Boeing's delayed 747-8F will not fly for the first time until around January 2010 under the latest development schedule, revised for the second time to include the effects of supply-chain delays, overstretched engineering resources and the recent Machinists' strike.

First deliveries of the freighter to launch customer Cargolux Airlines are now expected around September 2010, against the original target of August 2009 when the program was first announced in November 2005. Deliveries of the 747-8 Intercontinental passenger variant, launched in December 2006 following an order from Lufthansa Airlines, have also slipped by around one year against the original target and are now expected to begin sometime in the second quarter of 2011.

Boeing first signaled significant changes to the 747-8 plan a year ago when it re-jigged its production flow to allow completion of the final 747-400Fs by the end of 2008, rather than mix these with the first -8 models. Although this pushed back rollout three months to February 2009, Boeing still hoped to deliver the first aircraft on time by shortening the flight test program. The company believed the hiatus would allow more time for suppliers to ship parts and for production to prepare for the transition.

Supply-chain issues, exacerbated by the recent strike and stretched engineering resources, subsequently forced Boeing to announce this most recent slide to the schedule. The problems relate to "having more work statement and tooling changes, and that just grew on us," says 747-8 chief project engineer Michael Teal. "But we understand it now, parts are coming in and we just know we're going to be late."

The issues go back to early 2007 when tests revealed higher than expected loads on the aircraft's new supercritical wing design, particularly at low speeds. The wing is deeper, particularly at the root, and has a steeper twist angle to create additional lift inboard. In place of the complex double- and triple-slotted flaps of the current 747, the trailing edge of the -8 is configured with simpler 777-style double and single-slotted flaps. It also has fly-by-wire controlled spoilers and outboard ailerons, the latter of which are drooped. The wing has a raked tip in place of the -400's winglet, and a redesigned Krueger leading-edge flap with a "gapped" configuration.

Although the wing is all-new, its overall planform is the same as the -400's and the configuration at the root is the same. "Putting that additional load through the same shape required the biggest amount of strengthening," says Teal. The loads acting on the wing at lower speeds also shifted the center of gravity farther aft, requiring a higher balancing tail load. This meant further structural strengthening for the horizontal stabilizer. "We weren't going to make any changes to the tail and we ended up having to make changes," says Teal as an example of the expanding work scope.

Although individual changes included increasing material gauges on stringers and frames, it was the sheer volume that disrupted the supply chain says Teal. "We had significantly more changes than we originally anticipated," he adds. Although the wing is fabricated by Boeing's Auburn, Wash., site, "we had issues bringing in some of the locally supplied parts. But there is no single supplier or component that caused it. Some were on time and some were behind," adds Teal.

The other focus is on "essentially getting the performance out of the aircraft to what the customers need," says Teal. Although the new wing is expected to offer better-than-originally expected performance, this was offset by the higher weight. To compensate for the added weight and retain performance guarantees, Boeing raised maximum takeoff weight (MTOW) to 975,000 lb. in late 2007.

The 747-8I was originally designed with an MTOW of around 960,000 lb. and an operating empty weight (OEW) of just under 450,000 lb. Range with 450 passengers was more than 8,250 naut. mi. In 2006 the MTOW grew to 970,000 lb, while the OEW for the -8I increased to nearly 465,700 lb. and that of the -8F to 413,000 lb. The greater -8I OEW was attributed to the extra weight of the stretched double-deck fuselage section, and the additional seating, which took passenger capacity to 467 but that also saw range fall to around 8,000 naut. mi.

Boeing is now focused on maintaining and, if possible, exceeding this range. "We're an 8,000-naut.-mi. aircraft, and this is where we need to be. The Airbus A380 coming out of the gate is not, so we have the ability to beat that," says Teal. Airbus is working on a program to cut more than 4,400 lb. from the A380, thereby extending range comfortably beyond 8,000 naut. mi., but this will not be available on aircraft delivered from 2012 onward.

Early signs of where the final performance of the 747-8 will end up will come from flight tests of the aircraft's General Electric GEnx-2B67 engine on GE's 747 flying testbed in February 2009. Additional weight-saving "opportunities" are also being defined for follow-on aircraft beyond the first -8F, parts for which are accumulating at Boeing's Everett, Wash., site. These will not be introduced as a "block point" change, but rather when they become available. "It's about getting the improvement as soon as we can onto the aircraft," says Teal.

Boeing's latest predictions say the 747-8F will have a better than expected fuel-burn cash operating cost (COC) than the -400F. "Our goal was 12% better, and right now we think we're closer to 16%," says Teal. The margin improves with rising fuel costs; at $2.12 per U.S, gal., COC is 15% better, while at $3.50 it rises above 16%, he adds.