Boeing refines a classic.

While Boeing has so far shied away from offering a re-engined version of its single-aisle 737 family, it is offering substantial performance gains with aerodynamic and engine improvements, as well as an all-new cabin, writes Andrzej Jeziorski.

1st Feb 2011

At a time when Airbus has been trumpeting the launch order for its re-engined A320neo – the biggest single aircraft order ever, from India’s IndiGo – Boeing has held off from such a radical move.

The US company has remained sceptical of the idea of replacing the aircraft’s CFM International CFM56 engines with new-generation powerplants such as the CFM Leap-X or Pratt & Whitney’s PurePower geared turbofan, saying that the net economic benefit of such a move would be just 3-4 percent, when everything is taken into account.

Instead, Boeing is pinning its hopes on an all-new single-aisle family that would offer more radical savings but will not be available until beyond 2020. In the meantime, the manufacturer argues, it can continue to refine its well-established 737 single-aisle family to keep it competitive with any upgraded offering from European rival Airbus.

The Next-Generation 737 (737NG) – a term that applies to the -600, -700, -800 and -900 variants of that aircraft family – went into service about 12 years ago, and Boeing says that it has not stopped improving the aircraft since then. The incremental upgrades have ranged from the addition of fuel-saving winglets to lighter, carbon-fibre brakes first optioned in 2008.
Throughout, the aircraft family has consistently won a steady flow of new orders thanks to its reputation for reliability and solid performance.

“We have a 99.8 percent dispatch reliability,” said Beverly Wyse, vice-president and general manager of the 737 programme. “While we are proud of the progress we have made on this airplane, we are by no means done.”

Improved cabin, economy

Boeing’s latest improvements to the aircraft include: a complete makeover for the aircraft’s cabin, offering more room and passenger comfort; and airframe and engine enhancements that cut fuel consumption and carbon emissions by at least 2 percent.

“This is a perfectly efficient airplane,” said John Hamilton, chief project engineer on the aircraft family. “We are at the point now where the industry [regulators and airports] have to catch up with the airplane.”

Boeing said the new Boeing Sky Interior is “the most visibly satisfying development” of the aircraft, arising from studies of passenger concerns and needs. The new cabin interior includes design innovations “that not only provide more room and comfort, but embrace passengers in the airplane cabin, help to separate them from the frantic hustle and bustle and lines of airports, and restore the magic to flight”, according to the company.

“By the time people get to our product they are in the middle of one of the worst days of their year,” said Kent Craver, regional director of passenger satisfaction and revenue marketing. He adds that a psychologist on Boeing’s study team told designers that “we need to create a separation between events on the ground and flight – this psychological separation of events is created naturally when people are welcomed. We developed the architecture to provide this welcome.”

Redesigned overhead baggage bins offer more headroom while still accommodating more carry-on baggage. Soft blue light-emitting diode lights offer a greater sense of space and calm and psychologically link the passengers “to the natural environment of flight – the sky”, Boeing said. Sculpted sidewalls enhance the appeal of restyled windows. Light-switch panels are less confusing than before and cabin lights offer various levels of luminosity.

Craver added that the Boeing Sky Interior would become an industry standard, as well as a marketing draw for airlines. “We can’t introduce it fast enough,” he said.

First deliveries

The first 737 fitted with the new interior was delivered to flydubai of the United Arab Emirates on 27 October, while the first delivery to an Asia-Pacific carrier was to Malaysia Airlines (MAS) on 29 October. Three more customers received Boeing Sky-equipped aircraft before the end of the year, while total orders for jets with the new cabin run to 1,386 aircraft for 50 airlines.

Beyond the cabin interior improvements, Boeing is introducing aerodynamic improvements to the 737 airframe, as well as upgrades to its CFM56-7B turbofan powerplants. The upgrades, targeting a 2 percent reduction in fuel consumption and carbon emissions, are now under test, and scheduled for delivery starting in mid-2011.

