Boeing continues to optimise 737 MAX

During the first-quarter, Chicago-based airframer Boeing continues to rack up orders and commitments for its re-engined 737 MAX aircraft, garnering 301 firm orders, including 100 737 MAX 8s from Oslo-based low-cost carrier (LCC) Norwegian Air Shuttle (NAS) and 201 737 MAX 9s from Indonesia-based LCC Lion Air in the three months ending 31st March. Its transatlantic arch-rival Airbus, in contrast, received 143 firm orders for the re-engined A320neo (new engine option) aircraft, including 35 from Kuwaiti aircraft lessor ALAFCO, 45 from US ultra low-cost carrier Spirit Airlines, 33 from Avianca-Taca and 30 from Mexican low-cost carrier (LCC) Volaris, in addition to the Norwegian’s memorandum of understanding (MOU) for 100 A320neos.

Meanwhile, the world’s second-largest aircraft manufacturer is edging closer to the conclusion of the final phase of wind-tunnel testing on the re-engined 737 MAX, where QinetiQ in Farnborough, United Kingdom, will assess the re-engined narrowbody aircraft’s low-speed performance along with the company’s facility in Seattle to evaluate the aircraft’s high-speed performance, laying the foundation for the aircraft’s mid-2013 firm configuration milestone.

“Wind tunnel testing is on the critical design path of the programme. Based on previous work in the wind tunnel, we are confident this final phase of testing will substantiate our predictions of the aerodynamic performance of the airplane,” Boeing Commercial Airplanes (BCA) 737 MAX chief project engineer and deputy programme manager Michael Teal said.

“This final phase of wind tunnel testing confirms that we are on track to complete our design goals and deliver the 737 MAX to customers beginning in 2017,” Teal said.

One of the primary objectives behind the final phase of the wind-tunnel testing is to “update the model to incorporate the minor changes we’re making for the MAX and the larger engine nacelles. These initial test runs will give our engineers a baseline of the current airplane’s performance that they can compare with the MAX’s optimised design,” Boeing Commercial Airplanes (BCA) vice president (VP) of marketing Randy Tinseth said.

And as the next-generation narrowbody engines featuring advanced engine core technologies form the centrepiece of the upgrade from the existing single-aisle airplanes, which delivers the bulk of the 737 MAX and A320neo’s fuel-burn savings, the economics of engines, or “enginomics”, are likely to continue to be the prime focus of these aircraft programmes as they developments advance and progress.

During the quarter, Boeing and General Electric (GE) settled on a 68.4 inches (173.7 centimetres) engine fan size for the 737 MAX, from the previous fan sizes of 68 inches (172.7 cm) and the widely reported 68.75 inches (174.6 cm).

“It’s nailed down. We’ve finished all the installation studies, and for all practical purposes, it’s done. It’s going to be a very unique installation for the 737 MAX. We’re going to take full advantage of the integration we do with Boeing and with Spirit to make sure the overall engine-airplane combination is incredibly efficient from an integrated propulsion system and the engine is really optimised for this airplane.” General Electric (GE) Aviation chief executive David Joyce told Bloomberg.

As the final phase of the wind-tunnel testing is still ongoing at press time and the firm configuration is still a year away, Aspire Aviation‘s sources at the Chicago-based aircraft manufacturer cautioned that the eventual engine fan size will remain fluid before settling on the most optimised one.

Image Courtesy of Boeing

Indeed, Boeing acknowledged to Aviation Week that future changes in engine fan size are possible and Aviation Week quoted 737 MAX programme official as saying that the company is studying a fan size as large as 69 inches (175 cm).

“However, as detailed design work continues and we incorporate wind-tunnel testing results, we’ll continue to work with CFM to refine the engine [including fan size] as we work towards final configuration in 2013,” the company was quoted as saying.

Engine fan size matters since each inch increase in the fan size generally leads to a 0.5% reduction in engine specific fuel consumption (SFC), notwithstanding the penalty on the aircraft’s overall block fuel burn due to increased drag and added weight. However, it is a delicate balance between engine fan size, drag and weight that is often a complicated trade-off, as a large engine fan size also inevitably leads to an increase in drag and weight, and Boeing said the “sweet spot” is around 68 inches.

For the 737 MAX, not only does the engine fan size affect the re-engined aircraft’s overall fuel burn performance, it also has an implication on the modifications required to accommodate the bigger and heavier engine.

For instance, the squash-bottomed 68.4-inch CFM Leap-1B engine that sits in a much forward position than the existing CFM56-7BE engine on the next-generation 737 will shift the centre of gravity (CG) of the re-engined aircraft forward, of which one possible solution is to adopt the 787-styled trailing edge variable camber (TEVC) that redistributes engineering load inward and also moves the centre of lift forward, thus alleviating the situation of a forward centre of gravity (CG). Though the adoption of a TEVC will nonetheless carry a drag penalty that negates the benefits of a weight saving and a forward centre of lift, thus making such an adoption complicated.

Instead, the primary focus is reducing the weight of the engine. In doing so, not only could the block fuel burn penalty brought by a heavier engine be reduced, it could also minimise the extent to which the structural reinforcements need to take place, thus achieving a cumulative effect in reducing the overall weight, fuel burn of the 737 MAX.

