TCAS Change 7.1

The development of version TCAS 7.1 was initiated by EUROCONTROL following the discovery of two safety issues with the current TCAS II version. Development was undertaken jointly by the RTCA in the U.S. and by EUROCAE (European Organisation for Civil Aviation Equipment) in Europe with support and contributions from several other organizations, including major airlines and air navigation service providers (ANSP).

During a joint session in March 2008, the RTCA Special Committee 147 and EUROCAE Working Group 75 agreed on the final version of the TCAS II MOPS, to be known as TCAS II version 7.1. The MOPS were approved the RTCA Program Management Committee in June 2008 (document DO-185B) and by the EUROCAE Council in September 2008 (document ED-143). The MOPS were revised following the identification by EUROCONTROL of two safety issues in the existing TCAS logic (one relating to the performance of the RA-reversal logic, and the other involving incorrect responses to Adjust Vertical Speed RAs).

Version 7.1 Mandate

On December 16, 2011, the European Commission published Implementing Rule 1332/2011 mandating the carriage of ACAS II version 7.1 within European Union airspace from December 1, 2015 by all aircraft currently equipped with version 7.0 and from 1 March 2012 by all new aircraft above 5,700 kg maximum take-off mass or a maximum passenger seating capacity of more than 19.

Version 7.0 Safety Issues

Since its introduction in Europe in 2000, TCAS II version 7.0 has been the subject of monitoring. In the course of analyzing recorded and reported events, many cases were found in which pilots did not respond correctly to the “Adjust vertical speed, adjust” Resolution Advisories (RA) – the vertical rate was increased rather than reduced.

Additionally, there have also been a number of cases in which TCAS II version 7.0 failed to reverse an RA when two converging aircraft remained within 100 feet. This type scenario would be occur when one aircraft is not following the RA or is not TCAS II equipped and follows an ATC instruction or performs an avoidance maneuver based on visual acquisition.

Adjust Vertical Speed

“Adjust Vertical Speed, Adjust” (AVSA) RA was determined to be confusing, and there is a history of some pilots not responding as intended. The solution in Change 7.1 is to replace the four AVSA RAs with a single “Level Off, Level Off” RA.

TCAS Reversals

TCAS reversals were introduced in 7.0 to adapt to changing situations where the original guidance became the wrong thing to do if one of the pilots did not follow the RA or was instructed by ATC to perform a particular maneuver. Change 7.1 improves this reversal logic to address late issuance of reversal RAs and potential failures to initiate reversal RAs.


TCAS 7.1

Honeywell’s TPA-100B Change 7.1-compliant design meets the challenge for its broad base of airline and business aviation customers with solutions that not only meet the mandate requirements but provide a number of benefits ranging from fuel savings, greater situational awareness, fewer delays and expensive AOG situations.

Jet Aviation, one of the leading business aviation services companies in the world, recently completed STCs on the Dassault Falcon 20, Learjet 31 and Germany-based Aero-Dienst completed certification for the Learjet 35/36.

For owners of the Bendix/King (Honeywell) CAS-67A processor, Pro Star Aviation has developed an STC to address the EASA mandate. In December 2014, The FAA issued an approved model list (AML) STC to Pro Star for upgrade of BendixKing CAS 67A Change 7.0 to CAS 67B Change 7.1 for operators of many popular business aircraft including various Beech, Boeing® , Bombardier®, Cessna, Dassault®, Gulfstream®, Learjet, Lockheed and Saberliner models. STCs are in progress for the other affected platforms.

Operators and dealers can contact their Bendix/King sales representative for more information about STC ST00347BO and to get a list of approved models.

Read Now: Honeywell Experts Offer Advice on How to Comply

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