Airbus's A320 and Boeing's 737 are the most popular airliner ranges ever made. So how will the manufacturers top them? As suitable technology advances, the race is on for the superior successor
Attempting to forecast when Airbus and Boeing will launch new-generation successors to the A320 and 737 is a bit like trying to predict when the next big earthquake will rattle California. It is not a question of if, but when – and all you have to do is work out the timing, magnitude and epicentre or, in this case, the shape, size and range.
But, unlike seismologists on the subject of earthquakes, both aircraft manufacturers are reluctant to broach the subject – and with good reason. The A320 and 737 are the most successful jet airliner families ever developed, with nearly 6,000 orders between them, not counting the 3,132 earlier-generation 737s. Both are relatively young and have been upgraded constantly, the A320 ushering in a new era in air transport technology when it was first delivered in 1988, and the glass-cockpit, rewinged, re-engined Next Generation 737 marking the arrival of what was effectively a new model when it debuted in 1997.
With about 3,500 orders in the bag, Airbus has a firm backlog of nearly 1,070 A320 family aircraft. Of these, more than half are A320s, 355 are A319s, 106 are A321s and 39 are A318s. Boeing's 737-600, -700, -800 and -900 series has amassed almost 2,470 orders and has a backlog of 762. Apart from orders for more than 100 of the US Navy's P-8A Multi-mission Maritime Aircraft variant of the 737, the backlog is dominated by the two most popular versions, the -700 and -800, which total 335 and 389, respectively. The -600, -900 and BBJ1 and BBJ2 business jet derivatives make up the rest.
Factoring in a transition from current to projected higher production rates, Airbus could sustain full-rate A320 family production at Hamburg and Toulouse well into 2009, even if it did not take a single new order from today onwards. Boeing is in a similar position and, even with an eventual production rate of 30 aircraft a month by 2006, would not have to think about closing the hangar doors at Renton until late 2008 – again, assuming not one more commercial order is placed beyond the current backlog, plus around 100 P-8A MMAs.
Officially, neither Airbus nor Boeing has much to say on the subject. Asked to comment on what might follow the A320, Airbus chief commercial officer John Leahy deflects the question by pointing out what he expects Boeing to do: "They will build a whole new family around 2008. The ‘Y2' [see P59] will be a new, single-aisle aircraft, wider than the 737. In fact, it will look like an A320. It will be an all-new, fly-by-wire aircraft, which happens to be why we chose that technology."
The numbers support Leahy's confidence. Sales of the A320 family continue unabated, with more than 110 orders in the first quarter of 2005 alone, and plans are in the pipeline to raise production rates for both the A318/A319/A321 line in Hamburg and the A320 in Toulouse.
Sales success
The numbers are good at Seattle, too, where Boeing Commercial Airplanes vice-president sales Scott Carson is in no mood to play down the 737's continuing sales success. "The 737 is doing very well in the marketplace. There are a lot of legs left with the 737 family, and the market response this year surely demonstrates that," he says.
Both manufacturers are firmly entrenched as the twin pipelines supplying the perfect aircraft for low-cost carriers. But, with fuel prices rising and noise and emission limits reducing, Airbus and Boeing are aware of the looming imperative to prepare for a more environmentally sensitive future. With the A350 and 787 programmes well advanced, each company has a potential technology "pathfinder" for the next generation of small airliners, although arguably Boeing's 787 all-composite twinjet is more of a single leap.
"What we want to do is get some experience with the new aircraft, both in terms of its performance and manufacturing technologies, and learn from that," says Carson. "After we have learned the right lessons, then we can worry about a replacement aircraft." Asked about timing, he says: "It will be when the technology is mature enough, and when the customers tell us they need a new aircraft."
Behind the scenes, however, initial product development work is already being conducted on the 737 successor platform. Believed to be codenamed Yellowstone 1 (Y1), the project forms one of the three Yellowstone new-generation studies emerging from the broad-based "Project 20XX" advanced technologies initiative behind the Sonic Cruiser and subsequently the 787. In this sequence, Y1 is believed to cover the 100-200 passenger range; Y2, which became the 787, covers the 200- to 350-seat range; and Y3 covers the range for what could eventually become a long-term successor to the 777 in the next decade.
A handful of product-development engineers who were working on the Sonic Cruiser and the pre-launch phases of the 7E7/787 up to 2004 are now believed to have been redirected to work on the early stages of the Y1. Sources familiar with the project say the aim is to use as many technologies from the 787 programme as possible, but one adds: "It is not really clear how the technology for the 787 can make its way – dollar-wise – on to a smaller aircraft. It isn't easy, unless you've made it that way from the start. Everybody is jumping on that bandwagon and rolling over to the programme. Whole teams are setting up to carry it to firm configuration, though it is still years away."
Best solutions
Although scaled versions of the baseline 787 configuration are believed to be among the frontrunners, the Boeing team is thought to be casting its net wide for the best solution. Some of the more unusual include a pair of "twin-aisle small aircraft" concepts patented by a company engineer, Mithra Sankrithi, and assigned to Boeing. The patents, filed in October 2001, were awarded in 2003 and 2004, and cover several concepts for "less than 200-seat class" passenger aircraft with two longitudinal aisles. The designs are characterised by flattened cross-sections with the seating arranged around the twin aisles in a two-three-two configuration.
