In my trip back home from work in the bus, I thought about the 737 and the speculation about its future. Coincidently, my acquaintance and fellow blogger Saj Ahmad stated boldly today, “BOEING 737 WILL BE REPLACED – NOT RE-ENGINED” It’s a valid opinion. Why not?

However, the replacement might well be based on the 737.


Around the 737 there are several interesting concepts and question to consider.

  1. What is meant by “re-engining”?
  2. What is a “new aircraft”?
  3. When will the new product, be it “new” or “derivative”, will enter the market?

A friend of mine even asked a deeper question, “what is a “replacement”?” In his mind, a replacement is when a product is replaced by something very similar. He added that we often mix up “replacement” with “market change”. To illustrate his opinion he ask the question, “Is the 777-300ER the replacement for the 747-400?”. This friend, who works at Airbus asked further, “Is the A380 a replacement for the 747-400?”

He made a good point and I do not know the answer.

Now, back to the 737. Will the 737 replacement be a true replacement of the 737NG? Well, I do not know the answer although I have the feeling Boeing would like to focus on a slightly bigger capacity short-range aircraft. If my feeling is right then they will propose a short-range (transcontinental) product in the 160-210 seat category or the equivalent capacity of the 737-800 and 737-900. For the sake of simplicity we will call these “new” products as 737-8 and 737-9, after the 787-8 and 787-9 or 747-8.


Several months ago I wrote an entry related to a speculation about Boeing-Bombardier cooperation. In that blog entry there is a link to a press article in which Mr Jim McNerney reportedly said, “The CSeries and the other regional jets that are getting a little bigger, that’s not necessarily a market segment we want to be in.” The most interesting word here is “necessarily“. I like big guys’ discourse, they always have the right word to introduce some kind of fuzzyness. I did ask the question whether Boeing would focus on the bigger short-haul aircraft to a fellow blogger with whom I had a chat this summer in Montréal (by the way, if you go to his page, please click on the “$700 billion”). His answer didn’t give me a hint whether it was a positive one or a negative one.

If you ask me, I would say that the smaller short-haul narrowbody market is a crowded one and will be even more crowded in the coming years. Therefore, I do not think Boeing would focus on a product and fight in a market where the margins will be too thin. That will leave enough place for CSeries to grab a major share in the 100-130 seat narrowbody market permanently.

Efficient Fuselage

The 737 fuselage is well proven. The 737 fuselage production at Spirit Aerosystems facilities is awfully efficient. The transport infrastructure from Spirit’s plants to the 737 final assembly is also quite efficient. So, I do not see any reason to change this situation. Some clever people out there speculate about composite fuselage for a narrowbody. Frankly, I just don’t see any valid reason to switch to composite fuselage.

I once had a discussion with a very experienced weight engineer who worked at Airbus and who retired a couple years ago. He told me that there is not really a need, from the strength of material point of view, to use composite for a fuselage as small as 737’s. He added that 737’s skin can be as thin as 1.1 milimeter. In proportion it is the thickness of a coke can. Using a material as strong as carbon fiber would not give any benefit.

My conclusion is that if Boeing’s future short-haul aircraft is a narrowbody then they may want to keep a similar metallic fuselage as the current 737. Perhaps they will bring some alloy updates, but there is nothing revolutionary here.

I beg Boeing engineers to change the cockpit windows. I hope they read this blog.

Black Wing

If the fuselage remains metallic the question is whether they will do something about the wings. My humble opinion is that a Carbon Fiber Reinforced Plastic (“CFRP”) could well be a very good solution, including the wing ribs.

Metallic body and CFRP wings sound familiar, dont they? Yes, I think this combination is an excellent choice.

New Engines

In order to achieve the right ecological and economic efficiency, the new product will need new engines. Well, can’t we call this a “re-engining”?

As far as the 737-8 and 737-9 are concerned and considering Boeing past solutions, I honestly think they would adopt an engine with “moderate” fan diameter which will keep the weight down. Since they already put the CFM engines on the 737, I do not see any valid reason to put an engine other than the LEAPX. The Specific Fuel Consumption (“SFC”) of those engines won’t be as good as other solutions. But at overall aircraft level, the benefit of smaller nacelles, lighter structure and lighter engines will give an excellent efficiency.

Landing Gear

The changes described above are quite significant. Designing more appropriate and optimized landing gear would make sense. So yes, the landing gear will be a new one.

How Does It Look?

Should you call them new aircraft? Can it be considered as “re-engining”. I don’t know. Perhaps it should be considered as a new aircraft, especially when you know that the guts (“systems”) will be largely new.

Last but not least, the 737-8 and the 737-9 will have a “partial fly-by-wire” concept. I don’t think Boeing engineers want to put a full fly-by-wire on the narrowbody.

So, how will 737-8 and 737-9 look like? Considering the above mentioned aspects, the 737-8 and 737-9 will look very similar to the current 737-800 and the 737-900ER.

Window of Opportunity

The 737NG entered into service about ten long years after the A320 entry into service. In my very humble opinion, the 737-8 and 737-9 can enter into service well after A320 NEO. I believe Boeing will target LEAPX’ maturity for its 737-8 and 737-9 entry into service.

