Crew were serving a meal at the time and were sent crashing into the ceiling Nine people on board a Dragonair flight from Kota Kinabalu in Malaysian Borneo were injured yesterday, two of them seriously, when the plane encountered violent turbulence about 300 nautical miles southeast of Hong Kong. It struck shortly after a meal was served, sending food flying and stewardesses crashing into the ceiling as they tried to check passengers' seatbelts. After receiving treatment on arrival at Chek Lap Kok airport, three passengers and six crew members of Dragonair flight KA060 were flown by helicopter to Tuen Mun Hospital. As of last night, six of the nine were being held overnight for observation. One man was in a stable condition, while two women, both passengers, were in a serious condition. As a precaution, the airline also sent six other flight attendants from the flight to Princess Margaret Hospital for examination. All six were treated and discharged. The flight, which was carrying 236 passengers and 14 cabin crew, ran into the turbulence at its normal maximum cruising altitude of 41,000 feet, about 30 to 40 minutes before reaching Hong Kong. The turbulence lasted for 30 seconds. In a statement, Dragonair said the captain of the Airbus A330-300 jetliner had previously switched on the 'Fasten Seatbelts' sign in the cabin as a precaution. The crew had been in the middle of serving a meal when the turbulence hit. Passengers said later that staff had no time to return to their own seats. 'The jet dropped rapidly for about 2,000 feet and knocked the stewardess off their feet, sending them crashing into the aircraft's ceiling,' one said. 'Food placed in front of the passengers was flung on to their clothing ... two doctors on board immediately identified themselves to help the injured. There was no panic among the passengers.' A spokeswoman for the Airport Authority said the captain of the plane then radioed ahead shortly before 2pm, informing air traffic controllers of the situation. It was given priority clearance to land, with five ambulances dispatched to the tarmac runway. The Civil Aviation Department has begun an investigation. Peter Lok Kung-nam, a retired director-general of the department, said it was often difficult for pilots to avoid turbulence while airborne, if a plane hit the so-called 'clear air turbulence', which is invisible to the naked eye and radar. He said such turbulence most often occurred when hot and cold air-masses moved across each other in opposite directions, such as during seasonal changes in spring and autumn. Mr Lok said most commercial aircraft were now equipped with dynamic airborne windshear detectors that could help predict whether a plane was flying into areas of 'clear air turbulence', although they are not completely foolproof.