The CAA has now set a safe threshold for the concentration of ash
The suspension of UK flights after the volcanic eruption in Iceland might have ended sooner, the BBC has been told.
Flights resumed when manufacturers gave assurances six days after the eruption, which disrupted the plans of hundreds of thousands of people last month.
If airline engine manufacturers had specified a safe level of ash earlier, the Civil Aviation Authority says it could have reopened the skies then.
All aircraft engine makers contacted by the BBC declined to comment.
Ash from Iceland's Eyjafjallajokull volcano triggered a shutdown of European airspace, paralysing many airports and stranding hundreds of thousands of tourists and business travellers.
The flight ban was imposed because ash can turn to molten glass in the high temperatures of an aircraft's turbine and cripple the engine.
CAA chief executive Andrew Haines told Radio 4's The Report: "The critical path for this decision was the time it took for the manufacturers to satisfy themselves on the safe level of contamination.
"How long does it take for a manufacturer who has declined to determine something for many years to actually say, 'Given the evidence we've now got, we're happy to nail our colours to the mast and say that these are safe levels of contamination that don't present a hazard.'"
He said: "I suspect that manufacturers knew much of this, that they knew there was an acceptable level of safety but what hadn't happened is that they were prepared to underwrite that and validate it."
Mr Haines continued: "I suspect that a lot of these things come down to a combination of commercial and safety pressures and actually there are levels of contamination which might impact on the life of the engine without impacting on its safety.
"But that's only a speculation on my part.... I'm just grateful that they came to the table and worked very hard to get it resolved."
"If we'd had the assurances from manufacturers that we have now at the start of this crisis, the response would have been different."
Ongoing discussions about the safe level of volcanic ash to fly in had already been taking place between air regulators and the air industry, according to Richard Deakin, chief executive of the National Air Traffic Control Services (NATS).
"There had been a meeting of the volcanic ash advisory group with aero engine manufacturers in March of this year, so literally a few weeks before events unfolded," he said.
The question of what might be a safe level has been widely discussed across the industry for many years.
In 1982 a BA jumbo jet flew right into a plume of ash from an Indonesian volcano and all four engines stalled, although they were eventually restarted.
The normal procedure when planes encounter ash is to fly round it, meaning that manufacturers have not had to specify "safe" levels.
But the size and location of the ash cloud produced by Eyjafjallajokull, meant it was impossible to fly round it.
The government has also been criticised for its lack of leadership in the crisis.
Tim Jeans, managing director of Monarch Airlines, told The Report: "The government was not in control and I hope it will never pretend otherwise.
"There was no leadership demonstrated, nor has there been other than they understood there was a potential political problem brewing."
A Department for Transport spokesperson responded: "The government assumed clear and decisive control over events from the early stages of the ash crisis - it is wrong to suggest otherwise.
"The decision to restrict airspace was made in line with long-standing international guidelines and information from aircraft manufacturers that any volcanic ash could pose a danger to aircraft.
"The whole of Europe was in the same position, acting according to the same aviation safety rules."
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