Over and Under in Europe

From Radio Netherlands, How to weave round a volcanic cloud:

Europe's airspace has been divided in to three zones: a no-go zone, a safe zone and a zone where extra caution is required. The borders between the zones are continually monitored and, if necessary, adjusted by Eurocontrol, the European flight control authority.

In any case, passenger planes will now be taking off with a cloud of volcanic ash still hanging above Europe. Special security measures and procedures have been introduced. The chairman of the Dutch Civil Pilots Association, Evert van Zwol, explains how you go about flying with ash in the air.

"Partly matter of sight. You have to realise that there is, thankfully, only a relatively small amount of ash in our vicinity. It is concentrated in layers which you can see quite easily. There are areas where there is a kind of grey veil and other areas which are much clearer."

Rollercoaster
That means it's a question of evasion: flying around or over or under the ash. And because you can normally spot a ribbon or a layer in the air well in advance, the passengers needn't be subjected to a roller coaster ride. There is time to take gentle evasive action.

"So you start to turn the aircraft. There's a great deal of 'banking' involved in take-off procedures any way. When you're taking off in a westward direction, but actually heading east, you'll need to negotiate a number of turns. In that sense, there's no real difference."