THE Civil Aviation Department has ruled out an inquiry into air traffic control after severe turbulence put 45 passengers and crew of a Thai International aircraft in hospital last Monday. Immediately following the incident, the department said it was looking at both pilot error and air traffic control failures. But yesterday, a spokesman said air traffic control problems had been ruled out. 'Air traffic control radars are not designed to detect turbulence,' the spokesman said. 'It is the aircraft themselves that are equipped with weather radar.' The spokesman said the Thai aircraft had already requested and been given two diversions from its route by air traffic control because the plane's radar had detected severe turbulence. But the crew of the McDonnell Douglas MD-11 had requested no further diversion at the time it hit the severe turbulence about 30 kilometres southwest of Cheung Chau. The department received a report on the incident from the airline, which was otherwise unable to comment. When the plane landed at Kai Tak airport, 30 ambulances were needed to ferry the injured to three hospitals. Six people were detained overnight on Monday. Last night, two remained in hospital in satisfactory condition. After the incident, one stewardess said most of the injuries happened because passengers had ignored instructions to fasten their seat-belts.