The year 2020 sounds very well, “twenty-twenty“.


  1. Christopher Dye aka CubJ3 said,

    January 27, 2011 at 08:07

    Very timely. Same question arose in the mid-1950s: What will replace the DC-3/C-47 in commercial mkts? Many, many different planes, as it turned out. Before and during the war, DC-3s had provided local and long range (in puddle jumps) service. By the late 40s/50s, four engined piston planes had replaced it on long haul routes. Between 1955 and 1970, many different planes replaced it on short/medium routes, including the Martin 204/404, Convair 240/340, Vickers Valetta and Viscount, French Caravell, BAC 111, Fokker F-28, DC-9, 737-100, and lots of puddle jumpers. In upstate NY where I grew up, Capital/Mohawk airlines went from DC-3s to Viscounts and BAC 111s.

    The circumstances then resemble ours today: Very rapid tech improvements result in huge performance increases which in turn redefine route structures, permitting airlines to accommodate the burgeoning mkt by flying more and more passengers to more and more places over longer and longer distances, with many more flights. It is the performance which current and new tech can provide that will define the new 737. IMHO it will be a family of planes with the broadest differences in size and performance between the smallest and the largest that current/new tech can provide, while maintaining the highest commonality. In other words, the plane’s performance will likely define the mkt it serves.

    Right now, B’s narrow bodies stretch from 110/132 seats, 3225nm range (736) to 200/228 seats, 3900 nm range (752). (I’m not including the 753.) Albaugh has said he does not want to be in the CSeries mkt, but he certainly wants to be in the 752 mkt. So, is it possible to build a family of planes stretching from 737-700’s 126/149 seats, 3440 nmr to something close to the 752’s 200/228 seats, 3900 nmr, and maintain commonality? The recent Buckingham Research note says yes. They claim B will announce this year or early next a two-plane family that will do just that, with first delivery 2017/2018!? See http://www.leeham.net, “Boeing Could Launch 737 Replacement This Year.”

    I think yolur analysis of metal fuselage/composite wing is correct. I am not an engineer, but my understanding is that with composite’s higher strength, one can design an air foil that has higher lifting charactaristics across its entire length than metal wings, hence conferring substantial performance improvements. Is this correct, anyone? What are the advantages of carbon fiber over metal in wing design.

  2. January 27, 2011 at 14:58

    Looking at the issues between the A320NEO and a 737 clean sheet I have a few questions that perhaps more knowledgable people can answer:
    1. The A320NEO airframe is presumably a nonoptimal design for the new engine(s) given that the new engines have different weights, thrust, aerodynamics etc in association with a wing design that is 20 years old. Is it possible to guesstimate in the advances (presumably) in a clean sheet design for Boeing? For example. can people estimate the percentages of improvement in eg. weight, wing design, CF implementation, lighter electronics, improved alloys
    2. A similar question then would arise for an A321NEO versus a presumed stretched 737 clean sheet (your 737-9?)
    3. If there is a wish list for the clean sheet to include, what do you think would be on it? What would be the rank for each?
    Increased range
    Cargo capacity
    Maintenance costs
    Reliability ie >99%?
    Rapidity of turnaround time
    Seat number
    Future proofing ie new engine/technology
    Over building above specifications

  3. January 29, 2011 at 02:16

    Sounds very cricket. Very mythological take on the possible routes Boeing might take on “replacing” the 737NG.

    Stating the obvious: The 737-900ER has grown from the 737-100, which traces it’s barrel ancestry past the 707 to the 367-80 prototype. The 737-900ER is an excellent aircraft, entirely different from the -100 in all but similar appearance.

  4. February 22, 2011 at 14:25

    I’m bemused by your re-engining versus new terminology question, knowing that the 757 began by digging out drawings for the never-built 727-300, then morphed into a bigger 737. I wished Boeing had built the 757-100 not just the -200 – would it have been what the longer 737NGs are now? (I don’t know why the 757-200 is falling out of favour, though I hear rumblings about the cost of operating the RR engines many of them have.)

    As for using the present Boeing narrow-body fuselage, what about the desire for more room? Isn’t the A320 family a bit wider? Indeed, using existing tooling and processes provides low capital cost, unless a new design would be less costly to make (note for example that DeHavilland Canada paid the price of a new design for the Dash 8 instead of copying the Dash 7, getting nicer appearance and perhaps better vision in addition to lower manufacturing cost).

    Note too that the choice of engine technology may depend much on the range needed, a heavier engine may be better for longer range use if it is more fuel efficient, but for short range the weight penalty hurts.
    BTW Paulo, the 737 fuselage does not quite go all the way back to the Dash80 prototype, as the 707’s fuselage was widened from that of the Dash 80 used for the KC-135, albeit quite similar AFAIK.

    – Keith Sketchley

  5. Paulo M said,

    February 23, 2011 at 15:31


    Agree. The Dash-80 was seed. I think I get carried away with its significance not just for Boeing, but private enterprise and market forces in general.

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