Jet Engine Blast Likely, Thai Official Says : Air crash: A note seems to offer a clue that a fire caused an explosion that destroyed the airliner.

BANGKOK, Thailand — A senior Thai official said Friday that he believes an engine explosion, rather than a bomb, caused an Austrian airliner to crash in Thailand early this week.

Air Chief Marshal Somboon Rahong also told a news conference that a document was recovered from the pilot’s compartment with the word “fire” scrawled in English across the page. He said a circle had been drawn around the word.

Somboon said Thai investigators believe that the twin-engine Boeing 767-300 jetliner dropped from about 31,000 feet to about 9,000 feet before exploding, which he said supports the idea that a fire had burned for a time before igniting fuel on the plane.

“I think, and other officials agree, that the right engine caught fire and the heat from that fire caused fuel supplies in the wing to explode,” said Somboon, who heads the Airport Authority of Thailand.

The Lauda Air jet carried 223 passengers and crew, all of whom were killed in the explosion and crash of the plane. The plane was on a flight from Bangkok to Vienna and carried a full load of fuel.

Somboon came under intense criticism after Sunday night’s crash when it was revealed that Bangkok’s Don Muang airport, which he heads, did not routinely inspect checked luggage with X-ray equipment. Such searches had to be paid for by airlines.

Somboon was also criticized for suggesting soon after the crash that bad weather had caused engine failure aboard the plane. Thai government officials said publicly that the weather was clear.

Investigators from Boeing Co., the manufacturer of the airplane, and Pratt & Whitney, which supplied the engines, joined Thai investigators at the crash site about 100 miles northwest of Bangkok.

A Pratt & Whitney spokeswoman said there is no evidence yet to support the theory that one of the plane’s two engines exploded. Boeing also denied that the evidence points to a fire.

Thai and Austrian police officials said after studying the wreckage that the left engine of the plane appeared to be more burned than the right. This was evidence, they said, that one engine might have burst into flames well before the moment it crashed.

“We think it is more and more plausible that an engine caught fire, that it imploded,” Peter Blumauer, an intelligence specialist from Austria’s Interior Ministry, told journalists. But he added, “We don’t rule out a bomb.”

Thai villagers in the region told investigators that they saw flames shooting from the plane for some time before the crash, Somboon said.

Thai investigators flew to Washington on Friday carrying the aircraft’s flight recorders for examination by the U.S. National Transportation Safety Board.

The recorders are expected to show whether the plane’s American pilot, Thomas Welch of Seattle, had shouted for help or indicated that the plane was on fire. Ground controllers in Bangkok heard no radio transmissions as the plane vanished from the radar screen about 16 minutes after takeoff.

Western security officials had initially said that the plane’s rapid disintegration and the relatively small size of the pieces of wreckage suggested almost conclusively that an explosion took place aboard the plane in flight, most likely caused by a bomb.

So far, no group has issued any claim of responsibility for putting a bomb aboard the aircraft.