This remote-mounted filter helps to mitigate potential interference from 5G sources in the U.S. FCC-authorized 3700-3980 MHz band, along with other potential worldwide interference sources that are nearby or adjacent to the 4200-4400 MHz frequency band. The filter is accepted by the FAA for use by aircraft installers to eliminate aircraft operational limitations published in FAA AD 2023-10-02 for Part 25 and Part 23 Class IV aircraft, and AD 2023-11-07 for Part 27 and Part 29 rotorcraft. Installation of the GRA 5500/55 External Filter with the GRA 5500 or GRA 55 radio altimeters also allows compliance to be shown to corresponding radio altimeter 5G interference Airworthiness Directives issued by TCCA in Canada and ANAC in Brazil.