DEFINITION:
The
Traffic alert and Collision Avoidance System (or TCAS) is an aircraft collision
avoidance system designed to reduce the incidence of mid air collisions between
aircraft. It monitors the airspace around an aircraft for other aircraft
equipped with a corresponding active transponder, independent of air traffic
control, and warns pilots of the presence of other transponder-equipped
aircraft which may present a threat of mid-air collision.
WORKING:
The
heart of the TCAS system is the transponder. Aircraft with Mode C transponders will respond to interrogations with altitude information.Whereas an
aircraft with Mode S transponders will respond to interrogations with address information.If another
aircraft is within range, it will respond to the interrogation, the first
aircraft will measure the time difference to compute the range of the other
aircraft.Because TCAS operates
aircraft-to-aircraft, it is not dependent on ground stations.
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| WORKING OF TCAS |
TCAS BASICS:
TCAS monitors traffic and categorizes into 1 of 4 groups:
- Other/non- itruding
- Proximate
- TA (Intruding)
- RA (Threat)
OTHER/NON INTRUDING TRAFFIC:
Other traffic is any aircraft
- beyond 6 NM
and 1,200 feet
- displayed as an open diamond
PROXIMATE TRAFFIC:
- within both 6
NM and 1,200
- displayed as a filled diamond
TA (INTRUDING):
TA indicates that an aircraft
- is a potential threat
- most commonly displayed as a yellow circle.
RA (THREAT):
Resolution Advisory indicates that an aircraft
- Is a threat
- displayed as a red square
- accompanied by a recommended vertical maneuver
POSITION OF TCAS ANTENNAS:
TCAS consists of antennas on aircraft body, computer processor & TCAS display inside cockpit. These antennas continuously scan the airspace around an aircraft & transmit the signal. The aircraft that also equipped with TCAS in the surrounding area will reply the signal.
TCAS ON VSI(VERTICLE SPEED INDICATOR):
The red arc indicates the area to avoid, the pilot always
shoots for the green arc.
BLOCK DIAGRAM OF TCAS:
The following block diagram explains the function of TCAS system
TYPES OF TCAS:
There are three types of TCAS , which are mentioned as below;
a). TCAS-I
b). TCAS-II
c). TCAS-III
a).TCAS-I:
It is the first generation of collision avoidance technology. It is cheaper but less capable than the modern TCAS-II system .TCAS I is mandated on aircraft with 10 to 30 seats. They are able to monitor the traffic situation around a plane (to a range of about 40 miles) and provides information on the approximate bearing and altitude of other aircraft. It can also generate collision warnings in the form of a "Traffic Advisory" (TA). The TA warns the pilot that another aircraft is in near area by announcing "traffic, traffic".
b). TCAS-II:
This type of TCAS is used in the majority of commercial aviation aircraft .It is required in aircrafts with seats more than 30. It offers all the benefits of TCAS I, but will also offer the pilot direct, vocalized instructions to avoid danger, known as a "Resolution Advisory" (RA). The RA warns the pilot that another aircraft is in near area by announcing "descend, descend" or "climb, climb".
c). TCAS-III:
It was the "next generation" of collision avoidance technology Its purpose was to provide lateral guidance to the crew .It has been suppressed by ADS-B (Automatic Dependence Surveillance broadcast )
TCAS DEMONSTRATION:
In the video it is shown how the tcas works, it is shown that when two aircrafts are flying at same altitude and same line TCAS of the aircraft at back gives indication that there is an aircraft infront of it.Therefore an initiative has been taken of increasing the altitude by the aircraft at back to avoid mid-air-collision.
In the second video link mentioned below it is shown that when two aircrafts are flyng towards each other TCAS alerts the both pilots by giving red indications and both the pilots took decision of evasive maneuver as to avoid collision and to save important human lives.
BASIC DO’S AND DONT’S :
- 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 trained on TCAS operations.
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