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Frequency spectra of electromagnetic waves measured in the Boeing 777s in actual commercial flights are presented. The high intensity radio waves in the spectra are analyzed to identify their sources. The results show that in 795-995MHz and 1393-1693MHz ranges, some radio waves exceeding RTCA recommendation level are considered to be caused from portable telephones in the cabin. Such phenomenon appears even at very high flight level when multi-path transmission occurs. It is also certified that the radio waves exceeding RTCA recommendation level are observed in other frequency ranges. However, the sources of these radio waves are the ground TV or radio stations or the aircraft transmitters, which are necessary for normal flight.