In the immediate aftermath of the attacks on New York and Washington DC on 11 September, airlines tightened up baggage checks and banned sharp objects.
But further action will depend on talks between carriers and governments, not least because the really expensive measures - such as reinforcing cockpit doors or adding closed circuit television - have yet to be introduced.
"We don't know the extent to which the measures are going to affect us yet," said a spokesman for Virgin Atlantic, 60% of whose flights are trans-Atlantic.
"We expect governments to show understanding if they impose new measures on us."
Because direct assistance could turn out to breach European Union rules on state aid, many are hoping for a co-ordinated response - and perhaps for a relaxation of the tight limits on mergers within the airline industry.
Still cagey
As yet, few airlines are prepared to attach a number to the extra spending the new measures will entail.
"It's too early for us to say how much extra it will cost," said a spokesperson for British Airways.
The airline is not seeking direct cash aid from the UK government, she said, reiterating the company's position that it wants a "level playing field".
Virgin Atlantic also said things had not settled down enough to talk about costs.
But industry insiders say that position could change, especially now that one government - Italy's - has broken ranks on state aid.
Earlier this week Italian airline Alitalia unveiled a restructuring package of job cuts, aircraft mothballing and route cancellations broadly similar to that unveiled by most other major carriers.
The difference: the package included an offer of 300-400bn lire ($140-190m; £100-130m) from the Italian transport ministry to help with security and cut airport taxes and VAT on tickets.
The European Commission said that contrary to EU rules it had not been notified of the move.
Unless it forms part of a concerted push - and unless the Italian authorities can show it will compensate Italian airlines solely for the financial consequences of 11 September - the aid could prove illegal.
Or, say observers, it could spark a copycat round of offers of support.
Guns on board
One question on the agenda at meetings across Europe is been thrown into sharp focus by the likelihood that US President George W Bush is to announce a large-scale expansion of the Federal Aviation Administration's "sky marshal" programme.
Mr Bush wants more armed marshals, although he is thought to be unconvinced about suggestions that pilots should carry guns too.
The practice is rare in Europe, although some airlines flying in European airspace - notably Israel's El Al - are widely believed to use them as a matter of course.
But industry experts said the chances of widespread use of marshals are slim.
"In the US, aviation security has been quite appalling for some time," Chris Yates, aviation security editor of Jane's Aviation, told BBC News 24.
Unlike in Europe, where airport security is more often seen as a government responsibility, pay and conditions at US airports for security staff is generally accepted to be poor, especially after the aviation industry was deregulated by President Ronald Reagan in the 1980s.
Attempts to tighten up the rules have been blocked by concerted lobbying from the airlines themselves, who have to pay the airports for security.
For this reason Mr Bush is expected to include tighter background checks, better training and official supervision in a speech in Chicago today.
The situation is different in Europe, Mr Yates said.
"I can't for one moment believe that sky marshals would add to confidence for European air travellers," he said. "Having a shootout on board an aircraft is not a wise option."