Travellers could face delays as some airlines slow down to save on fuel. (CBC)

Drivers have long known that slowing down on the highway means getting more miles to the gallon. Now airlines are trying it, too — adding a few minutes to flights to save millions on fuel.

Southwest Airlines started flying slower about two months ago, and projects it will save $42 million US in fuel this year by extending each flight by one to three minutes.

On one Northwest Airlines flight from Paris to Minneapolis earlier this week alone, flying slower saved about 613 litres of fuel, saving the airline $535 US. It added eight minutes to the flight, extending it to eight hours, 58 minutes.

"It's not a dramatic change," said Dave Fuller, director of flight operations at JetBlue, which began flying slower two years ago.

But the savings add up. JetBlue adds an average of just under two minutes to each flight, and saves about $13.6 million a year in jet fuel. Adding just four minutes to its flights to and from Hawaii saves Northwest Airlines $600,000 a year on those flights alone.

United Airlines has invested in flight planning software that helps pilots choose the best routes and speeds. In some cases, that means planes fly at lower speeds. United estimates the software will save it $20 million a year.

"What we're doing is flying at a more consistent speed to save fuel," said Megan McCarthy, a United spokeswoman.

'If saving fuel costs me a few extra minutes out of my day, then … my inconvenience is nothing,'—Leah Nichols, traveller

Fliers, already beleaguered by higher fares, more delays and long security lines, may not even notice the extra minutes. The extra flight time is added to published flight schedules or absorbed into the extra time already built into schedules for taxiing and traffic delays.

"If saving fuel costs me a few extra minutes out of my day, then … my inconvenience is nothing," said Leah Nichols, a television producer who lives in San Francisco and was fresh off a flight at Newark Liberty International Airport, waiting for a train to New York. "I'm cool with that."

Airlines bump up fares to cover high fuel costs

Airlines are trying other measures as well to deal with higher fuel costs, including raising fares, adding fuel surcharges to tickets and charging extra for a second checked bag rather than a third. Several smaller airlines have filed for bankruptcy protection in recent weeks, many citing high fuel costs. Fuel costs have also resulted in sharp first-quarter losses by some airlines.

But not every airline is taking the slow-down approach.

"We have the flying schedule to protect," said John Hotard, a spokesman for American Airlines. He said the carrier does other things to save fuel — for instance, installing small vertical stabilizers called winglets to the ends of some aircraft wings, which boosts fuel efficiency by improving aerodynamics.

American also tries to keep its planes plugged in to ground-based power and air conditioning for as long as possible to conserve fuel, and pushes air traffic controllers to assign its flights to altitudes where they will have less headwind or greater tailwind. Many other airlines have adopted similar measures.

Slowing flights down isn't a magic bullet. It can help airlines conserve fuel, but it can also lead to greater labour and maintenance costs if airline employees work longer hours and planes spend more time in service, said Bob Mann, an independent airline consultant based in Port Washington, N.Y.

And slowing down to conserve fuel can only be pushed so far. Below a certain speed — which varies depending on the plane — an aircraft's fuel usage can actually rise.

Consumer advocates say the extra minutes shouldn't matter.

"If it means that airlines can keep their costs down, keep their ticket prices down, and save a little fuel, that's fine," said Travis Plunkett, legislative director at the Consumer Federation of America.

But others doubt the change will result in lower fares any more than previous cost cutting, such as eliminating meals or taking away blankets.

"I don't think so," Mann said. "When they took off the mystery meat, did they lower fares?"