ACAS and the South German Midair



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From: Peter B. Ladkin (ladkin(at)rvs.uni-bielefeld.de)
Date: Mon 12 Aug 2002 - 16:22:42 BST


I have put an extended version of the ACAS/Midair note on my WWW site,
accessible directly from http://www.rvs.uni-bielefeld.de 

For those who haven't had the chance to read it, but are nevertheless
interested, the paper points out some problems with ACAS; namely, that it
seems to have difficulty with some three-aircraft scenarios. In particular,
it argues that, given a three-aircraft scenario similar to that which 
obtained in the Southern German midair collision on July 1, the decision
to manoeuvre counter to an RA can be a least irrational strategy.

Andres Zellweger's scepticism concerning my brief comments on multiple-aircraft
conflict scenarios let me to argue these scenarios more carefully (to some
benefit - I had been mistaken about one scenario). There is one class of
conflicts which I do not see can be solved by the current TCAS II, namely
those in which an aircraft C is descending towards an aircraft B already
ascending due to an RA with an aircraft A, which got an RA to descend.
If the BC-conflict leads to a crossing RA, and aircraft C is already within
the alert threshold for a conflict with aircraft A, then I do not see that
the TCAS specification and algorithms can ensure a resolution between 
A and C.

The paper also benefitted from comments by Ira Rimson.

PBL

-- 
Peter B. Ladkin PhD FBCS CW(hon)
Professor of Computer Networks and Distributed Systems,
Faculty of Technology, University of Bielefeld, 33594 Bielefeld, Germany
Tel (Vx/msg/Fax) +49 (0)521 880 7319 http://www.rvs.uni-bielefeld.de
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