Addressing a Persistent Safety Challenge
Denver International Airport (DEN) has long faced a high frequency of Traffic Collision Avoidance System Resolution Advisories (TCAS RA) during final approach, particularly on Runways 16R and 16L. This persistent issue has been flagged in multiple FAA Safety Alerts for Operators (SAFO) and industry reports, citing concerns over:
- Converging approaches to 16R and 16L, where aircraft on parallel paths experience reduced separation.
- TCAS sensitivity to visual approaches, which often results in more RAs.
- Operational disruptions, including unnecessary go-arounds and pilot workload increases.
| Why TCAS-RAs Matter: Traffic Collision Avoidance System – Resolution Advisories (TCAS-RAs) serve as the last line of defense against mid-air collisions. When standard air traffic control separation fails or aircraft get too close, TCAS provides real-time, automated alerts, directing pilots to climb or descend to avoid a conflict. |
Despite previous mitigation efforts — including parallel approach spacing adjustments — the issue persisted. A FAA study in 2022 confirmed the continued high rate of RAs, prompting the introduction of a 3° lateral offset approach on Nov. 30, 2023, as an additional mitigation.
The Data: Before vs. After Implementation
Leveraging Aireon’s Safety Dashboard, we monitored TCAS-RA occurrences before and after the lateral offset procedure. The results show a dramatic reduction in TCAS-RA events.
Visually, it is easy to see the dramatic reduction in TCAS-RA events near Denver International Airport following the implementation of the 3° lateral offset approach on Nov. 30, 2023. The October and early November 2023 maps show a high concentration of TCAS-RAs, particularly along the final approach path. However, by December 2023 and January 2024, the number of events dropped significantly, with only a few isolated occurrences remaining.
Specifically,
- 466 TCAS-RA events occurred in the 60 days before the offset was implemented.
- In the 60 days after, TCAS-RA events plummeted to just 18 — a 96% reduction.
This dramatic decrease highlights how a procedural change can have a major safety impact and the speed at which mitigation efficacy can be determined using new techniques in system monitoring. Ongoing monitoring confirms that the TCAS-RA event rate has remained low, averaging 20 events every 60 days since the lateral offset implementation.
However, detailed hot-spot analysis reveals that the highest concentration of TCAS-RAs occurs approximately 7 NM from the runway threshold, outside of the final approach fix where aircraft are establishing on final approach. This area accounts for 68% of all observed TCAS-RAs for current arrivals at Denver, highlighting a potential opportunity for additional procedural mitigations to further reduce event frequency.
The success of this mitigation effort at Denver serves as a model for other airports facing similar TCAS-RA challenges. As the Aireon Safety Dashboard continues to evolve, its ability to provide timely, high-fidelity insights will be crucial in shaping the next generation of aviation safety strategies.
The Role of the Aireon Safety Dashboard in Mitigation Assessment
The Aireon Safety Dashboard played a critical role in validating this mitigation effort. By utilizing global space-based ADS-B surveillance data, we were able to:
- Monitor TCAS-RA Trends – Instead of waiting for manual incident reports, safety teams had quick visibility into daily RA event counts.
- Assess the Impact Rapidly – Within days of the lateral offset going into effect, the significant reduction in TCAS-RA occurrences was evident in the data.
- Provide Data-Driven Validation – The FAA and industry stakeholders could see quantifiable proof that the lateral offset was working—eliminating the need for extended trial-and-error approaches.
By moving from reactive safety monitoring to real-time, data-driven decision-making, aviation authorities can proactively address airspace risks before they escalate.
Next Steps
The Aireon Safety Dashboard delivers key safety metrics such as TCAS-RA event tracking, runway excursion risk, separation monitoring, and GPS interference detection. Looking ahead, new metrics are on the horizon, expanding the dashboard’s ability to detect altitude deviations, turbulence events, and other leading indicators of safety risks. As aviation safety challenges evolve, the Aireon Safety Dashboard remains a critical tool in providing objective, high-fidelity data to enhance operational awareness and risk mitigation.
