Many might not be aware of what TCAS in aviation refers to… it might just be one of the most important technological advances within an aircraft…
TRAFFIC! TRAFFIC!
The International Civil Aviation Organization prescribes that an Airborne Collision Avoidance System (ACAS) must be installed and operational for all aircraft heavier than 5700 Kg and all aircraft authorized to transport more than 19 passengers.
ACAS II is an aircraft system based on Secondary Surveillance Radar (SSR) transponder signals. ACAS II interrogates the Mode C and Mode S transponders of nearby aircraft (or intruder aircraft) and from the replies tracks their altitude and range and issues alert to the pilot.
ACAS II works independently of the aircraft navigation, flight management systems, and Air Traffic Control (ATC) ground systems. Aircraft that do not have an altitude reporting transponder fitted are not detected.
Currently, the only commercially available implementations of the ICAO standard for ACAS II (Airborne Collision Avoidance System) are TCAS II versions 7.0 and version 7.1 Traffic Alert and Collision Avoidance System (TCAS) to prevent a midair collision.
TCAS originated in the early 1970s and has been instrumental in saving many lives since its inception. It is estimated that over 1 million lives have been saved since it was first introduced. In addition, TCAS has reduced air traffic delays caused by potential collisions by 25% per year for nearly 30 years.
Today, TCAS is installed on all new commercial aircraft, ensuring the safety of passengers, flight crew, and pilots on board. These systems are also becoming increasingly popular in General Aviation and are offered as optional safety equipment by many manufacturers.
The purpose of this system is to warn the pilot about other traffic that is on a conflicting (collision) course with their aircraft and when necessary, to provide enhanced situational awareness and guidance for resolving these conflicts, in the form of a Resolution Advisory based on collision avoidance technology.
Other types of safety systems commonly found on aircraft include the Traffic Alerting System (TAS) which warns pilots when another aircraft is nearby, Ground Proximity Warning System (GPWS), and Terrain Awareness and Warning System (TAWS) which alert the pilot when the aircraft may be too close to the ground to avoid a Controlled Flight Into Terrain (CFIT) accident.
How does TCAS work?
Every pilot should maintain an awareness of other aircraft positions and not fly into potential conflict zones. However, there is no guarantee that all pilots can see all other aircraft or hear each other’s transmissions and therefore a wrong decision by one pilot could result in a situation where several aircraft could be involved in a potential collision.
In controlled airspace, Air Traffic Control (ATC) has the primary responsibility to monitor and de-conflict both civilian and military traffic for safe flight through the use of air traffic control radar.
However, as ATC can be adversely affected by human factors a secondary, autonomous system provides a second layer of safety. That system is TCAS.
TCAS involves communication between all aircraft equipped with an appropriate Transponder which provides the pilot with a collision threat message. TCAS issues accurate positional information on altitude difference and range for intruder aircraft to the pilot. The use of altitude reporting transponders has been legally mandated for many years to be able to fly in controlled airspace.
Each TCAS-equipped aircraft interrogates all other aircraft to ascertain their position. This interrogation/response cycle occurs several times per second.
TCAS II
TCAS II equipment provides two types of advisories to pilots: Traffic Advisories (TAs) and Resolution Advisories (RAs).
TCAS II provides a more advanced response to avoid collisions with intruder aircraft. This takes the form of information to help the pilot analyze the risk of a potential threat, the Traffic Advisory message (TA) on the traffic display, and presents a solution through the concept known as a Resolution Advisory (RA) by commanding the pilot to change his course, or descent rate or climb rate. Changing the aircraft’s vertical rate is the best way to reduce the risk of collision.
To do this TCAS II monitors the airspace around the aircraft and communicates with all traffic equipped with a corresponding active transponder. It queries all surrounding aircraft on the frequency 1030 MHz and each aircraft transponder replies on the frequency 1090MHz. It then warns pilots of the presence of other transponder-equipped aircraft which may present a threat of mid-air collision (MAC)
If the problem cannot be solved simply by changing direction or altitude, it advises the pilot to take evasive action such as turning away from the approaching aircraft or increasing vertical speed.
Common questions about TCAS in aviation:
1. What’s the difference between TCAS and ADS-B?
TCAS stands for Traffic Collision Avoidance System. It’s used on commercial airliners and all aircraft capable of carrying 19 passengers or more and weighing in excess of 5700kg.
TCAS is only able to detect aircraft that have an operating mode C or mode S transponder.
ADS-B stands for Automatic Dependent Surveillance-Broadcast. This technology allows air traffic controllers to track all flights in real-time. ADS-B transponders allow aircraft and ground vehicles to broadcast their identification, position, altitude, and velocity to other aircraft and ATC.
2. Is TCAS mandatory on all commercial aircraft?
Yes, the system is required on all commercial aircraft to help avoid midair collisions between aircraft. This is an international standard.
3. Are Transponders Mandatory on all Aircraft?
Generally no, but according to the rules for flying in controlled airspace (where commercial aircraft fly) and under instrument flight rules (IFR) they are required by law.
For example, in Europe, If a pilot wants to fly in any controlled airspace, or at an altitude above 10,000′, or within a 30 nautical mile radius of a large airport the aircraft must be fitted with a transponder and altitude encoder commonly referred to as “mode C”.
TCAS at Simuflight
SimuFlight has developed a simulation of TCAS II version 7.1 that positions and flies a simulated aircraft onto a conflicting flight path or simulates a collision threat.
The aircraft is “real” in that it appears in the simulated airspace and triggers the appropriate TA and RA annunciations. Pilots can fly a range of scenarios allowing them to practice their responses in a realistic, but safe environment.
In addition, the Instructor Station has been equipped with a representation of the pilot TCAS display allowing the Instructor or Examiner to fully monitor the developing conflict scenario and pilot response.
For more information, email updates or to book a session to try out TCAS contact SimuFlight.