British aviation regulators bring in measures on Tuesday to reduce the airspace closures fiercely criticised by airlines, as European skies were hit by new shutdowns caused by volcano ash clouds.
Plumes of thick ash from Iceland's Eyjafjoell volcano, which in April shut down much of Europe's airspace for a week last month, drifted over the continent Monday, closing major airports and cancelling some 1,000 flights.
Britain, the Netherlands and Ireland closed airspace, with London Heathrow, Europe's busiest air hub, and Amsterdam-Schiphol among those affected.
Airlines, which have lost millions of dollars due to the ash alerts, have expressed their fury with what they viewed as unnecessary restrictions introduced by overcautious safety watchdogs.
In a bid to keep the skies open for business, British aviation regulators introduce new measures from midday Tuesday that will to allow flights in thicker ash than previously permitted for a certain amount of time.
The new area -- called a "Time-Limited Zone" -- was created after discussions between regulators and manufacturers, said regulator the Civil Aviation Authority (CAA).
Experts believe high concentrations of volcanic dust can damage plane engines and even cause crashes.
But a CAA statement said: "Aircraft and engine manufacturers... have agreed that it is safe to allow operations in the new zone for a limited time.
"This means that areas of our airspace that would have previously been closed can safely open, further minimising disruption."
To operate in the new zone, airlines must present regulators with a safety case, which includes the agreement of the manufacturers, said the CAA.
This had already been achieved by British airline Flybe, which will be allowed in the zones from midday.
British Airways chief executive Willie Walsh led the attack on Monday's flight restrictions, labelling them "a gross over-reaction to a very minor risk."