Piloting Amid TCAS and ATC Conflicts: Navigating the Hierarchy of Command

Understanding the Priorities in Traffic Conflicts

The Role of TCAS in Modern Aviation

In the realm of aviation, the importance of traffic conflict avoidance (TCAS) cannot be overstated. However, the challenge arises when there is a conflict between TCAS Resolution Advisories (TCAS RA) and Air Traffic Control (ATC) instructions. According to ICAO Doc 8168 (PAN-OPS Chapter 3, Section 3.2), the ACAS (or TCAS) RA always takes precedence over ATC instructions. This rule ensures that the more accurate and real-time information provided by TCAS is followed.

A Historical Context: The Tragic Accident in 2002

This hierarchy was established following a tragic event in 2002. During a routine flight, a Russian airliner was given contradictory instructions by ATC and TCAS. The ATC asked the Russian plane to descend, while the TCAS instructed the pilot to climb to avoid a DHL cargo plane. Despite clear instructions from TCAS, the pilots chose to follow the ATC due to the urgency in the controller's tone, leading to a mid-air collision. This event led to a collision that resulted in the deaths of 71 people on board the Russian aircraft.

The Impact of Automated Systems: Reliability Over Human Error

These accidents highlight the importance of automated systems in aviation. Automated systems like TCAS are designed to be more reliable and precise than human decision-making. In high-stress situations, automated systems can provide clearer guidance that is less prone to human error. In the 2002 incident, the TCAS instructions were more reliable, and the pilots should have followed them.

Staying Safe: Steps to Take If a Conflict Emerges

Check Your TCAS Display

In visual meteorological conditions (VMC), pilots should look out the window for any signs of traffic. If not in VMC, they should refer to the TCAS display. This display will show the relative altitude of the traffic, allowing the pilot to take corrective action, such as climbing or descending, to avoid a collision.

Leverage ADS-B Technology

Smaller and slower propeller aircraft often have ADS-B equipment, which can provide preemptive traffic information. These systems use Traffic Information Service-Broadcast (TIS-B) to alert pilots of potential conflicts, giving them more time to maneuver and avoid a collision.

Communicate with ATC

If a conflict arises, pilots should request further instructions from ATC. An ATC instruction such as 'TCAS climb/descent' should be followed, and once the conflict is resolved, the ATC will provide traffic information only until the pilot is ready to resume normal flight operations.

Training and Protocols for Pilots

Today, pilots are thoroughly trained to comply with TCAS RA instructions until a 'Clear of Conflict' message is received. If the pilot cannot adhere to the TCAS RA due to ATC instructions, they should make this clear to ATC and follow the ATC instructions once the conflict is resolved.

The incident of 2002 led to important changes in how pilots and ATC operate. Pilots now have clear protocols to follow, and ATC operators are trained to provide clear and unambiguous instructions. The goal is to ensure that in any situation, the safety of passengers and crew remains paramount.

Despite the rarity of such conflicts, it is essential to have a well-defined and practiced protocol in place. Pilots must stay vigilant and be prepared to act quickly in the event of a TCAS RA. The key is to trust the automated systems for their accuracy and reliability, especially in high-stress situations.

Thank you for taking the time to read this. For more information on TCAS and ATC protocols, please refer to the resources below.

References

[1] Martin Strohmeier. Airsavvy Blog, 2023.