Volcanic ash disruption: UK flights resume
Most flights have resumed across the UK after a day that saw thousands of passengers affected by an ash cloud from the erupting Icelandic volcano.
Air traffic control company Nats said harmful concentrations of ash dispersed from UK airspace overnight.
But some flights within the UK and a number to Germany were cancelled.
Ash might return to affect much of the country on Friday with the potential to disrupt flights, although officials say the volcano has stopped erupting.
Iceland's meteorological office said no plume had been detected since 0300 local time (0400 BST) on Wednesday.
Services in and out of Scotland, Northern Ireland and northern England were hit on Tuesday as about 500 flights were cancelled across Europe.
Nats said UK airspace was expected to remain clear until 1900 BST on Wednesday.
Air traffic over northern Germany is also returning to normal after Hamburg, Bremen and Berlin airports closed for several hours.
Some 700 flights were cancelled in Germany on Wednesday, Europe's air traffic agency Eurocontrol said.Clearer picture
Forecasters said that if eruptions from the Grimsvotn volcano continued at "current variables", all areas with the exception of East Anglia and south-west England might be affected by ash on Friday.
"At between 35,000 and 55,000ft, there could be a risk of a high concentration of ash covering most of the UK," a spokesman said.
The Met Office said the concentration of volcanic ash in the UK's airspace was expected to decrease significantly throughout Wednesday.
Transport Secretary, Phillip Hammond, said modelling by the Met Office and the Civil Aviation Authority should provide a clearer picture soon.
"Information's coming in all the time from satellite imagery... for example, BA have just told us this morning the results of the test flight that they did yesterday.
"All of this data gets fed into the model to refine it and we'll be working very hard to see if we can shrink down the red area predicted for Friday."
On Tuesday, dozens of planes were grounded at UK airports including Glasgow, Edinburgh, Newcastle, Barra, Prestwick, Cumbernauld, Londonderry, Tiree, Carlisle and Durham Tees Valley.
Airports say they are hoping to resume normal services but have warned of possible delays and passengers are advised to check with their airline before travelling.
The UK's emergency response committee, Cobra, met on Tuesday to discuss the knock-on effects of the ash cloud.
The Civil Aviation Authority (CAA) divides the airspace into areas of high, medium and low-density ash. Airlines wishing to fly in areas of medium or high-density ash need to put a safety case to the authority and have it accepted.
The CAA said earlier that, although no airlines had applied to fly in high-density ash, some had been given permission to fly in medium density.
Willie Walsh, head of International Airlines Group, the parent company of BA and the Spanish carrier Iberia, said a 45-minute test flight on Tuesday at different altitudes over Scotland in the red zone had shown there was no risk to aircraft.
"The aircraft then returned and has been examined. All the filters have basically been removed, they will be sent to laboratories for testing. The simple answer is we found nothing.
"We've conducted video borescoping of the engine, where, similar to what you'd see on a medical programme, we inserted a borescope into the engine to check the inside of the engine and found no evidence of volcanic ash."
Tuesday's cancellations came just over a year after another volcanic eruption in Iceland caused widespread disruption across Europe, including the closure of UK airspace, amid concerns about the damage volcanic ash could cause to engine aircraft.
The Grimsvotn volcano in Vatnajokull National Park began erupting on Saturday and closed Iceland's airspace for a period.
Experts say the eruption is on a different scale to the one last year and is producing larger ash particles, which fall to the ground more quickly.
A meteorologist at Iceland's met office, Hrafn Gudmundsson, told Reuters on Wednesday: "Tremors have been decreasing somewhat so there are indications that it's ceasing really, that it is in the final stages."