Bjorn’s Corner: Hot competition in Middle east.

By Bjorn Fehrm


By Bjorn Fehrm

By Bjorn Fehrm


12 June 2015, C. Leeham Co: Earlier in the week we had an interesting interview with Sir Tim Clark, , president and COO of Emirates Airline. We discussed Emirates’ requirement for a twin aisle medium/long range complement to their Airbus A380 and Boeing 777 fleets. The competition is between Boeing’s 787-10 and Airbus’ A350-900. So far the assumptions have been that the 787-10 will be hard to beat on pure costs per seat for mid-range requirements in the 300-seat segment.

The 787-10 seats 323 passengers in Boeing’s old-fashioned IAC three class seating and 331 in our more modern, normalized two class seating with 60 inch angled lie flat in Business and 32 inch economy section. The A350-900 has so far seated 313 seats in the same normalized seating standard. Recent cabin changes by Airbus can now increase that to close to 330 seats. The configuration changes were originally conceived for A350-1000 but we believe Airbus will offer these to Emirates and they will make it into the -900 catalog.

The 787-10 is lighter and would therefore be more effective on fuel but the difference is small, given the A350-900’s more modern engines. So the overall discussion was that 787-10 had found its ideal customer, in need of many seats, a solid mid-range performance and lowest cost. That was until Monday’s interview with Clark.

We approached Clark at the side-lines of the International Air Transport Assn. Annual General Meeting in Miami Beach. We told him other media “understood that Emirates was leaning towards 787-10.” Clark responded:  “I don’t know where that’s coming from. If anything, the 10 is not coming up with the thrust requirements that we need. We’re working with Boeing on that, whereas the A350-900 has got bags of thrust.”

How can the Boeing 787-10 be short of thrust?  No other customer has raised this issue. We looked into the matter and here is why:

Take-Off from hot airports

Emirates is not a normal airline. Not only do they operate on a scale different from all other airlines but their main hub, Dubai International, can experience ground temperatures of over 45C degrees (113F) on many days of the year. This affects both aircraft and engines. For the aircraft, the density of the air diminishes with 10%, making the air that the wings pushes down to lift-off lighter. To get to the same lift force the aircraft now has to go faster, raising the lift-off speed. Higher liftoff speed requires stronger engines or longer runway. The runways of Dubai International are long, 12,000 feet, but there are other limits that come in like maximum tire speeds. Fix when this happens, lower take-off weight to lower the take-off speed.

For engines, it is worse. The lower air density lowers delivered thrust (turbofans function by throwing air out the back faster than it entered in the intake, lighter air = lower thrust, everything else being equal) but the engine is also suffering internally from the increased air temperature. The higher air temperature enters the intake and ripples through the whole front section of the engine. As it passes the high pressure compressor, it can cause the engine computer (the FADEC) to lower engine rotation speed as the high pressure compressor increases the airs temperature as part of the compression and the air temperature can exceed what the last compressor stages can take.  Lower rotation speed means lower compression which saves the last stages from being toasted.

Should the compressor be OK with the higher temperatures, the engine’s turbines will not accept higher temperatures than their so-called flat rating maximum without the engine computer throttling back. This flat rating max temperature is normally set to happen at outside temperature of +15°C over ISA temperature (ISA temperature is the worldwide agreed standard temperature defined at +15°C). Dubai presents +30°C over ISA, i.e. 45°C, on a large part of the year.

This results in reduced thrust from the engines and we have seen that we need more to compensate for the thinner air. The reduced thrust comes from the engine’s computer injecting less fuel in the combustor to save the compressors and turbines from melting. Thereby the turbine driving the fan only produce 60,000 hp instead of over 70,000 hp from a more normal airport.

The end result is that the engine loses power and that the aircraft has to back off on take-off weight as a result. The power loss can be considerable. A 787-10 engine is rated between 76,100lbf (GEnx-1B76) and  78,900 lbf (Trent 1000-K2 or TEN). The critical point in an aircraft’s take-off is the so-called Safety speed point directly after rotation, V2. Here the aircraft has to be able to continue on one engine with a climb-rate of 2.4%, i.e., it shall climb 2.4ft per 100ft forward motion.

We are now down to one engine which due to LAPSE (thrust loss due to forward speed, ref our fundamentals series #2) and the high temperature has gone from 76-78 klbf of thrust to around 55 klbf. Had the Take-Off taken place in Europe, where the high temperature day would have stayed below 30°C, the remaining engine would have delivered over 60 klbf of thrust and the air would have been 5% denser.

Range/payload suffer

The only way to compensate for the thinner air and thrust loss is to haul less payload or to have stronger engines on an aircraft with a bigger wing. An aircraft made for long range flying is designed to take-off at higher weights and therefore have stronger engines and a larger wing. This is why an A350-900 can fly with more cabin and cargo loads on the shorter flights that Emirates plan for than a more mid-range optimized 787-10. The draw-back is that the aircraft has those larger engines and wing; it is therefore heavier and weight costs efficiency. In the case of the A350-900, the difference is not large as the aircraft’s Trent XWB engines are newer than the 787 GEnx-1B and Trent 1000, and their higher efficiency can compensate for the higher aircraft weight.


