All of those things are designed, built and maintained for use on board commercial airplanes with EM shielding that’s maintained properly. There’s a big difference between that stuff and the electronics brought on board by passengers that may or may not be properly shielded.
There may not be any such documented case, but there may be undocumented ones; system, display, navaid, etc failure with no known root cause. Events like that happen all the time, which is part of why there are redundancies built into the aircraft. Maintenance checks out the plain, finds no faults with the system, sends the plane back up with a note to pilots to keep an eye on it (minimum equipment lists allow this for many systems). Does that mean it was a random glitch in the aircraft’s avionics, or did Passenger in seat 23B turn on his phone and it tried to broadcast? Really, how would we know?
Undocumented does not mean impossible, nor does it mean “has not ever happened.” It just means we don’t know whether or not is has happened, but it could. To our knowledge, no planes have crashed because of the use of electronic devices onboard. But no two crashes are alike, and it seems there’s a first time for pretty much everything - up until it happens, we’ve just been lucky! 
Avionics upgrades to aircraft don’t actually happen all that often - about once a decade, as far as I know, and not every carrier upgrades their fleet, so newer cockpits are only found on the newer planes coming off the assembly lines.
The average age of Delta airline’s fleet is 14.5 years. Their MD-80/90s (which haven’t even been manufactured in over a decade) average 19.4 years. United Airlines has an average fleet age of 14.3 years, with B757s, B747s and B767s all over 15 years of age (18.5 for the B757). American Airlines average fleet age is 15 years, also operating MD-80s/90s that are 19.7 years old, and lots of 16-18 year old Boeings. Southwest has 200 19 year old B737s and 351 B737NextGen which average 12 years old. (cite)
All of those planes were designed and built before the iPhone, before 3G networks, before wi-fi as we know it, before the “modern technology” we are so used to using in our everyday lives. Since concept to certification is something around 3-5 years, add at least that to the age of the planes in each fleet and consider the “modern” technology available at the time of design. The aircraft were simply not designed to be properly shielded from our “new” wireless technologies, no matter how well the electronic device is made. You really do have to test each device against each type of aircraft, as well as mixed loads at maximum use (say, every passenger using 1 or 2 devices at once, which is realistic in today’s world).
Commercial aviation is also very conservative; it took what, 20? 30 years to get fly-by-wire controls on a commercial airliner? Permission to use these devices onboard is coming…just don’t expect it to happen very quickly at all!
Of course, if they had anything resembling evidence that electronic devices were actually a problem, it would be spectacularly irresponsible to rely on passengers to voluntarily turn these off - scanning devices would be needed to detect such threats. Anyone who imagines that such devices are all off simply because the flight attendant has requested this is remarkably naive.
This is absurd, really. They are telling us that some electronic gadgets, which are permitted on the plane, should not be used because they could cause “problems” and are potentially dangerous.
Ok, if I am a terrorist org, I simply have ten people on the same flight who turn on their cellphones during flight. Wow! Spectacular crash? Obviously not.
On the topic of cell phones, unless things have changed in the last few years, even the cell phone companies are against allowing the use of phones in flight, mainly because they don’t want to be associated with the folks who annoy the unholy hell out of their neighbors by chattering incessantly into a cell phone for the entire fourteen hour flight between SFO and Incheon International.
And yes, the safety regs are paranoid, that’s how civil aviation works. They’re responsible for the safe transport of thousands of civilians in lightly built tubes made from aluminum and plastic and filled with thousands of pounds of jet fuel traveling at hundreds of miles an hour 30,000 feet above the Earth, so I can forgive them for wanting to make sure they’re taking proper CYA measures.
Turn off the leash for a few hours, and read a book. 
But, as noted, relying on voluntary compliance doesn’t actually address any real problem. It may be true, as you imply, that this is simply CYA. If a genuine problem happens, the attitude will be “Okay, we didn’t take any steps that would actually ensure electronic devices were not in use - but we did some pitiful and ineffective whining on the subject, so we really shouldn’t be held accountable.”
They do make sure you aren’t using prohibited electronics when they go up and down the aisles. Unless you thought they just walked the aisles for the cardio.
Insert “openly and conspicuously” before “using” and I’ll agree.
Plenty of people leave their cellphones on by mistake. Located in pockets and purses, these are most unlikely to be noticed.
And in the admittedly unlikely but possible event that the use of a cell phone or other device seems to be causing issues with the plane’s avionics, a non-cooperative passenger (a belligerent, argumentative person who refused to turn off the device, say) could be charged with a federal crime of interfering with a flight crew and could face up to 20 years in prison.
Far fetched? Maybe. But then again, I think it’s far fetched to assault someone who won’t give you beer, and that happens all the damn time on airplanes.
As an aside, I hate the Bell Canada commercial based on an airplane getting ready for take-of, and the flight attendant lets one moron continue to use his phone to record a show at home because the technology is just so awesome. Yay, let’s break the law! :rolleyes:
Sure it does: it significantly reduces the probability of interference. Suppose a plane carries 100 passengers. If one cell phone in a million has a quirk that makes it interfere with flight systems, and one passenger of those 100 leaves his cell phone on during the flight while the other 99 turn theirs off, then the odds of interference on any given flight go from one in 10,000 to one in a million. The threat hasn’t been *eliminated, but such a substantial reduction in risk does have value.
If you think my numbers are unrealistic, feel free to insert your own and recalculate.
When I said older equipment created interference, I meant the blender, CB radio, electronic ignition, or TRS-80 monitor that left funny lines on your TV; not cockpit equipment or carry-on electronics. Serious worry about EMF and its effect on reception was addressed statring in the late 70’s when unshielded home PC’s and CB radios started being a niusance.
Wonky electronics in the cockpit is just wonky electronics. It’s more likely that bad hardware or software is to blame, as EMF; after all, even the best-designed computers will do funny things from time to time. If a cockpit piece of equipment cannot say “signal lost” or “signal unreadable” due to picking up interference, then that is a poor design. The most likely source of interference is the cables running along the aircraft, acting as antennas. Nowadays those are shielded. The broadcast equipment a plane flies over are probably a more potent source of EMF.
Still, I think the current rules - no earphones or (broadcast) electronics during take-off and landing, no cell phones in flight - are pretty reasonable and sensible.
I fly in a small plane (single-engine 4 seater) quite frequently. I notice that cellphones often tend to cause buzzing and interference with the pilot’s headset. Flying 2 or 3 times a week, it’s inevitable that I’ll occasionally forget to turn it off (or forget it’s in my coat which I tossed into the back seat) and hear a BZZZZZZT in my ears when it gets an incoming text or call. I suppose a collection of cellphones in an airline cabin would play havoc with voice communication if nothing else.
FWIW: I’ve never noticed any problems with the nav reception. VORs, DME, and GPS seem unaffected. I suppose I really need to add the cellphone to the checklist.:rolleyes:
A reasonable point for cases where passengers are simply forgetting to turn devices off.