DW: The crash of the Malaysia Airlines flight MH17 over eastern Ukraine has raised many questions about why the airline was flying over a conflict zone airspace. Who decides whether or not airspace is safe?

Ken Thomas: The deciding body whether an airspace is safe or not belongs to the state - through their air navigation service provider and their civil aviation authorities. It's actually the state that owns the airspace to decide whether the airspace is open for civilian traffic, or if it's not safe they will close it for civilian air traffic.

In this case, Ukraine deemed this airspace to be safe for civilian aircraft?

They deemed this to be safe above 32,000 feet (9,750 meters). Below 32,000 feet, this particular airspace in eastern Ukraine where the crash occurred had been closed by the Ukrainian authorities.

This plane was allegedly flying at 33,000 feet. Details about the crash are still unclear but are you surprised that a plane flying at that level can apparently be shot down by a missile?

I'm surprised unless it is a very sophisticated missile system.

Do pilots also have the authority to determine which route they are going to fly?

Yes, the pilot actually has the final authority to decide whether or not to fly in an airspace that is open. If the airspace is closed, he may not fly there. And we will actually check that and stop his flight plan if he - by mistake - flies through a closed airspace.

Quite a few airlines that fly between Europe and Asia had already decided not to fly over Ukraine. Is it also a question of cost for some airlines? If you are going to reroute a plane, that does mean an increase in fuel and flight time, doesn't it?

Well, of course, when you make the risk assessment, you need to take all factors into account. Fuel would be one factor of many other factors. We expect that roughly a quarter of the airlines previously flying over that airspace above 32,000 feet were not flying there - but 75 percent were still using it.

Is your organization making any recommendations in the aftermath of this crash?

We are a technical and operational organization, so we now concentrate on the situation where a larger part of Ukrainian airspace, or a larger part then before - the east, not only the southeastern part - where we have airspace closure. And in order to accommodate flights to fly around these areas in the best possible way for them, but we are also looking at what is the impact on the neighboring air traffic control centers so that they do not get more traffic than they can safely handle.

Ken Thomas is Head of Network Operations Management Coordination with Eurocontrol, an organization involved with air safety.