Fredrik Thörnell wrote:
Eric Greenwell skrev den Tue, 03 Feb 2004
12:15:57 -0800:

It's my understanding that the conflict resolution algorithm is based
on much more realistic assumptions, so that climbing and turning
flight of the potential threats is included. The simple assumption of
straight flight might have been used in the very beginning, but no
longer. If you have a recent reference that suggests otherwise, I'd
like to know about it.


The algorithm is to look at a number of consecutive returns to determine
a rate of closure and then divide the distance with this rate to give a
'tau' value, of time to impact should there be a collision. When this
value goes below an [altitude dependant] threshold, you have a traffic
advisory. Another lower [also altitude dependant] threshold, and the
TCAS begins working on a resolution advisory.

After looking at an "Introduction to TCAS II version 7" more closely, I
have to agree that Fred's description is a good one. It says (page 7):

"In particular, it is
dependent on the accuracy of the threat
aircraft's reported altitude and on the
expectation that the threat aircraft will not
make an abrupt maneuver that defeats the
TCAS RA."

I'm guessing the relatively slow speeds (compared to the airliner) and
low G turns of a glider (compared to a fighter, for example) would still
allow the TCAS to sort things out to the benefit of all concerned. At
the least, the TCAS is providing range, bearing, and altitude to the
glider, a big improvement over a pair of eyeballs looking out a window
going 300 knots.

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Eric Greenwell
Washington State
USA