Boeing’s new 777X flagship is due to enter service in 2020. This seems like tomorrow to the company’s manufacturing side as it prepares for assembly, but for the 777 sales team looking to fill the production “skyline” during the transition it could be an eternity.

To smooth the move at the end of the decade from the current 777 family to the 777X, Boeing needs to drum up more sales to keep the Everett assembly line ticking at, or close to, the current 8.3 aircraft per month. There are currently 278 777-300ER and 777Fs in the firm backlog, representing just under three-years worth of production at the current rate. While the longer-term outlook appears to be positive—286 sales are already locked in for the 777X—the delivery trough between 2018 and the acceleration in deliveries of the new model from the 2020-22 timeframe onward is causing some concern.

But Boeing’s 777 sales team is about to get a shot in the arm. To help bridge the gap to the 777X, the company plans to inject additional life into the -200LR/-300ER by developing an upgrade package that will reduce fuel burn by 2% from 2016 onward.

Boeing plans to reveal full details of the upgrade in mid-March. News of the plan first emerged in January when John Wojick, global sales and marketing senior vice president, revealed “we are working on a fuel-burn improvement and other items for 2016 that will provide the equivalent of around 2% fuel-burn savings.” He adds that, although 2014 was “a good year” with 63 new 777 sales, “we need to continue to work diligently to keep that skyline full as we transition from the 777-300ER and 777F to the 777-8X and -9X.”

The coming availability of the upgrade, added to what Boeing Chairman/CEO Jim McNerney describes as the “enduring capability” of the 777, already appears to be bolstering prospects of new orders to fill out the mid-term production slots. During the recent fourth-quarter financial results call, McNerney said: “We took 63 orders in 2014, which bodes well for the 40 to 60 we need [per year] over the next few years. So I’m feeling increasingly comfortable [about] the long-term demand for the airplane. We expect demand for the 777 to remain healthy through this decade.”

General Electric, which is the exclusive engine supplier to the 777-300ER/777F with the GE90-115B, expects to start initial tests of the engine-improvement element by the end of the year. “We are targeting about a 0.5% specific fuel consumption (sfc) improvement in the engine,” says Bill Millhaem, general manager of the GE90 program. Focus areas include the aerodynamic “clean-up” of the fan module with elimination of steps and gaps to reduce drag, and improvements to the efficiency of the high-pressure compressor stage-1 blisk.

The most significant single change in the engine upgrade is an improvement to the active clearance control system which cools the casing of the high-pressure turbine section, helping to minimize clearances between the tips of the blades and the shroud during cruise. “We’re introducing a new style manifold and increasing the ‘muscle’ for better clearance control,” says Millhaem, who adds that the revision leverages active-clearance-control-system advances that were introduced with the GEnx engine for the 787 and 747-8. The new manifold improves the axial coverage area of the cooling flow over the casing. In parallel with this, GE plans to reactivate a valve in the core to improve modulation of bleed air to the manifold.

Slight aerodynamic changes will also be introduced to the first-stage nozzle of the low-pressure turbine, and the “grind” of the high-pressure turbine shroud will also be optimized to improve the match between the blades and shrouds in cruise. “In aggregate, all this adds up to around 0.5% sfc. We are in the process of finalizing the design of the hardware and will be doing some testing later this year,” says Millhaem. 

The upgrade is not considered a major certification effort because the engine thrust is unchanged and testing is aimed at “mostly assurance” work to confirm that none of the modifications affect durability, he adds.

The bulk of the planned 777 improvements is therefore expected to encompass aerodynamic changes, although it is not yet known what these will be. Whether some of the more novel drag-reduction features—such as the hybrid laminar-flow-control system developed for the 787-9—will be highlighted remains unclear. However, the most likely solution is expected to be a further package of aerodynamic tweaks similar in scale to upgrades introduced in the early days of the 777-200LR/-300ER program. Together with better-than-expected initial engine performance, these modifications improved the fuel burn of the 777-300ER by 3.6% compared with pre-service predictions at the start of the program in 2003. For the 777-300ER, every 1% improvement in fuel efficiency is roughly equal to 75 nm of extra range, 10 extra passengers for a load-limited flight or 2,400 lb. of cargo. 

The first set of improvements, introduced in 2005, resulted from changes made to counter unexpected drag from the environmental control system’s ram air exhaust duct, and from handling changes related to the introduction of the aircraft’s raked wingtips. The duct changes included the addition of exit louvres, the modulation of which was controlled by new software in the cabin pressure system. By introducing the louvres, Boeing improved thrust recovery and reduced the drag. The wing changes were based on the addition of seven outboard 737-size vortex generators which, to Boeing’s surprise, resulted in a 0.4% improvement in fuel burn.

Following the success of these changes to the longer-range models, Boeing subsequently introduced a retrofittable performance improvement package (PIP) based on the same modifications for the 777-200/-200ER and baseline -300 from 2008 onward. The PIP also included drooped ailerons that altered the angle at the trailing edge by 2 deg., reducing drag by creating aerodynamic loading on the outboard wing and making spanwise loading more elliptical. As the aileron droop increased loading, it also caused a change in the wing twist. This reduced local flow incidence toward the wingtip, which reduced the shock strength on the outboard wing and further cut drag.

The previous 777 PIP could be incorporated by operators via service bulletins and was independent of others. Only the ram-air-system upgrade had to be conducted during a heavy maintenance check, and Boeing said fuel savings would begin to pay off within 12-18 months of modification. It is not yet known if the non-engine-related elements of the 2016 PIP will be retrofittable.