The international body that monitors global air travel says ended 2011 on a positive note, with passenger travel increasing by a "healthy" six per cent.

The International Air Transport Agency said passenger demand for commercial flights increased 5.9 per cent last year over 2010's level.

"Given the weak conditions in Western economies the passenger market held up well in 2011," IATA's director general Tony Tyler said.

But that strong showing failed to keep up with a growth in capacity, as new airplanes added 6.3 per cent more available seats over the year. That put pressure on load factor, the percentage of available seats filled by passengers, which fell to 78.1 per cent in 2011, down from 78.3 per cent in 2010.

A decline in freight demand also hurt airlines' bottom line, IATA said.

"Healthy passenger growth, primarily in the first half of the year, was offset by a declining cargo market," which shrank by 0.7 per cent, Tyler said.

North American demand increased by four per cent, less than the global average. But that too, was less than the six per cent increase in capacity among North American carriers.

"2012 is still going to be a tough year," Tyler said.