* Germany opposes bid to relax flight ban rules
* Berlin says up to airlines to prove when ash is safe
* Deadllock over grounded UK research plane
By Tim Hepherand Maria Sheahan
PARIS/FRANKFURT, May 24 (Reuters) - New airspace closure rules decided after last year's Icelandic volcanic eruption have caused divisions in Europe on how to decide whether airlines can fly near the ash cloud.
A bureaucratic turf war has so far prevented Europe's controllers from applying the same rules to everyone, with Germany insisting on closing skies as a precaution where there are signs of significant ash, aviation sources said on Tuesday.
A European crisis cell founded after last year's six-day ash crisis was activated for the first time on Monday and met on Tuesday to try to hammer out a harmonised set of rules.
"Germany has been taking a tougher line than most of the other countries," a source familiar with the discussions said.
So far weather maps show a paw-shaped "red" zone of Icelandic ash spreading down to Scotland but sparing Germany, after the Grimsvotn volcano erupted on Saturday. [ID:nLDE74N02E]
European authorities were criticised by airlines last year for imposing sweeping airspace closures wherever computerised dispersion models told them ash ought to be present.
The bans effectively turned Europe's air traffic controllers into border guards and grounded more than 10 million passengers.
This time, two changes have come into effect which should reduce disruption, Britain's Civil Aviation Authority says.
Forecasters are providing information dividing airspace into three areas of concentration: low (up to 2 milligrams per cubic metre), medium (up to 4 milligrams) and high above that.
And a new UK-backed system would allow pilots to make most decisions on where to fly, as long as airlines have made a compelling safety case and prove their risk assessment methods.
So far no airline has presented a safety case that would allow it to fly in the red-coded high zone, the CAA said.
SAFE? PROVE IT, SAYS GERMANY
Some experts believe the patchy concentrations of ash even in these bands justify the decision to make it a judgment call.
Germany however told pilots on Tuesday that it would refuse to clear aircraft to fly through the medium or high zones except in emergency or under certain other conditions.
If airlines believe it is safe to fly above 2 milligrams, then they must provide hard scientific proof and not just rely on local safety audits, the German transport ministry said.
Berlin had already told engine makers last year that they should do tests to show what concentration is really dangerous, but nothing had emerged, a transport ministry spokesman said.
While the airline industry has welcomed the extra flexibility being offered by many countries, for some that poses its own additional risks in a lawsuit-ridden industry.
"They are putting the onus of proving it is safe on airlines and passing the buck," said a source with a major airline. In a further bureaucratic twist, officials told Reuters that a UK research plane remained stranded on the ground instead of being released to take samples, frustrating several airlines.
The problems in getting the BAE-146 plane aloft to tackle a new crisis were disclosed by Reuters on Monday [ID:nLDE74M1B9].
Ireland's Ryanair (RYA.I) took the matter into its own hands by sending its own plane up into the reported danger zone over Scotland on Tuesday, and said there was no visible ash.
The budget carrier has dismissed the red zone as a "myth".
(Writing by Tim Hepher, Editing by Michel Rose)