Airlines have urged to respect the 5G network. The Federal Aviation Administration (FAA) is giving civil aviation operators an extra year to fix 5G network interference issues on some aircraft instruments.
Compliance from February 1, 2024
Of the 7,993 aircraft registered in the US registry, about 1,000 are still affected by a radio altimeter interference problem, the FAA reveals in a document released by Ars Technique. To correct this interference it will be necessary to change 180 aircraft and 820 will be able to make do with anti-interference filters. Airlines are obliged to make the changes by February 1, 2024. Operators will thus be able to continue the implementation of 5G in C-band, which is more interesting for data transport.
As a reminder, an aircraft radio altimeter is used to measure the distance of the device to the ground. To calculate the aircraft’s altitude, the instrument uses microwave radar on a 4.2 GHz to 4.4 GHz spectrum. Frequencies very close to the C-band of the 5G network in the United States. Some radio altimeters can thus receive the waves emitted in the 3.7-3.98 GHz band, used by 5G antennas on the ground. The calculation of the plane’s height is therefore distorted and can generate false alarms, which are sometimes ignored by the pilots.
“False system alerts due to radio altimeter malfunction leads to flight crew desensitization to system alerts. Such desensitization negates the security benefits of the alert itself and can lead to a catastrophic event”alert the FAA.
Strict measures in France
The risks of interference with frequencies close to that of radar were not anticipated when radio altimeters were designed. Indeed, at the time, only satellites, on nearby frequencies, could disturb the reception of the waves by the device. A situation that has never occurred due to the low power used by space equipment to communicate. “This led early altimeter designers to decide that they could indeed ignore the limits of the spectrum assigned to them and consequently leave the transmitted energy in the receiver well beyond their band.”Dennis Roberson explained during a hearing before the US Congress in February 2022.
In France, the C-band of the 5G network is further away from the frequencies used by radio altimeters. The interference therefore, for the moment, would not be demonstrated in France. However, studies are still ongoing to ascertain this.
Pending definitive conclusions, strict rules govern the rollout of 5G around airports. The antennas can only be activated at low power within a one kilometer area around the runway. Moreover, “it’s time to remove the doubt about the reality of the problem highlighted by the manufacturers, 5G mobile operators are also prohibited from directing their antennas towards approaching aircraft”assured Gilles Bregant, director general of the National Frequency Agency (ANFR) in the columns of Parisian in January 2022.
