Volcano ash flight ban 'might have ended sooner'
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 earlier.
All aircraft engine makers contacted by the BBC declined to comment.
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.
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