Given the fact that the CFM Leap-1B engine will incorporate a resin transfer moulding (RTM) composite blades and fan case, as well as the ceramic matrix composite (CMC) that will contribute 1% of saving in engine specific fuel consumption (SFC) but which may not mature in time for application for the 737 MAX’s late-2017 entry into service (EIS), achieving further significant weight saving on the already efficient CFM Leap-1B engine is difficult, albeit not impossible.

According to Boeing, the 68.4 inches CFM Leap-1B engine will contribute 12% of the block fuel burn reduction and another 1% from aft-body aerodynamic improvement, which is negated by a 2% fuel burn penalty due to increased drag and weight, thus achieving an overall 11% block fuel burn reduction per seat than the 737-800 on a typical 500 nautical miles (nm) in a 2-class 162-seat configuration. In comparison, Boeing says the 150-seat A320neo will only be 12% more fuel efficient per seat than the existing A320 on a 500 nm sector, with 13.5% and 3% reduction in block fuel burn contributed by a larger, more fuel-efficient engine and the adoption of blended winglets, respectively, which is offset by 3.5% and 1% fuel burn penalty owing to increased weight and the removal of wingtip fence, respectively.

Airbus refutes these claims, saying the 150-seat A320neo (new engine option) will be 7% more fuel efficient per seat than a 157-seat 737 MAX 8 on a 800 nautical miles (nm) mission, whereas Boeing says a 162-seat 737 MAX 8 is 5% more fuel efficient per seat than a 150-seat A320neo, in addition a 7% all-in operating cost advantage (“Boeing 737 MAX sees a bright year ahead“, 20th Dec, 11).

Another less likely, yet a feasible but more controversial solution, is to feature the Pratt & Whitney (P&W) PurePower geared turbofan (GTF) engine on the 737 MAX, an industry talk that was rampant at the International Society of Transport Aircraft Trading (ISTAT) conference in March.

In doing so, not only are the structural reinforcement and modification required on the 737 MAX minimised, it will also further boost the market appeal of the 737 MAX to airlines around the world.

First and foremost, adding an engine option of the Pratt & Whitney (P&W) PurePower engine provides a hedge to Boeing for these engines with decidedly and fundamentally different architectures. The Pratt & Whitney (P&W) PurePower geared turbofan (GTF) relies on a gearbox that allows the engine fan to run at a speed 3 times lower than the speed the low pressure turbine (LPT) spins and consists of 7 moving parts and no life-limited parts (LLPs).

As a result, this maximises the engine’s propulsive efficiency while eliminating 20%, or 7 stages of life-limited parts (LLPs) in the engine, leading to a 20% lower maintenance cost than the CFM56-5B engine.

While Boeing and CFM have spent months refining the configuration of the Leap-1B engine since the 737 MAX’s launch in August 2011, given Pratt & Whitney’s experience and work done on the similarly-sized PW1524G engine with a fan size of 73 inches powering the Bombardier CSeries, the world’s third-largest engine-maker could easily design a downscaled PW1524G with a 71 inches (180.3 cm) fan sizes indicated by Aspire Aviation‘s sources at Chicago-based airframer that fit the 737 MAX with minimal investment and programme risk. In addition, the downscaled PurePower engine could easily incorporate any lessons learned and improvements from the post-EIS (entry into service) flight hours amassed on the PW1524G under Bombardier CSeries’ wings that makes the downscaled PurePower engine on the 737 MAX more fuel efficient.

From a performance standpoint, a 71 inches downscaled PW1524G engine could feasibly provide a 15% reduction in engine specific fuel consumption (SFC), which lost around 1% SFC saving due to a smaller engine fan from 73 inches to 71 inches, not taking into account the reduced weight and drag that are compensated on the aircraft’s block fuel burn separately. In comparison, the CFM Leap-1B will contribute a 12% lower engine SFC towards the 737 MAX’s 11% lower fuel burn per seat than the 737-800.

This will increase the 11% fuel burn reduction per seat of the 737 MAX by an additional 2% with little extra modifications already required to accommodate the CFM Leap-1B engine, similar to the situation on the A320neo (new engine option), where the 81 inches PW1100G-JM engine will provide a 16% lower specific fuel consumption (SFC) than the CFM56-5B engine, while the 78 inches CFM Leap-1A engine provides a 15% lower SFC, albeit both of them are being rated equal by Airbus.

Furthermore, airlines will view the option of two engines favourably, primarily because of the lower price tag resulted from a fierce engine competition. What is more, some airlines have hedged their engine strategies by splitting the orders between the A320neo (new engine option) and 737 MAX which are also due to the inability of airframers delivering such a large quantity of fuel-efficient single-aisle jets within a short timeframe, such as American Airlines (AA), Norwegian Air Shuttle (NAS), etc, offering an option of 2 engines will further improve the standing and widen the lead of the 737 MAX.

“There’s not a team on the MAX considering otherwise,” Boeing spokeswoman Lauren Penning emphasised to the Puget Sound Business Journal.

Despite Boeing continues to downplay the addition of an extra engine option on the 737 MAX, it ultimately comes down to a cost and benefit analysis, with the improved standing in the marketplace from airlines’ and lessors’ perspectives against a fiercer engine competition between CFM and Pratt & Whitney (P&W), of which Boeing has a traditionally good relationship with CFM International’s parent General Electric (GE).

