Can't they use their cellphones once they get low enough?

I am aware of a 777 incident quite a few years ago where all VHF, HF and Satcom communications were lost. 7600 was then selected on the transponder. On every frequency that was selected there was an unusual background hum in both pilots' headset. The same hum was there even when no frequency was selected. After 10 minutes of trying numerous different frequencies on all three boxes and Satcom the copilot could smell electrical burning and then saw a few wisps of smoke.

The smoke was coming from the copilot's hand mic on the right fuselage stowage. The side stowage mics are very rarely used.(Anyone remember on the 747 they used to be so emphatic in the scan checks that the mic had to be stowed facing the right way round?) Anyway this one was too hot to touch and the plastic surround was actually melting. When the mic jack was unplugged from the socket all the radios worked normally and contact with ATC was resumed.

It was an interesting lesson that what was clearly a massive short from the copilot's hand mic took out all the radios and not just the frequency that the copilot's transmit selector was set to. This would suggest some interrelationship between the bus bars of different radios.

But if you are NORDO and enter VFR conditions, I believe you are suppose to continue VFR and land ASAP.

They were in the process to be handed over to Skyguide (Swiss ATC) that controls parts of southern Germany as well. Skyguide refused to accept them without established contact. Continuing to Zürich was no option from that point.

Most of the hand held radios that operate on the dual frequency bands claimed for these radios are amateur radio frequency modulation. My understanding is that aircraft VHF & UHF is audio modulation. So unless the hand held radios are AM, communication with ATC and other aircraft will not be possible.
In my flying days, I carried an ATC compatible VHF AM transceiver. I also am a licensed amateur with a hand held FM radio that I would never have considered ATC suitable.

And a frightening lesson as well, given the effort we (engineers) put into doing failure mode and effects analysis of aircraft systems. Having one of a redundant set of systems take out all function isn't supposed to happen. I'm guessing that the one bad mic dragged the entire audio control system down with it instead of triggering some sort of isolation/protection on that input (a breaker of sorts).

This also brings up the subject of an old thread: Adapting headsets with one connector type to another system. While I'm not going to step in and tell people not to do it, this is one possible consequence of an unapproved mod.

None of you guys picked up on the AMU comment a page back did you...😎

I saw it. I wasn't sure whether that was a hypothetical (what might have happened) or if there was some evidence of an actual fault on KAL 917.

If there is some indication that this actually happened, and that failure was deemed to be extremely improbable during certification, this means that the fleet is safe for another 10^9 hours.:rolleyes: