Altimeters, a kind of sensor that measures the height of an aircraft above the ground, are at the center of an enduring battle between airlines, the FAA, and 5G wireless carriers—potentially affecting flight safety.
After more than a year of discussion, the US Federal Aviation Administration is holding airlines to a July 1 deadline to upgrade their airplane radio altimeters (also referred to as radar altimeters) so they can handle potential interference from 5G wireless technology. The FAA does not plan to extend the July 1 deadline before new rules take effect prohibiting certain landings in low-visibility conditions without upgraded altimeters.
The problem for airlines seeking to make altimeter upgrades is a familiar one: supply chain issues. “Supply chain issues make it unlikely that all aircraft can be upgraded by the 1 July deadline, threatening operational disruptions during the peak northern summer travel season,” said the International Air Transport Association in a statement dated May 2. IATA represents about 300 airlines with 83% of the global air traffic.
“Airlines did not create this situation,” said Nick Careen, IATA senior vice president of operations, safety and security, also in a statement. “They are victims of poor government planning and coordination. Industry concerns about 5G, expressed for many years in the appropriate forums, were ignored and over-ridden. Half-measure solutions have been foisted upon airlines to implement at their own expense and with little visibility into their long-term viability.”
IATA commented about supply chain concerns while also commending AT&T, UScellular, T-Mobile and Verizon for extending until January 2028 their voluntary mitigation measures for 5G C-band transmission at 188 US airports. The mitigation measures include lowering the power of 5G transmissions, which had been set to expire on July 1.
However, IATA said the underlying 5G -band safety and economic issues “have only been kicked down the road.” The organization said radio altimeter upgrades will cost more than $638 million across all airline fleets. Some airlines began upgrades in 2022. Also, IATA is concerned a current retrofit will not be resilient eventually against all full power 5G C-band transmissions, meaning airlines could have to retrofit most of their aircraft twice in five years.
A Boeing spokesman told Fierce Electronics: "Boeing continues to work with suppliers, regulators, the airlines and telecom companies to ensure long-term stability and help mitigate operational restrictions where possible in an effort to promote the safe co-existence of aviation and 5G environments for all models of the Boeing fleet."
An expert in altimeter technology also told Fierce that the potential for safety problems with older altimeters is not great. "Planes are not going to fall from the sky," said Dennis Roberson, president of Roberson And Associates, a wireless consultancy. "Most of the airplanes that needed to have altimeters changed have been, but not all." It is mostly much older altimeters in smaller planes used on regional trips, he said.
"Bottom line, the flying public should not be in danger, but there are some aircraft that the airline industry may not be able to use when severe weather is in the forecast," Roberson added. What that means is if weather is bad, a plane with an older altimeter should not be used which could result in disrupted schedules and unhappy passengers. "If the weather is bad enough, you don't want to go there anyway. Altimeters become extremely valuable in bad weather with low visibility when you can't see the ground. You really have to have it working."
Ironically, Roberson said the upgrades to altimeters can be very trivial, using a piece of 25 cent ceramic to block out the 5G signal that could be in conflict with the altimeter's radar.
Concerns over 5G interference with altimeters first became known last summer with the potential to disrupt flights. The activation of 5G C-band operations by the nation’s carriers started in January 2022 which IATA said “threatened enormous disruption to the US air transport system because of the potential risk of interference with aircraft radio altimeters (radalts) that also use C-band spectrum and are critical to aircraft landing and safety systems.”
AT&T and Verizon had initially agreed to power limit 5G C-band transmissions near airports but the FAA still only permitted airlines to operate at affected airports in low visibility conditions by either modifying existing radalts or replacing them with newer models or relying on alternatives with avionics and aircraft manufacturers to set up specific radalt and aircraft combinations with resilience against interference to allow low-visibility landings.
The principle behind a radio altimeter involves monitoring a beam of radio waves transmitted by an aircraft and their time to return when reflected from the ground to calculate altitude above the ground.