More than 1,500 flights were cancelled on Monday - a public holiday in parts of Britain, and one of the busiest travel days as the school holidays draw to close - when air traffic controllers were forced to switch to manual systems due to a technical problem.
Ryanair, Europe's biggest airline, would be operating a normal schedule by Wednesday, said boss Michael O'Leary, as he criticised how Britain's National Air Traffic Services (NATS) had handled the situation.
Harper chaired a meeting on Tuesday with NATS, the Civil Aviation Authority (CAA), airlines, airports, trade bodies and Border Force.
EasyJet (EZJ.L) said that the knock-on impact meant some flights were cancelled on Tuesday morning.
Heathrow Airport, Britain's busiest hub, told passengers to contact their airline before travelling to the airport on Tuesday.
Persons:
Maria Ball, Charles De Gaulle, Mark Harper, Michael O'Leary, haven't, O'Leary, Raphael Satter, Rishi Sunak, Sunak, Harper, NATS, Cirium, Sarah Young, Padraic Halpin, Farouq Suleiman, Kate Holton, Alistair Smout, Alison Williams, Mike Harrison
Organizations:
British, Ryanair, Europe's, Air Traffic Services, REUTERS, Civil Aviation Authority, CAA, Border Force, Aviation, British Airways, Heathrow, Thomson
Locations:
Europe, Britain, Liverpool, England, Paris, Edinburgh, London, Stansted, NATS