TCAS stands for Traffic Collision Avoidance System, an onboard safety system that helps prevent mid-air collisions. It is used in many passenger and cargo aircraft to detect nearby aircraft and warn pilots when another plane may come too close. TCAS matters because aircraft often travel at high speeds, so even a small delay in recognizing a conflict can be dangerous.
The system gives pilots clear instructions that help keep airplanes safely separated.
Key Facts
- TCAS = Traffic Collision Avoidance System.
- TCAS detects nearby aircraft by receiving signals from their transponders.
- Time to closest approach = distance between aircraft / closing speed.
- Relative altitude = intruder altitude minus own aircraft altitude.
- Traffic Advisory, or TA, means pilots should look for nearby traffic and prepare for possible action.
- Resolution Advisory, or RA, gives a vertical instruction such as climb or descend to increase separation.
Vocabulary
- TCAS
- TCAS is an aircraft safety system that detects nearby transponder-equipped aircraft and warns pilots about possible collision risks.
- Transponder
- A transponder is an aircraft radio device that replies to signals by sending information such as identity and altitude.
- Traffic Advisory
- A Traffic Advisory is a TCAS alert that tells pilots another aircraft is nearby and may become a threat.
- Resolution Advisory
- A Resolution Advisory is a TCAS instruction that tells a pilot to climb, descend, or adjust vertical speed to avoid a conflict.
- Closing Speed
- Closing speed is the rate at which two aircraft are moving toward each other.
Common Mistakes to Avoid
- Thinking TCAS is the same as air traffic control is wrong because TCAS works onboard the aircraft and gives immediate collision avoidance guidance.
- Ignoring the altitude difference is wrong because two aircraft can appear close on a map but be safely separated vertically.
- Following a visual guess instead of a Resolution Advisory is wrong because TCAS calculates the safest vertical maneuver using real-time transponder data.
- Assuming TCAS turns the airplane automatically is wrong because standard TCAS gives instructions to pilots, who must respond correctly.
Practice Questions
- 1 Two aircraft are flying toward each other with a combined closing speed of 900 km/h. If they are 15 km apart, how many minutes remain until closest approach if neither changes course?
- 2 An aircraft is at 32,000 ft and an intruder aircraft is at 31,200 ft. What is the relative altitude of the intruder compared with the first aircraft, and is the intruder above or below?
- 3 A TCAS alert changes from a Traffic Advisory to a Resolution Advisory. Explain why a pilot should follow the RA even if air traffic control has just assigned a different altitude.