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Monte Carlo in The Flight Deck: NextGen Collision Avoidance

Monte Carlo in The Flight Deck: NextGen Collision Avoidance

  • January
  • 31
  • 2025
  • Advanced Aircrew Academy

Unless you’re a card-counting whiz or a mathematician specializing in nuclear weapons, you may not be familiar with Monte Carlo simulations. Much like a gambler leveraging probabilities to gain an edge in a casino, the concept of Monte Carlo simulations is to use random inputs to explore a vast array of potential outcomes. This innovative concept is now being harnessed to develop the next generation of Traffic Collision Avoidance Systems (TCAS), known as Airborne Collision Avoidance Systems X (ACAS X).

What is ACAS

ACAS technology can analyze multiple aircraft movements and assess potential conflicts in three-dimensional space. It works independently of ground-based Air Traffic Control (ATC) systems. Once a threat is identified, it can recommend the most effective maneuver for collision avoidance for all aircraft involved.

This process is far more complex than simply displaying an aircraft’s position on a “fish finder” like with TCAS I iteration. It employs advanced algorithms to evaluate numerous variables, predicting the future positions of aircraft based on their current trajectories and providing an instant resolution. It provides both Traffic Advisories and Resolution Advisories (RA/TA) but on a shorter time scale. It knows where your aircraft will be before you do.

When TCAS was first introduced, today's dynamic programming techniques were not yet developed. ACAS X is set to succeed TCAS II, bringing a new level of sophistication to air traffic safety. With that in mind, the Federal Aviation Administration (FAA) published a revised Advisory Circular (AC) on ACAS to address the operational use.

Not Mandatory, However…

AC 90-120 (11/20/24) is not mandatory, but if you use the means described in the Advisory Circular, you should follow the guidelines. It applies to Air Carriers operating under CFR Part 121 and 135 and other organizations conducting air carrier training (e.g. training centers or MROs).

The AC defines TCAS vs ACAS, describes the approval process, acceptable methods for ACAS training, programs for maintenance operational policies, and appropriate actions for ACAS events.  It also incorporates Safety Management System (SMS) guidance, which is now mandatory.

(To clarify all the acronyms, Title 14 of the CFRs refers to the Collision Avoidance System (CAS) or TCAS, while Title 49 of the CFR and International Community refers to ACAS.)

Limitations

So far, you are not required to have ACAS/TCAS in Reduced Vertical Several Minimum (RVSM) airspace in the U.S., or NAT or PAC oceanic areas. However, IF you do have the equipment, it must be at least TCAS II version 7.0.

Euro control has mandated TCAS 7.1 since 2005 for any aircraft over 33,000 lbs and ACAS II is now required if over 12,500 lbs. As with any new technology, everything must be tested and proven first, so there are limitations in each controlling airspace worldwide.

The FAA permits variants of ACAS II in U.S. Airspace: TCAS II 7.0, 7.1, and ACAS Xa/Xo. If you have an ACAS II system, it must be TCAS version 7.0, 7.1, or ACAS Xa to operate within RVSM.

If you are flying outside of U.S. territorial airspace, you must also ensure that ACAS software updates are compatible with oceanic and international equipage and operation standards for ACAS.

Your Flight Department

In Safety Alert for Operators (SAFO) 11010, the FAA "strongly recommends" pilot training on use of TCAS for Part 91 and 135 flight crews because of a high percentage of noncompliance with TCAS RA alerts.

Advanced Aircrew Academy’s TCAS module highlights the issues published in the SAFO and reviews best operating practices outlined in Advisory Circular (AC) 120-55C – Aircraft Operational Approval and Use of TCAS II, Information for Operators (InFO) 11012—Transponder/TCAS Operations While on the Airport Surface, and AC 90-48D Pilots' Role in Collision Avoidance. This module addresses the NTSB Safety Alerts 45 and 58 and FAA SAFO 15006.

Although training on TCAS is not specifically required under Part 135, we typically include it with the initial Pilot-In-Command (PIC)/Second-In-Command (SIC) Basic Indoctrination curriculum. We review TCAS procedures specific to Reduced Vertical Separation Minimum (RVSM) airspace in the RVSM module and Precision Runway Monitor (PRM) approaches in the Instrument Procedures module.

All of Advanced Aircrew Academy’s modules can be customized to your specific OpsSpecs and or GOM/FOM’s process and procedures.  Email info@aircrewacademy.com to get started.

Reference: https://nbaa.org/aircraft-operations/communications-navigation-surveillance-cns/tcas/new-ac-provides-guidance-on-operational-use-of-tcas-acas/https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_90-120.pdf


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