TCAS BasicsCapt Craig Hinkley

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TCAS HISTORYTCAS HISTORY

1956 - Two planes collided over the Grand Canyon 1974 - Alternative airborne version using transponders

Beacon-Based Collision Avoidance System (BCAS) 1981 - The FAA chose to pursue the onboard design

BCAS was renamed TCAS 1986 - While TCAS still in development, collision occurred 1993 - Congress mandate all carrier acft operating w/in US 1997 - Final major change to the TCAS logic, version 7

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TCAS BasicsTCAS Basics

TCAS I - Aircraft with 10 to 30 seats Traffic Advisory Only

TCAS II - Aircraft with more than 30 passenger Traffic Advisory Resolution Advisory

Mode S – Detailed flight parameter information ATC Ground Based Radars Other Mode S equipped aircraft

Provides coordinated RAs

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TCAS BasicsTCAS Basics

TCAS II is designed to provide collision avoidance horizontally at any rate up to 1200 knots vertically up to 10,000 feet per minute (fpm)

TCAS II computes closure rates using relative bearing, distance and speed to estimated time to conflict and calculate Resolution Advisories

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TCAS BasicsTCAS Basics

Conflicting Aircraft Equipment TCAS II Response

No transponder No TCAS indications

Transponder w/out Alt TA Only

Transponder w/ Alt TA/RA

Transponder w/ Mode S Coordinated RA

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1

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3

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TCAS BasicsTCAS Basics

TCAS monitors traffic and categorizes into 1 of 4 groups:

Other Proximate TA (Intruding) RA (Threat)

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Other TrafficOther Traffic

Other traffic is any aircraft beyond 6 NM and 1,200 feet displayed as an open diamond

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Proximate TrafficProximate Traffic

Proximate traffic is an aircraft that is within both 6 NM and 1,200 displayed as a filled diamond

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Traffic AdvisoryTraffic Advisory

A TA indicates that an aircraft is a potential threat RA may be necessary w/in, approx, the next 25 sec most commonly displayed as a yellow circle

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Resolution AdvisoryResolution Advisory

An RA indicates that an aircraft Is a threat displayed as a red square accompanied by a recommended vertical maneuver.

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TCAS BASICSTCAS BASICS

When an RA occurs, the pilot has 5 seconds to assess the situation and maneuver the aircraft to the green or recommended area on the display.

If the TCAS displays an increase rate or reversal RA, the pilot should comply within 2.5 seconds utilizing 1/3 g Acceleration.

RAs requiring altitude excursion rarely exceed 300-500 ft. Except between “slow” and “fast” movers

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AFI 11-202 Vol 3AFI 11-202 Vol 3

5.29.1. Response to TCAS Alerts.

5.29.1.5. If a TCAS RA requires maneuvering contrary to ATC instructions, right-of-way rules, cloud clearance requirements, or other VFR/IFR flight rules, pilots are expected to follow the TCAS RA.

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Common Problem AreasCommon Problem Areas

Pilots not following RA Incorrect reaction to “Adjust Vertical Speed” Conflicting ATC - RA instructions Turns based off TCAS display Level-off with 1000 ft separation RA against VRF traffic

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Common Problem AreasCommon Problem Areas

Pilots Not Following RA

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Pilots Not Following RAPilots Not Following RA

It is important pilots follow all RAs even when there is:

An opposite avoiding instruction by the controller Conflict close to the top of the operating envelope Traffic information from the controller Visual acquisition

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Common Problem AreasCommon Problem Areas

Incorrect Reaction To

“Adjust Vertical Speed”

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““Adjust Vertical Speed”Adjust Vertical Speed”

Incorrect Reaction

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““Adjust Vertical Speed”Adjust Vertical Speed”

Correct Reaction

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““Adjust Vertical Speed”Adjust Vertical Speed”

Two factors contributing to the misinterpretation of “Adjust Vertical Speed” RAs have been identified:

The aural message "Adjust Vertical Speed, Adjust" does not specify the sense of the required maneuver

The RA display on the vertical speed tape and on the semi-circular VSI on the PFD may sometimes be difficult to interpret

"Adjust Vertical Speed" RA always requires a REDUCTION of the vertical speed.

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Common Problem AreasCommon Problem Areas

Conflicting ATC - RA Instructions

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Conflicting ATC - RA InstructionsConflicting ATC - RA Instructions

ATC Detect the conflict (possible delays) Asses the situation Formulate a solution Communicate to the pilot (possible delays)

TCAS Automatically detects any risk of collision Calculates the necessary maneuver Communicates the solution directly to the flight crew.

All in less than one second.

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Conflicting ATC - RA InstructionsConflicting ATC - RA Instructions

Following ATC – Disregarding RA

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Conflicting ATC - RA InstructionsConflicting ATC - RA Instructions

Following ATC – Disregarding RA

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Common Problem AreasCommon Problem Areas

Turns Based Off TCAS Display

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Turns Based Off TCAS DisplayTurns Based Off TCAS Display

Incorrect Turn

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Turns Based Off TCAS DisplayTurns Based Off TCAS Display

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Turns Based Off TCAS DisplayTurns Based Off TCAS Display

Delayed Turn

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Turns Based Off TCAS DisplayTurns Based Off TCAS Display

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Turns Based Off TCAS DisplayTurns Based Off TCAS Display

Actual Track Vs TCAS Track

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Common Problem AreasCommon Problem Areas

Level-Off With 1000 ft Separation

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Level-Off w/ 1000 ft SeparationLevel-Off w/ 1000 ft Separation

RA calculated based on vertical + horizontal convergence

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Level-Off w/ 1000 ft SeparationLevel-Off w/ 1000 ft Separation

Excessive Climb Rate

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Level-Off w/ 1000 ft SeparationLevel-Off w/ 1000 ft Separation

Altitude Bust

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Level-Off w/ 1000 ft SeparationLevel-Off w/ 1000 ft Separation

• Recommendation to prevent 1000 ft RA

“Vertical rate should be reduced to less than 1000 fpm in the last 1000 ft before reaching the cleared flight level. This will reduce the number of RAs generated in such geometries.”

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Common Problem AreasCommon Problem Areas

RA Against VRF Traffic

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RA against VRF trafficRA against VRF traffic

Poor Altitude Control

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RA against VRF trafficRA against VRF traffic

TA Vs RA w/ 500 ft Separation

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Common Problem AreasCommon Problem Areas

Pilots not following RA Incorrect reaction to “Adjust Vertical Speed” Conflicting ATC - RA instructions Turns based off TCAS display Level-off with 1000 ft separation RA against VRF traffic

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Review of RA ReactionReview of RA Reaction

5 seconds to recognize and maneuver 2.5 seconds to respond to an increase or reversal Required altitude excursion rarely exceeds 300-500 feet Report to ATC as soon as practical

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Ten Fundamental Dos and Don’tsTen Fundamental Dos and Don’ts

1. TCAS must be operated in RA mode to provide full safety benefit

2. Pilots must follow all RAs promptly and accurately

3. Pilots must never maneuver in the opposite sense of an RA

4. Pilots must report RAs to controllers as soon as possible

5. Controllers must not interfere with pilots’ reactions to RAs

6. Vertical speed must be reduced in response to “Adjust Vert Spd”

7. TCAS traffic displays must not be used for self-separation

8. Vertical speed must be reduced when approaching cleared FL

9. VFR pilots must operate their altitude reporting transponder

10. Pilots and controllers must be recurrently trained on TCAS ops