But given these engines’ vastly different architectures and upgrade paths, of which the CFM Leap engine is advancing materials technology and thermal efficiency while the Pratt & Whitney (P&W) will utilise on an increase in the gear ratio possibly to 5-to-1 from 3-to-1, running the engine core hotter should ceramic matrix composite (CMC) mature over time and become cheaper to make the PurePower engine more fuel efficient (“Special Report: The engine battle heats up“, 10th May, 11), hedging between them with a choice of two engine options seems wise.

After all, the CFM Leap-1B still holds the advantageous position of the installed base even after the addition of a Pratt & Whitney (P&W) PurePower engine option, given the large number of CFM engines on today’s industry workhorse 737 fleet, and if adding an engine option improves the 737 MAX’s market share and boosts its competitiveness, why not?

Air Lease Corporation (ALC) chief executive Steven Udvar-Hazy concurred, but said “I don’t think Boeing’s going to do it”.

“I’ve had long talks with [Boeing Commercial Airplanes (BCA) chief executive Jim Albaugh] and guys over there, where I showed them the dual engine has helped Airbus gain market share with the A320neo family, because they had two choices and airlines were able to leverage that to get better deals. I just don’t think Boeing is able to do that. I think they’re kind of stuck in this situation because of the airframe,” Udvar-Hazy was quoted as saying.

Image Courtesy of LeehamNews

Improved payload/range performance
Regardless of how the engine issue evolves on the Boeing 737 MAX, the 737 MAX family aircraft nevertheless hold an advantage over the A320neo (new engine option) on an all-in operating cost basis, albeit at a reduced level, and the CFM Leap-1B engine will be a highly-efficient engine, which Aspire Aviation‘s sources say have made progress in clawing back the rumoured 2%-3% shortfall in engine specific fuel consumption (SFC).

“Compared to Airbus A320neo, which is the European firm’s latest single-aisle plane, the 737 MAX is 10% lighter and 5% more fuel efficient. Its maintenance costs 7% less. The 737 MAX will have the lowest operating costs in the single-aisle segment with a 7% advantage per seat over our future competition, the A320neo,” Boeing vice president (VP) of marketing Randy Tinseth said.

Moreover, the 737 MAX will have a slightly better payload/range performance than the A320neo (new engine option), if not equal.

“We’re going to make some minor structural enhancements to the 737 MAX, so we can have a slightly higher maximum take-off weights so we can slightly increase the range of the airplane as well,” Tinseth said on the Pacific Northwest Aerospace Alliance (PNAA) conference in early February.

According to Aspire Aviation‘s multiple sources at Boeing, the 737 MAX 8 and MAX 9 will see a 3,175 kilogrammes (7,000 lbs) increase in maximum take-off weight (MTOW) from the winglet-equipped 737-800’s 79 tonnes (174,200 lbs) to MAX 8’s 82.2 tonnes (181,200 lbs) and from winglet-equipped 737-900ER’s 85.1 tonnes (187,700 lbs) to MAX 9’s 88.3 tonnes (194,700 lbs). The smaller MAX 7 sibling will see a 2,268 kg (5,000 lbs) increase in its MTOW from winglet-equipped 737-700’s 69.4 tonnes (153,000 lbs) to 71.7 tonnes (158,000 lbs).

In comparison, Airbus said the maximum take-off weight (MTOW) of the A320neo (new engine option) will increase by 1 tonne (2,205 lbs) to 79 tonnes (174,165 lbs) from A320 weight variant WV015’s 78 tonnes (171,961 lbs), the A320 weight variant featuring the highest MTOW.

In terms of range, the range of the 737 MAX 8 will be 6,426 km (3,470 nm), an increase of 405 nm with 162 passengers. The MAX 7 and MAX 9’s ranges will be 3,800 nm with 126 passengers and 3,430 nm with 180 passengers, respectively.

The existing CFM56-5B-powered A320 has a range of roughly 3,000 nm with 150 passengers at a payload of around 13,800 kg and Airbus has said the new engine option will either add 950 km (510 nm) to range, or 2 tonnes (4,400 lbs) in additional payload. The CFM56-5B-powered A319 has a range of roughly 3,200 nm with 124 passengers at a payload of around 11,000 kg. The CFM56-5B-powered A321 has a range of roughly 3,000 nm with 185 passengers at a payload of around 17,000 kg, according to payload/range graphics on Airbus’ aircraft characteristics documents.

On an apple-to-apple basis with the same payload on both 737 MAX 8 and A320neo at 13,800 kg and all increase in payload is used to boost range, the 737 MAX 8 will have the 737-800’s range at a payload of 13,800 kg of approximately 3,240 nautical miles (nm), plus the addition of 405 nm due to the re-engining. Simply put, the 737 MAX 8 will have a range of approximately 3,645 nm, more than the A320neo’s approximately 3,510 nm.

Similarly using the aforementioned Airbus document and Boeing’s chart, the A321neo will have a range of approximately 3,510 nm whereas the 737 MAX 9 will have a range of 3,430 nm. The A319neo will have a range of approximately 3,710 nm versus the 737 MAX 7’s range of 3,800 nm.

Therefore, the 737 MAX 7 and MAX 8 are slightly better in range than the A319neo and A320neo, respectively, whereas the 737 MAX 9 will be slightly inferior to the A321neo in range.

