It will take weeks, possibly months, to determine the cause of a twin-engine airplane's crash landing on the eastern shore of Utah Lake Saturday, a Federal Aviation Administration spokesman said Monday.

"It will be investigated. We don't have a probable cause yet," said Mitch Barker, an FAA public affairs officer in Seattle, Wash. He said the investigation is a low priority because the crash is considered an incident, not an accident. Barker said the FAA's search for a cause could take up to two months.A Piper Apache piloted by John Scott Riffle, 21, landed on the lake shore just north of the Utah Lake State Park boat harbor. Riffle and a passenger, Alfred Charles Schwab, 24, were uninjured. The planes's landing gear, propeller and engine were damaged during the landing.

The two men were on their way to Las Vegas from Salt Lake Airport No. 2 in a plane rented from Classic Aviation.

Barker said Riffle reported a problem with the gyroscope during flight and was headed back to Salt Lake when the plane went down. The gyroscope is essential to the function of three of the aircraft's six basic flight instruments - attitude, turn and heading, Barker said.