[MerelyMortal]

I met someone who says he helped develop TCAS, and that it decides which one to climb or descend based on the registration number.

I'm guessing that it does not issue turn instructions because it only gives a Resolution Advisory when a collision is imminent (otherwise they would be giving RAs all the time). At altitude, where the air is thinner, it is much easier for a plane to immediately climb or descend, planes turn very slowly when the air is thin.

[ceejayoz]

That's only partially true, in the case of a tie.

https://aviation.stackexchange.com/questions/92495/how-does-...

> But what if the other aircraft is "thinking" the same thing? That's the heart of this question. The answer is, whichever TCAS makes a decision first, and then in case of a tie, the lower Mode S address "wins":

[jll29]

Thanks for answering my question, namely how does the collision resolution in TCAS work? (Different from, say, TCP, which uses randomness)

EDIT: FAA PDF on TCAS 7.1 - https://www.faa.gov/documentlibrary/media/advisory_circular/...

This story is a moving example of the self-improvement going on in global air traffic industry; perhaps sometimes slowly, but definitely self-improving. The following book compares the transparency of the air traffic industry with the lack of transparency that currently exists in the medical sector, where errors are denied:

https://www.amazon.com/Black-Box-Thinking-Psychology-Paperba...