This unusual design, which in at least one concept features a fuselage cross-sectional width of around 5.1m (201in) compared with the 767's 5.03m, incorporates sufficient lower deck for an LD3-46 container. To balance the moment arm of the relatively short, plump fuselage, the design also features a swept T-tail. The patent also describes a modular concept covering a family of aircraft capable of carrying between 105 and 290 passengers in which three versions of the wing and various sizes of powerplant can be combined to meet several payload-range requirements.
The need for breakthrough engine technology is one of the few areas of agreement between Airbus and Boeing in the search for possible successors. Just as Bombardier's CSeries small airliner plan depends on the efficiencies of a new centreline engine, so does the go-ahead of any new venture further up the scale. "We're going to watch and see what happens there," says Carson. "Right now, there is no engine. To build a 737 replacement without a next-generation engine would be a dreadful mistake for us to make."
The race to develop new centreline engines for the next generation began unexpectedly at the Farnborough air show last year, when CFM International and International Aero Engines both announced preliminary studies. IAE president Mark King said the multinational company was "preparing to move to the next generation". Unlike CFMI, though, IAE had set its sights on Bombardier's CSeries as "the first [application] we can see in sharp focus – we see it as a very positive development towards the next generation of V2500 family".
However, in the light of IAE's decision to withdraw from the Bombardier project in early May this year, the engine maker now seems to be taking a tack similar to that of CFMI, which has consistently remained focused on studies of a new engine in a higher thrust bracket, aimed at service entry in 2012 or 2013.
All-new engine
There are several drivers behind the move for an all-new engine. CFMI president Pierre Fabre explains: "There is continuous pressure on fuel burn, there is the environmental aspect and there is huge pressure on noise, and some day the A320 and 737 won't be good enough. When that day is, nobody knows, but to satisfy these future needs there has to be a dramatic jump compared with today's levels. We need a breakthrough in terms of technology, so we are focusing on developing them."
Fabre appears slightly more circumspect now than he did in 2004, when he said: "The consensus is that 2012 could be the entry into service of a new-centreline engine." However, the initial target is still widely expected to be a family in the 23,000-35,000lb thrust (100-155kN) range, compared with the current 20,000-33,000lb, aimed at noise levels 15EPNdB below Stage 4. Describing the size of this task another way, CFMI executive vice-president Bill Clapper says: "That's effectively a 25dB cut with today's reliability, which is a huge challenge. It's a big movement in the state of the art."
Early concepts that could be included in the studies are a contra-rotating, two-stage fan, further fan-case treatment innovations and reduced stage numbers. "It would need a higher bypass, and that doesn't fit under the wing of the A320 or 737," says Clapper. Fabre adds: "To get a larger fan with a higher bypass ratio, you need a lighter-weight structure, composite fan blades, fewer stages and higher-loaded components." He points out there will be a build-up approach to the problem.
"It was different when we launched Tech 56 [the CFMI technology development plan]," says Fabre. "We had a strong suspicion that there would be no new engine, and that's why this will be different. This time there will be a new engine, and that's why we have to have a wide range of technologies from which to decide the architecture."
Although CFMI talked in 2004 of launching the next-generation engine programme in 2008, it is less forthright about schedules today. "We are in the process of finalising the technical plan, but we took more time," says Fabre. "The engine is part of an ensemble, and a new engine would not make sense without a new aircraft – and vice versa. Our focus is on what is ‘critical to quality', what we need to bring to the airlines of the world, rather than on timing. It has to be a giant step compared with today and you have to make sure you have all the technology to make it right. It is better to wait an extra year, if that's what it takes."
In the meantime, possibly the best clue yet has just leaked out that Boeing is preparing the ground for critical propulsion system research directly aimed at the next-generation 737 successor. The company has begun soliciting the industry for interest in a new phase of its Quiet Technology Demonstrator (QTD) project, to be dubbed QTD 3. What marks QTD 3 out as radically different from its predecessors is that the proof-of-concept demonstrator will be aimed at technologies appropriate for a 150-seater aircraft, rather than the 777-class aircraft of former QTDs.
Noise reduction
Boeing is currently working on QTD 2 with General Electric, Goodrich and NASA, and plans to begin a one-month flight-test programme with a modified GE90-powered 777-300 around August this year. The latest phase, which is a step on from the 2001 QTD 1 tests undertaken with a Rolls-Royce Trent 800-powered 777, is aimed at evaluating the noise-reducing performance of "smart" chevrons on the trailing edge of the bypass duct, both fixed and variable, a one-piece "jointless" inlet acoustic barrel with a treated lip, and a "low noise" main landing-gear bogie.
Although Boeing will not comment on the detailed specification for QTD 3, it is believed the requirement calls for novel noise reduction or suppression concepts for possible flight-test demonstration in 2007-8, leading to potential entry into service in 2012-13.
So there seems little doubt that the stage is being set for the next great leap in air transport beyond the A380, the A350, the 777 and the 787. Although virtually all the key questions about how, what, why and when remain unanswered, the aerospace industry at large can safely bet that the "if" question has already been answered.
GUY NORRIS/LOS ANGELES
Source: Flight International