In addition, Boeing is actively evaluating more weight-reduction and drag reduction initiatives in order to make the 737 MAX more aerodynamically and more fuel efficient, and it looks increasingly likely that this year’s continuous lower energy emissions noise (CLEEN) programme, scheduled to take place this late third-quarter on board an American Airlines (AA) Boeing 737-800 in collaboration with the US Federal Aviation Administration (FAA), will be a springboard for testing these initiatives, especially the drag reduction ones.

For example, Aviation Week reported the 737 MAX will feature an improved trailing edge from the CLEEN programme, incorporating the “mini-split flap” technology, a re-rigged outboard flap and drooped aileron, whereas Aspire Aviation‘s sources at the Chicago-based airframer say the test results of the variable area fan nozzle (VAFN) will also be watched closely on whether it delivers the promised 2% fuel burn saving.

The variable area fan nozzles (VAFN) system relies on a FADEC (Full Authority Digital Engine Control) to protect the fan against fluttering in the open position and could possibly cut 2% of fuel burn. The VAFN could also reduce noise in the intermediate position during climb.

The 737 MAX will also feature a reshaped pressure-relief port cavity, a 787-styled tail cone that incorporates a relofted design with the elimination of vortex generators, and a new design of the inlet door of the 737 MAX’s auxiliary power unit (APU) that features a “retractable intake door” found on other Boeing airplanes instead of the existing NACA APU inlet door design on the next-generation 737.

Re-engined airplanes not a long-term solution?
The founder and chief executive of Air Lease Corporation (ALC), Steven Udvar Hazy, the godfather of the aircraft-leasing industry, suggested the notion that the 737 MAX is “not a long-term solution” and while the 737 has “been a great bus for the industry, but at some point Boeing’s going to have to deal with it. Right now, I think the focus has been getting the [787-10X] launched and firming the competitive response to the A350 with its 777X”.

Hazy also commented that the 737 MAX still holds “a distinct advantage” against the A320neo (new engine option) despite a 10,000 lbs weight growth in the 737 MAX’s weight.

First of all, Aspire Aviation‘s multiple sources at Boeing confirmed that the 10,000 lbs weight growth figure is “inaccurate” and “way off mark”, and that the increase in the 737 MAX’s manufacturers’ empty weight (MEW) is currently between 2.0 tonnes (4,500 lbs) and 2.5 tonnes (5,500 lbs), whereas the MEW of the A320neo (new engine option) has increased by 1.7 tonnes (3,748 lbs) on the CFM Leap-1A-powered A320neo and 1.8 tonnes (3,968 lbs) on the PW1100G-JM-powered version.

Despite the weight growth, the 737 MAX variants nonetheless hold the weight advantage in being lighter than the A320neo (new engine option) variants. The 737-900ER with winglet has an operating empty weight (OEW) of 44.7 tonnes (98,495 lbs) whereas the CFM-powered version and International Aero Engines (IAE) V2500-powered version of the A321 have an OEW of 46.9 tonnes (103,300 lbs) and 47 tonnes (103,527 lbs), respectively.

Meanwhile, the business case of re-engined aircraft such as the Boeing 737 MAX, A320neo (new engine option) and the re-engined E-Jet remains sound, as airlines’ demand for fuel efficient aircraft ever grows in light of skyrocketing jet kerosene prices.

Most importantly, the game-changing small twin-aisle that airlines and lessors are looking for, simply will not be available until 2025 or so. The key enabler of such a game-changing small twin-aisle aircraft that features containerised cargo system, fast turnaround times and significant reductions in cash operating costs (COC), the 2nd or 3rd-generation composites with out-of-autoclave (OoA) technology, such as Australia’s Quickstep that trims the curing time by a dramatic 43%, a higher delamination resistance and a higher fibre-matrix adhesion achieved through “lower initial resin viscosity”, is emerging and will require time to mature and find its way into wider aerospace applications, as are nanotechnologies such as the carbon nanotubes reinforced polymer (CNRP) on the Lockheed Martin F-35 Lightning II Joint Strike Fighter (JSF) that promise to be 17% stronger and yet 30% lighter than the carbon fibre reinforced polymer (CFRP) found on 50% of the 787 Dreamliner by weight.

And as Boeing invests its financial and engineering resources into the double-stretched 787-10X and the potentially game-changing 777X late this year (“Boeing develops 777X to challenge Airbus A350“, 9th Feb, 12), an incremental upgrade of the single-aisle product, the 737 MAX, is the proper strategy going forward before the 3rd-generation composite technologies mature and enable the launch of a game-changing small twin-aisle aircraft that replaces the 757 and complements the existing 737 MAX aircraft family, not necessarily “killing” the 737 MAX or its Airbus counterparts altogether.

“Our intention is that we will build the MAX until the market doesn’t want to buy any more and we don’t know when that’s going to be. I wouldn’t predict 2025 or 2035, at some point, either something better will come along or the marketplace will decide they won’t continue to take it. We’ll make it until it runs out of gas and that could be a long, long time,” Boeing Commercial Airplanes (BCA) senior vice president (SVP) of marketing Mike Bair said.

As for this decade, Boeing’s priorities will be making the 737 MAX as best as possible, launch the 777X and 787-10X, while ramping up production by 40% across its product lines within the next few years, that would pretty much make Boeing’s plates full.

