicates whether the pilot should initiate a climb or a descent, as well as the vertical rate of climb or descent that must be achieved to increase separation from the threatening aircraft

Question 17

TCAS Speaker

Answer 17

When a TA is issued to the pilot the TCAS computer announces “TRAFFIC, TRAFFIC” to direct the pilot to look at the TA display

If the situation does not resolve itself, and the aircraft is equipped with TCAS II, the computer issues an RA and announces either:
“CLIMB, CLIMB, CLIMB” or
“DESCEND, DESCEND DESCEND”

When the conflict has been resolved (separation begins to increase), the TCAS computer announces
“CLEAR OF CONFLICT”

Question 18

TCAS algorithms classify intruders into one of four categories: (list and describe)

Answer 18

1. Intruder – aircraft that satisfy TCAS II traffic advisory detection criteria
2. Threat – intruder aircraft that satisfy the threat detection logic and thus require an RA
3. Proximate traffic – aircraft that are within 6 nm in range and +/- 1200 feet vertically from interrogation aircraft, but do not meet the TCAS II thresholds of a TA or RA
4. Other traffic – aircraft more than +/- 1200 feet vertically or 6 nm from interrogation aircraft that are neither RA nor TA

Question 19

Threat Detection: Time Criterion

Answer 19

TCAS considers the green area to be a safe zone as sufficient space exists

TCAS provides a TA if an aircraft enters the yellow area as the system senses the intruder aircraft is within the safe zone

TCAS II provides an RA if an aircraft enters the pink area as the system senses the intruder aircraft is a threat

Time criterion refers to the rate of closure between the aircraft. In this example the rate of closure is 300 knots

Question 20

Threat Detection: Altitude Criterion

Answer 20

TCAS considers the green area to be a safe zone as sufficient space exists

TCAS provides a TA if an aircraft enters the yellow area as the system senses the intruder aircraft is within the safe zone

TCAS II provides an RA if an aircraft enters the pink area as the system senses the intruder aircraft is a threat

Question 21

Threat Display

Answer 21

If a threat is present and the intruder aircraft has a Mode C or S transponder, a display in the cockpit shows the aircraft’s range, bearing, and relative altitude, with an arrow indicating whether the intruder is climbing or descending

If the intruder is within certain lateral and vertical limits, the display shows an icon that alerts the flight crew that traffic near but is not yet a threat

Question 22

RAs

Answer 22

If the situation worsens, TCAS ISSUES AN RA 15 TO 35 SECONDS BEFORE A POTENTIAL COLLISION (DEPENDING ON ALTITUDE) ONLY IF THE INTRUDER AIRCRAFT HAS A MODE C OR MODE S TRANSPONDER

“CLIMB, CLIMB, CLIMB” or
“DESCEND, DESCEND, DESCEND”

Question 23

RA, Pilot actions, both aircraft equipped with TCAS II

Answer 23

When both the intruder and the interrogation aircraft are equipped with TCAS II, the two systems will coordinate with each other and select complementary RAs

This ensures that if one aircraft climbs, the other will descend

A pilot receiving an RA should disengage the autopilot and manually control the aircraft to achieve the recommended climb or descent rate

Question 24

TCAS Levels of protection
Intruder aircraft does not have a transponder

Answer 24

Intruder aircraft without transponders are invisible to TCAS-equipped aircraft, so TAs and RAs are not provided

Question 25

TCAS Levels of protection
Intruder aircraft has a Mode A transponder

Answer 25

Intruder aircraft equipped with only a Mode A transponder cannot be tracked or detected by TCAS II because TCAS II does not use Mode A interrogations. Mode A transponder aircraft are invisible to TCAS equipped aircraft

Question 26

TCAS Levels of protection
Intruder aircraft has a Mode C transponder but without altitude input

Answer 26

These will be tracked as a non-altitude replying target. Neither a data tag nor a trend arrow will be shown with the traffic symbol. These aircraft are deemed to be at the same altitude as the interrogation aircraft

Question 27

TCAS Levels of protection
encounter between two TCAS II-equipped aircraft

Answer 27

the two computers will communicate using the Mode S data link, which has the capability to provide complementary RAs

Question 28

CARs and pilot obligations

Answer 28

CARs require pilots to comply with all ATC instructions they receive, and all clearances they receive and accept.

