Recommendations on downlinking airborne collision avoidance system (ACAS) resolution advisories (RA) directly to air traffic controllers will be published at the end of February, says Eurocontrol, having completed exploratory trials on the concept. Such a datalink system might have prevented the 1 July 2002 collision over southern Germany between a Bashkirian Airlines Tupolev Tu-154 and a DHL Boeing 757.

The trials have so far been exploratory, but the report is expected to say the potential benefits revealed suggest more thorough tests are worthwhile.

Pilots often do not have time to tell controllers that they are reacting to an ACAS RA, even though procedures suggest they should.

In the case of the Bashkirian/DHL crash the DHL pilot told the controller he was descending according to advice from an ACAS RA, but the Bashkirian pilot said nothing even though he had received an ACAS RA to climb and was in fact continuing a descent, still following the last instruction he had from air traffic control.

The trials involved 30 controllers from 10 different European area control centres. They were presented with 15 different simulated radar traffic scenarios, all based on real events that triggered ACAS RAs, with the same spoken radio messages, which they observed "as if they were watching an on-the-job trainee controller".

The difference was that, in this case, the information about pilot reaction to ACAS RAs was downlinked to them. The controller reaction was universally favourable, all saying that the downlinked data increased their situational awareness and helped them take decisions, particularly about third party aircraft that might be affected.

Source: Flight International