In particular, Boeing simply cannot afford to repeat its past mistake of a unsatisfactory programme execution on the 737 MAX, along with the 777X and 787-10X, and especially so when Boeing officials have indicated they want to advance the 737 MAX’s entry into service (EIS) date.

“There’s a decent chance they can actually beat that target,” 737 MAX launch customer Southwest Airlines chief executive Gary Kelly told the Dow Jones Newswires.

Last but not least, the sales prospect of the 737 MAX remains bullish and Boeing expects to receive 200 737 MAX orders from China this year to satisfy the world’s second-largest aviation market’s burgeoning air travel demand, and the strong underlying demand for re-engined aircraft, combined with a strong backlog, should insulate or minimise any risks should this upward industry cycle be halted by any unforeseen events in this volatile global economy. Though one thing is sure against this backdrop of a volatile global economy and this especially cyclical aerospace sector: the contentious debate on each airplane’s merits will continue unabated, both in good times and the bad.

Image Courtesy of Boeing

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    [...] MAX’s range and maximum take-off weight (MTOW) previously reported by Aspire Aviation (“Boeing continues to optimise 737 MAX“, 9th…
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  1. "Engine fan size matters since each inch increase in the fan size generally leads to a 0.5% reduction in engine specific fuel consumption (SFC), notwithstanding the penalty on the aircraft’s overall block fuel burn due to increased drag and added weight. "

    - The NEO / MAX use the same engines, but NEO has s 10 inch bigger fan size, so a 5 % better sfc?
    - The NEO's GTF option probably provides a few % extra better sfc.
    - Same for the sharklets, the NEO will get a 2-3 % better sfc, the MAX won't this improvement.
    - SUH saying the OEW of the MAX will grow by 10.000lbs. Say he's 50% of the mark and it's 5.000lbs the (often quoted but rather small) OEW advantage of the 737 is simply gone!

    We can quote Randy/Jim all we want, but I guess the writing is on the wall here. Please jump to conclusions!

    Furthermore it has become clear SW paid less then 40 million for their 737 MAX aircraft (60% discount), and Lionair (nobody knows what this small, poor, banned airline is gonna do with them) got the aircraft with full US government support / financing.

    Sole 737 operators AA and Norwegian "split" the deal with Airbus (AA took a telling 365(!) NEO options next to the 130CEO 130NEO order, "625 orders and commitments" anyone? ).

    "offering an option of 2 engines will further improve the standing and widen the lead of the 737 MAX."

    Looking at specs and orders I'm not sure what lead the 737 MAX has. Looking back at the broken promises we have seen in recent yrs and the 180 Boeing did on the 737 re-engining I guess consulting both parties on MAX vs NEO comparisons might be wise. The baselines Boeing invented to compare the aircraft (the NG is waaaay better, in hindsight..) have dramatically changed during the last 12 months and are not used by anyone but Boeing itself.

    I guess exiting times behind closed doors at Boeing HQ, were the real numbers are on the table. If not provided by Boeings own specialists, bluntly and un-supportive by visiting the airlines.

    1. keesje,

      For keeping the record straight, the 4,500 lbs-5,500 lbs increase on the 737 MAX's weight is MEW, manufacturer's empty weight, not airline-specific operating empty weight (OEW).

      They are very different and Airbus & Boeing's calculation methods are different as well. Because Airbus excludes seats, interiors in calculating MEW whereas Boeing does include some seats & interiors item in calculating MEW. It could distort the figures by as many as 2-4 tonnes, quite considerable for a 79-tonne MTOW A320neo & 737 MAX 8's MTOW of 82.2 tonnes. Therefore on an apple-to-apple basis with the same rules, the 737 MAX's weight advantage in MEW should be bigger than it appears, should you want a comparison to this precise level.

      Airline-specific OEW includes some standard items, personnel such as crew's weight, equipment such as catering cart, and supplies such as water, excluding usable fuel & payload.

  2. "the world’s second-largest aircraft manufacturer"

    It may change very soon

  3. CFM56-5B and CFM56-7B: what is the fan diameter difference and what is the sfc difference?

    1. VV,

      The CFM56-5B has an engine fan size of 68.3 inches and -7B 61 inches.

      The CFM56-5B4 on A320-214 producing 27,000 lbs has a "dry" (not cruise) SFC of 0.337 lb/lbf hr, the CFM56-5B3 powering A321-211 with 32,000 lbs of thrust is 0.356 lb/lbf hr, CFM56-5B6 powering A319-112 with 23,500 lbs of thrust is 0.327 lb/lbf hr.

      Figures already featured 2007's Tech Insertion on Airbus' CFM engines. The "Evolution" upgrade package was not adopted by Airbus.

      In comparison, the CFM56-7BE incorporating 1.5% reduction in SFC (which exceeded original 1% SFC saving target) and the 2007 Tech Insertion already shaving 1% is around 0.361 lb/lbr hr.

    2. sfc (lb/ is

      0.667 for the -3B1,
      0.545 for the -5B4,
      0.633 for the -7B20.

      1. keesje,

        You are using the "Cruise SFC", which is a different measure of the "Dry SFC" I used. Both are correct, though.

        But your figures for -5B4 and -7B20 did not take into account the CFM Tech Insertion in 2007 that cut 1% off & the 1.5% "Evolution" package for the CFM56-7B series.

