The problems with decisionmaking about whether to fly - or not - in the volcanic-ash-affected skies over Europe is that so little is known about these circumstances. The situation is unique in that this ash cloud is affecting a large area of intense aviation activity.
The Met Office weather research Dornier 228 at work
Vocanoes somewhere on the planet erupt frequently, but normally the ash they produce affects areas in which aviation activity is far less intense. The tactic for dealing with ash clouds, until now, has been to fly around them. We never needed to understand them, just avoid them.
Engine manufacturer Rolls-Royce has, today, absolutely refused to comment or to answer questions about anything to do with the current volcanic ash threat.
UK air navigation service provider NATS, in contrast, has been immensely helpful, but honestly admits that the biggest problem it has in making decisions about opening or closing airspace is lack of data about the risk associated with these precise circumstances, and the lack of precision reporting about the position of the ash cloud.
NATS quotes its remit - one which all ANSPs are supposed to follow: they are "not to direct flights into a known flight hazard". If they were to do so, their position would be morally and legally parlous. The question is, is this a "known" flight hazard, or just a suspected one?
Unfortunately in this case European airlines, and airlines bound for European destinations from outside, cannot fly around the ash cloud because it fills the sky above almost the entire continent. Unless it moves, they cannot arrive or depart without flying through it.
One of the consequences of applying the traditional technique of ash avoidance until now is that the aviation industry has never had to research the risk of damage, particularly to aero engines, of flight through areas of widely dispersed upper airspace volcanic ash, rather than the volcanic plume itself.
The industry fully understands the effects of flying through volcano ash plumes downwind of the eruptions. This concentrated ash clogs the hot section and abrades the cold section of turbine engines, stopping them or dramatically reducing available engine power. Engine core repair following this damage is usually unfeasible, making replacement the only option.
But volcanic plumes themselves are easy to avoid. They don't cover a wide area and Satellites can track them accurately. Unfortunately satellites cannot detect the type of widely dispersed very fine ash particles over Europe at present. Their progress is estimated by computer modelling and atmospheric sampling. But the particles remain abrasive to moving parts in engines.
There are greater and lesser concentrations of particles at different vertical levels, their distribution determined by a combination between the strength of the individual eruption that projected the ash skyward, then by the weather system. Meanwhile below these layers, the dust is constantly drifting down from the upper air to the ground, so no-where is absolutely ash-free. My car, parked outside in SW London, is covered by a thin layer of ash.
It looks as if today's videoconference of European ANSPs, aviation authorities and transport department officials has produced a decision to try to re-start operations in some of Europe tomorrow. The main reason appears to be a weakening of the volcanic activity - but that weaker level of activity is not guaranteed to be sustained.
Weather patterns, unfortunately, look as if they will sustain a drift of ash from Iceland toward Europe for the next five days at least.
In addition, consideration must have been taken of the results of test flights by aircraft of KLM, Lufthansa, Air France, British Airways and others. Their experience was universally benign. But did they get lucky? We don't know. What's more we don't yet know whether low level abrasion has affected the efficiency of the engines. An increase in fuel consumption for the life of an engine would be a high price to pay for an early return to the skies.
A fully-instrumented Met Office Dornier 228 returned from its flight yesterday saying it had found levels of ash that would probably represent a risk to flight safety.
The Met Office Dornier 228
And on 15 April a pair of Finnish Air Force Boeing F-18 Hornet fighters took off and had serious problems with their engines. When they returned, the inspected engines showed classic internal volcanic ash damage and they may never power an aeroplane again.
Finally, it is not just the Icelandic volcano that has provided Europe with this problem, it is the combination of the volcano and an untypical weather system for the time of year over the British Isles and northern Europe. High pressure and northerly winds have dominated for more than two weeks now, and look as if they will continue to do so.
If only typical April weather for the region were to return, the normal south-westerlies would bring frontal activity and rain showers, and they would drive the ash cloud north east toward northern Siberia, leaving Europe in the clear.