Pilots are being ordered to stop trying to make up time on Qantas flights running significantly late - so the airline can save on fuel costs.

In a snub for passengers, the airline has a strict policy of refusing to allow pilots to catch up if they can't land in the 15-minute window that qualifies as being on time.

"If the aircraft is running late and the pilot can't make it there within 15 minutes of the scheduled arrival time then he or she is not permitted to fly faster and burn more fuel," one pilot said.

"It would seem that the underlying assumption is that once a passenger is more than 15 minutes late, they may as well be an hour late."

Traditionally, if a flight is running an hour late a pilot could fly faster to minimise the delay.

However, late pilots are allowed to fly faster provided they are capable of landing within 15 minutes of the scheduled arrival time.

That would count as an on-time arrival - although Qantas denies this is the reason for the policy.

Australian International Pilots Association vice-president Captain Richard Woodward confirmed the policy.

"Pilots are capable of making up time in the air if needs be, but they obviously need to burn more fuel to achieve that," he said.

"The policy states that if you can't land the aircraft within 15 minutes of the scheduled arrival time, you're not allowed to try. So even if a pilot can improve the ETA from an hour late to 20 minutes late, they're not permitted to attempt it."

Qantas confirmed fuel -- which cost the airline more than AU$4 billion a year -- was a major factor in deciding whether or not to make up time.

"Fuel burn increases exponentially when the aircraft goes faster so in trying to make up just a few minutes, planes can burn through thousands of litres of jet fuel," a spokesman said.

"Airlines around the world are already charging passengers fuel surcharges and higher airfares because of high jet fuel prices and burning more and more fuel puts further pressure on airfares."

Under Bureau of Infrastructure, Transport and Regional Economics benchmarks, which Qantas and other airlines use to measure their performance, flight arrival is counted as "on time" if the plane arrives at the gate within 15 minutes of the scheduled time.

Qantas said the policy had nothing to do with boosting its on-time running figures and was all about fuel costs.