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Traffic Alert and Collision Avoidance System

Presentation By:-Arvind Kumar Singh

Traffic Alret and Collision Avoidance System

HistoryCAS is known as TCAS and internationally as ACAS

(Airborne Collision Avoidance System)Series of midair collisions led to airline and governmental

action to develop airborne devices that function independent of air traffic control (ATC) for alerting and collision avoidance

Early attempts (late 50s-60s) for reliable systems proved to be impractical

Mid 70s Beacon Collision Avoidance System (BCAS) became the basis for TCAS interrogation and tracking capabilities

Aircraft must have operating transponder for TCAS to provide collision avoidance protection

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Major Midair Accidents

1956 Grand Canyon, AZ — United DC-7 / TWA L-1049 (128 fatalities)

1960 New York, NY — United DC-8 / TWA L-1049 (134 fatalities)

1978 San Diego, CA — PSA B-727 / Cessna 172 (144 fatalities)

1986 Cerritos, CA — Aeromexico DC-9 / Piper PA-28 (82 fatalities)

1996 Charkhi Dadri, India — Saudi B-747 / Kazakhstan IL-76 (349 fatalities)

1997 Namibia (off-coast) — USAF C-141 / German AF Tu-154 (33 fatalities)

2002 Überlingen, Germany — Bashkirian Tu-154 / DHL B-757 (71 fatalities)

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TCAS• An airborne system that interrogates transponders in

other aircraft.(Independently of Ground based equipment)

• From the replies received, the system analyzes the intruding

Aircraft’s altitude (if altitude reporting), Closure rate, Projected flight path to predict a penetration

• Displays the other aircraft visually To alert any potential threats of airspace conflict.Report a resolution advisory (RA) only if the other transponder is transmitting an altitude.

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Terminology• Closest Point of Approach (CPA):Predicted point in space at which the intruder will be closest to

aircraft.

• IntruderAn SSR transponder equipped aircraft within the surveillance range.Recognizes as a potential threat

• Traffic AdvisoryIndication given to the flight crew that a intruder is a potential threat

and entering protected airspace20-48 seconds from CPA

• Resolution AdvisoryManeuver intended to provide separation from all threatsManeuver restriction intended to maintain existing separation15-35 seconds from CPA05/01/2023 5Traffic Alret and Collision Avoidance System

TCAS – System Description TCAS uses on-board surveillance to

detect transponder-equipped traffic and provides:

Traffic Display and Traffic Alerts (TA) for situational awareness of close aircraft

Resolution Advisories (RA) with vertical guidance

Alerts are based on both projected: Time to Closest Point of Approach (CPA) Miss distance less than

600 to 800’ depending on altitude (vertical miss distance)

0.2 to 1.1 NM depending on altitude (horizontal miss distance)

RAs are selected to achieve or maintain adequate vertical distance (300 – 700’) and minimize pilot response/vertical deviations

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Standardized Symbology for Traffic Display

Own-aircraft. Airplane-like symbol, in white or cyan.

Other Traffic, altitude unknown. Unfilled diamond in white or cyan

Proximate Traffic, 1100 feet above and descending. Filled diamond in white or cyan

Traffic Advisory (TA), 900 feet below and level. Filled yellow/amber circle.

Resolution Advisory (RA), 500 feet below and climbing. Filled red square.

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Functions of TCAS II•SurveillanceInterrogations at 1030 MHz and respond at 1090 Mhz.Reliable surveillance to a range of 14 NM and in traffic densities of up to 0.3 aircraft per square NM.

•Generation of TA

•Threat Detection

•Generation of RAs

•Coordination

•Communication with Ground Stations

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Salient Features of TCASCollision Avoidance SystemPredicts time to and separation at the intruders CPA using Range Closer rate Altitude and vertical speed

Issue TAIf further close, will issue RA ( Five second crew reaction

time to achieve separation)Display different traffic symbols , changes colour and shape

depends upon urgencyCan track 45 aircraft and display 30 of them21 aircraft in a 5 NM radius, can provide advisory

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Alerting Threshold Values

TCAS alerts based on time to closest approach and time to being co-altitude (tau)

All RAs are inhibited below 1,000’ AGL Fixed distance alerting thresholds are also used in some situations

Many parallel runway operations 500’ IFR/VFR separation when both aircraft are level

TCAS does not consider IFR/VFR status or pilot intentions

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Transition from Passive to Active Surveillance

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TCAS Protection Volume

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CAS Logic Functions

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Ground Estimation Logic

• Aircraft is below 1750 ft AGL.

