Flights are slowly getting off the ground again in Europe, but there are still many unknowns and things could change rapidly at any time.
The airspace over Norway, for instance, has been partially closed again following an earlier 'all clear'. Ireland is keeping its airspace closed, while Switzerland's is completely open again. All of this means the chaos looks set to continue and passengers should still not set out for any airport without checking whether their flight is actually going to depart.
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."
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."
It is possible that the cloud-related changes in procedure will be noticeable on the ground. Evert van Zwol points out that it is necessary to gain height rapidly and that's a little tricky in the 'tiny' Netherlands.
"Normally, you climb slowly and keep climbing on over Belgium or Germany. I can imagine that will have changed now; that you'll climb in a number of turns above the Netherlands until you reach the required altitude and then set out on your actual route."
Because of this, planes will have to carry extra fuel, another one of the special procedures.
The situation is still open to change during the flight. Clouds of ash do move and it's quite possible the concentration of ash particles and the size of the cloud may temporarily increase. Planes may then be forced to take long detours before they can continue on their route.
It's reassuring to know that the pilots themselves are well-prepared, even if it is a unique situation for Europe. Flying with ash in the air is something which can happen to a pilot anywhere in the world and therefore forms part of their normal training. Evert van Zwol says the biggest difference with the usual situation in the air is that the capacity of the airspace is much smaller than normal.
Unfortunately for the thousands of stranded passengers, this means it will be some time before the normal timetable can be resumed. It speaks volumes in this context that the 1,500 camp beds supplied by the Red Cross last week are staying on the far side of customs inside Amsterdam Schiphol Airport for the time being.