Forty-four per cent of those questioned said they didn't believe the phone would interfere with the plane's instruments, but — perhaps more worryingly — 27 per cent said they couldn't cope without a switched-on phone and nine per cent said they couldn't turn off their phone as being uncontactable was unacceptable (we're assuming they weren't the brightest in the sample). § There's much debate about whether phones really can interfere with instrumentation, with the general feeling that the risk isn't worth taking and that as they generally won't work anyway it's not a big deal to ask flyers to turn them off. Some planes do have in-cabin coverage, but that only gets switched on above 10km to avoid interfering with ground networks.