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Wednesday, 3 July, 2002, 20:40 GMT 21:40 UK
German air crash: Your questions answered
We put your questions on Tuesday's German air crash to aviation expert Jim Ferguson of Phillips Aviation and Aerospace. His answers appear below.

Why did Swiss ATC only attempt to correct the situation 50 seconds before collision, as reported?
Robert Manning, Dubai, UAE

The latest information we have is that only one rather than the two controllers mandated to be in position was on duty and if correct this may be a reason for the allegedly late descent instruction passed to the TU-154.

Does the TCAS warn the pilots?
Prabin Adhikari, Kathmandu, Nepal

TCAS Is designed to provide an increasing level of alert (white, yellow, red) to advise, warn or command pilots in the event of another aircraft intruding in their airspace. It can give a "dive, dive" command to the pilots of each aircraft, and so far this does not appear to have caused major problems. Newer systems are in the pipeline to provide more detail but the current equipment is well liked by aircrew.

Why can't planes have a video camera with the black box recorder to better determine the cause of accidents?
Raj, USA

Video technology has been looked into but modern flight data recorders provide dozens if not hundreds of pieces of information capable of an immediate computer readout. Like the proposed video recorders they do stop recording when power supplies fail as is usually the immediate result of an accident of a catastrophic nature.

Given the possibility now of high speed packet data transmission by radio, why is there not a system by which planes transmit their essential information automatically to a satellite monitoring station which can then relay it to a ground station?
Chris B, Brussels, Belgium

This is something I gather is currently under research at least and would perhaps be along the lines of data links used by military aircraft for all sorts of operational purposes.

Would a "Single European Sky" have helped to avoid this? Why are metric and imperial units used to measure altitude by Russian and European pilots respectively?
Peter Bowes, Durham, UK

It does not seem that the "Single European Sky" concept would have prevented the accident. In response to your second question, just as English is the international language of aviation, feet are used for altitudes.

Does it make any sense that European traffic control is split into as many centres as the number of our tiny European countries?
Carlo Berruti, Milan, Italy

There are well-advanced plans to "unify" European airspace, but their implementation awaits ratification by the nation states involved and presently there does not seem to be a definite timescale. Until the political will is there among all nations, the implementation of the plans cannot proceed.

There has long been support for such a move, given that this would result in far more efficient use of increasingly congested skies. However, domestic control would necessarily have to remain within the nations concerned.

If TCAS was resolving the conflict for both planes then they would also have been sent in opposite directions. Does this not highlight the problem where some aircraft use TCAS to overrule ATC instructions whereas others do not?
Paul Goodwin, Winchester, UK

It is understood at this stage that both the 757 and the 154 were equipped with TCAS as is now the requirement for operation within controlled airspace.

When can we expect the results of the investigation? Is there an authorised international body that will serve as a kind of referee in investigating the causes of the accident? How does the tragedy influence the work of the air traffic control bodies?
Nina Karagodina, Riga, Latvia

Investigations take as long as they need to take, but in the event of a potential repeat of the incident taking place, the industry is advised immediately that remedial action can be taken. Accidents are investigated under rules set by the International Civil Aviation Organization (ICAO) but no one has any kind of refereeing authority over the proceedings and in such cases each country will issue its own version of events. It is too early to say what changes, if any, will be made to ATC procedures, but as in the case of any accident, lessons will inevitably be learned.

Each aircraft should have been flying according to ATC clearance. Have those clearances been made public yet?
Kevin Carty, Curacao

No clearance or flight plan details have been made public, but they will necessarily form part of the inquiry.

One report suggests that the Russian pilot's TCAS system would have been telling him to ascend whereas the Swiss traffic controller was telling him to descend. Is this possible and, if so, which instruction should the pilot follow, given the need for immediate action?
John Walter, Asolo, Italy

This most interesting question will no doubt form a major element of the investigation.

It has been reported that there was less than one minute for the Swiss air traffic controller to take action to avoid the collision. How can this be failsafe?
Antonio d'Agostino, Peterborough, UK

The alleged length of the interval between ATC telling the TU-154 to descend and the collision will also be a major element of this inquiry.

Does the recent reduction in safe distances between aircraft make this kind of accident more likely?
Andrew Amos, London, UK

Nothing emerging thus far from the accident indicates that the recent reduction in separation lengths was a casual factor, presuming that both aircraft had operational TCAS equipment. It's too early to say if there will be a return to the original criteria, but if there were, ATC delays would almost certainly become endemic.

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