Does the Boeing 737 Have ANOTHER Major Flaw!?

- That's a busy morning of news here for Boeing. - Boeing 737 MAX planes with defective rudders. - A warning has just been issued about some Boeing planes with functions that could jam during flight.

- The NTSB recently released an urgent safety alert affecting the Boeing 737 MAX and even some older 737NGs. So what's the problem now? Is it serious and, crucially, how quickly can it be fixed?

Stay tuned. I know I have started a lot of my recent videos this way, but Boeing really doesn't need yet another crisis right now. As I'm recording this, the company's workers in most of its key production sites in Washington State and elsewhere are still on strike, affecting both Boeing's customers and its suppliers.

But of course, the news cycle waits for no one, so Boeing now finds itself once again in the news for the really, really wrong reasons. Because on the 26th of September, the NTSB issued an urgent safety recommendation involving the rudder system of the Boeing 737. The document explains that under very specific circumstances, the rudder system on affected Boeing 737s could become jammed or restricted.

Now, the rudder is the large flight control at the very back of the vertical stabilizer, and it normally controls the aircraft around the yaw axis, which is crucial for coordinated turning, ground directional control, crosswind landings and also in case of an engine failure. Now, I'll explain what these specific issues with the rudder is this time, but I'll want to make one thing very clear before I continue. This issue has nothing to do with the rudder hardover accidents involving older generations of the 737 that you might have heard of.

Now, I might go into more details about those accidents at a later point over on the Mentour Pilot Channel, but what you need to know is that those events involve the hydraulic actuation of the rudder itself, which is not the mechanism that the NTSB is now talking about. So, what is this new problem all about then? Well, this story emerged after an incident which took place earlier this year, on the 6th of February 2024.

It happened to United Airlines Flight 1539, operating from Nassau in the Bahamas over to Newark, New Jersey in the United States. Now, here I should stress that we still don't have the final report on this incident, but the NTSB published a preliminary report about a month after the incident laying out the basic facts. The aircraft involved was a four-year-old Boeing 737 MAX 8 with tail number November 47280, and it was originally built for Air Italy, who sadly stopped operating in 2020 before they could even take delivery of it.

And this, the fact that this specific plane was originally built for someone other than United, is a key part of this story, which you will soon see. On board the incident flight, there were 155 passengers, two pilots and four cabin crew, and by all accounts, most of the flight was completely standard and uneventful. But the pilots faced an unexpected problem, just after they had touched down on Newark's Runway 04R.

You see, when the captain, who was pilot flying, tried to move the rudder to keep the aircraft centered on the runway, he quickly realized that the rudder pedals were completely stuck, or at least they seemed stuck in a response to the normal application of foot pressure, as he later put it. Now, thinking fast, the captain then used the tiller on the left side of the cockpit to steer the nose wheel and maintain directional control that way. The rudder pedals are also connected to the nose wheel and can steer at a limited amount, so we normally wouldn't use the tiller during the landing roll, since it can move the nose wheel very quickly and abruptly and is therefore quite uncomfortable at high speeds.

Again, all of this was happening really fast, but in the end it worked out fine. ADSB data from the flight doesn't show any significant deviation from the centerline, and as the aircraft took a high speed exit off the runway, the captain asked the first officer to check out to see if his rudder pedals worked better, but the first officer found that his pedals were basically frozen too. Shortly after this, one of the pilots, probably the first officer, gave the pedals a good forceful whack, which finally got them unstuck, and after that, the captain tried his pedals again and found that they now were also working normally.

Meanwhile, nobody sitting behind the two pilots had noticed anything out of the ordinary. The aircraft just continued taxiing to its gate where everyone disembarked normally and went on their merry way, except for the aircraft, which obviously was taken straight out of service. Initially, when the airline's engineers started looking at it, they couldn't find any obvious malfunctioning parts in the rudder mechanism, but when they downloaded the flight data recorder, they did see that the rudder had remained stuck during the landing and the rollout, and also that it had taken a pretty good amount of pedal force for the system to get unstuck.