A 2 percent improvement may sound meagre, but Boeing stresses that the figure translates into an annual saving of US$120,000 on fuel costs per aircraft – based on a fuel price of US$2.58 a gallon over a 500 nautical mile trip. That translates into a net present value of US$1 million saved over 20 years, said chief engineer Hamilton.

In terms of environmental benefits, a 2 percent improvement equals an annual reduction in carbon emissions of 470t per aircraft. If a carrier has to pay a carbon tax, that means it would save US$11,700 per year at US$25 a ton per aircraft, said Jamie Jewell, director of strategic communications for CFM International.

Aerodynamic improvements include redesigned wheel fairings, louvered exhaust duct doors, wing surfaces and a new, teardrop-shaped anti-collision light, all of which reduce the aircraft’s aerodynamic drag. Boeing says that the airframe modifications account for half the performance benefit, while engine upgrades bring about the other half.

CFM is improving the design of airfoils in the engine’s high- and low-pressure turbines to boost efficiency, using advanced, computer-aided design techniques. The engine maker is also improving engine durability and cutting the parts count to trim maintenance costs.

But even with all these upgrades, Boeing and CFM engineers remain confident that there are more to be found.

“The new performance-improvement package to the airframe and engines may get more, but we are telling customers it is 2 percent [improvement],” said Hamilton. Jewell added that CFM may have underestimated the fuel-burn gains from its engine upgrades.

“What we’ve seen in the test cell on our engines is actually better than the 1 percent committed to Boeing,” she said. “But for now we are sticking with 1 percent until we see how it performs on the airplane.”

Cheaper maintenance

Beyond the fuel savings, CFM’s engine improvements also cut maintenance costs by as much as 4 percent, in part thanks to the fact that the upgraded powerplants have fewer airfoils and more durable parts. Offering higher thrust, the engines also benefit from a large exhaust gas temperature (EGT) margin – the difference between the actual EGT and the upper permissible limit – extending the powerplant’s time-on-wing.

Since the first 737NG entered service in 1998, the aircraft’s fuel consumption has improved by about 5 percent. With the additional 2 percent, that becomes a 7 percent reduction in fuel burn over 12 years, Hamilton noted.

“Every five years we have ... improved the fuel consumption of the airplane,” the engineer said.

Ground testing of an aircraft featuring the improvements – scheduled for delivery to Continental Airlines in mid-year – began in November. The aircraft is expected to begin flight-testing in April.

The latest improvements to the aircraft are the latest in a long series introduced over the years by Boeing. Perhaps the most eye-catching of those previous upgrades was the introduction in 2002 of Blended Winglets for drag reduction and improved fuel-efficiency.

“As the ‘swoosh’ is to Nike and Mickey Mouse is to Disney, winglets became the Next-Generation 737’s most recognisable and in-demand feature,” said Boeing. “They are a prime example of the marriage of artistic form to engineering function.”

The winglets “are a real value to airlines in terms of 3.5 to 4 percent fuel consumption improvement,” said Hamilton. They are featured on 95 percent of all aircraft leaving 737 final assembly – a number that has steadily increased since the winglets’ introduction.

In 2008, Boeing introduced carbon brakes for the 737 family, reducing weight by 700lb – the equivalent of adding three passengers, or yielding a .04 percent gain in fuel burn. The brakes also last three times as long as their steel equivalent.

High-altitude package

In the mid-2000s, Boeing made several upgrades to the 737’s flight deck. Engineers developed a high-altitude package that Chinese airlines had been seeking, improving climb performance at airports 14,000ft to 15,000ft above sea level, said Hamilton.

“Boeing continues to think outside the box to cut costs in other ways, working with airlines and regulators to improve efficiencies,” the company said.

In the summer of 2010, for example, a 737-700 was used for flight tests over Puget Sound by the ‘Green Skies Project’, saving 400lb of fuel and cutting greenhouse gas emissions by 35 percent in tests of more efficient landing approaches using satellite guidance. The project was being led by Alaska Airlines, with the participation of Boeing, the US Federal Aviation Administration (FAA) and the Port of Seattle.

