I'm not in airline business, so don't know how airlines do their accounting, but I'm guessing that airlines' accounting practice is to recognize ticket sales as revenue when a flight is booked, payment received, but flight is in the future. So when a flight is cancelled and airlines have to refund, the refund has to be recognized as an expense; so P+L looks good in the past, but refund bombs the P+L in the present.

Whereas if the ticket booking and payment is recorded as a Contingent Liability and the ticket sale is recognized as revenue upon when the flight is flown, then when a cancellation occurs and a refund has to be paid out, the refund is charged against the Contingent Liability, and is not an expense. Of course, cash flow has to be managed to ensure sufficient cash is available to pay the refund.

Does anyone know how ticket sales and refunds are accounted for in airlines' accounting practices?