Bjorn’s Corner: Aircraft engine maintenance, Part 1

By Bjorn Fehrm

March 3, 2017, ©. Leeham Co: We will now go through how airline turbofans are maintained. First, we will describe the typical work which is performed, then look into the markets for engine maintenance.

In the markets for engine maintenance, we will look at who the players are, how they are related to the engine OEMs and why the market dynamics are very different between engines for single-aisle aircraft and wide-bodies.

Figure 1. Principal picture of a direct drive turbofan. Source: GasTurb.

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Bjorn’s Corner: Turbofan engine challenges, Part 4


By Bjorn Fehrm

By Bjorn Fehrm

November 18, 2016, ©. Leeham Co: In our series on modern turbofan airliner engines, we will now go deeper into the compressor part. Last week, we covered the fundamentals of compressors. As compressors and turbines use the same principles, we also covered the fundamental working principles of turbines.

We also described that compressors are temperamental parts, which can protest to wrong handling with violent “burps” (burst stalls with the combustion gases going out the front of the engine) or end up in a rotating stall where it simply stops working.


Figure 1. Stylistic cross section of a two shaft turbofan with both axial and radial compressor. Source: GasTurb.

Turbines, on the other hand, are your robust companions. Aerodynamically they just work, albeit more or less efficiently dependent on what one asks them to do (mechanically it can be very different; we recently saw a turbine disintegrate with large consequences on an American Airlines Boeing 767 in Chicago). More on the turbines later.

In the GasTurb cross section of a two shaft turbofan in Figure 1, the engine has both an axial and a radial compressor. We will consider why engine designers combine these two for certain engine types. Read more

CSeries out of London City Airport, Part 2. UPDATED 2017.01.24

By Bjorn Fehrm

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This article, which was published on the 14 November, has been updated with new information from Bombardier. The range of the CS100 from London City airport has increased due to improved performance from the aircraft and a new engine version with more thrust, the PW1535G engine.

November 14, 2016, ©. Leeham Co: In the last article about operating the Bombardier (BBD) CS100 from London City Airport (LCY), we could see that the runway is about half the length of an international airport’s runways. This will have a significant impact on the Take Off Weight (TOW) that can be used when commencing a route from London City.


Figure 1. London City airport, housed in the docklands of London’s east end. Source: Wikipedia.

The manufacturers have data in their aircraft brochures that state that one should be able to takeoff with e.g. the CS100 at Maximum Take Off Weight (MTOW) from a runway which is 1,463m/4,800ft long. London City Airport’s runway is 1,508m/4950ft long, so then things should be fine?

No, the figures from the OEMs is the planning figure for actual runway used and London City airports usable take-off Runway is given as 3,934ft. In addition there is 394ft stopping distance available.

To understand how this can be used required a bit of information that we did not have at the time of writing the original article. Some of the information we used was not up to date and we did not use the strongest engine available (PW1535G) when analyzing if an operator could fly direct between New York from London City.

Bombardier came to our help and we have now been able to update the data with which to feed our performance model. This shows among other things that it’s possible to operate a direct connection between London City airport and New York, given that the number of passengers (the payload) is restricted to around 50 passengers or below.

We have revisited the two cases, SWISS European operations from London City and how would a direct operation London-New York work. You find the updated article below.


  • London City Airport puts special requirements on the aircraft serving it.
  • It puts stringent requirement for takeoff and approach/landing.
  • We use new information and our performance model to present what routes can be served with a CS100 from the London City Airport.

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Bjorn’s Corner: Turbofan engine challenges, Part 3

By Bjorn Fehrm

By Bjorn Fehrm

November 12, 2016, ©. Leeham Co: In our trip through a modern turbofan airliner engine and its technologies, we looked last week at the engine intake and the fan. We now continue with the compressor parts.

As compressors and turbines use the same principles (but in opposing ways), we will look at these principles this week and how their roles in the engine create their special characteristics.


Figure 1. Stylistic cross section of a three-shaft turbofan with section numbers. Source: GasTurb.

As before, to make things concrete, we use a GasTurb simulation of a Rolls-Royce Trent XWB 84k engine to look at practical data when needed. As before, I have no specific knowledge about the engine and will not use any data outside what is public information.

The GasTurb cross section of a three-shaft turbofan is shown in Figure 1. We will examine the sections between station numbers (22) and (3) and (4) and (5) in the general discussion of compressors and turbines. We will then look at some data for common compressors. Read more

Engine industry clamoring for road back

By Bjorn Fehrm

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October 13, 2016, ©. Leeham Co: The airline engine industry is like a ticking bomb. Over the years, a business practice of selling the engines under manufacturing cost and planning to recover costs and make a profit on the aftermarket developed. This goes back decades.

The practice was fostered by fierce competition over the engine contracts for aircraft which offered alternative engines. The losses of the engine sales could be made up later by selling spare parts and services at high margins.


Figure 1. Trent 7000 from Rolls-Royce. Source: Rolls-Royce.

These “jam tomorrow” practices have several implications. The engine industry is now confronted with these and wonder how it could put itself in such a bind. How to handle these and what is the way back?


  • High competition in engine sales forced ultra high discounts for the up-front engine sale.
  • Aftermarket schemes was created that should recover profits over spare parts and services.
  • But these maintenance practices create all sorts of problems in the used engine market.
  • The engine industry now wants to return to more normal business practices. But how do they find the way back?

