It is reported that an airplane was preparing for landing nearly had an accident because of getting off course almost which flew form Shanghai to Guangzhou in 11th July, 1986. The main reason was that because of several passengers using their cell phone during landing. According to statistics, there were nearly 20 aviation accidents in the word for the past few years. Therefore, many airlines have their regulations that they would prohibit the use of cell phone when the flight is flying.
While a mobile phone is working, it will give off electromagnetic wave and which will disturb the navigation equipment and control system of the aircraft. So that the plane automatic maneuvering device will receive the wrong information and proceeding the wrong operation. Thus initiating dangerous case even leading the airplane crash.
And in additions to mobile phone, using notebook computer and games consoles and so on will also give off electromagnetic waves so these devices can not be used in the airplane.
If you bring a cell phone jammer or a Wi-Fi jammer with yourself this will not be a big case. It is a piece of cake for you.