Radar at Beijing's airport was subjected to interference from radio-controlled cameras on a building 14 kilometers away, an investigation by China top radio watchdog has found.

"Fuzzy signals" affected the radars for almost a week, potentially putting flight safety at risk.

"The radio waves severely disturbed normal flight take off and landings," Su Qing, of Northern China Air Traffic Management Bureau's communication navigation sector, said.

Three mini-cameras with radio aerials installed in building elevators were responsible for the interference.

Niu Kai, from China's top radio watchdog, said the case has been reported to Radio Management of China, and was also being handled by the Beijing radio management bureau.

Several monitoring stations and mobile monitoring facilities were used to use to track the source of the interfering radio waves.

The cameras were located in the Dashanzi area, some 14 kilometers away from the airport, in a dorm building affiliated with Panasonic, after a two-day investigation.

"The radio was using the same frequency channel as the airport radar, therefore, largely dampening the performance of the radar," Su told China Daily.

Interfering signals can result inaccurate flight traffic data being reported.

Flights are especially susceptible during take-off and landing because all frequency bands are working.

Aircraft need clean and clear radio channels.

Power and signal are two decisive factors that determine how strong a radio wave is.

In this case, two buildings blocked the signal from two of the cameras, leaving one camera to interfere with the airport's radars.

The radio management regulation, issued in 1993, falls short of describing the "safe distance and area" regarding a radio's affected area, Niu said.

(China Daily June 9, 2007)