Regulators and the airline industry are trading recriminations as air traffic in Europe returns to normal.
Analysts say the almost week-long disruption, caused by volcanic ash from an eruption in Iceland, is the worst since World War II.
The International Air Transport Association (IATA) says the crisis hit almost a third of global flights and estimates 1.2 million passengers a day were affected.
The association, which represents airlines, says much of the blame lies with bad decision-making by governments.
British Transport Minister Lord Adonis has conceded that international safety regulators erred on the side of caution.
Demands are also being made for financial help for the carriers, the BBC reports.
IATA says airlines have lost more than $US1.5 billion over the past week as planes were grounded in much of Europe.
The flight ban has been described as devastating for the aviation industry and one that could take companies three years to recover from.
Airlines are asking governments to give them financial help - something which the European Commission is considering.
Air traffic almost back to normal
Officials say air traffic across Europe should be almost back to normal by Friday.
The BBC reports the decision to lift the flight ban followed safety tests that showed plane engines could cope in areas of low-density ash.
Lufthansa and KLM ran test flights on Sunday and gave their jets a clean bill of health, with no sign of the feared engine damage that volcanic ash can cause.
Flights started landing in Britain on Tuesday night after a six-day shutdown of British airspace.
The European air traffic control agency says it expects some 21,000 out of almost 28,000 scheduled flights to go ahead.