Guy Norris/RENTON
Boeing opened the next, and possibly last, major chapter in the history of the ubiquitous 737 on 3 August when it conducted the maiden flight of the stretched Next Generation 737-900.
The flight kicked off a planned 380h-long flight test programme, with a further 120h of ground tests scheduled before planned certification in late February next year. First delivery to launch customer Alaska Airlines is set for early April, with Continental Airlines due to receive its first -900 the following June.
With an overall length of 42.1m (138.2ft), the -900 is 13.5m longer than the first member of the 737 family from which it is derived. This represents the greatest proportional growth ever accomplished within a single family of jet transports, outdoing even the stretched McDonnell Douglas DC-8 series. To underline this feat, it is noteworthy that the -900 even exceeds the 707-120 in length by 0.4m.
Planned to counter the similarly sized Airbus A321, the -900 is aimed at both scheduled and charter operators. "The straw that broke the camel's back" and led to the go-ahead of the stretch, says 737 regional director of product marketing Stephen Ford, was the key loss to the A321 in the mid-1990s for a British Midland fleet contract.
"We needed three more seat rows on the -800, and that's what we set out to do - a very simple stretch of the -800." Board approval for the -900X was obtained in June 1997, and the programme was launched the following November with an order for 10 from Alaska.
The aft fuselage of the -800 is extended by 1.06m and the forward by 1.57m, to create space for up to 189 passengers in a one-class configuration. In a two-class layout, the stretch can seat 177, or 15 more than the -800. Because the -900 has the same number of exits as the -800, the overall capacity cannot exceed 189 passengers, although the stretched aircraft would physically be able to accommodate over 200 passengers in a high density layout.
In the 177-seat arrangement, Boeing predicts the -900 will have a range of 5,080km (2,745nm) at a maximum take off weight of 79,000kg (174,200lb), compared to the 4,720km range of the A321-200 carrying 183 passengers and equipped with a single auxiliary fuel tank.
Significant challenge
Added to the strengthened wing and more powerful CFM International CFM56-7B engines of the heavier -800, the longer -900 is expected to pose a significant challenge to the A321. Although 370km range was lost with the stretch, Kevin Scott Brown, director of 737 programmes, says up to 240km could be recoverable with blended winglets, which will be available from 2002 onwards on the -900. Even without them, Brown says the -900 will have 12.4% lower trip costs than its Airbus rival.
Boeing devised a stretch plan for the -900 that took into account the geographically distributed manufacturing and assembly process used for the Next Generation 737 family. Ensuring that the longer fuselage could be transported to Renton in one piece from Wichita, Kansas, where it is manufactured was crucial. Digital mockups were run through cyberspace factories and railway lines before a metal fuselage shape was run along real tracks.
As with the other Next Generation fuselages, the -900 is mounted on a 27.1m long flatbed railcar attached to an identically sized aft idler car. "The second car gives space for the tail to 'wag' around," says body and Wichita integrated product team leader Sharon Tanner. No scrapes or collisions occurred along the standard preferred rail route, which covers 3,250km, 775 bridges and 10 tunnels. The only changes required to trackside fixtures or buildings were in the last few metres of the "train well" sidings at Renton itself where a 1m notch had to be cut into an adjacent structure.
The overall -900 design evolution at Wichita and Renton has also been smoother, says 737 product development manager Ed Kane. "The -900 was a natural outgrowth...and we tried to keep the original design team together which made a huge difference. We didn't have to go back and revisit any basic engineering decisions." Brown adds: "The recipe was not only developed; it was fully refined." The same influence was felt in manufacturing and assembly where the introduction of the -900 into the furiously paced Next Generation 737 programme caused concern. "We had 28 days budgeted to catch up, but we used only one," says Tanner. Now the question is if this performance can be matched through to certification.
Source: Flight International
