Bjorn’ s Corner: Engine development. Part 1. Introduction

March 29, 2024, ©. Leeham News: We finished our article series about New Aircraft Technologies last week. It dealt with the different new technologies that a next-generation airliner could use to increase efficiency and by it environmental emissions.

An area that we touched upon but didn’t dig deeper into was engine development. When airframe development historically decided how long a new generation of aircraft took to develop, it gradually changed to engine development being the more calendar-time-consuming and riskier development for the last generations. This article series will discuss why and what can be done about it.

Figure 1. CFM RISE, a new engine development for the next generation of airliners. Source: CFM.

Why is engine development so difficult?

Before we discuss why it’s so difficult to develop new airliner engines, let’s look at the developments of airframes and engines since the propeller days.

From propellers to jets

In the days of propeller airliners, a Douglas DC-6 or -7 often arrived at its long-range destination with one engine throttled down due to some problem. The long-range airliners of the day had four engines and for good reasons.

Two-engined propeller airliners were domestic types and not configured to fly over water or remote land areas, where the distances to diversion airfields were long. The aircraft engines were the unreliable part of an airliner rather than the airframe.

The jet age changed this. In the transition to higher speeds and altitudes, the airframe technology faced new problems. There were numerous cases of catastrophic control and structure failures both in development and service. The airliners were flying at higher altitudes and at higher speeds, which uncovered several unknown unknowns.

The new jet engines also had initial reliability problems (failing during a mission) and durability problems (staying on the wing for a long time), but the engine industry managed to increase the reliability to the point where two-engined flights over water or remote areas with 120 minutes to a diversion airport was accepted in 1985.

The Atlantic could now be crossed with a twin-engined Boeing 767 or Airbus A330. These aircraft had reliable medium bypass Pratt&Whitney, GE Aviation, or Rolls-Royce engines. Over time, these engines matured in durability until they stayed on the wing for up to 30,000 flying hours, which for these aircraft meant 10 years between overhauls.

Durability arrives

Airlines grew accustomed to the mature engines on their twin jets. But several of the engines gained their reliability by doing the early part of their life on three or four engined aircraft like the Douglas DC-10 or Boeing 747.

When the engines migrated to the 767 and A330, they were already honed on these aircraft, and many early problems were sorted out on the multiengine platforms.

The Boeing 777 was the first twin-engined long-range airliner with engines specifically developed for it. Despite its new engines, the FAA approved it as the first twin airliner with ETOPS 180 at its introduction.

Previous larger engines started their lives on four-engine platforms like the Douglas DC-8, Boeing 707, and 747 (PW4000), or three-engine Douglas DC-10 (the CF6) or Lockheed Tristar (Rolls-Royce RB211).

The 777 engines performed well, and EASA approved its ETOPS 180 rating after a one-year demonstration of reliability under ETOPS 120.

The non-acceptance of engine problems

The trend toward reliable engines continued in the Boeing 787 and Airbus A350 generations. However, durability problems surfaced in service. The Rolls-Royce Trent 1000 has had large durability problems on the 787, and airlines deem the time spent on the wing of the A350-1000 engine in harsh environments unacceptable.

The same goes for the engine upgrades of the Airbus A320 series and Boeing’s 737 MAX. While flight safety is not questioned because of engine reliability, a large number of aircraft are parked because engine durability is not OK, and overhaul shops can’t repair the parts that need replacing.

While the engines are causing trouble, the airframes of the 787, A350, or A320 series are virtually trouble-free (unfortunately, this has not been true of the 737 MAX).

Why can’t the engine OEMs develop trouble-free engines when the airframe OEMs can produce trouble-free aircraft? We will explore this question in the new article series.

52 Comments on “Bjorn’ s Corner: Engine development. Part 1. Introduction

  1. Actually the DC-10-10 had GE CF6-6 engines and the more popular DC-10-30 CF6-50. That engine really improved reliability and was choosen for the A300 and 747-200 at many operators. Most commerical engines benefit from decades of military engine technology funded over decades. Complete new jet engines often are many years apart and the risk of new engineers repeating old misstakes are rampant.

    • “Most commerical engines benefit from decades of military engine technology funded over decades”

      Mostly valid for US connected engines only
      and more performance than reliability related?

