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The 777X family (777-8/-9/-10) features wingtips that fold up on the ground to let the aircraft fit in tight spaces. These have to be extended and locked in place before a revenue flight can take place, but can a 777X legally be ferried with one or both wingtips in the folded position - for instance, if one of the wingtips is jammed in the up position while at some backcountry airport that doesn't have maintenance facilities for a 777?

For the purposes of this question, I'm assuming that it's physically possible to operate the aircraft. The non-folding part is the same length as the wing of a regular 777, so it would still be able to take off safely, just with considerable performance penalties compared to normal, wingtips-folded-down flight. Ferry flights for maintenance purposes can get away with a lot that wouldn't be allowed during line operations (for instance, multi-engine jetliners can be ferried with one engine - or, for quadjets, two - inoperative, and the 747-400 can be ferried with one of its winglets broken off).

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    $\begingroup$ Having one wingtip folded and the other unfolded would result in asymmetric lift. I'm guessing that this would result in a fatal loss of roll control, even with the aircraft empty. There is also the risk that a folded wingtip would break off as a result of aerodynamic forces in flight. $\endgroup$ – Thomas Feb 8 at 5:38
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    $\begingroup$ @Thomas I'm not sure that a missing 3.5 meters wingtip will cause a fatal loss of roll control $\endgroup$ – DeepSpace Feb 8 at 10:09
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    $\begingroup$ @DavidRicherby a diversion one $\endgroup$ – Antzi Feb 8 at 15:23
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    $\begingroup$ If the aircraft managed to land at an airport without a maintenance facility, they would fly in the engineers/equipment to repair it before it took off again. This isn't unheard of in the industry. So no, they would not take off knowingly having an issue with the folding wing tips. $\endgroup$ – Ron Beyer Feb 8 at 15:35
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    $\begingroup$ @Thomas The lift drops off significantly as you go towards the tips. The integral under the curve of the last 10% is small. $\endgroup$ – user71659 Feb 8 at 23:41
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As Ron notes in the comments to another answer this is a perfect situation for a Ferry Permit/Special Flight Permit. The FAA via your local FSDO can authorize aircraft to fly for the purpose of being fixed elsewhere via a ferry permit. This question covers whats needed for that.

However in some cases it may be cheaper to fly (or drive) in a maintenance team and fix it on site. Moving an empty 777 even short distances means burning quite a bit of Jet-A. For the cost of the reposition it may just be cheaper to send a team (possibly in car) with the parts and tools they need to get the job done.

On a similar note its likely that the majority of fields big enough for a 777 to touch down have at least some form of maintenance on hand. Again it may be cheaper for an airline to contract the job to a local shop than bother with the ferry logistics and costs.

Boeing also offers these services if you should need them in a pinch as part of the AOG services.

Our technical experts will provide on-site, comprehensive and integrated assistance to recover an airplane. Our goal is to quickly and safely return airplanes to service, using methods and procedures that avoid costly secondary damage.

From what I can tell they will basically show up with parts and people to get the plane back in the air just about anywhere you can fly it out of.

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    $\begingroup$ If it's just flying mechanics on site with personal tools and some parts to swap out parts or perform an MMEL M procedure, that's one thing, but if a procedure requires tooling or special equipment that isn't available on site and has to be shipped as cargo, the logistics become extremely expensive and time consuming. An airline will almost always try to ferry an airplane to a maintenance base where it has the equipment if it can. $\endgroup$ – John K Feb 9 at 16:09
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Not with one tip up and one tip down, but it could be possible to ferry with BOTH tips folded, or removed, if Boeing has tested it. A scenario might go like this:

  1. Airline can't get one wing tip to unfold, or the tip gets physically damaged somehow, at a location where required equipment is unavailable.
  2. Airline contacts Boeing customer support (why not; they have nothing to lose by asking) and asks if they can get an authorization for a non-revenue ferry flight with both tips folded or removed.
  3. There will be an internal discussion within the Boeing engineering/test/customer support organizations. It'll depend on whether Boeing did any experimental flight testing to document the airplane's behavior with tips folded or removed. If not, it will probably end there and the airline will have to fly facilities to the airplane instead of the opposite.
  4. If they have test documentation that demonstrates that airplane can be flown safely with the tips folded or removed, and the engineering heads who have to sign off have done a risk evaluation and are comfortable (and their relevant FAA counterparts are ok with it), it's theoretically possible that the FAA could issue a one-time ferry permit with a list of operating limitations (such as weight, altitude and speed restrictions). My guess would be a flight with tips removed is the most likely configuration to be authorized, if at all.

I'd be surprised if this sort of thing hasn't already been evaluated within Boeing and has been determined to be feasible or not feasible. Only someone within the Boeing engineering organization would know.

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    $\begingroup$ Boeing can't issue ferry permits, only the FSDO can, which they would probably want Boeing's blessing. $\endgroup$ – Ron Beyer Feb 8 at 18:03
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    $\begingroup$ Ok I modified my post. I was with an OEM in Canada and we would issue ferry permits by delegated authority but for something like this they would probably want Transport Canada's approval as well, so same thing in practical terms. In any case, FAA certainly wouldn't go near it if Boeing hadn't done some testing and was confident there were no issues. $\endgroup$ – John K Feb 8 at 23:01
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    $\begingroup$ @Ron Beyer: Perhaps we're using a different definition of the word "can"? I take it to mean the ability of the plane to actually fly, not the legality of the FAA or whatever body issuing a permit. $\endgroup$ – jamesqf Feb 9 at 18:13
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    $\begingroup$ No doubt it would fly even with one up and one down. The asymmetry in wing area is not that great. You could easily offset it with some fuel imbalance. With them both up or removed it would be almost unnoticeable, a negligible reduction in total wing area, notwithstanding vibrations/flutter or other side effects from exposed bits. You never know what hidden side effect can jump out of the shadow. It would have to have some minimum level of test, or at least very convincing and complete engineering calculations and analysis. $\endgroup$ – John K Feb 9 at 20:58
  • $\begingroup$ @JohnK: If you're worried about flutter, fly slower. $\endgroup$ – Sean Feb 9 at 21:41
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I don’t believe Boeing authorizes flight of the 777x with a wing fold failure. To be blunt, if you can afford a \$425 million airplane, you can afford a \$30,000-\$40,000 maintenance call where an AOG team is dispatched to the airport to repair the airplane and return it to service. Even if Boeing approved flying the airplane with a wing fold failure, I doubt your Company SOPs, not to mention the insurance underwriters would approve.

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    $\begingroup$ It’s often not money but time to fix which is the issue. Flying to next base might be more expensive in fuel but save days or weeks in parking and lost revenue. $\endgroup$ – Cpt Reynolds Feb 9 at 13:55
  • $\begingroup$ Well that’s why they dispatch an AOG team like that. They can usually get the problem resolved in a day or two. Again both the airlines will prefer that cost to a hull loss in a crash and subsequent lawsuits and bad publicity. $\endgroup$ – Carlo Felicione Feb 10 at 1:07
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    $\begingroup$ It depends on the issue. In my airline, we use whatever means comes out best. All I‘m saying is that sending an AOG team is only one tool in the box and that a ferry flight might be the preferred option. After all, three engine ferries on quads or gear down ferries are, while special events, not unlikely to be at least considered. $\endgroup$ – Cpt Reynolds Feb 10 at 10:54

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