The warning system has worked in addressing Europe's current volcanic ash problem, but it needs further improvement, said several British experts.

Since no plane has been put in danger in the incident, "I personally think that the warning system has been a success," Carina Fearnley from the Aon Benfield UCL Hazard Research Centre here in London, told Xinhua in a recent interview.

The expert, who focuses her research on the volcanic ash early warning system, recalled that several serious incidents involving aircraft flying through volcanic ash in the 1980s prompted the aviation industry to set up a warning system.

The system divides the international airspace into nine parts, assigning a volcanic ash advisory center (VACC) in charge of each part.

The VACC in London is collecting data and making forecasts for the ash originated from the erupting Eyjafjallajokull volcano in Iceland. The ash has crippled the air travel in Europe.

"We are very fortunate because we have got the capabilities and the technologies to do this, and by grounding all the aircraft we have avoided the possible encountering with ash," Fearnley said.

With inadequate warning, there have been more than 80 serious incidents involving commercial aircraft and volcanic ash clouds since the 1980s.

However, "the fact that none has occurred during the start of the Eyjafjallajokull eruption shows how effective a good warning can be," said the expert.

But the current warning system still needs improvement because it is unable to precisely describe the distribution and concentration of the ash in the atmosphere. That is why nearly all planes in Europe were grounded in recent days.

A British National Air Traffic Services spokesperson told Xinhua that the current "international guidelines do not permit us to fly if there is any ash in the air",

As a result of the imperfect warning system, the "blanket ban" on air travel has dealt heavy economical blows to European airlines, which are suffering an estimated of more than 200 million U.S. dollars in losses per day.

After personally taking a test flight, British Airways chief executive Willie Walsh said the overall ban was unnecessary

"So the problem is we need to establish a criterion", said Simon Day, another expert at the Aon Benfield UCL Hazard Research Centre. "When the ash is below such and such level we would let the aircraft to fly, and when the ash reaches such and such level we have to accept that the air traffic is going to be disrupted."

"We did this with other things such as pollutants and chemicals in drinking water, we have safe limits," he said.

Day also said that the airways between the U.S. state of Alaska and Japan are always interrupted by volcanic ash for as much as 45 days each year, and those flights got used to managing the situation, which implies they do have a safety decision-making criterion because there is always a little bit of ash somewhere in the atmosphere.

Fearnley agreed, saying that a lot of countries are experienced in dealing with the issue. Therefore, Europe, for which the ash problem is a relatively new phenomenon, could learn from them.

Though there is still no general international standard for that, a statement issued by the UK Civil Aviation Authority (CAA) on Tuesday night may provide some hint.

Announcing reopening British airspace from 2200 GMT Tuesday, it said:

"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."