The morning outbound flight left Luqa airport an hour late, at 8am, landing in Heathrow at 10.45am GMT.
The inbound flight, usually leaving the same airport at 10.50am, left at 1pm arriving in Malta some three hours later. The system crashed at 6am and lasted just over an hour.
However airports had built up backlogs that took until lunch-time to clear, with Heathrow having delays averaging two hours.