engine tech

Apr 12, 2017

Troubles persist for ‘revolutionary’ GTF engine vital for new tech jets

The triumph of marketing over reality in terms of new engine technology is starting to hurt badly

Ben Sandilands — Editor of Plane Talking

Ben Sandilands

Editor of Plane Talking

US carrier Spirit is having a bad time with its Pratt and Whitney GTF engined A320 NEOs

Update: Qantas has chosen the CFM International LEAP engine alternative for the Jetstar A320 NEO order.

The long running problems with Pratt and Whitney’s ‘revolutionary’ GTF or geared turbo fan engine are if anything, getting worse, and casting shadows over some Airbus A320 NEO operators as well as the all new smaller jet designs from Bombardier, Embraer and Mitsubishi.

It’s a story many industry observers had been hoping would go away, but as the highly visible problems being experienced by low cost carriers Spirit (in the US) and Indigo (India) show, the lack of a clear and definitive solution is putting mounting pressure on the American engine maker.

Fortunately for Airbus, the Pratt and Whitney design isn’t the sole engine used by its high selling A320 NEO single aisle family, the alternative being an apparently reliable and efficient version of the Franco-American CFM International LEAP engine, another version of which is also the only engine available on Boeing’s competing 737 MAX family.

The various problems that have dogged the all American engine have been apparent since late 2015, when A320 NEO launch customer Qatar Airways refused to take delivery of them, and subsequently specified the competing engine on a number of deliveries.

Pratt and Whitney last year insisted that those early problems would be solved in engines delivered from about July 2016. They weren’t. Qantas, which has ordered 99 A320 NEOs for its Jetstar subsidiary but doesn’t have to make an engine selection until later this decade, is a no doubt keen observer of the on-going issues. (As noted subsequently to this post first appearing, Qantas has chosen the LEAP alternative to the troubled Pratt and Whitney design. This decision avoids any rush by other undecided or disaffected A320 NEO customers to obtain the CFM International engine.)

Those airlines that are using the American engine on their A320 NEOs are reporting as having experienced excellent results in terms of fuel efficiency, but suffered operationally by not being able to obtain those savings across high utilisation scheduling because of the need for ‘enhanced’ maintenance and checking requirements.

The results for operators of CFM powered A320 NEOs is said to have been good. And reliable.

Versions of the Pratt and Whitney engine are used exclusively in the Bombardier CSeries jets, which have after long delays, started to enter service in Europe. The CSeries, like the similarly powered Embraer E2 family now doing certification flights, is a potential candidate for becoming a Boeing 717 and Fokker F100 replacement in the later part of the next decade, as those jets in service for Qantas or Virgin Australia reach the likely limits of their economic lifetime without costly on-going aged airframe maintenance.

Mitsubishi also uses a version of the GTF engine in its MRJ regional jet, which has experienced so many design issues related to its essentials that it is unlikely to be considered by an Australian operator in the foreseeable future.

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16 thoughts on “Troubles persist for ‘revolutionary’ GTF engine vital for new tech jets

  1. Jacob HSR

    What aircraft could regularly use Bankstown airport?


  2. Ben Sandilands

    Agree. Technically speaking. So could the CSeries 100, maybe the CSeries 300 and the smaller E2s. But will Bankstown be all big box retailing and small box housing by the time someone with fortitude and the necessary fortune pursues a business case that might survive?

    1. Jacob HSR

      Free tickets to politicians from BWS airport might do the trick.

      London has a city airport with a 1500 m long runway. BWS has a 1416 m long runway that can be 220 metres longer:

      “a 220 metre extension of Runway 11C/29C may be required
      from 1,416 metres to 1,636 metres. The current runway
      is not of sufficient length to enable all Code 3C aircraft to
      operate at Maximum Take-Off Weight (MTOW)”

      http://www.bankstownairport .com.au/assets/documents/Final%20MP%202014.pdf

  3. derrida derider

    A turbine with very high-speed high-power gears is inherently much less reliable than just the turbine; it took navies a long time to get the gearbox right and that was at far lower speeds.
    What I would worry about if I was contemplating buying these engines for bigger planes is not the more frequent maintenance but what it means for ETOPS. I can’t see even a tame FAA approving 8 hours for a twin with these.

    1. Dan Dair

      I’m confused by all this.
      I assumed that P&W’s problems were of the ‘teething’ type because I presumed that the majority of the problems Derrida Derider is talking about were solved decades ago, with the invention of the turbo-prop.?

      Reduction gearboxes in turbo-props have been successfully operating with minimal problems for almost ever. AFAIK the GTF engine has an effectively similar setup, with the compressor fan array at the front of the engine, running at a much slower speed than the ‘combustion’ fans at the rear.?

      What is it that’s so radically different in the GTF design that they can’t get it to work in service, as smoothly as it worked on test.?