      • Can’t think of a comercial jet engine manufacturer that hasn’t benefitted hugely from the vast amounts of money hosed on them during the Cold War and the technological advances this brought.
        The US DOD is currently exploring re powering C17 with a new engine. This would be rather useful for a Boeing MOM airliner

          • The GEnX is too big. There is lack of 40k thrust modern engines. P&W would be happy if the congresz funded a 45k PW1045G engine

          • The current C17 engines are functionally identical to the PW2000 that powers the B757. If they are looking for indentical thrust it would be approximately 40000 lbs.

            Now if you decided to replace 4 engines with 2…we have a different decision. Have a hard time seeing that happen.

        • “The US DOD is currently exploring re powering C17 with a new engine.”

          That certainly wont be a ‘new new’ engine, but a existing type or derivative
          In fact they arent looking for a new engine at all, but some PIP for the existing type
          “One specific product improvement we are looking to incorporate under this contract is a compressor blade coating technology, which according to the Air Force Research Laboratory’s estimates, can extend time on wing by up to 16% and reduce fuel burn by over 1%,”

          • Not sure what that’s going to be. There is a donut hole between 35k and 60k for thrust for in production engines

          • The USAF might want a 45k very durable engine and you can use the GEnX-1B core engine with a suitable LP system to make one. You benefit from the high core engine flow to lower Turbine inlet temp. Still to make it a usaf certified engine you are locking at 2-3 bn program with maybe a MoM application as well

      • Correct me if I’m wrong, IAE V2500 is based on a RR design. Did it benefit directly from military spending in substantial ways?

        • The only piece of the V2500 that was RR designed was the compressor.

  2. The issue is that they want to get more efficiency out of a jet engine.

    That means exotic materials and heat and more a use of both.

    Its stunning that you give ETOPs to the MAX with its new to service engines, its spent most of its life grounded. LEAPs on the A320 also have had issues.

    So now they hand ETOPs out like it was candy.

    GE pushed the exotic materials and heat to do so to the MAX (pun not avoided).

    P&W did less heat and exotics as they had a huge edge with the GTF they could avoid that. They then messed up other aspects. Those are hard to fathom as seals are well known.

    Bottom line any time you jump the tech you have issues. 747 had them from the get go, they were carting engines all around the world.

    It just take time to mature.

    That is another reason you don’t want RISE. Its all new and its going to have issues (not to mention no one wants props)

    But a GTF on the TTBW would be a mature design and the issues worked out on the current GTF.

    What is ignored is there are only 8000 testing hours in a year. Even if you ran 24 x 7 it would take you years to really prove an engine and they don’t.

    • You have to differentiate between
      * premature deterioration
      * catastrophic failures

      the T1000Mk1 vagaries shew both.

      but in general ETOPS is about predictability.

    • A couple of years on and they still had some 50 sitting in Inventory from the delivery stoppage.

      One might say that this is a production issue and that once a properly assembled aircraft is in service, it is trouble free – but as I recall the aviation authorities are still mulling over what to do with those 787’s that were put into service with the incorrect gaps. We haven’t heard a lot on the subject, lately.

      IIRC, given the young life of the fleet, there was talk that these issues would be dealt with when aircraft start making their way into MRO’s for their heavy maintenance check and it was not a safety of flight issue.

      I guess time will tell.

  3. “The Boeing 777 was the first twin-engined long-range airliner with engines specifically developed for it. Despite its new engines, the FAA approved it as the first twin airliner with ETOPS 180 at its introduction.”

    Actually it was the P&W PW4084 version of the 777 that had 180min ETOPS at EIS.
    The GE version had some reliability issues and its first customer British Airways withdrew the type from North Atlantic service. It was the heaviest of the 3 versions and BA soon changed to RR engines.

    Later extra heavy payload/fuel 777s had major modifications GE engines

    GEnX engines had major reliability issues on the 787 similar to RR. But they get better press……
    That was 2016 and earlier

    Even newer issues as the AD suggests in 2022

    “This AD [GEnx–1B and GEnx–2B model turbofan engines] was prompted by a manufacturer investigation that revealed that certain high-pressure turbine (HPT) stage 2 disks, forward seals, and stages 6–10 compressor rotor spools were manufactured from powder metal material suspected to contain iron inclusion. This AD requires replacement of the affected HPT stage 2 disks, forward seals, and stages 6–10 compressor rotor spools.

    WOW , yet its unnoticed that complete compressor stages have to be replaced.
    Talk about favourable press…. its blindness

    • Well other than the fact that RR had engine failures they failed to determine why, GE had found this themselves, reported it and had a fix for the POSSIBLE problem.

