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 [The content of this part has been removed by the mailing list software]