why can't you use your cellphone on an airplane? why airplanes are banned with use of cellphones? What were the impacts while we answer an call or make an call ,what was the physical reason behind the ban of using cellphone inside airplanes ?
I expect answer related to physics here
 A: This problem originated with passengers using electronics (they call them PED's - portable electronic devices) during flight.  While all consumer electronics have to be qualified by a regulatory body (FCC, etc.) to prove they do not emit harmful interference, this doesn't mean they emit no interference especially to high gain sensitive navigation equipment.
"The first national committee that investigated interference by passenger-carried PEDs was created in the early 1960s. Its activities were initiated by a report that a passenger-operated portable FM broadcast receiver caused an airplane navigation system to indicate that the airplane was off course by more than 10 deg. The airplane was actually on course and, when the portable receiver was turned off, the malfunction ceased. A final report from this committee, RTCA DO-119, was issued in 1963 and resulted in the revision of the FAA Federal Aviation Regulations (FAR) by establishing a new rule (FAR 91.19, now 91.21), which states that the responsibility for ensuring that PEDs will not cause interference with airplane navigation or communication systems remained with the operator of the airplane."  -- from Boeing  This reference also has some incidents which I hightlight here:


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*1995, 737 A passenger laptop computer was reported to cause autopilot disconnects during cruise.

*1996/1997, 767 Over a period of eight months, Boeing received five reports on interference with various navigation equipment (uncommanded rolls, displays blanking, flight management computer [FMC]/ autopilot/standby altimeter inoperative, and autopilot disconnects) caused by passenger operation of a popular handheld electronic game device.

*1998, 747 A passenger’s palmtop computer was reported to cause the airplane to initiate a shallow bank turn. One minute after turning the PED off, the airplane returned to "on course."


Now this "all electronics off" rule has become legacy and broadly applied.  There are a mix of opinions about how relevant it is today.  But the fact remains that while manufacturers do a decent job of limiting RFI (radio frequency interference) there is still a good chance that the very sensitive radios on board aircrafts could have a problem with one of the RFI emissions.
And due to the nature of the aircraft radios it is almost impossible to test every possible interference scenario.  These radios do a lot of frequency mixing, amplification and filtering.  If you have ever done a detailed spurious analysis on a mixer, you'll know that each time you mix a single you create a tremendous number of possible interference problems.
There has been recent studies showing RFI issues but with a very low probability (1:1,000,000) of harmful interference.  (Sorry, you have to pay $63 to read the report). So for everyone's safety the "all electronics off" rule during critical takeoff/landing has remained in effect.  For a good overview, I suggest you read the first link in my answer from Boeing.