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Airline assets and lessor assets

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Part 1: The Big Two OEMs

Oct. 3, 2016, © Leeham Co.: There are airline assets and there are leasing assets.

That’s a good airplane but it’s not a good leasing asset.

These are the succinct remarks of just two lessors who decide what aircraft to add to their portfolios.

What do they mean by this and why do they say this?

We’ll take a look today at the thoughts behind these positions.


  • Not all aircraft, however good operationally they may be, make a good acquisition for lessors.
  • Lessors have requirements that are beyond those for airlines.
  • Lessors play increasing important role in the airline industry.

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Airbus will recover 2016 production

By Bjorn Fehrm in Hamburg

May 30, 2016, ©. Leeham Co:

Airbus has got off to a slow start for A320neo and A350 production this year. The Airbus Hamburg and Toulouse airfields are filled with A320neo aircraft waiting for engines and the A350 Final Assembly Line (FAL) in Toulouse has 40 aircraft in different states of readiness but very few are being delivered. Out of target of 50 A350 delivered in 2016, a total of nine have been delivered to customers so far.

Tom Williams

Airbus COO Tom Williams. Source: Airbus

“We have been making gliders for some time now,” said Airbus COO Tom Williams in an Airbus briefing in Hamburg,”but that is about to finish. We are getting delivery of engines from our partner Pratt & Whitney, which has a fix for a prolonged starting time and we have fixed other issues for the A320neo with software updates and changed procedures”.

“When it comes to A350 we have enough aircraft in final production ready for customer delivery after cabin installations,” Williams said. “Now we just got to work through some persistent supplier problems for the cabin side.”  Read more

Rolls-Royce, short and long term outlook

By Bjorn Fehrm

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Feb. 18, 2016, ©. Leeham Co: Rolls-Royce reported earnings for the full year results for 2015 Friday. The share price took a hike after more than one and a half years of being pressed down by bad news.

There was nothing really new that was presented last Friday, with revenue of £13.4bn and profits before tax of £1.4bn. Both results were within the market’s expectations. It was rather the lack of more bad news that made the stock soar to a new high.

We now go behind the scenes to analyze why the stock is depressed and if this is a long term state for Rolls-Royce.


  • Rolls-Royce has delivered one bad news after the other since May 2014.
  • The causes behind the bad news have varied between challenges in its Marine business to more competition and lower deliveries for its best-selling Civil Aerospace engine, the Trent 700.
  • Rolls-Royce has also been criticized for boxing in of customers with its after-market TotalCare maintenance program. We describe what has changed and how this affects the situation.
  • The company is also facing some accounting standard changes with the introduction of IFRS 15 for 2018. We discuss what consequences this might have.

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Bjorn’s Corner: What did we learn in 2015; engines

By Bjorn Fehrm

By Bjorn Fehrm

15 January 2016, ©. Leeham Co: Last week we looked back on what happened in 2015 on the airframe front. We finish the retrospective by looking at what turbofan engine technology came to market in 2015. New engine technology is vital, as it is on the engine side that the quest for higher fuel efficiency has the largest successes.

While advances on the airframe side might bring an additional 5% per generation, the engines typically increase their efficiency per new generation with up to three times that value. Fuel efficiency per delivered thrust unit was improved with a whopping 15% over the engine it replaces for the Pratt & Whitney Geared Turbofan (PW GTF). It was certified for use on the Airbus A320neo in Q4 2015

The competing CFM LEAP-1A shall deliver the same improvement level to the A320neo once it is certified in the summer of this year. This engine has a smaller sister that started ground tests last year, the LEAP-1B, which is developed for the Boeing 737 MAX series.

The engine that is easily forgotten is the Rolls Royce Trent XWB. It entered service on the Airbus A350-900 during the year. It brings an improvement level of around 10% compared to the engines of the aircraft that the A350 replaces (Airbus A340/A330ceo and Boeing’s 777-200 range).

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Pontifications: Boeing moves in China only the beginning

By Scott Hamiltn

By Scott Hamilton

Sept. 28, 2015, (c) Leeham Co.:The move by Boeing to establish a 737 Completion Center in China is only one step in a series of moves to increase its footprint there.

Boeing also said it will join with China’s National Development Reform Commission to develop:

  •  Industrial cooperation;
  • A “world-class” aviation transportation system through deliveries to China of Boeing airplanes and services;
  • Technologies to reduce aviation’s environmental impact and enhance sustainability;
  • Leadership and training for the next generation of leaders in China’s aviation industry;
  • Continued cooperation to support the safety, efficiency and capacity of China’s air transport system
  • Further cooperation in biofuels.

“Boeing and Aviation Industry Corp. of China (AVIC) will broaden their long-term collaboration to support Boeing’s commercial airplane programs,” the company announced last week in connection with the visit to Seattle by the president of China. “In a framework agreement, the companies said they intend to further advance AVIC’s manufacturing capabilities by adding major component and assembly work packages; strengthening leadership; and developing AVIC’s broad aviation infrastructure and business practices, including supply chain management.”

I believe this is only the beginning of a new push of Boeing’s expansion outside Washington State, elsewhere in the US and overseas.

Separately, last week it was also announced that a key supplier is done expanding in Washington State. Future expansion will be elsewhere.

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