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TCAS Basics Capt Craig Hinkley
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TCAS 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 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 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 Basics
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TCAS Basics

• TCAS monitors traffic and categorizes into 1 of
  4 groups
• Other
• Proximate
• TA (Intruding)
• RA (Threat)

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Other Traffic

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

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Proximate 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 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 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 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 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 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 Areas

• Pilots Not Following RA

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Pilots 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 Areas

• Incorrect Reaction To
• Adjust Vertical Speed

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Adjust Vertical Speed

• Incorrect Reaction

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Adjust Vertical Speed

• Correct Reaction

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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 Areas

• Conflicting ATC - RA Instructions

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Conflicting 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 Instructions

• Following ATC Disregarding RA

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Conflicting ATC - RA Instructions

• Following ATC Disregarding RA

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Common Problem Areas

• Turns Based Off TCAS Display

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Turns Based Off TCAS Display

• Incorrect Turn

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Turns Based Off TCAS Display
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Turns Based Off TCAS Display

• Delayed Turn

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Turns Based Off TCAS Display
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Turns Based Off TCAS Display

• Actual Track Vs TCAS Track

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Common Problem Areas

• Level-Off With 1000 ft Separation

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Level-Off w/ 1000 ft Separation

• RA calculated based on vertical horizontal
  convergence

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Level-Off w/ 1000 ft Separation

• Excessive Climb Rate

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Level-Off w/ 1000 ft Separation

• Altitude Bust

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Level-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 Areas

• RA Against VRF Traffic

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RA against VRF traffic

• Poor Altitude Control

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RA against VRF traffic

• TA Vs RA w/ 500 ft Separation

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Common 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 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 Donts

• TCAS must be operated in RA mode to provide full
  safety benefit
• Pilots must follow all RAs promptly and
  accurately
• Pilots must never maneuver in the opposite sense
  of an RA
• Pilots must report RAs to controllers as soon as
  possible
• Controllers must not interfere with pilots
  reactions to RAs
• Vertical speed must be reduced in response to
  Adjust Vert Spd
• TCAS traffic displays must not be used for
  self-separation
• Vertical speed must be reduced when approaching
  cleared FL
• VFR pilots must operate their altitude reporting
  transponder
• Pilots and controllers must be recurrently
  trained on TCAS ops