DAVID LEARMOUNT / LONDON
Tupolev pilot was obeying Russian operating procedures, acting on controller instructions rather than on-board warning
Events just before the 1 July mid-air collision over southern Germany have put the spotlight on crew training after a conflict between obeying air traffic control (ATC) instructions or airborne collision avoidance system (ACAS) alerts has emerged as the cause of the disaster.
Pilots say a mid-air collision could happen again unless training is modified. European airlines decline to comment while the inquiry into the collision involving a Bashkirian Airlines Tupolev Tu-154M and a DHL Boeing freighter continues, except to confirm standard operating procedures (SOP) are for pilots to follow ACAS warnings. But individual pilots from two UK airlines, a Danish carrier, the UK Royal Air Force, Russian airlines and two European pilot unions tell Flight International they would probably have made the same decision as the Russian pilot - to follow the two urgent ATC instructions rather than his ACAS advisory alert - despite knowing SOPs dictate the contrary. The Russian pilot was following his brief: other Russian pilots are adamant ATC commands take precedence over ACAS advisories and Russian authorities confirm this, which puts them at variance with practice in Western Europe and North America.
The key to this disaster is the order in which instructions were given when collision was imminent (see table). The German accident investigation agency BFU, says the Bashkirian Airlines Tu-154 ACAS told the pilot to climb, but a second later ATC told him urgently to "expedite" descent to flight level (FL) 350 (35,000ft/ 10,700m) from his cruising level of FL360. The pilot did not reply. ATC repeated the order 14s later. The pilot responded, descended and collided with the DHL 757, which was descending from the same cruising level in compliance with an ACAS "resolution advisory".
None of the airlines contacted has a recurrent simulator training routine in which an ATC "expedite" command follows the ACAS alert and reverses its advisory. One UK carrier says it does not believe this event will change SOPs, but highlighting this incident in its human-factors training will reinforce the need for faith in ACAS.
Meanwhile, Swiss air traffic services provider Skyguide has enacted a new rule to ensure there are always at least two controllers at their stations. At Zurich that night one duty controller was working as the other took a break.
| Conflict chronology | |
| All times local (not all timings have yet been co-ordinated) | |
| 23.33.24 | Controller at neighbouring Karlsruhe air traffic control centre (ATCC) gets short-term conflict alert warning on the converging Boeing 757 and Tupolev Tu-154, but telephone link to Zurich ATCC, which is controlling the aircraft, is at first engaged and then fails to connect. |
| 23.34.33 (Approx) | Both aircraft get "traffic, traffic" alerts (traffic advisory - TA) from airborne collision avoidance systems (ACAS). |
| 23.34.48 (Approx) | Both crews get resolution advisories (RA) from their ACAS, the Tu-154 "climb, climb" and the 757 "descend, descend". |
| 23.34.49 | Zurich ATCC controller issues first descent clearance to Tu-154: "Descend flight level (FL) 350, expedite, I have crossing traffic." There is no response from the Tu-154 pilot, but at about this time the Karlsruhe controller sees the aircraft's height increase to FL361. |
| 23.35.03 | Zurich controller repeats: "Descend level 350, expedite." The Tu-154 descends. "At about the same time", the 757 reports to Zurich ATCC that it is descending in response to ACAS RA. |
| 23.35.33 | Collision |
Source: Flight International
