Government officials will face questions today from a House of Lords committee over Whitehall's handling of the ash cloud crisis which devastated air services.
The peers will ask whether the six-day complete ban on air travel in Europe was an overreaction that could have been avoided.
The officials will also be questioned on whether existing compensation regulations place an unfair financial burden on airlines.
Peers will also seek answers to whether a standardised limit for ash concentration levels to which aircraft flight could be permitted should be established by the European Aviation Safety Agency.
The officials are appearing before the Lords EU sub-committee on the internal market, energy and transport, chaired by Baroness O'Cathain.
Those giving evidence to the committee are the Department for Transport's (DfT) aviation director Jonathan Moor and two other DfT officials - international aviation and safety division head Francis Morgan, and aviation safety branch head Susan Hamilton.
The spread of ash from the eruption of Iceland's Mount Eyjafjallajokull caused days of travel chaos for air passengers, with thousands of travellers stranded abroad, airports shut and flights cancelled.
British Airways chief executive Willie Walsh and Virgin Atlantic boss Sir Richard Branson were among those sharply critical of the handling of the crisis.
Sir Richard said the crisis cost Virgin around £10 million to £15 million a day, adding that the authorities dealing with the crisis had made "crass, stupid decisions".
Ryanair had to cancel 9,400 flights over an 18-day period, while another budget carrier, easyJet, lost an estimated £50 million to £75 million.