A United Airlines Boeing 747 jetliner carrying 308 passengers and a crew of 12 lost power in all four engines and dropped more than two miles in altitude during a flight to Hawaii Sunday, officials revealed.

Federal Aviation Administration and airline officials said the plane landed safely in Honolulu after the crew restarted the engines through emergency procedures.

Officials said there was no early indication of the cause of the simultaneous malfunction.

The jet was on a flight from Newark, N.J., to Honolulu with a stopover in San Francisco. It was cruising at 39,000 feet over the Pacific Ocean about 50 minutes from Honolulu when the engines stalled.

FAA officials said crew attempts to restart the engines using normal high-altitude procedures failed. The plane dropped to 26,000 feet before the crew successfully used engine-starting procedures normally employed on the ground.

Officials believe the problem is caused by ice crystals that form in kerosene fuel used to power the aircraft. In most cases, crews have been able to restart the engines after gliding the planes to a lower altitude.

An FAA official said that, because of the 747's "glide ratio," passengers may not have been aware the plane dropped two miles. "The plane doesn't go into a dive," he said.