747-8 FLUTTER ISSUE

[SAMPUBLIUS]

By Julie Johnsson
Bloomberg News
Boeing’s newest 747 jumbo jetliner faces a risk of dangerous vibrations, known as “flutter,” in limited situations, the Federal Aviation Administration said.
Data analysis shows that “divergent flutter,” oscillations of a wing that could cause it to break up, may occur on the 747-8 during a “high g-load maneuver in combination with certain system failures,” the FAA said Wednesday. G-loading refers to the stresses on a plane that can increase during acceleration and turns.

Operators of the passenger and freighter versions of the humpbacked jets are required to make wing repairs during the next year to five years to avoid safety issues, according to an FAA bulletin.

[MarkerInbound]

Got to be a big deal if the FAA is giving 5 years to fix the problem.

[7478ti]

The 2014 NPRM for the AD and its recent final issuance is old news, long ago addressed by service bulletins that operators had previously received. This appears to largely be an FAA administrative followup action. The one to five year compliance period further illustrates the low level risk status of the situation regarding the AD, recognizing that the theoretical condition is a very remote flight envelope corner case, combined with another necessary required failure, for this situation to even become an issue. Operators were already aware of all this via prior service bulletins, with any mods necessary likely completed or already planned.

[Euclideanplane]

Before the Valujet crash, the FAA spoke with McDonnell-Douglas about the issues with fire detection and suppression in the cargo hold of DC10. Was it more or less than 5 years they got to fix it? Maybe 5 years really does mean that it is a big deal...:confused:

[dixi188]

I don't think fire suppression in the cargo hold of the Value Jet DC-9 would have made any difference to the outcome.

Quite often ADs and SBs have quite a long compliance time so that the mods can be embodied at the next major maintenance input. Also there is often a long lead time for parts.

[lomapaseo]

If you tried to fix in one year every problem that the FAA has spoken about then no plane would fly today.

The idea is to prioritize resources to fix things and get it right a very high percentage of the time.

[Design Engineer]

Curious. I seem to recall the the original prototype 747s had a flutter problem too but it was fixed before production.

[rottenray]

Before the Valujet crash, the FAA spoke with McDonnell-Douglas about the issues with fire detection and suppression in the cargo hold of DC10. Was it more or less than 5 years they got to fix it? Maybe 5 years really does mean that it is a big deal...:confused:

First, DC-9, not -10.

I think that decision was made based on the assumption that no one was shipping pax oxy generators in unauthorized, unlabelled containers illegally. Given the rapid propagation of that particular fire event, it's doubtful even the "fix" would have prevented it.

Oxy generators are, under the wrong conditions, "somewhat" more active than lithium batteries which have reached thermal runaway.

Wing flutter was recognized during test flights, and an initial fix - through software - was put into place. This appears to be a follow-up to make sure that all operators are compliant.

Curious. I seem to recall the the original prototype 747s had a flutter problem too but it was fixed before production.

Yes, I recall that as well... Well, not really recall it, but feel sure that I've read it some where.


Cheers!
Ray

[KriVa]

My memory's a bit hazy on this one, but I recall the original flutter problem being fixed through a software intervention in the FBW control signal, countering the flutter?
I feel those "certain system failures" are failures which would take that step out of the process, though I may be entirely wrong of course.

[vetles]

Curious. I seem to recall the the original prototype 747s had a flutter problem too but it was fixed before production.

I'm guessing you might be referring to the famous "Sutter Twist" by the 747 programs original chief engineer, Joe Sutter?

/G

[Machinbird]

The following link should clear this little mystery up as well as describe the "Sutter Twist":
Boeing 747 programme updates (http://www.flightglobal.com/features/Paris-special/civil-programmes/747/)

It seems that Boeing was calling the oscillation a limit cycle oscillation, and the FAA was calling it a flutter. From my standpoint, limit cycle oscillations will not immediately tear your aircraft apart, but will accelerate fatigue and wear of the oscillating structure, so not a good thing.

[rh200]

Must be a slow news day in Aus.

747 vibrations: ?Flutter? a hidden danger in Boeing plane (http://www.news.com.au/travel/travel-advice/the-danger-on-board-the-boeing-747-8-plane/story-fn6yjmoc-1227447914550):ugh:

[mustafagander]

Vetles, I think the reference is to the ballasted outboard nose cowls on the 747-200 blow in door series.

We were told that the #1 and #4 nose cowls were ballasted to alleviate a risk of flutter. Oddly enough when the solid nose cowls - noise suppression mods - were fitted, no ballast was required.

I preferred the sound of the blow in door cowls!

[roulishollandais]

Thank you Machinbird for that excellent link.

OAMS seemed to be the solution usable in 2012-2013. But news.com.au seems to say the flutter/limit cycle oscillation is still a problem in 2015. What about OAMS and Sutter twist today (Boeing and FAA) ?

Again the definition of stability in case of quickly converging / non converging oscillations comes on the table:O

[GHOTI]

Assume most folks have seen this:
Wing Flutter on a 747 | Air & Space Magazine (http://www.airspacemag.com/videos/category/flight-today/wing-flutter-on-a-747/?no-ist)