A United Airlines 777 jet headed from Maui to San Francisco turned back to Honolulu about two hours into Sunday's flight after bad weather forced the pilot to fly at a lower-than-usual altitude that burned through fuel at a faster rate, according to the airline.

United Flight 34 left Maui at 2:03 p.m. Sunday headed for San Francisco, and was expected to arrive just before 9 p.m.

Instead, air traffic controllers from the Federal Aviation Administration advised the flight crew to "fly at a significantly lower altitude" because of bad weather conditions," United Airlines spokeswoman Robin Urbanski said.

After the flight was about an hour from Honolulu, she said the "much, much lower altitude" prompted the pilot to say that he would need more fuel to continue to fly at that level.

Urbanski said this kind of turnaround midflight happens infrequently. She said figuring the fuel for the jets involves balancing weight as well as the route, so it isn't as simple as topping off the car's gas tank each time you pull into a gas station.

"We do put a certain amount of fuel," she said, but added that weight restrictions must be calculated as well.

Urbanski said the flight was full of passengers and left with ample fuel to reach San Francisco. When the plane arrived in Honolulu just before 7 p.m. to add more fuel, she said the pilot had reached his maximum allowable flying hours and the airline had to switch crews.

The flight was rescheduled to leave yesterday morning.