Air Canada, Canada's biggest airline, and tiny rival Porter Airlines filled more seats on their flights in September but the planes of No. 2 carrier WestJet were emptier even though it offered seat sales during the month.

Air Canada said its September load factor edged up to 82.8 percent in September from 82.2 percent in the same month last year as traffic on its routes increased 3.8 percent, more than the capacity increase of 3.0 percent.

This was despite threats of a strike by the airline's 6,800 flight attendants.

"This third consecutive month of record load factor results underlines Air Canada's focus on disciplined and efficient capacity deployment," Air Canada Chief Executive Calin Rovinescu said.

WestJet's load factor fell to 74.7 percent last month from 75.5 percent in the same month a year earlier as capacity rose 8 percent, outflanking a 6.9 percent traffic increase. Despite the weaker traffic numbers last month, forward bookings "remain healthy", WestJet Chief Executive Gregg Saretsky said in a statement.

Privately owned Porter Airlines said its September load factor rose to 68.0 percent from 55.8 percent, as capacity rose 20.4 percent, and traffic rose 46.8 percent.

Early in the month Porter ran a high-profile coupon promotion, offering 50 percent off travel between September and mid-December.