The altimeter design problem goes back decades. "Fundamentally, the problem is a design issue with the aviation industry's radar altimeters," Dennis Roberson, who runs a technology consulting firm and is a research professor at Illinois Institute of Technology, told lawmakers during a House subcommittee hearing in February.

When altimeters were designed, "they had very low-power neighbors, i.e., satellites beaming their information to the earth from very distant orbits... This led the early designers of the altimeters to decide they really could ignore their assigned spectrum boundaries, and as a result they allow transmitted energy far outside their band into the receiver," Roberson explained.

The aviation industry's slowness in fixing altimeters may lead to the FCC cracking down on bad wireless receivers. In April, the FCC voted unanimously to launch an inquiry into poorly designed wireless devices that receive transmissions from outside their allotted frequencies.

The inquiry could result in new receiver regulations similar to the rules that already require wireless devices to transmit only in their licensed frequencies. "To avoid harmful interference, we typically have rules about how and when transmitters can operate," FCC Chairwoman Jessica Rosenworcel said at the April meeting. "But wireless communications systems involve transmitters and receivers... so we need to rethink our approach to spectrum policy and move beyond just transmitters and consider receivers, too."

UPDATE (Thu Jan 20): After the debacle on Tuesday, with the cancellation of 777 and 747-8 flights by multiple international airlines, it seems the FAA was embarrassed (or forced) into accelerating the issuance of AMOC approvals for additional altimeters, approving the 777 on Wednesday morning, and the number of altimeters approved and percentage of the US fleet covered has now grown very quickly:
Tuesday Jan 18: 2 altimeters and 45% of the US fleet
Wednesday Jan 19: 5 altimeters and 62% of the US fleet
Thursday Jan 20: 13 altimeters and 78% of the US fleet.

The result has been that most disruption has been avoided, although regional jets remain a concern, with some problems resulting from low visibility. However, the rapid pace of approvals, and the expectation from airlines that there won’t be “any material disruption going forward”, further discredits the FAA’s fearmongering over the weekend, not least because an AMOC has now been issued covering all 787 jets, which were supposedly the cause of greatest alarm. Suggestions that airlines would need to “swap out the altimeters” in a process lasting years and costing billions of dollars, also appear to be well wide of the mark. //

But the FAA’s statements appear to confirm that they are only issuing AMOCs approving altimeters to operate while the current 5G deployment restrictions remain in place: “The new safety buffer announced Tuesday around airports in the 5G deployment further expanded the number of airports available to planes with previously cleared altimeters to perform low-visibility landings.”

So it is perhaps no wonder Boeing is refusing to comment because they don’t want to get into a public shouting match with the FAA, despite the behind the scenes confrontation over the 777 at the beginning of this week outlined above. But you can be sure that many aviation interests are demanding that the restrictions continue permanently and the FAA is preparing for another showdown on July 5th, when the current six month period of restrictions is set to expire.

All barking up the wrong tree.

The FAA should have evaluated some actual altimeters before the FCC approved the use of C-Band for 5G and fed into that process.

This, coupled with the 737Max debacle - means heads really have to roll at the FAA. Problems with both attitude and competence.

Prior would have been challenging. The FAA was unusure how much spectrum to allocate to 5G. The band in question is 3.7 to 4.2 GHz. Prior to 2020 it was ALL used for fixed sattelite service (FSS). The FCC had a long negotiated process to determine how much or little or that would be reorganized to be used for mobile services (5G) and how much would remain as FSS. That dividing line would determine how far the new 5G c-band would be from the radio altimeter band. The FCC looked at reallocating as little as 100 MHz and as much as all 500 MHz to mobile services (although that was very unlikely). Boeing and the avionic companies simply said don't reallocate more than 400 MHz (5G would end at 4.1 GHz). The FCC reallocated even less. 300 MHz and then stripped off 20 MHz for a guard band so it ended at 3.98 GHz.

So while the FAA maybe could have done some preliminary testing of a few possible scenarios they didn't know the realignment plan until the FCC completed it. Still that happened in 2020 almost two years ago. At that point the FAA should have known that baring credible actual evidence of interference the auction and rollout would eventually happen. They could have mandated testing then or a year later when the auction was completed.

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After stalling for almost two years, FAA cleared 78% of planes in the past week. //

These statements marked a sudden shift, coming just three days after Parker and Kirby signed a letter claiming that 5G on the C-band would cause "catastrophic disruption" to air travel. //

The biggest recent development is that the FAA finally started a process to evaluate and approve altimeters after claiming without proof that 5G on C-Band spectrum (3.7 to 3.98 GHz) would disrupt altimeters that use spectrum from 4.2 GHz to 4.4 GHz. While the Federal Communications Commission created a 220 MHz guard band to protect airplane equipment, poorly built altimeters may be unable to filter out transmissions from other spectrum bands.

