TTR-4000 TCAS II System Change 7.1It is backwards compatible with TCAS II version 7.0. Meaning it can work with inputs generated by an older product of the older version of the TCAS.

Based on the issues garnered from TCAS II logic version 7.0, the Change Proposal 112E (CP112E) brought improvements to the reversal logic of TCAS II logic version 7.0 by detecting geometries close to that of the 2002 Überlingen mid-air collision, and by easing the triggering thresholds of reversal RAs in encounters in which the aircraft remain vertically within 100 ft of each other.

CP112E firstly adds a feature which monitors RA compliance. When it is detected after a certain period of that time that an aircraft is not responding correctly to an RA, it circumvents the "100 ft box" rule, allowing reversal RAs for aircraft closer than 100 ft vertically.

CP112E also adds a prediction of the vertical separation at the closest point of approach, based on current vertical speeds, to detect the need for reversal RA. This prediction shows that when the aircrafts are going to be closer than a predefined threshold, reversal RAs are considered as a valid option for aircraft closer than 100 ft vertically.

Moreover, reversal RAs are not triggered too early in an encounter, to leave time for the initial RAs to be efficient before reversing. In addition to that, they are not triggered too close to the predicted closest point of approach, to avoid useless reversal RAs.

That being said, let it be known that the 4MCU TTR-4000 Change 7.1 logic only requires one-third less space and is 15 percent lighter than the predecessor TCAS II units. Pricing could not be found for this model and not much can be said to get a better one for replacement.