Podcast: Engine Trouble

As the Pentagon is grappling with how to maintain the F135 engine powering F-35 fighters, the engine on a Boeing airliner failed on a flight in the western U.S. Aviation Week editors discuss what these incidents mean for safety and reliability as well as the future of military engines.

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Rush transcript:

Jen DiMascio:

Hi, and welcome to Check 6, Aviation Week's podcast. I'm Jen DiMascio, the executive editor for Defense & Space, and I'm here with Guy Norris, our Technology editor, and Steve Trimble, our Defense editor. We're here because it's been a rough couple of weeks for news about aircraft engines. The F135, which powers the US Air Force's F-35A fighters grappling with support in turbine coding issues. Then on February 20th, the engine on a Boeing 777 flying from Denver to Honolulu failed in the air, scattering debris into a Colorado neighborhood. The event, which thankfully ended with a safe single-engine landing back in Denver, seemed to be the latest in a worrying series of high-profile civil engine issues. So, let's start off with the United Airlines incident first. Guy, could you tell us what happened to that Pratt & Whitney engine?

Guy Norris:

Yeah. Thanks, Jen. It was on takeoff, as you mentioned, from Denver. It was climbing at the time over the neighborhoods around the city of Denver when the number two, the right-hand engine, one of the fan blades severed near the root and the engine basically suffered incredibly large failure at that point. The fan lip, the cowling around the fan and the inlet lip basically detached from the engine, and those are the parts, along with the bits that were liberated from the fan itself, which cascaded down into this neighborhood.

As you said, the crew were able to bring the aircraft back in for a safe landing, thank goodness. But obviously, it was a spectacular looking event. There was a fire that ensued despite the fact the crew shut off the fuel and let the extinguisher bottles. So, all in all, it was an interesting event and the one that really has sort of longer term repercussions going forward. But anyway, that, in a nutshell, is what we saw last weekend.

Jen DiMascio:

Well, what are some of those repercussions? What does the incident mean for certification standards for safety?

Guy Norris:

Yeah, right. Good question. So, the thing about the engine itself, the event, was when the blade came away at the root, the certification requirement is that it should be contained within the cell itself or within the collar, which they call it the containment collar, around the inlet. It's made of Kevlar and it's a lightweight, soft material, which is big enough to enclose a 112 inch diameter fan. A huge amount of energy is obviously liberated at that point. So, the rule is that parts should be contained preventing them from impacting the aircraft, of course, and causing further damage. And it did its job and met the letter of the law. What did happen though was, of course, parts flew back out of the engine forward and aft. That's part of the certification. That's allowed to happen. But so much destruction was caused to the inlet and to the cell itself that parts of that then impacted the airframe. Of course, luckily, the aircraft got down safely, as we've said, but this isn't the first time we've seen a fan blade create such consequences for the containment system.

So, what does all this mean? I think one of the things that's really going to be a question as a result of this, it's now the third incident in a row that Pratt has had on this particular type of engine, the 4000-112. It's the second time, since the first was in 2018, that we've had a fan blade off like this and a lot of damage caused to the inlet. CFM, the GE and Safran Group had an incident on a Southwest Airlines in 2018, similar thing where the fan blade was released and caused this devastation really with the inlet.

And we've been lucky so far that we haven't had anything more catastrophic happen as a result of these. So, I think one of the things they're probably going to look at is obviously in this particular case, there's a way of inspecting the blades. And that obviously didn't really work. This was the third in a row, as I've mentioned, of this particular failure, but I think longer term people will begin to question, "Well, are these containment cases and these cell systems up to the job? Do we need to beef them up?" Remember, for the last 30 years really there's been this push for more and more efficiency, lighter and lighter engines. And that's included lightweight containment systems, particularly as they've got larger and larger with the growth of bigger bypass engines. So, it's part and parcel of that approach.

And there's no way of testing ever really the full integrated effect of a fan blade off. You can only do it on the ground. And of course, by necessity, that's at zero air speed. All you're testing is the energy released from the fan blade and the containment capability. You can't take into account the effect of doing that at 200, 300 knots plus. So, and I think that's the situation that we're looking at here. So, it's early days yet, but once they've got the investigation solved to the actual incident, then we'll begin to perhaps see this downstream questioning of certification.

Jen DiMascio:

And what about, are there wider issues at play for the propulsion industry at large to contend with on this?

Guy Norris:

Yeah, I think because the spotlight has been massively on commercial aviation safety since the MAX accidents. And now of course, the scrutiny of the worlds, not just the FAA's certification agency, has now pushed back the entry into service and certification of the 777X, for example, by a whole year. And really part of that is to do with this, are we letting things get away from ourselves at the moment in terms of safety? So, I think this will buy into this argument. Not necessarily because of the specific incident, but because perhaps it's more systematic or it's emblematic of perhaps areas of escapes. I mean, for example, this is the third incident in a row involving the same engine type, the same aircraft type, and you'd have thoughts that, "Okay, happens once. Low cycle fatigue in a fan blade, a metallic fan blade. It's not unexpected. It can happen. That's why you have inspections."

