Tcas

[PhoenixDaCat]

Hi,

I have been watching a series of documentaries on one of the Discovery type channels on Sky, about aircraft collisions, and the tragic incident in which a DHL transport and russian airliner collided in 2002 was the subject of the most recent one. TCAS was mentioned many times and I was wondering how the system knows whether to instruct a climb or descent. I have googled, but only manage to come up with links to manufacturers sites, with no detail on how it works.

Thanks in advance

[MackMeeter]

Phoenix,

I can't remember too much about TCAs now as the aircraft I fly aren't fitted with it, so all I can recall is from my exam studies several years ago now. I apologise then if some facts aren't entirely correct but you'll get the principle.

TCAS provides traffic information on other transponding (i.e. they have a radar signature from a gadget in the cockpit) aircraft, and plots their with respect to you. It projects a kind of "protective bubble" around the aircraft based on distance and time. Any targtes likely to enter this zone produce a "traffic traffic" auidble warning in American robotic computer speak and show up as a coloured symbol on the TCAS screen - can't remember what colour or symbol though!). These are called "traffic advisories". Traffic not in the bubble but near by are called "proximates" and also given a symbol and colour.

If the target gets closer then the system will issue a "resolution advisory" when the time to collision has got really quite cheeky. It will command a climb or descent or tell you to go faster if already climbing or descending. RA's are given another symbol and colour, once again I can't remember what!

When all the excitement has passed, "clear conflict" is given.

Hope that helps

MM :ok:

[FlightDetent]

On the contrary, electronic info on TCAS / ACAS is
plentiful (http://www.eurocontrol.fr/ba_saf/acas/Version7.htm). Take the previous link as an example.

For he sake of simplicity, let's say that the TCAS boxes in two (or more!) aircraft exchange data on position so to calculate trajectory vectors and the point of closest approach and distance at it. If the separation breches certain limits, visual and for some instances aural alerts are presented to pilots. These alerts come at four levels of importance, the highest called "Resolution Advisory" which in fact provides steering cues away from conflicting traffic. Under standard conditions these alerts are co-ordinated among the aircraft involved and observe certain performance boundaries of individual aircraft, also margins for reasonable reaction time and inertia are applied.


Cheers,
FD.

[BOAC]

Phoenix - there is some excellent coverage of TCAS on PPrune as well - if you search.

In particular, to reduce the enormous number of references you will find, try searching for posts by 'Capt Pit Bull'