Since December, several planes lost their radar signal while flying above Dangyang city, Hubei province, due to the use of illegal wireless devices on the ground, Wuhan evening news reported Tuesday.

The planes lost their radar signal above Dangyang city for a few minutes on Dec 26, 2012. Several other planes experienced the same phenomenon days later, according to Wuhan's air authority.

After a joint investigation by air authorities from several cities in the province, they identified the cause on Jan 16: wireless transfer devices illegally set up by a company.

The devices were immediately shut down, and the planes returned to normal operations.

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