Tcas

[StillDark&Hungry]

Old ATCO who obviously doesn't understand this piece of hardware as much as he thought:

This mornings scenario;

A/C 1 in level flight (370),
A/C 2 in descent (to 380), gonna cross 90 degrees, right over the top.

A/C 2 (passing overhead) says " callsign TCAS climb"

Traffic info given.

No probs, but asked A/C 1 did you get TCAS as well?

A: Traffic Advisory only.

So, the question is, if TCAS systems are meant to "talk" to each other, why only 1 RA and 1 TA, If a collision really needed to be avoided surely best both move! or, does it say "I might just graze you, so you stay, I'll move!"?

[RadarContact]

You can select most TCAS systems to "TA only" if you choose to do so. Some do at high altitude where manouverability is restricted... :(

This might be what happened.

[BigGreenPleasureMachine]

Could also be that TCAS calculated best course of action as one aircraft climbing and one maintaining altitude, it doesn't always do what may seem 'obvious' when obsevered on a scope.

Another possibility is that one of the computers made an error. I believe this happened once before, the result of a single bit error which threw the calculations off by several hundred feet. the two crews just about had time to wave to each other as they broke cloud. I think they addressed that problem, though........:eek: