The BFU report on the 2002 mid-air collision over Southern Germany is masterful in showing how the systems failed, inter alia, the mass of conflicting guidance on TCAS use. But the BFU's proposal to make ACAS/TCAS manoeuvres mandatory is misguided.
First, any mandatory manoeuvre must be known to work. The TCAS algorithms fail for some multiple-aircraft conflicts. As I noted in 2002, they may well fail even for some three-aircraft conflicts.
The report confirms my then suggestion that the Russian crew believed that they were in a three-aircraft conflict.
Second, it is hard to imagine a more appropriate dynamic situation for issuing a Reversal-RA. Yet BFU says that the technical requirements for issuing one were not met.
Third, a verbal slip by a controller meant that the Russian crew had a different decision problem (to resolve a three-aircraft conflict) from the reality (a two-aircraft conflict). TCAS RA "system philosophy" says that controller inputs no longer count. But changing a decision problem is a major influence, needing analysis.
It would be inappropriate to force pilots to follow algorithms which are inadequately analysed and not even known to be correct.
Prof Peter B Ladkin
University of Bielefeld, Germany
Source: Flight International
