Air Canada cancelled about four per cent of its flights because its pilots have reached the limit of their monthly flying time, spokeswoman Laura Cooke told CBC Newsworld on Sunday.

"We do apologize," she said.

But "today should be the end of it" because the airline starts a new block of time – the August quota – at midnight, she said.

Cancellations force passengers to switch flights.

It's not clear exactly how many flights or passengers are affected.

Cooke blamed the problem on a 70 per cent increase in cancelled flights in July because of the weather.

• FROM JULY 2, 2005: Foggy days bring delays at Halifax airport

Under their contract, Air Canada pilots can fly 84 hours a month.

When a flight is cancelled or delayed, the pilot may still be on duty, sitting in the plane and eating up his flying time.

It's even worse if a pilot is held over in one city, because then the airline may have to find a replacement for him at his intended destination for his next flight.

Air Canada had 177 flights cancelled in Halifax in July, and electrical storms in Manitoba and the northest U.S. raised the total, Cooke said.

The airline has reserve pilots, but they also "have reached their max," she said.

Cooke said the airline started calling customers several days ago and the "vast majority" were able to take a different flight on their scheduled day of travel.

International flights protected

Flights to and from Toronto, the airline's hub, are the most affected.

Air Canada is protecting its international flights because there may only be one a day to some destinations.

But for frequently served city pairs, like Toronto-Vancouver, it is consolidating flights.

The airline is looking at compensation on a case-by-case basis, Cooke said.

Under their contract, pilots can fly 84 hours a month. Government rules allow slightly more flying time each month.