You are seriously giving me wicked ideas...
The Boeing 737 series is the best-selling jet airliner in the history of aviation...
It was found that cell-phone signals, specifically those in the 800-900 MHz range, do interfere with unshielded cockpit instrumentation...
The captain of a Boeing 737 airliner on an instrument approach to Baltimore-Washington International Airport one night in March 2003 reported that his course indicator, called a localizer, had been centered during the approach, then suddenly showed a full deflection. Just then the aircraft, flying on autopilot, broke out of the clouds—at an altitude of 2,500 feet and a full mile off course. The incident is described in NASA’s Aviation Safety Reporting System (asrs.arc.nasa.gov). The 737 pilot theorized that after announcing that the United States had started attacking Iraq (information received from air traffic control), passengers had placed calls on their mobile phones.
To the frustration of Boeing engineers, follow-up testing never duplicated the problems, either on subsequent flights or in the lab.
The government first began investigating disruptions from carry-on devices in the early 1960s, when an FM radio was blamed for an incorrect off-course indication...
A popular mobile phone broadcasts its intended signal at a frequency of 1,850 to 1,910 megahertz and a power level of 30 milliwatts. At the same time the phone is emitting its intended broadcast loud and clear, it is also putting out an unintended, or spurious, low-power background buzz of radio signals ranging in frequency from 100 to 2,000 megahertz. It happens that the very high frequency radio that air traffic control uses to communicate with cockpit crews broadcasts at frequencies of 118 to 137 megahertz, which falls within the frequency range of the mobile phone’s background buzz. Interference is not likely to occur, however, as long as the VHF transmission is sufficiently stronger than the phone’s background buzz. But the farther the airplane flies from an air traffic control tower, the weaker the tower’s signal is when it reaches the airliner. And if the phone transmits a signal that has the same frequency as the tower’s and is nearly as powerful, the two signals will compete with each other. Result: interference.
Thanking Wikipedia and Air&SpaceMag for the information. Now, an interested hijacker would need to go into physics of mobile phone’s background buzz, and probably low-level programming to increase the power output of the 'buzz'.
Best wishes...
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Per aspera ad astra...