One of the problems is that the effects of Radio Frequency Interference (RFI) vary among the different models of airplanes. A Boeing 747 has mechanical steering and the pilot can take over from the autopilot when it acts weird. In a "fly by wire" Airbus the pilot may lose all control over the airplane due to RFI when it hits the controls.
For that reason it is unavoidable that in different planes different equipment is deemed acceptable. Even a simple division in classes may be impossible because some planes may be more sensitive to certain frequency bands than others.
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For that reason it is unavoidable that in different planes different equipment is deemed acceptable. Even a simple division in classes may be impossible because some planes may be more sensitive to certain frequency bands than others.