They found it, but then in December last year, the same incident almost exactly happened to a Japanese airline aircraft on the way to Tokyo. And of course, you have this near accident over Denver. So, certainly the second one should have been avoided. This third one should never have happened. So, just sort of it's part and parcel of this sort of, I think when really start to get back into the DNA of the safety culture. And then the second thing as I mentioned is perhaps the bigger picture is to look at certification requirements for the cell structures as well, which are just going to get bigger as bypass increases for these big wide bodies.

Jen DiMascio:

Thanks Guy. I wanted to turn to the defense engines and the matter of powering the F135 for the U.S. Air Force for their F-35 fighters, there's been talk about grounding issues involving the propulsion system. What's really the problem going on?

Steve Trimble:

It's a lot different than what Guy was talking about, where there's one single sort of explosive event that occurred with a PW 4000-112, but it's a bunch of things that are all sort of piling up on the F135 propulsion system for the F-35. So, if you go back a few years, they knew all along the 2021 was going to be the year that they started scheduled removals for depot repairs for the Air Force's F135 engines. And those were going to be going to the Air Logistics Center at Tinker AFB in Oklahoma. And on top of that, a coding issue appeared last fall where the coding applied to the high pressure turbine in the power module was wearing off too quickly. And they were going to have to apply a fix for that, which they had already developed. They developed it last year, and that was going to be applied on unscheduled removals coming into the depot.

On top of that, they've had other unscheduled engine removals coming into the depot. And so between the scheduled removals and the unscheduled removals all coming at the same time, the depot seems to be overwhelmed. Now, when you talk to Pratt & Whitney about this, the point they make is that actually the F135 engine is far more reliable than the F100 engine at this point in its life cycle. Of course, if people who have studied what happened to the F100 engine in the late 1970s as it was coming into service in the early 1980s and, I mean, really profound reliability issues they were having with that engine, which created the great engine war, not to go too far back in history.

So, it's a good thing that the F135 isn't having those reliability issues, and of course they're setting kind of a low bar for improvement, but it is improved. They say 10 times more reliable. And in fact the unscheduled removals, they say overall are lower than what they had projected. That's including for this coding issue for things like [inaudible 00:11:05] and for things that just happen when you're operating a fighter engine. But be that as it may, for some reason, and we honestly don't quite understand why, they just don't have the capacity built up at Tinker to support all of these engine depot visits. And that is creating a capacity shortage for propulsion systems over the long term throughout the fleet. And so we heard General Brown, C.Q. Brown, who's Chief of Staff in the US Air Force last week was speaking to the defense writers group and said that the issue has become such that we're actually going to have to possibly fly these F-35s less in order to avoid wearing out these engines so that they have to go to the depot where they're just adding to the bottleneck.

Now Guy and I talked to Matt Bromberg, the president of Pratt & Whitney Military Engines today about this and he said that they're trying to do several things. They are trying to build up capacity at the depot. They're also talking about adding more spares to the production flow so that those can be distributed in the fleet and hopefully reduce the pressure on the depot. But ultimately they're just going to have to, over the course of probably a year or two, if not longer, build up the capacity at that depot to handle what is the actual workflow of both the scheduled removals and this unscheduled removal demand flow coming into it that is aggravated, it seems at least slightly, or perhaps more by this coding issue problem that they've known about and they've got to resolve, but they've still got to fix it.

Jen DiMascio:

At Tinker, is that sort of a workforce issue, something that might have been exacerbated by COVID, or is it a spare parts thing? Can you help me understand what's going on?

Steve Trimble:

We'd like to know more about that. We really don't. I mean, Matt Bromberg, he talked about this issue that COVID did deprive the company of basically three months of productivity this year because of labor shortages. So, that probably fed into it. There's 1,000 different tasks that all have to come together at a depot visit, and they all have to be acted upon and ready there when the engine's there. And clearly that is not happening. Why that isn't happening, they knew this was coming, right? I mean, everybody knew this was coming, but they're not ready for it. They do have a plan to catch up. We don't know exactly when they're going to catch up, but in the meantime, it seems the US Air Force is going to put some operational, I wouldn't say limitations, I mean, they're going to run the engines in the air the way they would normally do it, but they're not going to fly them as much just to reduce the flow going into the depots.

Jen DiMascio:

Do you think this also adds to the cost or could add to the cost of maintaining the engines over time?

Steve Trimble:

Well, yeah, probably. I mean, I'm not the cost estimator for Pratt & Whitney, and there's a lot of different things that go into that. One of the big factors in cost is scale. And that's really one of the biggest problems that's coming is because of this wave. I mean, we're starting to get into engines that came through five years ago. So, and that was really the start of the big procurement ramp up for the F-35. So, now you're getting a lot of engines that are reaching the time that they have to go to the depot. And there's a learning curve associated with that. They went through this with the F-22, just a couple of years ago where the F-22 started scheduled engine removals and going to the depot. And they said then that they had taken the lessons learned from the F119 depot visits and applying those the F-35 so that they would be ready when the scheduled removals started coming in 2021. But I guess based on this aggravation with the blade, with the COVID situation, perhaps other things they haven't caught up completely.