• Ground level estimate is

subtracted from the pressure

altitude received from each Mode

C equipped aircraft.

to determine each aircraft above

the ground.

• If this difference is less than 360

feet, TCAS considers the

reporting aircraft to be on the

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Resolution Advisory

RA Sense Selection

Selection of Non-crossing RA Sense

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Increase Rate RA

Resolution Advisory

RA Reversal

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Concept of Operation• TCAS creates a “bubble” of protected airspace around aircraft.

• TCAS begins to “track” other transponder equipped aircraft.

• At approx 40 NM out other transponder equipped aircraft can be displayed on the active PFD/MFD (or depends upon range).

• At 30 approx NM a data-link is established with other Mode S transponders to begin conflict resolution planning.

• At 20 to 48 seconds prior to CPA a TA is issued.

• AT 15 to 35 seconds from CPA an RA is generated.

• If the RA is ignored, the crew response is too slow, or the conflict traffic alters its course a corrective RA is issued.

• When the traffic is no longer a threat TCAS announces “CLEAR OF CONFLICT”.

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Operational Concept

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Carriage of Airborne Collision Avoidance System(GEN-1.5)

Unless otherwise authorized by DGCA , no person shall operate in the Indian airspace , an aeroplane having a maximum certified passenger seating configuration of more then 30 or maximum payload capacity of more then 3 tonne.

After 31st December 1998, if it is not equipped with an approved TCAS II and

After 1st Jan 2003, if it is not equipped with an approved TCAS II with change 7 (equivalent to ACAS`)

After 1st Jan. 2002 for the purpose of registration and operation within, to and from India shall be fitted with TCAS II with change 7

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Operational Circular 4 of 2002

All crew must reduce the aircraft rate of climb or

descent as applicable

500 ft per minute or less when the airplane is 2000 ft

to level off altitude.

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Controller’s Responsibilities • If an aircraft responding to a TCAS RA

Do not issue control instructions that are contrary to the RA,

which crew are executing.

Provide safety alerts regarding terrain or obstructions and traffic

advisories

• Unless advised by other aircraft to responding to a TCAS RA,

Do not assume that the other aircraft in proximity involved in the RA

Continue to provide control instructions, safety alerts, and traffic

advisories as appropriate to such aircraft.

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Controller’s Responsibilities • Issue traffic advisories

• Except more RAs, when working aircraft that climb descend quickly.

• Controller is not responsible for providing standard separation

between the aircraft that is responding to an RA and any other

aircraft, airspace, terrain, or obstructions.

• Responsibility for standard separation resumes when-

The responding aircraft has returned to its assigned altitude.

The flight crew informs that the TCAS maneuver is completed and

standard separation has been established.

The responding aircraft has executed an alternate clearance and

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PhraseologiesCircumstances PhraseologiesAfter a flight crew starts to deviate from any ATC clearance or instruction to comply with an ACAS resolution advisory (RA)

* TCAS RA; ROGER;

After the response to an ACAS RA is completed and a return to the ATC clearance or instruction is Initiated

*CLEAR OF CONFLICT, RETURNING TO (assignedclearance);ROGER (or alternative instructions);

After the response to an ACAS RA is completed and the assigned ATC clearance or instruction has been resumed

* CLEAR OF CONFLICT (assigned clearance) RESUMED;ROGER (or alternative instructions);

After an ATC clearance or instruction contradictory to the ACAS RA is received, the flight crew will follow the RA and inform ATC directly

* UNABLE, TCAS RA; ROGER;

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Thank You for your patience