The aviation crisis caused by Iceland's Eyjafjallajokull volcano has fuelled calls for Europe to improve its air traffic management.
The ban on flights in areas affected by volcanic ash was very costly for airlines and passengers, who now want compensation.
EU transport ministers will meet on 4 May, and are under pressure to speed up implementation of a plan that would introduce trans-national airspace blocks.
The authorities were right to put passenger safety first, weren't they?
The volcanic eruption on 14 April triggered a shutdown of European airspace, starting with the UK, which acted on scientific advice from the Met Office in London.
The volcanic ash cloud paralysed airports across Europe for five days
The European Commission says the EU member states were applying risk assessment models in line with guidelines laid down by the International Civil Aviation Organization (ICAO), a United Nations agency.
The Commission says EU states were "absolutely right" to put safety first, calling it "the first priority of aviation policy".
But the scale of the airspace closure was unprecedented, leaving millions of passengers stranded. As it became clear that the ash cloud was not shifting the Commission and aviation officials agreed that a more differentiated approach was needed urgently.
The losses made airline bosses furious - an estimated $200m (£131m; 149m euros) was lost daily while fleets were grounded. They demanded an improvement in Europe's air traffic management.
Is it fair to say that the EU was slow and unco-ordinated, faced with an escalating crisis?
There has been widespread criticism of the EU's response, with Euro MPs and airline officials complaining that the Commission and transport ministers did not hold emergency talks until 19 April.
The EU Transport Commissioner, Siim Kallas, blamed "fragmentation caused by a patchwork of different national decisions".
David Henderson, spokesman of the Association of European Airlines, said Eurocontrol, the body that oversees European air safety, should have been directly involved in the decisions on air traffic management.
"The unpreparedness of the whole decision-making chain was evident from the start," he said.
He called the shutdown country-by-country "a sort of domino effect across Europe".
A Eurocontrol official, Bo Redevorn, told the BBC that "we were not well prepared to deal with an issue of this kind". There was insufficient data on the hazard posed by volcanic ash, he said.
Interpretations of the scientific data used for risk analysis differed from country to country.
In their defence, EU officials pointed out that no such threat had come previously from an Icelandic volcano in modern times.
If the EU is frustrated with the air traffic control 'patchwork' why didn't it reform the system earlier?
EU integration does not yet extend to air traffic control - as the Commission points out, only member state governments can decide whether or not to close their airspace. That power has been jealously guarded for reasons of national defence and sovereignty.
The EU expects air traffic over Europe to grow by 5% annually up to 2020
So Europe has 27 different air traffic zones, each able to impose flying bans.
Nevertheless, the Commission is now pushing to get a new structure adopted - nine Functional Airspace Blocks (FABs) to replace the existing 27 areas. This is part of the revised blueprint called Single European Sky II (SES II).
Eurocontrol, which co-ordinates flight information for 38 states, says it wants "a seamless, pan-European air traffic management system".
The Commission's policy paper on SES II noted that the US air traffic control system "manages double the number of flights for a similar budget [to the EU's] from some 20 control centres". Europe has about 60 control centres.
Is there a deadline for overhauling Europe's air traffic management?
The original deadline for putting the SES II package into effect was January 2012. But in light of the ash crisis Commissioner Kallas said "I don't think we can afford to wait that long".
He plans to fast-track the package this year. By the end of this year the EU plans to have in place an air traffic network manager. That manager would co-ordinate Europe's air traffic resources - but without taking over from the national air traffic controllers.
The network manager would deal with route design, traffic flows and technical tasks, such as allocating transponder codes and aeronautical frequencies, which are done for every flight.
The hope is that the communication delays and confusion over data seen in the ash crisis would be avoided.
Another big part of SES II is technological innovation - the need to upgrade and harmonise systems across Europe to cope with the expected doubling of air traffic by 2020. The deployment phase of the project, called Sesar, is due to start in 2013.
Apart from the volcano threat are there any other reasons why Europe needs to do this?
Yes. The Commission says CO2 emissions from aviation are growing rapidly, though at present they account for about 3% of Europe's emissions.
A more efficient air traffic system could cut emissions by up to 12% for the average flight, the Commission says.
The airspace fragmentation means that planes on average fly 49km (30.4 miles) longer than strictly necessary, according to the Commission. In addition, airport slots are allocated independently of flight plans, causing extra costs and waste, it is argued.