To prevent disruption to the cellular phone network from the effects of fast-moving cell phones at altitude (see Technical discussion, below), the FCC has banned the use of mobile phones on all aircraft in flight.[33] The FCC did, however, allocate spectra in the 450 MHz and 800 MHz frequency bands for use by equipment designed and tested for air-ground radiotelephone service. These systems use far more widely separated ground stations than standard cellular systems. In the 450 MHz band co-channel assignments are at least 497 miles apart and in the 800 MHz band only specific sites were authorized by the FCC.