A better 73

This suggests the 737’s replacement by an all-new Boeing single-aisle airliner is still some time away.

“We’ve got a great selling airplane in the 737, it’s been very successful and we think we can continue to enhance it, keep our customers more successful, like with some of the improvements we announced today, and that’s just raising the bar for a replacement aircraft, so that’s going to have to be that much better (again),” Boeing 737 chief project engineer John Hamilton told Australian Aviation.

Indeed, squeezing further improvements out of the 737, as Airbus has also looked at with its rival A320 Family, illustrates just how hard it will be for both manufacturers to develop new single-aisle airliners that offer significantly lower operating costs over their current products. In part this is due to the relatively short flights narrowbody airliners are operated on. Most fuel burn improvements are realised in the cruise, so the longer an aircraft spends in cruise flight, the larger the gain from efficiency enhancements. Boeing says the average 737 sector length today is just under 1000nm (a little further than the distance from Sydney to Townsville), a much shorter flight than widebodies such as the A330 or 777 would operate, and so proportionally more time is spent taking off and climbing at higher power (and hence less fuel efficient) settings.

And while the 737’s planned two per cent fuel savings sounds small, it is the kind of meaningful improvement airlines get excited about – Boeing estimates it would save an airline around US$80,000 per aircraft per year (based on flying 1375 sectors with an average stage length of 1000nm). In all, Hamilton said the 737NG family will now be some 16 per cent more fuel efficient compared to the 737 ‘Classic’ models they replaced.

Boeing’s aerodynamic improvements are relatively minor, but the small incremental gains should improve fuel efficiency by one per cent. They comprise reshaping the anti collision light on the top of the aircraft, refining the wing control surfaces to improve flow over the top of the wing, redesigning the seals of the tyres in the wheel wells, adding an exhaust door to the environmental control system (ECS) outlet, which reduces drag, and modifying the engine exhaust nozzle and cone. The nozzle and cone were originally optimised for reducing noise rather than optimal fuel efficiency, so instead they have been reshaped for efficiency by shortening the nozzle and recontouring the cone (or plug), which will also be fitted with noise reduction materials to ensure the 737 has the same noise signature as today.

“It was really looking at what we can do . . . today to improve the fuel consumption of the airplane,” Hamilton said of the drivers behind the improvements.

The other one per cent fuel burn improvement will come from the 737’s new CFM56-7B Evolution engine.

“I approached them (CFM) a couple of years back not too long after we introduced the Tech Insertion engine, which improves emissions from the engine and improves the life of the engine on-wing, and I said what else can we do to this engine in terms of fuel burn,” Hamilton told AA. “So they scratched their heads and said ‘let’s get back to you on that’, and about a month, two months later they came back with a series of proposals. ” Those proposals matured into a redesign of the blades and vanes in the engine’s high and low pressure turbines to increase efficiency, while the number of blades in the high and low pressure turbines will also be reduced.

“I think what they have been able to come up with is a set of changes that are ready today, that are proven, and improve the fuel efficiency of the engine,” Hamilton said. The engine and nozzle combination will require a “pretty significant” flight test program for FAA certification. Flight testing will also validate the overall fuel burn improvements for all the aerodynamic and engine changes in total. This will use a new Continental 737-800 from October 2010, before certification with the new engine in the second quarter of 2011. (Flight testing of the engine will begin in February 2010 onboard CFM partner General Electric’s 747-100 testbed. ) The Boeing airframe improvements will be progressively rolled into production as their designs are refined, while CFM will switch production from the current Tech Insertion to the -7B Evolution engine once the latter is certified. Boeing says the 737’s price will not rise despite the introduction of the improvements.

Where Boeing is asking for an increased price is for the new Boeing Sky interior, which features a range of changes designed to increase the sense of space in the cabin.

These include pivot bins that, despite being larger than the 737’s current ‘big bin’ option, take up less space in the cabin, resculptured cabin sidewalls with enlarged window surrounds and integrated (and hence tamper proof) air grilles, and the use of coloured LEDs in place of fluorescent lighting. Other features include LED rather than incandescent passenger reading lights, the option of mounting passengers’ lifejackets in the overhead passenger service units in tamper proof compartments, and treatments to reduce ambient cabin noise by up to 2dBA.

Boeing is currently offering the new interior (which should weigh no more than the existing interior) as an option to existing 737 customers, but aircraft for all new customers will be fitted with the new interior as standard. Deliveries of Boeing Sky fitted 737s will begin from late 2010 – to new LCC FlyDubai – and the manufacturer expects in time that all 737s will be delivered so configured. So far seven airlines have ordered the new interior. As well as FlyDubai they include Continental, Malaysia Airlines and Indonesia’s Lion Air.

“There are a lot of customers out there who are very close to signing, or are very excited about it,” Hamilton said. “I think before long we’ll see a high percentage of our production with the new Sky interior. ” Beyond the interior and performance improvements, Hamilton says 737 customers are also continuing to push for further improvements to the aircraft.

“We’re continuing to look at what technologies are available today that we can roll into this airplane and you don’t have to wait for a new airplane. ” That may even include new engines such as Pratt & Whitney’s Geared Turbofan (GTF), which is now in flight test. “We’re continuing to talk with CFM, we talk toRolls-Royce, we talk to Pratt & Whitney about their future engine designs and programs, and every one of them wants to be on the single-aisle airplane. ” Hamilton says Boeing is waiting to see “good data” on the GTF, “But certainly if it’s a viable engine that would significantly improve fuel burn we’re going to have more conversations with CFM on how we stay competitive going forward. ” Then there is the challenge of fitting a new engine under the 737’s wing. “That’s one of the challenges that we look at, could you put one of these newer engines on. A lot of it is defined by the fan size, but we’ve got a great set of engineers at Boeing and they’re looking at various combinations, but right now the improvements we’re doing today keep the 737 very competitive, it’smore efficient than the Airbus product, but we’ll continue to study what enhancements we can do going forward. ” As for the timing of an all-new 737 successor, “It’s really understanding where is technology today and where do we think it’s going to be in the latter half of the next decade,” Hamilton said.

“Obviously we’re continuing to understand the technologies, you don’t want to bring a replacement to the market too soon because your competitor may now wait a year and be able to introduce even more advanced technologies and we’re leapfrogging. ” So with that momentous decision seemingly a long way off, and further running enhancements to the 737 in prospect, it seems there plenty of life left in this evergreen airline favourite.