AIRLINES often sell more seats than they have available on the basis that some passengers will cancel or not show up. If too many passengers do present themselves, the carriers will have to bump some to another flight—and those flyers bumped by Air Canada have apparently been getting shortchanged. The Canadian Transportation Agency ruled on Monday that the airline's 12-year-old practice of giving delayed passengers either C$100 ($96) cash or a $200 travel voucher is unreasonable, except in cases where the delay is caused by operational or safety reasons.

The agency received a complaint about Air Canada's overbooking policies in December 2011 from Gabor Lukacs, a former maths professor at the University of Manitoba who has repeatedly taken on Canada's airlines. Mr Lukacs asked for Air Canada to be prohibited from overbooking domestic flights and, if it does so, for its bumped passengers to receive between C$200 and C$800, with the exact amount depending on the length of the delay. The carrier defended its overbooking system, saying it was applied reasonably and in a well-controlled manner. And it noted that on average just 0.09% (9 in 10,000) of its domestic passengers are affected. WestJet Airlines, Canada's other big carrier, does not overbook flights.

In its ruling the agency said that Air Canada's rate does not reflect the current price of airline tickets, accommodation and other incidental expenses. It noted that bumped passengers in the US receive up to $1,300 depending on the length of the delay, and that the European Union has set a maximum compensation of €600 ($776) depending on both the length of the delay and the distance of the flight. Both figures are substantially higher than Air Canada's current offering.

The agency ruled that Air Canada could continue to overbook, but gave it 30 days to adopt either an American-style compensation package or the one proposed by Mr Lukacs, thus proving once again it does not pay to over-promise and under-deliver.