British budget airline Flybe Group swung to a pretax loss in the first half, hurt by one-off costs and a charge related to its exit from its Finland joint venture.
Flybe's stock fell as much as 23% in London trade today.
The carrier posted a pre-tax loss of £15.3m in the six months to the end of September, compared with a profit of £13.8m the same time last year.
Flybe was hurt by an increased flight delay claims provision, external costs related to surplus capacity and revaluation of US dollar aircraft loans.
The company also booked an impairment charge related to the sale of its 60% stake in loss-making Flybe Finland to partner Finnair.
The embattled carrier had only just returned to profitability last year, helped by brutal cost-cutting that involved giving up airport slots, slashing jobs, exiting unprofitable flight routes and grounding surplus fleet.
However, new EU 261 flight delay compensation regulations that dictate procedure in events of denied boarding, flight cancellations, or long delays of flights, forced the company to record a £6m provision in the first half.
Flybe's chief executive Saad Hammad called the rules "unfortunate" and "discriminatory".
In terms of fares, on most of the routes Flybe operated it mainly competes with rail roads and ferry operators who do not have compensation regimes.
"It's unfortunate because (compensation for) any delay of three hours or more is more than three times the average ticket price of Flybe," Hammad saidl. Flybe pegs its average ticket price at less than €85.