NEW YORK – 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.

AP

Airlines are saving millions of dollars a year by reducing the cruising speeds of their planes to conserve fuel.

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

On one Northwest Airlines flight from Paris to Minneapolis last week, flying slower saved 162 gallons of fuel, saving the airline $535. It added eight minutes to the flight, extending it to eight hours, 58 minutes.

That meant flying at an average speed of 532 mph, down from the usual 542 mph.

"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 four minutes to its flights to and from Hawaii saves Northwest Airlines $600,000 a year.

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.

United expects to pay $3.31 a gallon for fuel this year – not much less than what the average American driver pays for a gallon of unleaded at the pump. Southwest, which has an aggressive fuel hedging program, expects to pay about $2.35.

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 time 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 San Francisco television producer fresh off a flight at Newark Liberty International Airport

David Gannalo, a Phoenix financial software executive, is more than willing to give up four minutes to help airlines cut costs.

"Anything that helps the airlines, you know, because they're going bankrupt left and right," Mr. Gannalo said. "Anything that helps them out will probably be good for the industry in the long term."

Across the board, airlines are feeling the pain of higher energy prices. For jet fuel delivered at New York Harbor, the spot price – airlines pay it when they need more fuel than they've already locked down in a contract – has jumped 73 percent in the last year to $3.54 a gallon, according to government data.

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.

It's a tough time for the industry. 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.

Not every airline is taking the slowdown 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 into 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. 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 labor and maintenance costs if airline employees work longer hours and planes spend more time in service, said Bob Mann, an independent airline consultant in Port Washington, N.Y.

And slowing down to conserve fuel can only be pushed so far: Below a certain speed – which varies by plane – an aircraft's fuel usage can actually rise.

Airlines must strike a delicate balance, seeking an aircraft's "sweet spot" on fuel use without slowing down so much that other costs and flight delays rise, Mr. Mann said.

"Everything's a trade-off," he said.

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," Mr. Mann said. "When they took off the mystery meat, did they lower fares?"