FAA warns 5G may interfere with Boeing 737 systems

The US Federal Aviation Administration warned on Wednesday that 5G C-band transmissions may interfere with landing operations at a limited set of airports for most Boeing 737 aircraft.

It issued an advisory calling for affected planes to observe modified operating procedures where 5G interference might occur. The FAA in January green-lit all 737 models to land at airports when using radio altimeters in low-visibility conditions even if 5G-C cellular towers are nearby.

The aviation watchdog’s U-turn on the 737 “was prompted by a determination that radio altimeters cannot be relied upon to perform their intended function if they experience interference from wireless broadband operations in the 3.7-3.98 GHz frequency band (5G C-Band)…” and by a determination that attempts to deal with interference and the resulting pressure put on aircraft personnel “could result in reduced ability of the flightcrew to maintain safe flight and landing of the airplane.”

The radio altimeter measures the aircraft’s distance from the terrain below; it’s used in conjunction with other equipment for approach and landing, particularly in low-visibility conditions.

Concerns about the effect 5G signals may have on aviation systems have been discussed for years but became more contentious with the US rollout of 5G service from AT&T and Verizon last month.

The FAA issued its Airworthiness Directive (AD) [PDF] because several of the systems on the Boeing 737 rely on the radio altimeter to function properly.

The Boeing 737 flew its first commercial flight in 1968. A version of the plane that entered into service in 2017, the 737 Max, was grounded in 2019 following the fatal crashes of Lion Air Flight 610 (2018) and Ethiopian Airlines Flight 302 (2019). The 737 Max returned to service in December, 2020.

The FAA directive affects about 2,442 aircraft in the US and 8,342 worldwide. That’s around a quarter of the estimated commercial aircraft inventory in the US as of 2020.

The directive follows from a series of Boeing reports issued earlier this month on how its aircrafts’ radio altimeter-dependent systems perform when faced with potential 5G C-Band interference. The FAA says Boeing’s data helped the agency identify an additional hazard associated with 5G interference.

“The FAA determined anomalies due to 5G C-Band interference may affect multiple other airplane systems using radio altimeter data, regardless of the approach type or weather,” the AD explains. “These anomalies may not be evident until very low altitudes.”

“Impacted systems include, but are not limited to, autopilot flight director system; autothrottle system; flight controls; flight instruments; traffic alert and collision avoidance system (TCAS); ground proximity warning system (GPWS); and configuration warnings.”

The AD covers Boeing Model 737-100, -200, -200C, -300, -400, -500, -600, -700, -700C, -800, -900, and -900ER series airplanes, except for Model 737-200 and -200C series airplanes equipped with an SP-77 flight control system (which lacks autoland and flare modes that might be affected by 5G signals).

The FAA directive, however, is not an issue at most US airports.

“The AD does not apply to landings at airports where the FAA determined the aircraft radio altimeters are safe and reliable in the 5G C-band environment,” the agency said. “It also does not apply to airports where 5G isn’t deployed.”

Rather than specifying which airports are affected, the FAA said it intends to issue Notices to Air Missions (NOTAMS) “where the radio altimeter is unreliable due to the presence of 5G C-Band wireless broadband interference).” These can be found by querying FAA’s NOTAMS service for specific airport identifiers.

The agency previously identified 87 airports that have low-visibility approaches – making an altimeter check relevant – where 5G service has been deployed.

Britain’s Civil Aviation Authority (CAA) has found no reason to believe that 5G signals interfere with aircraft equipment. The CAA contends the 3.4-3.8 GHz 5G spectrum allocation in Europe and the 4.2-4.4 GHz band used by radio altimeters has enough separation to avoid interference.

But in the US, where 5G service uses a higher part of the spectrum – the 3.7-3.98 GHz band – the FAA believes signals in proximate parts of the spectrum could be disruptive to altimeter readings, particularly because US 5G operates at higher power levels than in Europe.

“The receiver on the radio altimeter is typically highly accurate, however it may deliver erroneous results in the presence of out-of-band radio frequency emissions from other frequency bands,” the AD says.

Boeing did not immediately respond to a request for comment.