CARs does permit pilots to deviate from an ATC instruction or clearance in order to follow TCAS RAs

CONTROLLERS ARE NOT RESPONSIBLE FOR PROVIDING SEPARATION BETWEEN THE AIRCRAFT RESPONDING TO AN RA AND ANY OTHER AIRCRAFT AFFECTED AS A DIRECT CONSEQUENCE OF THE MANOEUVRE INITIATED BY THE RA

Question 29

Responsibility for Separation

Answer 29

CONTROLLERS ARE NOT RESPONSIBLE FOR PROVIDING SEPARATION BETWEEN THE AIRCRAFT RESPONDING TO AN RA AND ANY OTHER AIRCRAFT AFFECTED AS A DIRECT CONSEQUENCE OF THE MANOEUVRE INITIATED BY THE RA

Aircraft that manoeuvre as a result of an RA and that may affect an ATC clearance will notify controllers when beginning the manoeuvre or as soon as workload permits

If an aircraft manoeuvres outside of the limits of its clearance, the controller is NOT RESPONSIBLE for separation between it an other aircraft. The controller is also not responsible for airspace protected for other aircraft, terrain or obstruction

When the RA has been resolved, the aircraft must advise ATC that they are returning to their previously assigned clearance or subsequently amended clearance

Question 30

Pilots responding to an RA must take two imporant actions:

Answer 30

1. As soon as possible after initiating the collision avoidance manoeuvre, they must inform the appropriate ATC unit of the deviation
2. Immediately after completing the collision avoidance manoeuvre, they must return to the last ATC clearance they had received and accepted, or comply with any new or revised clearances recieved upon reporting the conflict

Pilots may use the term “CLEAR OF CONFLICT” to advise ATC that the aircraft has completed its RA manoeuvre and has returned to its original clearance

Question 31

What steps must the controller take when an aircraft is performing a manoeuvre in response to TCAS? (List, with brief description)

Answer 31

Manual of Air traffic services (MATS) outlines the steps you must take:

• Provide Traffic Alerts

Do not attempt to modify the aircraft’s flight path until the pilot reports returning to the terms of the current ATC clearance or instruction

• Inform your supervisor
• Advise other aircraft

If an aircraft is responding to an RA, do not assume other aircraft in the vicinity are aware of the maneouvre unless you are advised by them that they are also responding to an RA
Continue to provide control instructions and traffic advisories as appropriate to other aircraft

• Resume responsibility when:

The aircraft informs you that:
- The manoeuvre is complete
- It has returned to its assigned altitude
- it is following an alternate clearance

You have verified that separation exists

Question 32

resume responsibility for separation after an aircraft has responded to an RA when:

Answer 32

The aircraft informs you that:
- The manoeuvre is complete
- It has returned to its assigned altitude
- it is following an alternate clearance

You have verified that separation exists

Question 33

TCAS Phraseology

Answer 33

Use conventional phraseology

“MONTREAL CENTRE, AIR CANADA THREE FOUR FIVE, TCAS CLIMB”
“MONTREAL CENTRE, AIR CANADA THREE FOUR FIVE, CLEAR OF CONFLICT, ONE ZERO THOUSAND RESUMED”

Question 34

TCAS Protection Overview
(My own summary - sanity checks)

Answer 34

• TCAS I cannot provide RAs, only TAs
• Only TCAS II can provide RAs, but the intruder aircraft must have a MODE C or MODE S transponder.
• If the target aircraft only has mode C, TCAS II on the interrogating aircraft will provide a RA, but it will be NON-COORDINATED
• If the target aircraft has TCAS II and Mode S, TCAS II on the interrogating aircraft will provide a COORDINATED RA