      1. TomM

        @DanDair, article here (http://aviationweek.com/commercial-aviation/new-pw-president-has-nothing-hide-gtf-starting-issue) that goes into some depth on the bowing issue for the GTF. What is potentially making this more of an issue is that because the LP turbine shaft can spin at a higher speed, it will be transmitting less torque, which allows P&W to use a thinner shaft saving weight. However, a thinner shaft makes the shaft more susceptible to rotor bow.

        1. Dan Dair

          An interesting article,
          but its over a year old & the same problem appears to still be current……
          Are GE ‘sliming’ P&W with a fake/negative-news release
          or have the GTF ‘bowing’ problems genuinely not been remedied.?

      2. Arcanum

        You’re correct. Everyone focuses on the geared aspect of the PW1100G and forgets that there’s a new core behind that gearbox too. The problems have been primarily with the rotor shaft and combustor. There were also some early issues with fan blade manufacturing.
        From what I understand, the gearbox itself has been performing flawlessly. As you say, reduction gearboxes have been used forever in turboprops with extremely high reliability. In fact, I vaguely recall reading somewhere that the gearbox on the PW1100G is a sealed system which is not intended to require any maintenance for the life of engine.

        1. caf

          Haven’t they also been using reduction gearboxes on turbine-powered helicopters for years as well?

        2. Dan Dair

          In my case it’s not so much ‘forgets’ as didn’t realise in the first place.???

          I knew it was a new engine, but didn’t realise that it was more than just an upgrade on a previous engine model.!

          What do you think;
          Are these real problems for P&W or are the problems really just specific to the A320.?
          If so, where are these ‘bad-news’ stories coming from.?

  4. TomM

    There’s an excellent breakdown here (http://theflyingengineer.com/flightdeck/pw1100g-gtf/) of the various trade-offs that each manufacturer faced in trying to produce the next generation of engines.

  5. Arcanum

    Most of the problems have been with the PW1100G variant used on the A320neo. The PW1500G variant for the CSeries has had far fewer issues with a > 99% dispatch rate reported at Swiss to date. The problem for the CSeries is apparently that P&W pulled staff over to work on urgent fixes for the A320neo (Airbus being a more important customer than Bombardier), which resulted in slowed production of the PW1500G.

  6. comet

    Boeing must be laughing that the engine it could not fit under the wing of its 1967-vintage 737 airframe is now having troubles.

    1. Dan Dair

      I’m sure they’ll not be laughing in a couple of months,
      when P&W have resolved the problems with the A320 mountings.
      Once they’ve cured that, there’ll be nothing holding back the A320 from excelling in the market-sector.?

      Meantime, the ‘1967-vintage 737 airframe’ will still be just that & little else.?

  7. Dan Dair

    I’ve just read the link Ben posted & noticed this;
    “We are flying at 30,000 feet to provide a better ambient pressure differential for the number 3 Bearing compartment lift off seal contact issue”
    Can anyone explain the significance of ‘the number 3 Bearing compartment lift off seal’.?
    Does anyone know how the rest of the operators are getting-on with their engines.?

    This appears to be a totally different issue to the rotor shaft ‘bowing’ problem previously identified, which has by now presumably, been remedied.?

    Is this more of a good ‘bad-news’ story, than a real issue with the engines.?
    From what the linked article is saying, it appears that the only reason the Spirit aircraft are grounded is because P&W haven’t yet got a stash of spare engines to lend to Spirit, to keep their aircraft flying.?

  8. Tango

    It would be good if people really did read up on what the problmes were and then make comments based on that.

    The gearobos has not nor shown any sighns of faioure.

    While it is a poor entyr into service, its miner seal failures and such that are at the heart of it.

    This may be an industrializing issue like GE has and RR had with their engines in the past. RR had to make a whole new engine for the 787 because they could not fix the problems with their original engine.

    They also had to replace the blades on the ENITRE ANA fleet because they corroded. Duh, Japan. , sea water corrosion ? Really, who knew.

    So, let me ask you this, do each of you meet the same perfect standard in your work and life as you expect P&W to do?

    Or do you make mistakes, learn from them and try not to repeat them or make other mistakes?

    Or are you the type that points fingers and expects others to conduct themselves perfectly while you make excuses for your poor conduct?

    Its gotten a lot of press, but I also have it on good authority that CFM has its issued, they have just covered them up better.

    So once and for all, its not the gearbox.

    Gearboxes have been used as main drive on huge turbines (in the air) and they work just fine.

    For P&W its an embarrassing teething issue but miner items that are not flight safety nor fatal.

    Be grateful its miner, it could be a battery burning in mid air with no chance to land.

    And maybe try doing what P&W is and be successful at it.

    I know I would fail before I made the first step because I have not a clue how to do it.

    I do know some of the processes and how things work.

    Being a critic takes no skill, understanding it more so, doing it, now that is a mountain that is harder than Everest.

    Expecting their best is fine, expecting perfection is really not understanding how it works.

    Give P&W credit for putting a billion bucks into a system that is the wave of the future.

    Expect them to fix it. Never expect zero mistakes or problems.

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