See more here: theregister.com

Header image: Getty Images

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Comments (5)

  • Avatar

    STEVYN R DEMBO

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    Like the pandemic, industry is rushing out solutions without proper long term testing. Like the vaccines, people are going to pay with their lives and the companies will escape consequences.

    Reply

  • Avatar

    Tom O

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    Yet another way to keep us from traveling and seeing what is happening as opposed to seeing it on the idiot box? You have to wonder, because, actually, it seems that they are trying to sectionalize us so as to keep us from knowing what truly is happening around us. And yes, I will probably believe “my lying eyes” before I will believe “Big Brother’s Boob Tube” if I see a difference.

    Reply

    • Avatar

      Wisenox

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      My understanding of their great reset future is that people will be confined to designated areas. If you’re detected outside of your area, your car won’t work, can’t access money, etc…
      The people will have to apply for travel passes to go outside their limits.

      Reply

  • Avatar

    Jerry Krause

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    Hi Howdy,

    This comment is specifically to Howdy because I want only his comments about the ‘radical design change of the Boeing 737.

    I have read that the Wright Bros observed soaring birds and saw that these birds seemed to control their flight by very subtle movement of a few feathers of the wing. Hence, when one of the two saw how the surfaces of a rectangular box subtlety changed when the box was simply twisted. Hence they designed the wing surfaced to subtlety change as the two wings of their biplane were simply twisted.

    But soon others seemed to see that this subtle effect could achieved by adding a small adjustable extension to the rear of a large fixed airfoil. And they added a smaller fixed airfoil to the rear of the plane to stabilize the plane’s horizontal flight with another adjustable extension at the rear of this smaller airfoil. And that had been the general case for transport (as opposed to small fighter planes) planes until the Boeing 737 whose horizontal flight stabilizer was not fixed and the entire rear airfoil was made moveable. So even the slightest movement of airfoil was no longer subtle. And its needed slight adjustments were intended to be controlled by computers to maximize fuel efficiency. But a problem occurred when adjustments in altitude needed to be made. For because of the large surface of the movable rear stabilizing airfoil any desired adjustment of it could not be subtle and the influence of the adjustment was not immediate with the result that two 737’s crashed before it was grounded.

    What you and I reason will not likely make any difference. But my question to you, is given the history of what the Wright Bros saw and designed, would you, as the FAA, ever allowed it fly with a great number of passengers on board. And this article should alert someone that the FAA still recognizes that the 737 has a problem which most other airplanes do not have. So test the plane by flying it for five, or so, years only carrying cargo instead of passengers.

    Have a good day, jerry

    Reply

    • Avatar

      Howdy

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      You are referring to the 737 MAX. Jerry. A ‘evolution’ of the 737. If you only want my answer to whether it should fly, skip the below paragraph.

      As I understood it, the whole forward wing mass was shifted to accommodate the more efficient engines which created the imbalance and handling that resulted in needing new software to counteract. As I recall, the big problem was the software’s response to input from the external sensor which caused the aircraft to repeatedly climb, then dive. I expected there would be 2 sensors as redundancy is usually the best option, but in this case, they used one Actually, I was wrong there and two are indeed fitted, but the software only responded to its own sensor, never comparing it to the other, so basically the same outcome. Very short-sighted in my view.
      What is unforgivable, is that the flight crew were never made aware of the new control system, nor was it in the operations manual, so really had no idea what was happening when it went bad.
      Other airliners have crashed from wrong sensor input also, where the flight crew got confused and the plane brought down. In other cases the defective system was disabled and the flight continued. The difference in the 737 max is that it was totally preventable.

      A link that describes far better than I can:
      https://spectrum.ieee.org/how-the-boeing-737-max-disaster-looks-to-a-software-developer

      Would I allow It to fly passenger service?
      I believe I would. There has been a software update that now addresses the lack of comparing two sensors by the software. The 737 isn’t a very good cargo plane, so I guess airlines would find that unacceptable. Most other aircraft of it’s type, and larger, fly on software. I recall the Airbus A380 does away with the flight yoke altogether and is replaced by a small joystick. The control system specifically takes matters out of human hands if It detects conditions liable to lead to loss of control.

      Reply

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