        1. Daniel,

          I think the concept of CFM willing to do a better job for Boeing then for Airbus is just hope. For the CFM56 as well as the LEAP. They are the basically the same engines and enhancements are transferred to other members of the family if they are worthwhile. The operators/ owners demand it.

          The A320 burns a few % little less fuel (also according to Boeing) but the 737-800 can spread it out over more seats (of course Boeing says many, Airbus a few), if the load factor is close to 100%. What always made me wonder why Airbus specified the A320 and A321 as they did. The 737-700, -800 and -900 is a gradual build up. When Airbus specified the A321, it seems they went as long as they could get. The 737-800 and 737-900 are both in between the A320 and A321 in terms of length. I always thought Airbus at some point would do a 200 seat version inbetween the A320 and A321, there's a gab of nearly 8 meters / 8 seat rows.. Ryanair and Jetblue asked for it.


          1. 320.5 seems like the obvious move. Airbus could make a sweet machine by stretching the A320 three or four meters. No extra doors and no center tank mean less weight. Range will be less than the new A320, but with the new engines probably still better than the old A320.

      2. Keesje, your number for the -5B4 for cruise sfc is way way too low. If the -5B4 would be really 13.9% better than the -7B20, the A320 family would be way better in fuel burn than the B737 family. As a starting point take 0.6 for the V2500 and add something like 2-3% for the -5B.

        1. We can discuss the exact numbers but the -5B is significantly more efficient then the -7 because of its higher BPR and uncompromised air inlet.

          Contrary to popular believe the A320 burns a little less then the 737-800 and the A320 NEO will most probably have a lower OEW then the 737-800. It has better payload-range capability, cargo container/pallet capability, a spacier, quieter cabin and was already outselling/ outproducing/ outbacklogging the 737NG BEFORE the NEO/MAX. Specially if we look at new operators that had the option to go for A or B. I have yet to discover an airline willing to switch from the A320 family to the 737 MAX.

          I think Boeing has a problem. For us av geeks good news because they most probably will (have to) come up with innovation to re-balance the NB market earlier then they hoped.

          1. Keesje, please don't trust the numbers from the second source - or do you really believe that the GE90-76B has the same SFC as the CFM56-5B4? Or that the Trent772 has an even higher SFC (0.565 in that table, seems reasonable though). The first source seems to be more realistic, but only takeoff sfc is given there. Relationship between two engines at cruise should be similar though.

  4. Keesje,

    You are truly an Airbus sockpuppet! The day you say something nice about a Boeing, I'll start shorting EADs stock in large quantities. The truth of the matter is that every Boeing in service today has kicked the pants off its Airbus counterpart. The A330 might be the only exception, but the 767 is really just a smaller aircraft that continues to sell well nonetheless. The 777 literally killed off the A340, and the 737NG still holds high single digit seat cost advantages over the A320 family. The only reason the 320 has sold so well is because of a massive 737 backlog and deep discounting made possible by massive and illegal EU subsidies.

    Based on history, I see no reason to doubt that the Max will be superior to the NEO. Boeing's wing technology is simply more advanced than Airbus'. You can see that just by looking at them. The 747-8 is testimony to this as the aircraft continues to outperform expectations despite being overweight and hanging GEnx engines that have missed SFC by some margin. While the 787 program is looking like a train wreck, the composite technologies on the aircraft are at least 5 years ahead of Airbus and the A350, which looks likely to incur massive delays.

    I'm not saying Airbus does not build good airplanes. They do. It's just that they lack the engineering horsepower that Boeing employs, despite the fancy cockpits which pilots seem to like. Time will tell, but my prediction is that Boeing will continue to enjoy superior pricing for superior products which explains why the company is more profitable than EADs by about 100% in terms of return on investment (ROI).

    1. While I can dismiss most of your post as baseless cheerleading, I agree on the 767/A330.

      Two different segments. A real good 767/A330/A310 replacement doesn't exist IMO. The A330/787/A350 are way heavier, bigger and more expensive to buy and operate. The longer 737s and A320s way smaller and less capable. I guess at some point Airbus will beef up the A321 (A322 ? ) and/or (hopefully) Boeing will bite the bullet and come up with a real 757/767 replacement, unbeatable at 200-280 seats up to 5000NM for TATL, transcon, intra Asia, Leisure etc.

      1. Keesje,

        With all due respect, the 787-8 (albeit these figures are for a/c after LN 90) is a very good 767 replacement.

        It has lower trip costs at essentially every distance, 15-20% more range, and 5-9% more seats depending on configuration. More revenue potential at a lower absolute trip cost, and more capable to boot.

        1. Vinay, the 787/A330 are empty 20-30 t heavier then the 767, don't fit the domestic ICAO Cat D gates and carry many more passengers in real world configurations. The A330 and 787 are optimized long haul machines as ANA/JAL/Boeing found out with the 787-3. If you need something larger the a A321/739, the 787/A330 is double size/costs..

          1. Keesje,

            The 767 today operates very few domestic routes, even United is pulling them from domestic to more lucrative international routes. Outside of 1200 nm or so, the 787 is far more efficient than the 767, cost-side. And any short haul route that sees the 767 can likely handle the 787 as well

  5. Hello folks

    You might want to dig in some interesting datas from a neutral Turkish source...
    And try to compare the MEW/MWE/BOW/DOW for A320 and B737

    No doubt the MAX will be as good as the NEO or possibly the NEO might be as good as the MAX

    Nécessité fait loi

    Bonne journée

  6. Great article Daniel, always impartial and well researched. Keep up the good work.


    It seems that the 737MAX has just restore the relative positioning of the A320neo and 737MAX like it was with the A320 Classic and 737NG. Status Quo, back to square one.