  4. RR Trent 1000 was grounded by the airlines. The entire engine was redesigned to be 1000 ten. The ten stands for technology enhancement. The turbine hot section is prone to sulphur degradation decay.

    • There were two era of RR issues. The blades degraded and had to be replaced.

      The other part was cracked blades that ultimately was traced to a Harmonic.

      The cracked part was what lead to a number of failures and diversions that lead to the Trent 10.

      The Trent 10 was 75% new, but the 25% they kept had the core and that meant the problem transferred to the 10.

      RR kept saying they had a computer program that said when it would happen and confidently and gave how many cycles and hours

      The program was hopelessly flawed and was revised 3x as I recall.

      They finally found the harmonic and have a correction for that but now they have plenty of fix capacity due to groundings, Covid and people no longer ordering the engine.

      Of course the equally flawed Trent 7000 (bleed air Ten) also had to be fixed. But A330NEO owners are stuck with it as its the only engine on that bird.

  5. ETOPS 120 minutes came in 1985, just after the A306/A310 EIS (1983/1984). The 767 EIS in 1982, and later came in ER-variants. Bjørn writes 767 and A330, but the A330 didn’t enter service until 10 years later, in end of 1994. I think there is a mix-up here. It should say A306/A310, not A330. The A310 was specifically designed for crossing the Atlantic.

    Additionally, Airbus didn’t use any RR-engines until the Trent 700, which became an engine option on the A330 in 1995. (If you don’t count the Cordorde as an Airbus aircraft, as it had RR-engines.)

    • Well
      A300 flew under ICAO 90minutes rule. ( but not in/for the US )
      IMU to level the table for the upcoming Boeing Twin FAA ETOPS 120 was invented )
      767-200 was first with ETOPS 120
      A310 followed couple of month later.

    • The Pearl 10X is side mounted and a new version for the A220 need to be wing mounted. Then comes the question if it can take 20 000 cycles on wing as it might be a “hot rod” for biz jets only with just a few 1000 cycles between heavy shop visits. RR has a history of develop airline engines to finally be reliable for its time (Spey, Tay, BR715..)

  6. Spirit Airlines to Receive up to $200 Million for Pratt & Whitney Engine Problems

  7. Boeing’s new chairman has scrapped formal meetings planned with CEOs of its largest US customers . 🙄

  8. LNA has an article about Airbus’ A350-1000 or Boeing’s 777-9.
    @Scott Realistically, when can Boeing deliver the 777-9? Will there be a reset of the tineline by the new CEO? There’s still no TIA?

    • Emirates thinks 2026 rather than 2025. But who knows.

    • AFAIK the cert plan was to be: Max 7, Max 10, 777X.

      In the Q3/2023 financials, BA had this to say (and I use the Q3’s because it was before the Q4’s which were submitted after the Alaska accident):

      ‘We continue to expect the 737-7 to be certified in 2023 with first delivery in 2024. We continue to expect the 737-10 to begin FAA certification flight testing in 2023 with first delivery in 2024.’

      ‘We continue to expect the first delivery of the 777X-9 to occur in 2025. We are working towards Type Inspection Authorization (TIA) which will enable us to begin FAA certification flight testing. ‘

      ‘We launched the 777X-8 freighter during the first quarter of 2022 and continue to expect first delivery in 2027.’

      pg 40


      Max 7 – 2023
      Max 10 – 2024
      777-9 – 2025

      Now push everything back at least a year

      • Isn’t it very peculiar that it’s taking SO long to get something as basic as a TIA?
        We were told many months ago that the “surprise” 777X flight control software issues had been ironed out with the EASA/FAA, so that wouldn’t appear to be the bottleneck.
        I suspect that the “surprise” fuselage rip-out after that failed wing load test may be playing a role. Remember that the FAA is now in “no exceptions mode” when it comes to safety. Boeing probably did (or still has to do) some modifications of the wing box, followed by calculations/simulations of how it would bear up under load; however, seeing as the process of submitting acceptable SSAs for the MAX-7/10 is taking Boeing forever, one can imagine a similarly drawn-out scenario for those calculations/simulations for the 777X.

        It’s been said here many times: now that self-cert is no longer available to Boeing, the company doesn’t appear to know how to deal with a “normal” certification process workload.

        • ‘ “surprise” 777X flight control software issues ..’

          “surprises” like company.
          ( actually such things trash the formerly built up “trust envelope” : what other surprises are hidden.)

          gaming the 777X ultimate load test via overpressuring the hull probably did not further required trust either.