The FAA didn't start its process of evaluating the actual altimeters used by airplanes after February 2020, when the Federal Communications Commission approved the use of C-Band spectrum for 5G. The FAA also didn't start this evaluation process after the FCC auctioned off the spectrum to wireless carriers in February 2021. Instead, the FAA continued arguing that 5G deployment should be blocked long after carriers started preparing their equipment and towers to use the C-band. //

The FAA saying that deployment at these frequencies might cause problems doesn't make any sense at all because its already been done. Is the US some special case where laws of physics don't apply?

As someone joked in another post, metric vs imperial wavelengths? //

The FAA could have been in CYA mode even three months ago and had 99.9% of aircraft cleared prior to the Jan 17th go live date. They didn't even start to do their job until Jan 4th. I would point out the original go live date was 1 Nov so the FAA got a homework extension twice and still didn't turn it in on time. //

The FAA came up with a testing regime this year and now we've got most altimeters in use having been cleared, just 3 weeks later. The resources it and the airline industry spent fighting 5G C-band deployment seem quite clearly to far exceed the resources it spent on testing and discovering there's actually no problem. //

I can't help but think that some airline CEOs tinfoil hat wearing, 5G conspiracist brother-in-law got a hold of them at a holiday get together to let him know of the imminent air disaster due to the 5G transmitters and now caused this ridiculousness for the past several weeks.

The rollout of 5G cellular phone service has started affecting operations around the country—a terrific story in The Air Current by Jon Ostrower detailed the confusion at Palm Beach International yesterday, writing, “The aircraft’s radar altitude abruptly ran down to zero, causing repeated loud aural warnings: PULL UP WHOOP WHOOP DON’T SINK TOO LOW GEAR. The flight landed without incident in good weather, but it wasn’t the first time. ‘Exact same location multiple times the past two weeks,’ the pilot, who was on the flight deck for both anomalies, told The Air Current.”

And now Airbus has issued guidance to pilots that details the many things that could go wrong with their planes’ systems if the radar altimeter, built into a handful of systems, including Autoland and Ground Proximity Warning Systems, were to get erroneous readings.

https://theaircurrent.com/aviation-safety/5g-network-disruption-cluster/

Radio spectrum, according to the U.S. Department of Transportation, is divided into different frequency bands that have been allocated for data, voice, and wireless communications used by a variety of different industries. Aircraft radar altimeters operate within 4.2–4.4 GHz, the lower half of which falls within the C-Band—a frequency range from 3.7–4.2 GHz where the combination of the range of signal transmissions and capacity are optimum.

A graphic shown by AVSI's Andrew Roy during a Dec. 7 NBAA webinar shows power levels of the previous satellite emissions that were occurring in the 3.7–3.98 GHz band that 5G stations in the U.S. will start using next year.

The 5G wireless networks scheduled to be switched on by AT&T and Verizon next month will occur within the 3.7–3.98 GHz frequency range, close to the altimeters. As the FAA indicated in its Dec. 7 AD, while it has heard concerns from airlines, the FAA, and aircraft OEMs over the potential interference issues posed by the deployment of 5G in the C-Band, it has not yet been presented with data or information that shows altimeters are not susceptible to interference.

The wings program was launched in 2004 to promote the nascent commercial launch industry and the first recipient was Scaled Composites’ test pilot Mike Melvill, who rode SpaceShipOne to the edge of space in 2004. To qualify for the pin, one had to reach 50 miles in altitude. Just after Bezos launched with his brother and some Amazon employees in and autonomously operated Blue Origin in July, the FAA decided to tighten the qualifications for the pin by requiring that those receiving it actually do something to contribute to the safe completion of the flight (other than pay for it). In abandoning the program altogether, the FAA has also thrown out those restrictions and anyone who got weightless in 2021 and applied for the wings will get them.

How the FAA is Working to Reduce the Impact of Aircraft Noise

By Tom Hoffmann, FAA Safety Briefing Managing Editor

In a scathing response, Jack Pelton called the new interpretation a “solution to a nonexistent problem.” //

Pelton concluded by writing, “This entire episode is a scary example of how new interpretations of the regulations can upend the entire community. While this short-term fix allows operations to continue, it never should have come to this point. Creating more than 30,000 new LODAs and exemptions is a paperwork exercise that does nothing to advance safety.”