    I guess they are now stuck with the current status quo during another ten years or so. Read this:

    1. V V

      I like this one

      "Just restore relative postioning ..."

      Very elegant

  8. The 737 MAX so far has not restored the balance. Not in terms of specs nor in terms of sales.

    There's a lot of hope, but as far as I can see (LionAir, SW, AA, Norwegian, all special deals), the jury is still out on the Boeing 737 MAX. Saying parity has been re-established 99 times doesn't help.

    As big 737 operator rather un-elegant Ryanair CEO said:

    O’Leary said all evidence Ryanair has seen indicates that Boeing’s MAX, “as a product, is rubbish.” The Airbus neo, announced before the Boeing model, “does credibly deliver” a 12 to 14 percent saving on fuel burn, he said, while the C919 is a “glorified” version of the A320 and thus lacks development risk.

    1. Any argument backed up by O'Leary's insane claim that the C919 is "less development risk" is from it's basis frivolous. O'Leary is a huckster. He's only saying that because he wants Boeing to give him a really good deal on planes, and Leahy won't talk to him.

    2. keesje,

      Please keep in mind that these are just "best guesses" from me, so to speak.

      But, that being said,

      my estimates have the 737 MAX 8 beating the A320neo on operating costs all in (keeping in mind that price is a component), as well as excluding price, by 1-2% primarily because of larger size.

      The 321neo should have a tangible (3-5%) advantage over 737 MAX 9, and 319neo v 737 MAX 7 is a wash because both are soundly beaten by the C-Series.

      Michael O'Leary is a master of playing the press; his words on the C919 are essentially a negotiating ploy to get lower prices from Boeing, but Boeing might not be willing to deal this time, as they don't have much margin on Ryanair NGs. Airbus and MOL aren't exactly the best of friends, and if MOL were truly serious about C919, then he'd lose his very lucrative resale business.

      And remember, there is indication that Boeing might add a GTF option for the MAX, which would lower fuel burn potentially.

      The overarching point is that we tend to get caught up in the numbers put out by Boeing and Airbus without realizing that they are not comparing "apples to apples" so to speak. Please see here for an overview of the jargon used by both OEMs to skew the figures.

      1. As for the MAX 7 and 319NEO, there is the CSeries plus the MAX 8 and 320NEO are a better value. For most of the life of the 737-700, Boeing has produced about 20 in the first quarter of the year versus just one for the first quarter of this year.

        Why don't Boeing and Airbus redefine the lenths of the entire NEO and MAX families? With heavier engines they have to rebalance and retest the aircraft anyway.

      2. Vinay, for both the MAX and NEO I have seen engines, BPR's, sharklets and modification weight gains. Without listening to anything Airbus or Boeing say, physics kick in & the writing is on the wall. I simply have not seen any MAX numbers that make me believe the aircraft will outdo the A320 NEO.

        Boeing now claims the 737-800NG was far better anyway. Fact is the CFM56-5B engines had a 8-10% better sfc then the -7B ( ) and the OEW advantage for the 737-800 was marginal / if any at all. Maybe the -800 has bigger fuel tanks and flies further. The seat count advantage for the -800 would be relevant only on flights that are sold out. How many are those?

        BTW, I don't think it is unlikely at one point Airbus will build the A320 Plus to close the 40 seat gab between the A320 and A321..

        1. Keesje,

          Independent estimates from various sources at airlines, as well as a few public ones (such as one from Lufthansa a proud A320 operator), give an average of around 2-4% operating cost advantage to 737-800 over A320 all in, varying based on network composition. This advantage largely evaporates when you add in things like commonality with the 319 and 321, and other factors, but that's what the numbers say.

  9. Does anybody know the difference of Operating Empty Weight between an A320 Classic and a 737-800?
    How do you translate the weight difference into fuel burn?

    And what about the comparison of Maximum Fuel Capacity (without aux tanks)?
    Has anyone notice that the 737-800 wing area is slightly larger than the A320 Classic's wings?

    1. V V

      Have a look here

      737NG A320'
      777', A330 et A340
      weight in customer configuration

      Very very interesting !


      1. I think we already knew the A320-200 is a few tons lighter then the 737-800. Some try to mistify by introducing OEW, ZFW and MEW. It is confirmed by these customer configurations. The -5B engines also have a 8-10% lower sfc then the 737-800. The 737 flies further because it has bigger fuel tanks, also visible in your link. That doesn't change the endlessly stimulated perception that the 737 is lighter / more efficient though. I've given up, many just do not want to know & simply block/ ignore. Boeing is better and if not, you are biased. Its all speculation because Boeing did not confirm. Until Boeing admits themselves by changing course. Then its a smart move & the new party line is quickly embraced & endorsed.

        1. Keesje,

          Is the implication of your statement that I am biased towards Boeing? Because I don't believe that's a fair characterization based on the work I do.

          Secondly, typical OEW for the A320 is larger than that of the 737-800, I don't even see how that's a question.

