New images have surfaced of what really happened during the September structural testing of Boeing’s new 777X aircraft. September’s test was widely reported to have failed, with a cargo door being blamed for the issue.
Now, it seems that the situation was a lot more serious than that.
Explosively ripped apart
The news that a cargo door had blown off the 777X during its stress test in September was shocking enough. However, it now appears that the situation was far worse than we could ever have imagined.
According to reporting by the Seattle Times, it wasn’t just the door that ruptured, but the entire fuselage!
Apparently, as the stress test was nearing its target level, a weakness at the keel caused the structure to fail, leading to an ‘explosive depressurization’ ripping through the fuselage. The Seattle Times has obtained photos showing the extent of the damage, something which Boeing has reportedly been keen to keep to themselves.
The fuselage of a Boeing 777X ground test airplane was split by a high-pressure rupture. The failure occurred just shy of the ultimate load required to certify the airplane. (Via @dominicgates) https://t.co/Mk0J9LakpdAdvertisement
— Seattle Times Biz (@seatimesbiz) November 27, 2019
Earlier reports that a cargo door blew out are not entirely unfounded. Apparently the fuselage skin ripped open just behind the wing, and as such a passenger door was dislodged and fell to the factory floor. The damage is clearly far worse than originally revealed; the test aircraft is a complete write-off.
Boeing spokesperson Paul Bergman was kind enough to provide Simple Flying with the following statement in regards to the incident.
“In the final load testing of the 777X static test airplane, our team conducted a test that involves bending the wings of the airplane up to a level far beyond anything expected in commercial service. A testing issue occurred during the final minutes of the test, at approximately 99 percent of the final test loads, and involved a depressurization of the aft fuselage. The test team followed all safety protocols.
“As we shared on our Oct. 23 earnings call, our root cause assessment continues, and we are pleased with the progress we are making as we complete our detailed analysis. What we’ve seen to date reinforces our prior assessment that this will not have a significant impact on the design or our preparations for first flight. We do not see any impact from the test on the overall program schedule.
“On the call, we did update our target for first delivery from late 2020 to early 2021. As we’d said for some time, there had been significant risk to the late 2020 timeline. What changed is that we now have a clearer understanding of how the GE9X engine issue has impacted the details of our flight test program. For example, the timing of engines for the remaining flight test airplanes will affect when they begin flying, which in turn affects our detailed test schedules. When we account for all these factors, we expect to fly in early 2020 deliver in 2021.
“We remain fully focused on safety as our highest priority as we subject the 777X to a rigorous test program.”
Immense amounts of stress
Airframe structural testing is an incredibly demanding process, and aims to exert some 1.5 times the normal stress that would be experienced by an airliner in use. The wings are pulled upwards some 28 feet from their normal position, the fuselage is bent downwards with millions of pounds of force on the front and aft.
Inside the plane, in this case, pressurization is raised to around 10lb per square inch, far beyond regular levels. This is not an FAA requirement but was something Boeing had opted to do voluntarily.
The FAA requirement says that forces need to be piled upon the airframe up to 1.5 times the maximum load that would ever be experienced in normal flight. It then has to be held there for at least three seconds. The 777X had reached a load of 1.48 times the maximum, around 99% of the target, when the structure gave way.
The weak point was under the center fuselage, just behind where the landing gear is stowed. The extremes of stress on the fuselage caused the skin of the aircraft to rupture. Because the inside was so strongly pressurized, this led to rapid depressurization that a whistleblower described as “a loud boom, and the ground shook”.
It was this rapid depressurization that caused the extent of the damage. The fuselage skin split up the side of the aircraft, damaging an area around a passenger door that fell out of the fuselage to the ground.
Will not require a retest
Because the test was within 1% of its target levels, the Seattle Times believes that the aircraft will not have to undergo a retest. While that might sound alarming to some, it’s important to remember that these sorts of tests exert immense amounts of stress on the airframes, far more than would normally be encountered in a natural environment.
Boeing maintains that nothing has happened to delay planned delivery schedules.
According to reports, an anonymous source at the FAA said that, because the blowout happened so close to the target load, it barely counts as a failure. Although Boeing will need to look at the area of the keel where the weakness presented itself, the airframe is unlikely to be represented for this test again.
What do you think about all this? Let us know in the comments.