The growth in the number of Melbourne-Sydney passengers in May is because of the come back of business travellers, according to federal government figures released yesterday.

The data showed an 18.5 per cent rise in Melbourne-Sydney passengers, as well as an overall 5.3 per cent increase in Australian domestic airline passengers for the month compared with last year and a more modest year-to-date climb of 2.1 per cent to 51.38 million.

While some of May's Melbourne-Sydney surge is credited to the arrival on the route last July of Tiger Airways, the Tourism and Transport Forum said the statistic reflected rising business confidence and spending on business travel.

"The almost 100,000 additional passengers on that route in May will have generated additional spending in the NSW and Victorian economies, benefiting operators that support business travel, including hotels and serviced apartments," said TTF aviation national manager Caroline Wilkie.

"There have now been consistent national domestic airline passenger number increases each month since January 2010 -- this type of growth has not been seen since September 2008."

The surge in passengers, however, has not meant crowded planes as the number of aircraft trips climbed 7.1 per cent to 49,310 in May. Traffic growth lagged behind an 8.2 per cent rise in capacity, and nationwide passenger load factors dropped from 76.9 per cent to 73.9 per cent.

Aside from Melbourne-Sydney, other routes that saw surges included Adelaide-Brisbane climbing 17 per cent, Gold Coast-Sydney up 16.2 per cent, Port Macquarie-Sydney higher by 16.1 per cent and Adelaide-Sydney with 13.5 per cent increase.

Some routes, on the other hand, slumped significantly, with Brisbane-Hamilton Island sliding 19.4 per cent and Adelaide-Canberra falling 17.7 per cent.