If someone has flown on a light plane with analog instruments they've noticed that there's no reason to turn off your mobile (but keep it in your pocket when we

If someone has flown on a light plane with analog instruments they've noticed that there's no reason to turn off your mobile (but keep it in your pocket when we're taking off please). Yet, a B737 or an A320 is a much more complex plane. For instance, it has a lot of different electronic systems, ranging from the displays to the multiple, backed-up computers that enable flight controls (manual flight) and manage auto-pilot inputs. I've seen a CRJ-200's first officer's (copilot) flight PFD and ND gone black and reboot because someone in the back was trying to call home, without much success. The thing is, that never happened to my friend pilot before even with passengers trying to call. And the power output of a phone trying to call without much coverage isn't the same as the power needed in the center of a big city (and at 8000ft, inside a huge metal tube, the cell reception isn't great). That's one of the main reasons. Granted it shouldn't happen and plane manufacturers do test against these kind of things. And really important systems, like backup instruments (standby) or flight computers are hardly going to be affected by any kind of interference, so, no, the plane isn't just going to drop from the sky. Yet an automatic A/P disconnection on long final on the PF's (pilot flying) PFD and ND displays going nuts is something serious. And on the side of that, you don't want people having unknown electronic devices sending signals when pilots have to be more focused (take off and landing) and you better have them keeping an eye outside (or at their newspaper, but you can't help that). That's pretty much the same reason why they ask you to have everything stowed and leave your window 'opened' (you can see if there's something wrong outside, like fire, and report it) during takeoff and landing.