Why you should care about TCAS?

According to the recent reports from the various aviation regulatory bodies as ICAO FAA, and EASA, nowadays airports across the globe are seeing the record number of passengers. Along with that, the airspace is becoming increasingly crowded.

Despite the fact, the flow of air traffic is organized and controlled, yet many different issues still can cause a mid-air collision. By understanding this and learning the lessons of the past (one of them – Überlingen accident), industry realized a need for practical solution and predictive system to prevent any chances of mid-air collisions.


One of the main solution in order to prevent mid-air collision and monitor the airspace around the aircraft is Traffic alert and Collision Avoidance System (TCAS) or internationally called – ACAS (Airborne Collision Avoidance System). By reducing the risk of mid-air collisions between aircraft, TCAS/ACAS has to be mandatory installed to almost every passenger carrying aircraft: airplanes with a maximum certified take-off mass exceeding 5 700 kg; or airplanes authorized to carry more than 19 passengers. System’s configuration should be implemented into the Full Flight Simulators too.

Introduction to TCAS

Traffic alert and Collision Avoidance System was designed for collision avoidance only and developed to improve collision avoidance by enhancing pilot awareness of traffic situation. Basically, TCAS is avionic updates providing two types of alerts – TA (Traffic Advisory) and RA (Resolution Advisory):

  • TA is designed to assist the pilot in the visual search for the intruder aircraft and to prepare the pilot for a potential RA;
  • RA is meant to recommend maneuvers that will either increase or maintain the existing vertical separation from an intruder aircraft.

Talking about airplanes (not about Full Flight Simulators), TCAS installation consists of three main components such as TCAS computer unit, Antennas, and Cockpit presentation. The new version is designed as an independent system and is based on secondary surveillance radar (SSR) transponder signals, and it can also work independently off of ground-based systems to provide advice to the pilot on potential conflicting aircraft.

TCAS: v7.1

The original release of TCAS is associated with software version 6.0 / 6.04a which was followed by version 7.0. Unfortunately, airplane crashes as well as extensive safety studies became the foundation for the crucial safety improvements laid upon TCAS upgrade.

The new version, named 7.1, covering improved collision avoidance algorithms, aural annunciations, and RA displays, was designed and introduced in 2011. So, what has changes within it?

“Level Off, level Off” – if the answer should take just a few words.

To eliminate any confusion, the phrase “Level Off, level Off” replaced the existed “Adjust vertical speed, adjust” RA. The new version is able to recognize a specific situation when two converging aircraft are within 100 feet as well as one aircraft is not responding to the RA. Also, within v7.1 pilots reduce the vertical rate to 0 ft/min.

Additionally, an improved reversal logic feature has been added. The new feature monitors RA compliance in coordinated encounters. When it detects that one aircraft is not responding correctly to the RA, a reversal RA will be issued to the aircraft which maneuvers in accordance with the RA.

Please see below the illustrations that show two main safety issues created by European Organization for the Safety of Air Navigation (EUROCONTROL):

1. Level Off, Level Off:


2. Improvements to reversal logic:


Other Minor Enhancements were also included to version 7.1:

  • Corrects issue when descending through 1000 ft. AGL.
  • Modifies the “Datalink Capability Report” (Status report sent by the TCAS processor to the Mode S transponder) to tell the systems that the TCAS processor is hybrid-surveillance-capable.
  • Allows for the transmission of the TCAS processor part number and software level.
  • Corrects TCAS multi-aircraft logic issues, which reduces the risk of “close-encounters” of multiple aircraft in RVSM airspace.

What else? What’s next?

“In Europe today, in America tomorrow” – aviation experts would say. As EASA required mandatory installation of TCAS v7.1 to all civil airplanes currently equipped with version 7.0 and exceeding 5700 kg or authorized to carry more than 19 passengers within European Union airspace, same requirements are issued by ICAO with a deadline of the 1st of January, 2017.

Along with these changes (although there are so few visible differences) flight crew training is required. All aviation training centers should ensure that pilots are aware of this upgrade as well as to be trained how to respond to the new RA correctly.

So whether you are a passenger, a pilot, an aviation student, a flight instructor or even an engineer who must ensure that full flight simulator operates properly, you should care about TCAS. Regarding it, the best decision would be to install version 7.1 as soon as (or always better earlier on!) it becomes mandatory for the airplanes.

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