The problems with a very high thrust requirement for take-offs from Dubai International are well known from the larger aircraft. The 777X has been called “Tim Clark special” for the need for extra large and powerful engines to handle the high temperatures of the Middle East.

It remains to be seen what this means for a more normally optimized aircraft like 787-10. Emirates want good hot performance and good reliability at the same time, a hard nut to crack for engines which are dimensioned for more normal hemispheres.

43 Comments on “Bjorn’s Corner: Hot competition in Middle east.

  1. Nice interesting and educational article.This is what I like about Leehamnews.

  2. The issue is further exacerbated on the 787 as the engine thrust design point was originally less than 70k. With the engines now producing over 76k they are really being pushed to their limits without fundamental changes to the design. Turning faster and hotter can only give you so much thrust.

    • Thanks Scott, you pointed this out hours before I did, being new your comment needed approval therefore it aired later then my reply to keesje.

      • No problem. It’s an interesting point that hasn’t been discussed much in the media. The next logical thought is maintenance cost impact because surely time on wing is affected by hotter engine temps? It’s probably a moot point with OnPoint though.

    • The picture from Boeing is a typical OEM picture, they exaggerate any differences. The empty weight diff is around 5 tonnes, not the 17 to 20 tonnes postulated, that comes from comparing 789 with 359. With the cabin changes 7810 and 359 are the most comparable in the line-ups.

      Re engines, you have to look at the history. The 787 engines were designed for a mean thrust of 65klbf when 788 was 215t and 789 230t. This is now strecthed unusually far to 76-78klbf, those engines are on the limit in most respects.

      The 359 engines were designed with 89 klbf as mean thrust (original TXWB should serve 84k 359 and 93k 35J ), that means the 84k version of Trent XWB shall have margins. That makes the TXWB larger and therefore heavier as well, here the extra grunt seems to be needed.

      Whatever margins an engine has gets called by hot and high conditions.

      • Hi Bjorn,

        Very good information as always!

        I would have a question if you will, disregarding any other aspects, do you think and/or have any information whether Boeing would have any feasible (and not too complex) solution or not to use more powerful engines that would elliminate any concerns for the Hot Weather operation?



        • Not really, what might help Boeing is if Clark is using the interview to send them a message. He might want the airplane and also wants GE or RR to step up and give him better engines then offered. One never knows the full truth but I know of no other way than increasing the thrust to solve any hot take-off problem.

          • Increasing wing span a few feet helps, also extending and modify high lift devices can help enought not requiring the higher TO thrust

  3. Thanks Bjorn for this enlightening piece! Any idea on how is the hot and high performance of the 350-1000 perceived? Emirates had some thrust complaints, right?

    • That is harder to predict. The 97klbf Trent XWB is a redesign of the 84k version, the core was enlarged 5% which should give it some margin, perhaps not as large as the 84k version (ref history discussion in answer to keesje).

  4. You nailed it!
    Have I ever read an article that explains things this logic and clear?
    Excellent how you made the point that it is not the lift on the wings
    that is the main problem but the heat in the engines.

    Concerning the order, I still see Boeing in the better position. Emirates might calculate that in the hottest months cargo to Europe is a bit less, as it is holiday season there. A densely seated 787-10 for India, near East and most of Europe fits exactly their business model.

    However, I consider the 787-9 as too small for their needs. So at a later point, for the thinner longer distance routes, it might be Airbus’ call again.

  5. Is there any chance they’ll simply order more 777 Classics, at a knockdown price? Maybe some sort of paper regional variant, a la A330 Regional?

    • Emirates still have about 50 classic on order and I guess the did get a knockdown price for their 150 X.

      Emirates has 20 A330-200 and 5 A340 accompanied by 17 B777-200. Even an A330-200 offers more range than a 787-10. So I guess Emirates needs an aircraft with about the same range (take-off performance) as the old ones with slightly more passengers (~ 300).

      Interesting article!

      Here a solution for Boeing that might work for the 787-10:

      • I wonder if Emirates price for its previously ordered classic 777 can be altered down now that Boeing is offering everyone super cheap prices, even for a small number. This is what happens in agreements for stock market takeovers, if the price increases those who signed up early get same price as those who signed up late.

  6. More modern engines, ….a suppose the upcoming trent 1000 ten is considered antiquated, such a pity ,considering its based on XWB architecture. ..The 787 10 will do what the 330neo did to the 787 8.!!

    • The Trent 1000-TEN is not antiquated in its detail solutions like rising line HPC, latest cooling technology etc. But an engine gets its large castings deciding things like flowareas etc defined at original design point. When you raise the thrust with 20% or more these flowareas starts to get narrow forcing non optimal air speeds through the channels and compressor/turbine areas and more thrust gets harder and harder to achieve.

      Also your turbines who shall deliver the shaft hp to pump the air via fan and compressors are running out of breath at some point despite upgrades with better cooling etc.

