Boeing 747-8F et I

FARNBOROUGH -- Since its first flight in February, Boeing's 747-8F flight test program has
completed roughly a third of its 1600h flight test campaign, though steady momentum has been elusive, as the new jumbo freighter has encountered one time consuming technical issue after another.

The sum of three main issues, including two more recent ones, have eaten Boeing's remaining margin, causing Boeing Commercial Airplanes president and CEO, Jim Albaugh, to caution that "The entry into service could slip into 2011."

With the landing gear door flap vibration issue now resolved, flight test challenges have given way to troubleshooting two primary issues.

The first centers on the aircraft's inboard ailerons and the power control unit that drives them. Boeing found that when a pilot makes a slow input on the jumbo jet's controls the high pressures in the hydraulic system cause an oscillation, requiring a fix in the actuator, according to two 747-8 program sources.

Apture™
by Jon Ostrower


The second, the freighter was found to encounter a structural flutter at mid-weight near cruise speed, requiring engineers to dampen out the aeroelastic vibration. Options for resolution include adding structure to the wing or potentially developing a new control law to avoid the condition.

RC501, the lead flight test aircraft based at Boeing Field in Seattle, has for the last month and a half has been dedicated to trouble-shooting both issues. Programme sources say the company aims to complete resolution on the flutter issue by the close of the month.

Boeing declined to address the specific issues encountered by the program, though the company continues to caution that while first delivery to Cargolux remains "at risk", certification is remains targeted for year end, adding:

The 747-8 Freighter flight test development program is a dynamic process of performance demonstration, validation and issue identification and resolution. To date, we've flown approximately 550 hours and completed substantial airworthiness, aerodynamic performance and systems testing. Over the course of testing, technical issues are discovered and resolved. As we advance toward completion of flight testing, fewer and fewer discoveries are expected. As we have previously demonstrated, when an issue arises, we address it immediately.

With five months to go in that goal, Boeing's remaining flight test margin is virtually gone, with the company's Flight Operations, Test & Validation organization looking for ways to find - or create - contingency where available. Boeing has already opted to grow its flight test fleet from three to four, with the addition of RC503, which may fly before the week is out, heading immediately into high intensity radiated field (HIRF) testing in Arizona.

Compared to its composite stablemate the 787, which has progressed more swiftly through its flight test campaign, 747-8F has struggled to find its footing along side the company's flagship program. While still technically a derivative aircraft of the 747 family, the aircraft's all-new fly-by-wire wing, engines and avionics, make it a significantly different aircraft from the variants that preceded it.

Albaugh was also cautiously optimistic on the 747-8.

He said his engineers have been struggling to remove a slight vibration of the wing tip in flight — "like a one-inch deflection in the tip of the wing."

But he said flight tests this past weekend had shown "promising" results, and "I think we're getting to the end of it."

He said the problem is not a question of structural integrity, nor a fatigue issue that would weaken a wing over time, but it does need to be addressed before certification.

Boeing will delay first delivery of the 747-8 freighter by several months and add a fifth aircraft to the flight test fleet to correct a series of problems.

First delivery to 747-8F launch customer Cargolux is reset from late 2010 to mid-2011, Boeing says. The company has not disclosed any schedule changes for the 787-8 Intercontinental, the passenger-carrying variant expected to be delivered in late 2011.

The delay follows a series of "discoveries" that disrupted the schedule for completing certification testing on time: a low-frequency vibration that appears in "certain flight conditions" must be resolved, Boeing says.

Secondly, an inboard aileron actuator is not working as expected. Boeing says that neither issue requires structural changes to fix the problems.

"We understand the issues encountered in flight test and are working through the solutions," says Pat Shanahan, vice-president and general manager of programmes for Boeing Commercial Airplanes.

Delay to the 747-8F comes one month after Boeing pushed back first delivery of the 787 from late 2010 to the first quarter of 2011.

Boeing originally planned to deliver the first 747-8F in late 2009, but first delayed the programme in October 2008. That delay caused Boeing to take a $1 billion charge on the programme.

However, the new schedule setback "is not expected to have a material impact on Boeing's 2010 financial results", Boeing says.

Boeing annonce un retard de livraison du premier 747-8 Freighter, désormais prévue pour le milieu de l'année 2011, en raison de modifications à apporter sur certaines pièces de l'avion cargo.

L'avionneur américain avait précédemment indiqué qu'il y avait de fortes chances pour que le calendrier de livraison de l'appareil prenne du retard.

Boeing précise que ce changement n'aura pas d'impact sur ses résultats financiers 2010.
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