Jen DiMascio:

Thanks, Steve. Well, how does this, do you think, affected the larger military propulsion market in the U.S.?

Steve Trimble:

It's an interesting story right now with military propulsion. In addition to the, and again, it's still the most produced military fighter engine in the world right now. Pratt & Whitney has delivered over 600 engines and on the way to 700 engines, and they're going to be building potentially 200 more this year. But in addition to that, propulsion seems to be the really popular thing to buy right now. If you look at the major acquisition programs, the biggest ones, at least by the Air Force, are all propulsion related in terms of aircraft. You've got the B-52 re-engining program and the F-15EX propulsion competition between GE and Pratt & Whitney. So, the B-52 has got 600 engines up for grabs. There's at least 400 more coming with the F-15EX. Something very interesting that Matt Bromberg at Pratt & Whitney told us was that they're expecting potentially sales of 1000 to 2000 engines with the F-15EX program, which would include both the U.S. but also a substantial number of international orders for the F-15EX.

So, it's going to be a very interesting year or two in the whole competitive landscape of U.S. military propulsion, where you could have this competition between Rolls-Royce, Pratt & Whitney Canada, and GE on the B-52 re-engining plus this really interesting competition between GE and Pratt & Whitney on the F-15EX. We don't know if that's going to be a winner take, or if they're going to continually compete that every year over the life of the program, which could be really interesting, sort of revives the old great engine war with the F100 versus the F110 back in the eighties and nineties. So, yeah, it's a really interesting time right now for the military propulsion market.

Jen DiMascio:

Definitely. Guy, did you have something to add to that?

Guy Norris:

Well, it just occurred to me that we might've been bashing Pratt & Whitney a bit unnecessarily, not unnecessarily, but we didn't want a single them out. I was just wanting to briefly say at the end of my comments that GE and Rolls have had their fair share of issues too, in fact, on the commercial side. But we should remember that when we're talking, and Steve mentioned this with the reliability on the F135, we're now dealing with overall incredibly reliable pieces of machinery now, and compared to previous generations, I mean, the dispatch reliability, for example, I've slipped this up recently, the GE90 family on the 777, 99.97%, thereabouts, over 100 million flight hours, roughly thereabouts, and 14 million cycles. I mean, it's just astonishing the amount of, and it's mostly the same for Pratt and for Rolls. So, even though these are very high profile events, the reality is it's still the safest way to go. And we should remember that really.

Jen DiMascio:

That's a very important point and we need to wrap up soon. I just wanted to give you both one forward looking question regarding military propulsion and that's, where is it headed in the future? The U.S. is pursuing the next generation air dominance program. In Europe, they're pursuing the Tempest program, the future air combat system. What's on the horizon for military propulsion technology?

Guy Norris:

I mean, I think one of the key things that we're looking for this year, it's going to be very exciting, is going to be the first of the next generation adaptive engines that the U.S. is really looking to push its continued dominance of superiority into the rest of this decade. It's a technology which nobody else has come close to getting yet. Of course, it's early days, but the XA100 of the Pratt engine, XA101, which is a GE engine, will be both due to run this year for the first time. And the other thing I'd just quickly say about that is a lot of the technology which is coming as part of that, it's going to spill into other programs as potential upgrades. So, that's my thought.

Steve Trimble:

And since we're talking about air breathing propulsion writ large, I thought I'd just add that the big thing going on there is scram jet propulsion is coming back, obviously for cruise missiles at the moment. The potential to go beyond that. We're still waiting for the first flight test of a scramjet powered vehicles since 2013 in the United States, but that should be happening very soon. We just got an update from Raytheon about that yesterday. And I do think, this is going to be kind of a teaser, Guy and I know about this, but I think there's going to be some really interesting reporting on hypersonic propulsion over the next week or two.

Guy Norris:

Oh, what a tease. What a teaser.

Jen DiMascio:

Well, you'll have to keep looking at aviationweek.com for that big news and tune in again next week for another thrilling edition of the Check 6 Podcast, which is available for download on Apple iTunes, Google Play, and Stitcher. Please a review our podcast, and thank you for listening

Jen DiMascio

Based in Washington, Jen manages Aviation Week’s worldwide defense, space and security coverage.

Guy Norris

Guy is a Senior Editor for Aviation Week, based in Colorado Springs. Before joining Aviation Week in 2007, Guy was with Flight International, first as technical editor based in the U.K. and most recently as U.S. West Coast editor. Before joining Flight, he was London correspondent for Interavia, part of Jane's Information Group.

Steve Trimble

Steve covers military aviation, missiles and space for the Aviation Week Network, based in Washington DC.