Three days after the incident, United Airlines then made a test flight to see if the problem could maybe be replicated, and to their amazement, they found that it could. Except at this time, the pilots obviously checked and identified the stuck rudder when they were still at altitude. So after the issue had been identified, the test flight was cut short and the aircraft returned to Newark, where the crew landed safely, presumably after getting the rudder unstuck again.

And it was at this point that the NTSB was notified about the whole sequence of events, and their investigation into this whole thing began. Now, in addition to the NTSB itself, the investigation also involved United Airlines, Boeing, the FAA and also a company called Collins Aerospace. And the reason that Collins were part of all of this was because the NTSB had found that the problem involved a part called a rollout guidance actuator, which had been manufactured by Collins Aerospace.

When tested on the ground in normal conditions, the NTSB found that this part worked perfectly fine, which was also what the United Airlines engineers had found after the incident on the 6th of February. But when the NTSB tested the part again, after subjecting it to very cold temperatures, they found that its function was severely compromised. So why was that then?

Well, we'll get to that soon, but what makes this whole story particularly strange is that the part involved wasn't even being used when it started acting up, because it had actually been disabled at the request of United Airlines. So, how rare is this problem? What does this part even do?

And if it wasn't in use, then what was it even doing there? Well, as you can imagine, there were loads of different stories floating around in the press when this news broke, and with the flood of Boeing-related updates, I wanted to gain a truly comprehensive understanding of the situation. So I turned to Ground News, today's sponsor and my go-to source for getting all of the angles of emerging news stories.

More than 100 articles were published on the 737 rudder problems, and Ground News brings together all of these viewpoints in one place, giving you a great view of how different publications with different agendas can skew the information. Like how US-based left-wing Business Insider dove into the regulatory response to the issue while the right-leaning Fox Business instead focused on NTSB's warnings. Without access to all of these perspectives, I'd only have a partial understanding of this story, which is where Ground News really shines.

Their app and websites give more insight into any topic than a single article ever could, and, of course, that includes Boeing and aviation. They even specifically show blind spot stories that are not being widely covered by the media, and you have all made it pretty clear in the comments how frustrating the lack of context and abundance of sensationalism found in mainstream media can be. So I can't recommend checking out Ground News enough.

Scan this QR code, or go to ground. news/mentour. They are subscriber-funded, and you, my viewers, save 40% off the same Vantage plan that I use for unlimited access.

By subscribing, you're not only supporting my work directly, you're also helping to bring transparency to the information that we all consume. Thank you, Ground News. Now let's continue.

To understand what the rollout guidance actuator is and what it was doing on this aircraft, we have to talk a little bit more about the 737's rudder system. The rudder pedals on the 737 can move the rudder in a couple of different ways. First of all, they are connected via cables to a torque tube mechanism, which in turn is connected to a main and a standby power control unit, or PCU.

This is a closed-loop system, which means that the position of the pedals will correspond to the position of the rudder and vice versa. But there are more complications to this system, because it is also designed to reduce the amount of deflection that the pedals import on the rudder as the aircraft speed increases in order to lower its effect and avoid large forces on the fin. And on top of that, the PCU is also incorporating the operation of the yaw damper, which moves the rudder automatically in flight to counteract something known as dutch roll, and also to help the pilots coordinate the turns with the roll from the ailerons.

But the autopilots work together with the yaw damper, so under normal circumstances the autopilots don't actually control the rudder directly, which will soon become important. Now, there is of course a lot more to the rudder system than this, including a lot of redundancy and failure procedures, but what you need to understand is that these systems have been updated and modified several times throughout the 737's history. That includes what we did with it after those rudder hardover accidents back in the 1990s, but again, those accidents and their resolution predated the introduction of the 737NG and the MAX families, so those modifications had nothing to do with this incident.

But some 737s have another separate system, which can also move the rudder. And that is where the rollout guidance actuator comes in. You see, what this actuator actually is, is a type of electric servo mechanism.

In the interim report, the NTSB described the malfunctioning part as a rudder rollout guidance servo, with part number SVO-730. And what this part actually does, has to do with the autopilot of the 737. Specifically, it has to do with ILS approaches and auto-lands.