“The savings equals removing more than 4,000 cars off the highways each year, reducing jet-fuel consumption by 2.1 million gallons annually [and] cutting carbon emissions by 22,000 metric tons while curtailing noise,” Boeing said.

As the manufacturer seeks more and more improvements to the aircraft, engineers are exploring new concepts as well as dusting off past ideas to look at them in the light of new technologies, Hamilton said. One option being explored now is the introduction of lighter floorboards.

“If we can find another three to four percent [reduction in fuel consumption], that is going to be our challenge,” Hamilton said.

He added that the company is still exploring the option of re-engining the aircraft, but is not getting a strong response from operators. “The customer is not telling us to go for it,” he said.
Customers want fuel-consumption reductions, but not at any price. The fear is that major technical changes could snowball into a negative impact on the aircraft’s operational reliability.
“You have to balance technology with the inherent reliability of the airplane,” said Hamilton. Indeed, reliability was found to be the top concern in a 2009 survey of lessors and airlines carried out by CFM.

“The planes have got to be ready to go or the business model for most low-cost carriers does not work,” said CFM’s Jewell.

After reliability, customers surveyed said they were most concerned about maintenance costs and engine time-on-wing. Fuel consumption ranked fifth among the customers’ priorities.
The market leader in the Next-Generation 737 family is the 737-800, which seats 165-189 passengers and has gained more than 3,400 orders. But the larger, extended-range -900ER is gaining as airlines replace ageing, out-of-production 757s, which are no longer economical to fly.

“The -900ER is a great plane if customers want capacity. It serves over 90 percent of the markets 757s are in,” said Hamilton.

Production efficiency

While the manufacturer strives to improve the aircraft’s operational efficiency and reduce emissions, it has also been working towards efficiency gains and waste reduction in the assembly process and supply chain. Boeing has adopted ‘lean’ manufacturing principles first put into practice by Japanese automaker Toyota to create its innovative, moving production line.
From 2000 to 2006, Boeing replaced stationary construction with a line that moves at an average speed of 2 inches a minute. At the same time, the factory building was redesigned to encourage better communication between engineers, administrators and mechanics.

Production workers are encouraged to come forward with their own ideas for improving the manufacturing process and rules are in place to make sure those ideas are given proper consideration. Offices were installed among the rafters above factory floors, so that engineers and other support personnel could be closer to the production line, allowing quicker problem-solving and easier idea-sharing.

The production lines function around the clock, with special teams ensuring that mechanics working on the aircraft have all the tools and parts they need at all times, so that no time is wasted hunting for supplies.

“As many as a million parts in 360,000 assemblies convert empty fuselage tubes from hollow shells into flying machines,” Boeing said.

These efficiency-boosting efforts have halved the production time for a single aircraft from 22 days to 11 days – one reason why Boeing can now confidently ramp up its production rate to 38 737s per month in two years.

“A lot is just learning to spot waste ... [and] doing it right the first time,” said Helene Michael, vice-president of 737 manufacturing operations.

Boeing started the year 2011 on a high, with the announcement on 4 January of an order for 38 737NGs from lessor CIT Aerospace, with purchase rights for an additional seven aircraft. Deliveries are scheduled for completion in 2017 and the order includes 15 737-900ERs and 23 737-800s.

The manufacturer says the order is the largest placed by a leasing company to date for the 737-900ER. It is also the largest ever placed by CIT for Boeing aircraft.

“As a leading aircraft lessor, it is important that we continue to maintain a portfolio of operationally dependable and fuel-efficient aircraft for our customers,” said C Jeffrey Knittel, CIT’s president of transportation finance.

"CIT's choice of the Next Generation 737 shows its confidence in the product family and especially in its newest member, the 737-900ER,” said Marlin Dailey, vice president of sales and marketing with Boeing Commercial Airplanes.

CIT’s aircraft will include the Boeing Sky Interior and the aerodynamic and engine improvements “that will keep its airplanes at the leading edge of passenger comfort, efficient operations and reduced fuel consumption,” Dailey added. 

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