reporter: the issue, 5g operates on a frequency range very close to that used by the altimeters. so as we can see, they can coexist, if they stay within their own lane. reporter: separating those frequency highways requires a buffer zone. europe has no reports of altimeter interference. verizon and at&t insist the u.s. buffer zone is even bigger. we want to enable 5g, c-band deployment, make no mistake about that. but we ve got to do in a way so that aviation safety is not compromised. reporter: since tuesday, the