Interference of 5G with aircraft radio altimeters: How to protect aviation safety in rapidly changing environment of expanding C-band networks

The topic of 5G network development is resonating in the aviation world. According to the information from aircraft manufacturers, aircraft radio altimeters could be interfered with in the C-band frequency spectrum. Radio altimeters are electronic devices that measure the precise altitude above the terrain and are very important for flight safety in the phase of the final approach and landing. The problem statement was, firstly, how safe the aircraft approaching and departing Prague Airport have been and secondly, how to protect aviation safety in the rapidly changing technological environment of expanding C-band networks. The methodology of the paper was, firstly, to assess the impact of existing installations on flight operations using the Safety Management System principles; and secondly, to assess the impact of planned C-band installations on flight operations according to the technical parameters of proposed installations. This is a methodology proposed in the paper for newly defined coordination zones around Prague Airport. The methodology can be used by other airports aiming to assess the risks of C-band interference. Through all safety promotion means, the crews were encouraged and motivated to report all outages of radio altimeters via safety reporting channels. From the period September 2021 to November 2023, one safety report concerning the radio altimeter was received. The report informed about a safety incident, the failure of the radio altimeter. An investigation into the causes of the incident has taken place and the results are provided and discussed in the paper. According to the data collected and investigated, the failures of radio altimeters are rare and no case has been discovered where the failure of the radio altimeter of an aircraft on the ground or an aircraft arriving or departing Prague Ruzyně Airport was caused by interference with C-band. The new C-band installations can be assessed according to the previously published model of the French civil aviation authority, however, a modification of the evaluation procedure is proposed in the paper.