The bosses of ten US airlines on Monday warned US authorities of the potential “chaos” of Wednesday’s rollout of superfast 5G mobile internet technology around airports, less than two miles (3.2 km) of control towers.
“Immediate response is required to prevent significant operational disruption to passengers, carriers, supply chains and the delivery of essential medical supplies,” they wrote in a letter.
Airlines, such as American Airlines, Delta Air Lines, and United Airlines, have warned that the new 5G service “might potentially strand tens of thousands of Americans abroad.” So much so that on Monday evening they were considering starting to cancel some international flights that were due to arrive in the United States on Wednesday.
What’s the problem ?
On board planes, the radio altimeter uses frequencies that are too close to the C frequency band, the one that the new 5G service will use. Potential interference might therefore affect the aircraft’s sensitive instruments and significantly hamper operations in low visibility, warns the Federal Aviation Administration (FAA, the American air safety agency).
This is a problem in the United States because their C-band frequencies are “higher” in the spectrum, and therefore closer to those of radio altimeters, than in Europe, where a radio altimeter’s band is between 4 .2 and 4.4 GHz, while the C-band of 5G in the United States is between 3.7 and 4 GHz (3.98 precisely). “This low difference of 0.2 GHz allows interference”, summarizes Olivier Rigazio, airline pilot and spokesperson for the SNPL (national union of airline pilots).
Moreover, some small radio altimeters, rather old, are poorly protected in relation to the arrival of this new band. “They ignored the protection of the adjacent band, because it was previously occupied by services which emitted few waves, and the risk is that they find themselves blinded by its power”, explains Gilles Bregant, director General of the National Frequency Agency (ANFR).
What are the risks ?
The radio altimeter is an essential instrument for pilots: by sending waves towards the ground, it very precisely measures, to within 30 cm, the distance from the ground, especially when the plane is approaching the landing strip.
“It’s a tool we use all the time, explains Olivier Rigazio. It is mandatory on landing when visibility is reduced by fog, hence the significant risk of traffic disruption in winter. But we also use it in flight, the radio altimeter can trigger in an emergency another system that would help us avoid a mountain, for example. »
It is also linked to other on-board instruments such as flight controls or braking. “From the moment this radio altimeter starts to malfunction, the repercussions on the operation of the plane are enormous,” he continues. And the problem with interference is that it is not predictable. »
In October 2020, the RTCA (equivalent in the United States of the European Organization for Civil Aviation Equipment) already warned of the danger of 5G for aviation: “The results presented in this report reveal a major risk associated with 5G telecommunications systems, whose 3.7-3.98 GHz band will cause harmful interference to radar altimeters of all types of aircraft. (…) They make it clear that this risk is widespread and has potentially significant impacts on U.S. aviation operations, including the possibility of catastrophic failures resulting in numerous fatalities. »
“No case of jamming has ever been reported”, relativizes a French operator, giving the example of Asia where the frequencies are even closer, almost glued. “In Japan, their 5G band is 4.5-4.6 GHz. Without taking the subject lightly, we do not worry. »
Which solution ?
In response to concerns, the FAA recommends limiting the use of the radio altimeter in certain situations. The transport industry is therefore preparing for service interruptions, and calls on the authorities to quickly find a solution.
In its report, the RTCA recommended increasing the frequency gap between the 5G bands, from 0.2 to 0.3 GHz. The United States might also, like France, direct the antennas of mobile operators downwards.
Above all, Europe and the United States are busy testing radio altimeters, in order to quickly replace the most vulnerable. The operation will have a colossal cost for the companies: with two aircraft per plane, thousands will have to be changed.
And in France ?
In Europe, the risk of interference is less, because our C band oscillates between 3.4 and 3.8 GHz. It is therefore quite far from that of 5G. Nevertheless, since the publication of the RTCA report, Europe and the United States have been conducting studies to more accurately assess the risk of interference.
France, well advanced on the subject, immediately set up a “ protective protocol » around large airports: 5G antennas can only be deployed at low power in an area of 1 km on either side of the runway. “The time to remove the doubt on the reality of the problem highlighted by the manufacturers, the 5G mobile operators are also prohibited from directing their antennas towards approaching planes”, assures Gilles Bregant.
At the same time, the National Frequency Agency has been testing gendarmerie helicopters for several months. Those on aircraft, which are more complex, are in progress. “We haven’t noticed the problem so far. Helicopter tests show that we can be confident regarding the resilience of these radio altimeter models. The ANFR now expects “complete and reliable information” from altimeter manufacturers to maintain or not the transitional protection measures.