said by AlexNYC:We all know what frequencies cell phones and wifi uses. They are all licensed by the FCC.
Yes, and some of them are very near the aircraft communication and navigation frequency bands. GPS downlink frequencies are at 1.2 and 1.6 GHz. That signal is already just barely about the noise threshold, and it doesn't take much to interfere with it.
And I don't think you are understanding: A transmitter generates harmonics on multiples of the original frequency. Their power level is much lower, and it depends on the waveform that is used (sine, square, etc.). But, without filters that won't fit in a consumer device, you can't eliminate them.
said by AlexNYC:The airplane com equipment is designed not to be bothered in general by those known licensed frequencies.
If that were true, there would be no problem. But, it's a lot more complicated than just the radio. The antennas are typically mounted on the belly of the aircraft, and you may be sitting right over it. Or you may be sitting close enough to the cockpit to interfere with the cockpit audio system. Newer aircraft avionics are more resistant to interference, but there are plenty of older systems still in service.
said by AlexNYC:And as far as two devices generating a third frequency that can interfere, I think your chances of winning the lotto are much higher is real life.
It's pretty rare. But, it does happen. You can do a search through NASA's ASRS database and you'll find many reports of interference. Do you want to bet on whether it will interfere with a pilot's navigation or communication at a critical moment? As I wrote above: just because have been texting while driving and haven't had a crash, does that mean it is safe?
I have both a pilot's license and an amateur radio license. I've personally experienced interference, and sometimes I caused it (I was in my own plane, in VFR conditions).
I think it's reasonable to allow use of portable electronic devices during all phases of flight, because they are much better shielded than in the past. But, transmitters of all kinds (WiFi, cell, bluetooth, etc.) should be turned off during the takeoff and landing phases -- generally below 10,000 feet. It's during that phase of flight where traffic separation is critical, and things happen quickly. During the en-route phase above 10,000 feet, there's much more time to switch to a backup and recover if interference occurs.
It will be interesting to see how the airlines implement this recommendation. That's all it is: a recommendation. The aircraft operator is still responsible for making sure that electronic devices do not interfere with the aircraft system, and ultimately that decision (and responsibility for the outcome) belongs to the pilot-in-command.