          Third, your figures for sfc are from 2005, sfc for engines isn't static, the delta is different today. Sfc is different than block fuel burn, which is the truly important measure in comparing aircraft. And the difference in fuel burn between the two aircraft is minimal enough that the 737-800 has an advantage in block fuel burn per seat by virtue of its 5-8% advantage in size.

  10. Looking at the 72" GTF for the CSeries and the 81" GTF for the NEO, the GTF seems to take advantage of a larger slower fan. Reducing that to 68" for the MAX and speeding it up may negate some of the efficency advantage of the geared design.

    1. Hi Tcook,

      All sources are indicating a 71" GTF for the 737 MAX & Boeing's decision to lengthen the nose landing gear by 8" may help enable that to happen.


      1. Yes, the PW1524G would make a nice addition to the 737. With the head start on the CSeries, I wonder if it could be delivered in 2016 on the MAX? A 24Klb GTF on a lightweight MAX 7.5 could be the ultimate 149 seat aircraft.

  11. Vinay,

    Why do you feel that the CS300 will beat both the MAX-7 and the 319neo so easily? While I haven't seen a very good breakdown yet of which MAX/neo variants are being ordered, it certainly seems like airlines are vastly preferring the MAX/neo over the CSeries, which has only 158 orders despite being available for 4 years. I realize Bombardier is the new kid in this size class, and both B and A are targetting them heavily, but that's still a huge disparity given that the MAX and neo were only launched 4 and 15 months ago, respectively. Future article topic?

    Also, do you think it would be at all viable for Boeing or Airbus to look into Al-Li technology and/or composite re-winging a la the 777x for the MAX/neo? I remember we covered some of this ground in the article about the potential A330neo, and I'd imagine the primary issue would be the timeline and resource committment, as you said it would be for the 330. Nonetheless, could we see one or both companies look into this as they continue desperately striving for the competitive edge?

    1. Brian,

      C-Series operating economics (purely operational) are better than those of MAX 7 and 319 neo. Remember, C-Series has outsold the combined MAX 7 and 319 neo, it's just that the MAX 8/9 and 320/321 are much larger segments today. I don't think BBD have done a great job of selling it though, as Udvar-Hazy pointed out.

      The C-Series is definitely a topic for a future article on Bombardier, assessing their overall performance.

      As for the re-winging and Al-Li: it's a time value of money thing; Boeing is better served getting MAX to the market ASAP as it is a product competitive with neo. But if the supposed 4% gap between GTF and LEAP exists, and MAX eschews the GTF, then Boeing may be forced into it.


    It is interesting to note that the 737-800 has one or more rows compared to the A320. I guess it make a kind of advantage in term of seat-mile cost. I think it also increase a better revenue potential. Did I get it wrong?

    1. VV

      The 737-800 has typically a 7-12 seat advantage over the A320, (5-8%), which does create a "seat" advantage in CASM ( in the sense that 737-800 can have higher trip cost than A320 and still have lower CASM.

      More seats = More revenue potential so yes

      1. truth, however, it does imply that larger is per definition better. It helps when the flight is sold out. Not sure what percentage of flights that is. And take impacts total operating revenues. It seems the a320 uses a little less fuel on average (engine sfc, weight) specially on flights longer then 500nm. How that works out depends on operations and markets.

  13. [...] aircraft's overall block fuel burn due to increased drag and added weight … Read more on Aspire Aviation (blog) Three villa models debut today at Traditions at Grey Oaks Wall colors include flaxen tan, [...] Reply
  14. Vinay Bhaskara,

    I guess I won't be wrong if I say that the 737-8MAX burns more or less the equivalent of fuel per seat-mile as the A320neo, but the 737-8MAX has a revenue generation potential.advantage.

    Does it make sense?

    I am not sure about the Cash Operating Cost comparison.

    1. It does have a revenue generation advantage, but that depends on the price-elasticity of demand in a specific market.

      But generally speaking, more seats=more potential revenue.

  15. Vinay Bhaskara,

    Indeed big risk = big reward.
    However, too big empty aircraft = big losses.

    I guess it applies to big quads too.

  16. just stumbled over Boeing comments last yr. In hindsight (and not only in hindsight) the arrogance is real thick.

    A former Boeing sales manager on Leeham explained all Max "orders" are pending yet to be confirmed fuel burn numbers. CFM really seams to be struggling to realize those with the just 68 inch fan. Some thing the program can still implode, there are no signed contract only commitments for the MAX.

    The Boeings claims the MAX has better efficiency have been falling appart rapidly in the last few weeks.

  17. It was obvious since the very beginning that both Airbus and Boeing were going to build a derivative aircraft. I just do not understand how people can think otherwise. Read this link

  18. The silence around the 737 MAX is getting uncomfortable IMO.

    In recently years it always ended with unpleasant revelations.

  19. [...] MAX The re-engined 737 MAX is continuously being optimised as time progresses (“Boeing continues to optimise 737 MAX“, 9th Apr, 12), with the Chicago-based airframer confirming the elimination of vortex [...] Reply
  20. [...] Airbus counterparts, while the A321neo has the slight range advantage over the 737 MAX 9 (“Boeing continues to optimise 737 MAX“, 9th Apr, [...] Reply
  21. [...] MAX’s range and maximum take-off weight (MTOW) previously reported by Aspire Aviation (“Boeing continues to optimise 737 MAX“, 9th Apr, [...] Reply

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