Core UK airspace, including the London airports, has re-opened after days of closure as a result of the Icelandic volcanic ash cloud.
The UK Civil Aviation Authority has allowed a phased re-introduction of much of the affected airspace from 22:00 local, citing an easing of tolerance limitations from aircraft manufacturers which has resulted in the development of new guidance.
"Current international procedures recommend avoiding volcano ash at all times," the CAA states.
"We had to ensure, in a situation without precedent, that decisions made were based on a thorough gathering of data and analysis by experts. This evidence based approach helped to validate a new standard that is now being adopted across Europe.
"The major barrier to resuming flight has been understanding tolerance levels of aircraft to ash. Manufacturers have now agreed increased tolerance levels in low ash density areas."
The CAA says the decision has been based on evidence from previous volcanic ash incidents, new data collected from test flights, and additional analysis from manufacturers over the past few days.
Under a new procedure, airline will be allowed to conduct their own assessment of residual risk and develop their own mitigating processes. Carriers will also have to conduct ash-damage inspections before and after flight, and report ash-related incidents to the CAA.
"It is a conservative model allowing a significant buffer on top of the level the experts feel may pose a risk," says the CAA.
British Airways has welcomed the decision. "Safety is always our overriding priority," says BA chief Willie Walsh. "We have many years of experience of operating in areas of volcanic activity all around the world.
"On behalf of the tens of thousands of customers stranded around the globe, we are delighted the authorities have paid heed to the arguments we and the industry have put forward."