Now, if you're a regular viewer over on the Mentour Pilot channel, you may remember that we generally refer to three types of instrument landing systems, or ILS approaches, depending on available equipment of the airport, on the aircraft, as well as certifications of the pilots. And which type of ILS that we will use depends on the weather conditions that we're facing. ILS approaches are numbered Category I, or CAT I, CAT II and CAT III, and as the numbers get higher, their accuracy gets better, and therefore, the bad weather and visibility that we can handle also improves.

But in order to actually do an auto-land, where the aircraft touches down on the runway all by itself, we need to do either a Category II or Category III ILS approach. In a Boeing 737, this involves the use of both of our autopilot systems, backing up each other, and as I mentioned, the aircraft, the airport and the pilots have to maintain their certification to make these operations possible. But the thing is though, these are just the broad categories of ILS approaches that we have.

There are even more subcategories, so when it comes to Category III auto-lands, we also have Category III Alpha, Category III Bravo, and at least theoretically, Category III Charlie. In a Category III Alpha autoland, the aircraft will basically fly itself all the way down to the runway, flare automatically and then land, but afterwards, the pilot flying needs to maintain directional control of the aircraft by using the rudder pedals. So in such an approach, we would disconnect the autopilot after touchdown and then steer the aircraft down the runway and this is by far, the most common Category III approach.

But then we have Category III Bravo, where the autopilot instead remains connected and will maintain directional control after the landing and during the rollout. Category III Charlie is essentially the same as Category III Bravo, except that with III Bravo, we still need to be able to see a little bit of the runway or its lights before we land, which we don't on a Category III Charlie. This means that theoretically, with a Category III Charlie, you might not be able to see anything after landing, which is terrifying to say the least, but in practice, as far as I know any way, Category III Charlie doesn't really exist, because with visibility that is that low, even taxiing off the runway and onto a parking spot would be nearly impossible.

And on top of that, there would be some serious problems with fire and rescue vehicles reaching an aircraft safely under those kind of conditions if it would be needed. By the way though, let me know in the comments here below if there are any new developments around this, because I might have missed something, so just tell me and while you're down there, make sure that you leave a like and subscribe to the channel as well. Anyway, the point here is that as I'm sure that you've already guessed, the device that enables the autopilot to maintain the runway's centerline after touchdown during a Category III Bravo landing is the rollout guidance actuator, which is an add-on that will enable the autopilot to work directly with the rudder.

But the thing is, out of the many thousands of 737NGs and MAXes in service today, only a fraction of them are configured to be able to do Category III B auto-lands, and therefore, most 737s don't have these rollout guidance actuators. There are different reasons for why the airlines choose to do this, mainly involving cost, available airport infrastructure and perhaps airline-specific procedures. And for consistency in training, airlines generally try to keep their fleets configured so that all aircraft use the same systems and procedures.

So remember when I said that the 737 MAX 8 in this incident was originally built for a different airline, who then never picked it up? Well, as it turns out, that airline, Air Italy, had ordered its aircraft configured to do Category III Bravo approaches, and therefore it was fitted with all of the necessary systems to make that possible. However, as it turns out, United Airlines didn't use this system on their 737 fleet, so when they decided to pick up this particular 737 MAX and a few other like it from Boeing, United asked Boeing to deactivate this Category III Bravo capability.

But even though this was done, the rollout guidance actuator was not completely removed from the rudder mechanism. Instead the system remained in place, deactivated but still connected to the rest of the rudder mechanism. Now, we don't know exactly what type of approach that the United crew were flying in this case, but it doesn't really matter, because even though it wasn't activated, the malfunctioning rollout guidance actuator still caused the rest of the rudder system to get stuck in the same neutral position that it had been during the flight.

After that first test flight following the incident in February, the rollout guidance actuator was then removed and the aircraft was test-flown again, and this time there was no further problems affecting its rudder system, so basically, problem solved. Now following even more checks, United ultimately returned the aircraft to service on the 22nd of February, two weeks after the incident. But what was it that had actually happened to that part?

Well as it turns out, the part had literally frozen in position. It appears that moisture had made its way inside the part, which then froze when subjected to the low temperatures at cruise altitude, and after that had happened, the tolerances within the part were tight enough to jam everything else, until enough force was applied to break it free. Now as I said earlier, the NTSB subjected the problematic part to super low temperatures on the ground, confirming the problem, and when they repeated the test with an identical rollout guidance actuator from a different aircraft, the same thing happened.