  7. There was this hint of more thrust from GE in this FG article back in September 2014…

    “GE is now studying an even more powerful version of the GEnx, which would raise maximum thrust at sea level to 80,000lb. Although Boeing has not publicly discussed a requirement for such an engine -– perhaps to power a high-gross-weight version of the 787-10 – GE is preparing “in case the airplane needs increased thrust”, How says.”

    • If there is such a project that can get ready in time we can be sure it gets presented to Emirates.

      • Is this with absolute certainty?

        For all I know, Tim Clark simply said that RR has a “good chance” of winning back the lost business under the cancelled A350 order. He has also handed RR a huge deal with the 50 A380s.

  8. Just to comment on the old versus new technology debate. The Trent 1000 TEN is I think a scaled version of the Trent XWB-97. So it’s the newest of the newest. If RR had any sense – and they do – they would have scaled it to be 787-9 -10 and not worry about the -8 because Boeing are saying it is history. Further, RR are saying the -TEN is 3% better than the competition. See RR web site. So comments of non-optimal airflow need to be guarded.

    I do think the -10 is under powered for hot and high. But we will have to wait and see

  9. turning an engine faster and hotter can only go so far ,for providing additional thrust…
    So why will it work on the a350- 1000, but not on the 787 10..

    • The A350-1000 trent XWB variant has an enlarged core to cater for the higher thrust. No such changes on the 787 engines, the variants are so called throttle push variants ie the same base engines spun faster. Certain variants like the TEN has improved detail technology to enable such throttle pushes with improved SFC but they don’t change the size of e.g. the core.

      • The FG story about the GEnx said they were increasing the ‘flow path’ by 0.5in in the PIP2 config.
        This means more airflow so is essentially the same as a bigger fan. They seem to be doing the same with the Leap1B for 737Max even before its flown.

        • The question is where, it is easy to open up a flow path locally, if you do it through e.g. the core it is a redesign as you touch every large casting and these have very long lead-times. Look at how long RR needed to do the 97k redesign.

  10. The original thrust was higher for the -900 engines was 84K I believe Bjorn said.

    They scaled the 1000 engine up a bit as well.

    Ergo, it starts at a higher base thrust , been tweaked physically a bit bigger and its inside the ballpark for how far you can push before you have to limit yourself,.

  11. I can imagine that in EK’s case overall unit costs and absolute payload for given ranges weigh in heavier then cost per unit, structural efficiency, CASM etc.

  12. To reply to my comments. I accept a single HTP for the TEN. The TEN doest not need to be a replica of tge XWB. But, for example, a rising line compressor has a completely different geometry to a straight line compressor. One does not fit within the other. The Trent 1000 was gutted and replaced with Trent XWB technology. That is why it has taken so long

    The TEN is the baby of the XWB but not the 84 the 97. Are you sure the TEN still has shrouded HTP blades. The SFC provides the proof, 3% before it has flown. RR are known to be conservative. Rumours are 5%. Therefore SFC of the TEN is likely to exceed the XWB-84

    The end point is that the XWB-84 is behind at the moment. It will catch up to the TEN and a XWB-97

  13. Thanks for the extremely informative report. I had been wondering why “thrust” was important to Emirates Airline. I do have a question, however. I know nothing about airplanes, but know a lot about software. Why can’t a 787-10 engine (or any other engine) be designed to minimize wear and maintenance due to heat – unless there is an emergency. If an engine loss occurs at V2, why can’t the remaining engine go into maximum thrust mode, as opposed to maximum thrust while minimizing maintenance and wear on the engine mode?

    • That is exactly what they do, the max thrust which is Take-Off level is only allowed for 5 min then you have to back down to max climb of max continuous. If you loose an engine you are normally allowed 10 min TO level before the engine needs to be torn down after an event. All managed by the engine computer (FADEC).

  14. I suppose I should give up, but one more try. You said the Trent 1000 is airflow/casting compromised. RR will have spent 5 years doing the TEN, it is not compromised. Yes there are differences with the XWB (2 versus 1 IPT), but those differences are just horses for courses. The reason RR have created the TEN is they wanted to achieve the performance of the XWB and to do that they needed to align the TEN with the XWB. This also had the advantage of allowing technology insertion into both e.g. the un-shrouded HPT

    The SFC proves it. The TEN is comparable if not better than the XWB-84. This means the TEN and the XWB-97 are the new benchmark, the XWB-84 needing technology insertion

    Compromised airflow/casting. No. The 787-10 is though underpowered for hot and high

  15. I’m sorry. I don’t speak English. Your information are very good. I wanna ask you about 787-10 and 787-9. I read on a site that the stabilizers of 787-10 and 787-9 are the same. An engineer received an award “Engineer Of the Year ” for instead of making new stabilizer for 787-10, he designed a software for using the same stabilizer of 787-9. Can you explain to me how does it work? Is this related with fly by wire? Thank you.

    • Looks like they’ve invented what Airbus has been doing for decades ( on all their FBW aircraft ).

      The Boeing 797-9 FBW is configured to present the same control input behaviour from the -8 on the -9.
      ( In the Airbus case all FBW craft are “fitted” to behave like the same abstract aircraft. )

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