Why is the FAA transitioning away from radar and towards ADS-B technology?
ADS-B is an environmentally friendly technology that enhances safety and efficiency, and directly benefits pilots, controllers, airports, airlines, and the public. It forms the foundation for NextGen by moving from ground radar and navigational aids to precise tracking using satellite signals.

With ADS-B, pilots can see what controllers see: displays showing other aircraft in the sky. Cockpit displays also pinpoint hazardous weather and terrain, and give pilots important flight information, such as temporary flight restrictions.

ADS-B reduces the risk of runway incursions with cockpit and controller displays that show the location of aircraft and equipped ground vehicles on airport surfaces – even at night or during heavy rainfall. ADS-B applications being developed now will give pilots indications or alerts of potential collisions.

ADS-B also provides greater coverage since ground stations are so much easier to place than radar. Remote areas without radar coverage, like the Gulf of Mexico and much of Alaska, now have surveillance with ADS-B.

Relying on satellites instead of ground navigational aids also means aircraft are able to fly more directly from Point A to B, saving time and money, and reducing fuel burn and emissions.

The improved accuracy, integrity and reliability of satellite signals over radar means controllers will be able to safely reduce the minimum separation distance between aircraft and increase capacity in the nation's skies.

The FAA published Federal Regulation 14 CFR 91.225 and 14 CFR 91.227 in May 2010. The final rule dictates that effective January 1, 2020, aircraft operating in airspace defined in 91.225 are required to have an Automatic Dependent Surveillance – Broadcast (ADS-B) system that includes a certified position source capable of meeting requirements defined in 91.227. These regulations set a minimum performance standard for both the ADS-B transmitter and the position sources integrated with the ADS-B equipment.

Does your aircraft have an electrical system?
NO →
Typically balloons, gliders

14 CFR 91.225 (e) states the requirements under the provision of 14 CFR 91.225 (b) do not apply to certain aircraft without an electrical system, including balloons and gliders. Refer to 14 CFR 91.225(d) & (e) for specific exemptions and airspace limitations.

Do you operate your aircraft above 10,000 feet MSL within the 48 States or DC?

YES

If you operate your aircraft above 10,000 feet MSL within the 48 States or DC do you remain below 2,500 feet AGL?

YES

ADS-B not required

Regardless of the antics of its CEO, SpaceX and others innovating with speed and urgency need to operate with different rules.

Boeing relied on computers with the same processing power as the SNES. //

Of course, old and slow isn’t always worse: the 737 Next Generation series is the safest narrow-body airplane ever made, in part due to these reliable, if unspectacular, computers. To keep costs down, Boeing wanted to reuse them in the next iteration of the 737 as well. The Max might still be flying today if those computers simply had to perform the same tasks that they had for almost 30 years. //

The important thing to know about the 737 Max is that it was a rush job. In 2010, Boeing’s only rival, Airbus, unveiled the A320neo, a direct competitor to the 737 Next Generation that could fly farther on less fuel and with lower emissions than any other narrow-body airplane. Boeing was caught by surprise: while Airbus had developed the neo in secret, Boeing’s engineers had spent five years debating whether to design a new 737 replacement or simply update the airframe, without resolution. The neo changed that in a matter of months. //

But in order to offer its own new product when the new Airbus came out, Boeing would have to rush the airplane out the door in just five years — less time than it took to develop either the 777 or the 787. The main selling point of the new 737 was clear: new engines that would increase the airplane’s fuel efficiency and range. But to hit that ambitious launch date, Boeing would have to take shortcuts on just about everything else.

The new engines, which were larger and heavier than the ones on the Next Generation, did indeed make the Max just as fuel-efficient as its rival. But they also disrupted the flow of air around the wings and control surfaces of the airplane in a very specific way. During high-angle climbs, this disruption would cause the control columns in the airplane to suddenly go slack, which might cause pilots to lose control of the aircraft during a dangerous maneuver.

Boeing could have fixed this aerodynamic anomaly with a hardware change: “adaptive surfaces” on the engine housing, resculpted wings, or even just adding a “stick pusher” to the controls that would push on the control column mechanically at just the right time. But hardware changes added time, cost, and regulatory scrutiny to the development process. Boeing’s management was clear: avoid changes, avoid regulators, stay on schedule — period. //

Boeing’s software shortcut had a serious problem. Under certain circumstances, it activated erroneously, sending the airplane into an infinite loop of nose-dives. Unless the pilots can, in under four seconds, correctly diagnose the error, throw a specific emergency switch, and start recovery maneuvers, they will lose control of the airplane and crash — //

For comparison, Airbus’ A320neo has computers of similar vintage — but it has seven of them. //