To be clear though, this wasn't a problem with the design of the rollout guidance actuator. Moisture shouldn't have made it into the part in the first place, and the reason it did was because the component hadn't been assembled properly. Collins Aerospace subsequently reported that a sealed bearing was incorrectly assembled during production of these actuators, leaving the unsealed side more susceptible to moisture that can freeze and limit rudder system movement.

Collins also notified Boeing that the same assembly issue may have affected a total of 353 rollout guidance actuators, which the company had delivered to Boeing since back in 2017. And the fact that this goes that far back means that the affected aircraft could include both 737 MAXs and all their 737 NGs. Now it seems like United Airlines actually had a total of nine 737 MAX 8s with the faulty part installed, and these nine jets were the only ones with these particular problems in the United States.

According to Dominic Gates in the Seattle Times, airlines in the US actually took delivery of 16 more 737s with the same affected parts, but these jets were then leased out to other airlines outside of the United States. But neither the NTSB nor Boeing have so far revealed how many of the 353 affected components actually made it onto operational aircraft. Some of them might still be sitting in drawers used for spare parts for example.

But on the 30th of September, the NTSB stated that as many as 40 airlines outside of the United States could have aircraft with these parts fitted. Now, since that incident, United has removed these components from the rest of its fleet, and as I already said, the interim report identified the role of these parts quite early already back in March, which should provide plenty of time for affected aircraft everywhere to already have been taken out of service and rectified. But that's, of course, assuming that all operators of 737s worldwide actually know that their aircraft have these parts.

That's why the NTSB wants to see more action on this issue, adding that two other airlines suffered similar problems with their 737s as early as back in 2019. From its side, Boeing has stated that they have informed affected 737 operators about this potential issue, and they did so already back in August. But just passing on this information isn't all that the NTSB wants from Boeing on this matter.

Because another interesting bit of information that came from the NTSB's urgent safety alert in September involves what we, the pilots, are actually supposed to do if we find ourselves with a stuck rudder like these United pilots did. The NTSB specifically took issue with Boeing's guidance in this matter. Because the 737 flight manual says that if pilots are confronted with jammed or restricted rudder, they should overpower the jammed or restricted system using maximum force, including a combined effort of both pilots.

Now, the NTSB pointed out that this guidance is far from ideal if the problem is discovered during the landing roll. As I'm sure that most of you can see, giving the plane a sudden hard boot full of rudder just after touchdown could actually cause a loss of control and a runway excursion in worst case scenario if the pilots would be successful in getting the rudder un-stuck. Now here, it's also worth pointing out that most 737s only have a tiller on the captain's side of the cockpit.

And this means that, had it been the first officer who was pilot flying when the incident happened back in February, keeping the plane on the centerline by using the tiller would have become much more difficult. Both pilots would have needed to react super quickly, handing over controls and then decide to either continue the landing or go around depending on what they would feel was most appropriate. So instead of facing this potentially confusing situation, the NTSB wants Boeing to come up with alternative responses to just using brute force in order to get the rudder unstuck.

And also to vary these responses depending on whether the problem appears in flight or during the landing roll. The NTSB also wants Boeing and the FAA to ensure that crews and airlines outside of the US know about this problem and act appropriately to make sure that this just can't happen again. But I think the main takeaway here is that this isn't a problem that the industry first learned about in September when the NTSB's urgent safety recommendation came out.

Instead, during the months since the United incident happened, this problem should have been resolved in the majority of cases and it wasn't especially widespread to start with. Now, we will, of course, need to wait for the final report on the incident to learn more details about the failure of the affected parts and to get the definitive responses from Boeing and the FAA, but I would be surprised if they vary much from what we have already seen. Now, I hope that you liked this video and that you found these explanations reassuring and easy to understand because that's exactly what my team and I are trying to do with all aviation news that are coming out and if you want to support our cause and also get to preview our videos and even give inputs on them, then please join our Patreon crew by going to patreon.

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Bye bye.