Door blows out during ground test on Boeing 777X jet
 

I don’t think that this has been posted yet but this happened tonight. https://www.seattletimes.com/busines...eing-777x-jet/

Door blows out during ground test on Boeing 777X jet

Dominic Gates
Sep. 6, 2019 at 6:55 pm Updated Sep. 6, 2019 at 8:31 pm
By Seattle Times aerospace reporter

Boeing’s new widebody jet, the 777X, suffered a setback Thursday afternoon during a high-pressure stress test on the ground when one of the airplane’s cargo doors exploded outward.

One 777X employee working in a nearby bay at Boeing’s Everett plant said he heard “a loud boom and the ground shook.”

The accident happened to what’s called the “static test airplane,” one of the two airplanes in any new jet program that are built for ground testing only and will never fly. It was during the final test that must be passed as part of the airplane’s certification by the Federal Aviation Administration (FAA).

The failure of the door will require careful analysis to find out why it happened, and it may mean Boeing will have to replace the door and repeat the test.

The 777X program is already delayed due to a problem with development of the GE-9X engine that will power it. In July, Boeing CEO Dennis Muilenburg revealed on a quarterly earnings call that the first 777X intended to fly, which rolled out of the Everett factory in March, will not make it into the air until next year.

This ground test failure is another blow.

The static test plane is the one that is deliberately stressed well beyond the limits of normal service. The airplane is surrounded by a metal framework while weights passing through pulleys are fixed to the wings and other parts of the airframe.

During the ultimate load test, the wings are then pulled upward. To pass the test and be certified, the wings must bend without breaking until the load on them reaches at least 150 percent of the normally expected load.

In addition, the skin panels that cover both the wings and the fuselage are pressurized to the maximum stress that would be expected at the edge of any extreme maneuver anticipated in service. The pressure is ratcheted up by pumping air into the cabin.

Sometimes this final test is continued beyond the 150 percent load target until a wing actually breaks. But not always. The carbon-composite wings on the 787 Dreamliner are so flexible that when Boeing tested those in 2010 they bent upward by about 25 feet and, having comfortably surpassed the target load, Boeing halted the test without breaking them.

The massively larger wings of the 777X are also carbon composite, with a folding tip, and during Thursday’s test those must have flexed in a similarly impressive way to those of the 787. This time, however, though the wings did not give way; it was one of the doors that failed — an outcome that is definitely not supposed to happen.

The entire area around the static airplane is typically cleared during this test, with all the measurements taken by monitoring equipment and with engineers watching anxiously on a video link as the load slowly inches up toward the target and the pressure increases.

No one was injured in Thursday’s door explosion, which happened shortly after 1:30 p.m., and everyone was able to exit the building.

On Friday, according to Boeing employees, caution tape was attached to all the entry doors and no one was allowed into the building.

After the incident was first reported Friday by KOMO News, Boeing confirmed that a serious incident had occurred but offered few details.

“During final load testing on the 777X static test airplane, the team encountered an issue that required suspension of the test,” it said in a statement. “The event is under review and the team is working to understand root cause.”

Boeing went on to emphasize that “the testing conditions were well beyond any load expected in commercial service” and that the plane used in the test “will never fly or be used in passenger service.”

Because the GE engine issue has already pushed the jet’s flight tests into next year, it’s possible Boeing may have time to analyze and redo the ultimate load ground test without a further hit to the schedule.

Dominic Gates: 206-464-2963 or [email protected]; on Twitter: @dominicgates.

The real blow to Boeing, though, is that in all their years in Seattle, they failed to raise a new generation of aviation journalists. In the heart of American civil aviation you'd expect slightly higher standard of reporting.

No but the way I read it, they seemed to be tying wing testing to destruction to the door blowing off. Or maybe it is just late and I should re-read it.

I think the piece confuses or combines stress testing and pressure testing, as in this passage:

I don't think that however early you get up in the morning, that passage is going to make sense.

The article is a bit amateurish. Even with the poor article information, it's clear that the test they were doing was the positive g wing loading ultimate load test. Ultimate load is defined as 1.5 times the limit load. I don't know what limit positive load factor is used for the new 777, but it is required to be at least 2.5 g. So their target was to apply loads corresponding to the airplane pulling at least 3.75 g. That test is required by regulation to be done with the fuselage pressurized to the maximum cabin pressure differential. They apparently got a surprise before they made it to the target load. They are trying to give the impression that the door just popped out. However, plug doors don't just pop out. I suspect some significant structural failure of the fuselage occurred to cause the door to be released like that.

Are the cargo doors on the 777X plug doors? That seems unlikely. The doors from the 777-300ER don't seem to be plug doors:

https://i.ytimg.com/vi/539ZeAbu7yk/maxresdefault.jpg

Underfloor container hold doors on widebodies are rarely plug-type. They certainly aren't on the current 777 and I'd be very surprised if they are on the 777X.

I would suspect an issue with the locking mechanism rather than any significant structural failure.

I know the article above says cargo door, but from other articles I had the impression it was one of the main cabin doors that had failed. I don't know if that's correct.

I would expect max diff will have been tested prior to wing loading. If that is true it is not a locking mechanism failure, but stuff is bending/breaking in the structure when wing loading is applied.

I believe that is correct. The wing bending test is usually taken to a destructive result, so it is usually planned to be the last test performed on that test airplane.

No, that isn't necessarily the case, surely?. Tension applied for a wing loading text could just as easily distort part of any door locking mechanism (load transmitted through the airframe, of course) such that the locking mechanism gives way, rather than the airframe.

Many of the reports on the Net say simply "a door", but I haven't seen any that contradict the Seattle Times article and explicitly identify it as a passenger door.

If the airframe distorts to break part of the lock mechanism, I will call it a airframe structural failure.

Beefing up the lock could work, but is a band-aid.

If that is the problem and not just a new problem now the FAA have been woken.

Let's hope the FAA have been properly woken. I’m surprised that nobody has mentioned the DC-10 yet.

Probably because it's highly unlikely that any of the factors that contributed to the AA or TK accidents were present in this latest event, despite the outwardly similar (npi) outcome.

At least they were present, but surprised they were "quiet" after the event. I would expect they would have had questions.

Well yes, but beyond the centre wing box probably not that much. It's possible, of course, that the reason the door let go isn't connected with the wing flexing.

https://cimg9.ibsrv.net/gimg/pprune....1a1c36d438.jpg

The "least worst" outcome for Boeing, it terms of its effect on the development programme, would be if it turns out to be an unrelated defect with the locking system that manifested itself at 150% of max cabin diff (still not good news, of course). I'm not familiar with the 777 cargo door, but looking at photos it appears to use a fairly standard combination of C-latches and shoot-bolts, which are normally pretty robust and reliable.