The Palestinian, Osama R.M. Shublaq, 27, is said to have hidden in the well on Flight SQ 119 from Kuala Lumpur.

Ground crew waiting to serve the twin-engine Boeing 777-200, which had just taxied to Gate F33 at the airport's Terminal 2, were stunned when he fell about 2.4m from the wheel well to the ground.

He was arrested immediately by airport police. Passengers on the flight said they saw several police officers amid a wail of sirens and blinking lights.

An SIA spokesman said yesterday that the company would not comment on a matter under police investigation.

Pilots and aviation industry sources were amazed the stowaway survived his stunt.

A veteran pilot, noting that the well had just enough space to accommodate the nose wheel, said: 'He could have been crushed by the retracting nose wheel, depending on where and how he was positioned.'

Meanwhile, the Malaysian authorities are puzzled as to how the man could have breached ground security at Kuala Lumpur International Airport (KLIA) and climbed into his cubby hole unnoticed.

Mr Azharuddin A. Rahman, a director at the Department of Civil Aviation Malaysia, said: 'You've got to be a superhero to try such a thing!'

Dato Azmi Murad, the senior general manager of operations of Malaysia Airports Holdings, the body which runs KLIA, said the airport would cooperate with the Singapore authorities in investigations.

Industry sources said they believed this was the first case involving a stowaway in a wheel well at Changi Airport.

The danger behind what the man is said to have done is underscored by previous cases of stowaways found dead on arrival elsewhere in the world. They were either killed by the cold, the lack of oxygen at high altitudes, or crushed by retracting landing gear. The air in the wheel well is not pressurised or heated.

But three weeks ago, a 15-year-old Russian boy survived a two-hour flight in Russia by hiding in the wheel well of a Boeing 737 jet.

The short flight time was probably what saved this latest stowaway, pilots told The Straits Times.

They explained that while schedules put a KLIA-Changi flight, which covers a distance of 300km, at 55 minutes, the actual flight time was only about 35 minutes, with the remaining time spent on the ground.

One pilot noted that the cruising altitude for such flights was around 23,000 feet, but the aircraft spent only about six minutes at that height.

He estimated that the temperature outside the aircraft could have dipped to minus 15 deg C.

The stowaway was said to have been wearing a coat and long pants when he was arrested.

The pilot said, however, that the man could also have been saved by the hatch closing immediately after the plane's landing gear retracted, which would have protected him from winds.

But as Flight SQ 119 came in for landing at Changi, the hatch would have been open for about four minutes.

The pilot added: 'However, what he did was risky because even in the air, the nose wheel gear continues to spin. He could have been crushed by the moving parts.'

In court yesterday, Osama was charged with entering Singapore without a valid pass or permit. If convicted, he could be jailed for up to six months, caned three strokes or more, or fined up to $6,000.