        • I’m not sure if this is the issue, but as has been talked about in here by those who have contacts inside BA, the shop talk was that there was a high alpha issue with the tail being too small for the aircraft.

          Apparently, they were trying to fix the problem with flight control software, which I was told is usually not a big problem.

          Unless maybe you’ve had a couple of ‘incidents’ with said software and now everyone is hesitant to agree to said fix.

          Disclaimer; I can’t verify this info as fact and perhaps in the flurry of other more pressing matters, it has been lost in the shuffle. It could be something, or not.

          As I recall, there was an uncommanded pitch event on a test flight, which might be related.


          Somebody posted this in a forum in 2021:

          “There is a stability issue with the tail section…in reality, the 777 already had this, hence the infamous “flutter” “fix” which makes the rear pax and crew seasick…

          Rather that redesign the tail, which would have taken the ac out of rapid approval, BA chose the usual software fix…last test fight was what 8 months ago, and yet still no idea from BA what went wrong.

          the results from several tests, as well as test flights, have been hidden, until this latest FAA report…

          cert maybe by mid 2024?
          Emirates was supposed to get the ac delivered in 2020….and they are not happy…now they must be livid.”

          • EK must have gotten their 787s for pennies on the dollar but still no delivery in sight?

            How about route verifications for EK? What does that mean now without TIA??

            P.S. Found this!!!
            According to the project pilot for the 777X:
            “We’ve also got some other stability and control (S&C) testing as we evolve the flight control laws and as we make some changes we’ll go out and re-do that phase,”
            “The whole program is involved in focusing on trying to get some of those safety assessment reviews completed and the paperwork closed out so that we can document it—then we can work through completing the remaining items before TIA.”

            Doesn’t look good IMO.

          • From AW:
            Stan Deal at Dubai Airshow l/y “I anticipate shortly we’ll be at the first phase of type inspection authorization on the airplane and getting the FAA and eventually [the European Union Aviation agency] on for score for all those test cards we’ve been flying,”

            Is this what Jon Ostrower described: “Senior airline leaders lamented unrealistic schedules for airplane development, production and delivery repeatedly put in front of them with the knowledge they can neither be achieved nor disproven as inaccurate today”

  9. On Boeing, Airbus & Spirit

    ‘Industry sources say Airbus may have to invest over $1 billion to make the Belfast wings more affordable to build, as it tries to lift the Canadian-designed A220 jet out of the red.’


    If Airbus puts in $1 billion to the plant and it would cut the cost of each A220 set of wings by $1 million, it’ll take 1,000 A220’s to recover that investment. (ignoring the time value of money)

    • Perhaps Airbus could also use the Belfast plant to manufacture wings (or wing parts) for other models, such as the A320/A321…as a nice supplement to Broughton and Bremen?

    • One wonders if PW’s manufacturing records are accurate enough to be able to definitively reveal which engines contain which problematic components?

      Boeing’s 787 manufacturing records could not provide such info vis-à-vis the shimming and composite contamination issues…

  10. How often we are being told the 787 is a success?

    Dominic Gates at the Seattle Times:
    “Boeing long ago conceded that developing the 787, its introduction delayed by years, was an operational and financial disaster.”

    • …which will conveniently provide some early slots for UA, AA and/or QR….

      • Who said airlines have to buy from the other major airframer because AB has mostly sold out into early 2030s?

  11. “Boeing’s 777 ‘Gliders’ Signal More Cash Woes”

    “(Bloomberg) — Boeing Co. likely didn’t deliver any 777 freighters during the first quarter, adding to its cash woes at a time when 737 Max handovers are sluggish amid heightened government scrutiny.

    “The planemaker as of last week had 11 newly built “gliders” — an industry term for finished aircraft that are lacking engines — stashed in and around its factory in Everett, Washington, Jefferies analyst Sheila Kahyaoglu said in an April 5 report citing data from Aero Analysis Partners/AIR.

    “The cash-flow drag from 11 newly built but undelivered 777 freighters would translate to roughly $1.16 billion, according to George Ferguson, analyst with Bloomberg Intelligence. He estimates each aircraft not delivered represents a cash outflow of about $105 million.

    “The bottleneck highlights how Boeing’s manufacturing challenges extend beyond its cash-cow 737 Max jet. The aerospace giant is working to bring its factories and supply chain back to a steady cadence under scrutiny from US regulators following a series of quality lapses. ”

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