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deicer

777x Door Blows Off During Testing

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It seems that even on other product lines, Boeing's problems continue...

http://newsinflight.com/2019/09/07/a-door-blew-off-a-new-boeing-777x-during-the-pressure-test/

A door “blew off” a new Boeing 777X fuselage during a “load test” yesterday in Boeing hangar.

The incident happened during an ultimate load testing on one of the two 777X static test airplane, a standard final structural inspection procedure required ahead of first flights.

Plane was pressurized, under extreme load conditions on the ground, as FAA inspectors watched, door flew off.

The tests push the aircraft structure beyond its limits. Engineers pressurise the aircraft well beyond capacity and bent its wings in an extreme manner, to be certain that aircraft will withstand unlikely extreme conditions in the real world.

Following the incident, Boeing called off the tests, which will further the delay the first flight…

In a written statement to KOMO Newsradio, a Boeing spokesman said “…during ultimate load testing on the 777X static test airplane, an event occurred that forced the test team to halt testing. Safety is the highest priority at Boeing. The test team followed all safety protocols and there were no reported injuries. The team is currently working to understand what happened and ensure the area is safe for work to continue. The ultimate load test is the latest in a series of tests that Boeing has been conducting on this full-scale test airplane over the past several months.”

The 777x maiden flight was delayed due issues with GEnx engines and the maiden flight is likely to take off in January 2020…

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Exactly and I’m not even sure why this is a story other than to take a proverbial kick at Boeing while they’re down. These same tests often result in the wing failing but the loads are so extreme, it is not considered a “failure”. It’s simply providing an understanding of the real load limits.

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What I would like to question,  is this a one of, or has it happened as well in previous tests? 

Having watched the testing videos, usually when they test to failure it is usually because they exceeded 150% of requirement.

Did this failure occur before or after this point?  If it happened prior to, then was it an engineering failure?

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While testing is intended to exceed design failure limitations by a significant amount, there are also estimates for when the failure (if any) will occur.

If failure is above design limit but premature to the estimated failure point, it must be determined why.

So much aircraft design is done on computer now that static and dynamic structural fatigue testing and results are critical.

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ALL airframes have to undergo a Max Differential pressure test and Leak rate test.  This ensures there are no excessive leaks at Max Diff and that any structural issues that could be catastrophic are located (which is very rare).

It is a scary test to be around when being conduced.  The doors are wrapped in heavy netting in case of a failure.  When the Max Differential pressure is reached you can actually see the windows bulging.  If a door eve let go or the fuselage rupture it would be a very large explosion for sure.  That amount of air at somewhere around 9-11 PSI  would be a killer.

This airframe was being tested far beyond these limits with other things being done as well.  This gives the engineers real world proof of design and failure modes.

As a note the 727 was tested to 150% of its design tolerance (slide rules and drafting tables) and still did not fail.  The engineers them selves were astounded at how far that airframe could be pushed.

 

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When the DC-10 was being pressure tested a lower cargo door blew open.  The floor then collapsed on the flight control cables.  This failure chain had been predicted by the subcontractor who was involved in the fuselage build.  It was also predicted this would result in the loss of the aircraft.  We all know how this ended.

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Boeing Suspends 777X Loads Tests After Pressure Failure
Sep 7, 2019 Guy Norris | Aviation Daily

Final loads testing on Boeing’s delayed 777-9 has been suspended while investigations continue into the failure of a cargo door during pressurization evaluations on the static test airframe at Everett, Wash. on Sept 5.

The incident occurred during the final phases of the 777X major structural test campaign, which is being conducted in a specially built 1.6 million lb. steel rig in Building 45-12 at the company’s production site.  At the time of the failure, the “testing conditions were well beyond any load expected in commercial service,” says Boeing. The company adds the event, first reported by Seattle’s KOMO News radio station, is “under review and the team is working to understand the root cause.”

The ongoing delay to the 777-9 flight test program due to issues with the aircraft’s General Electric GE9X engines means that Boeing will likely have ample margin to modify the failed part and re-run the test. The 777-9 had been scheduled to begin flight tests in late June, but these have been pushed back until early 2020 while GE validates redesigned stator vanes to improve durability.

However, the failure, which occurred during static test condition 12, or the ‘high-blow’ pressure test, holds potentially greater significance depending on the outcome of the investigation. Although the 777X fuselage is constructed of standard aluminum rather than the stiffer composite material used in the 787, the aircraft has been designed to operate at a higher internal pressure than the current model. The change will allow the 777X to cruise with at the lower 6,000 ft. equivalent cabin altitude of the 787 rather than the 8,000 ft. industry standard altitude of the present version.

Boeing also increased the size of the 777X windows by 22 sq. in. as part of the redesign, locally stiffened ribs and made other slight redesigns to counter potential fatigue life concerns and increase static strength to accommodate the 0.6/0.7 lbs. per sq. in. (psi) increase in cabin pressure. The current 777 operates with a normal cabin pressure in the range of 8.4 to 8.7 psi. The cabin pressure in the 787 is usually set between 9 and 9.4 psi, to reflect the lower equivalent altitude of 6,000 ft.

The manufacturer, which has not provided details of the failed part or the test condition at the time of the incident, is thought to have been pressurizing the 777-9 fuselage towards similar levels reached during structural tests of the 787 in 2008. These saw the fuselage pressurized to 14.9 psi, or 150% of the maximum level expected in service. Positive pressure relief valves, which in operational aircraft are set to open at prescribed levels (up to around 9.78 to 10.23 psi in the case of the 787) to avoid over-pressuring the aircraft, are adjusted accordingly for such tests.

The 777-9 is configured with up to 13 significant fuselage openings, with 10 passenger doors on the main deck, two of which are optional emergency exit/service doors, as well as three lower lobe cargo doors. The cargo doors, all located on the right side, consist of doors to access the forward and aft cargo holds as well as a smaller bulk cargo door.

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On 9/7/2019 at 9:51 PM, vanishing point said:

As deicer asks, it would be enlightening to know how much pressure was on the airframe when the door blew off.....but then that wouldn’t be nearly as news-worthy

 

1 hour ago, airbrake said:

 

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The test is normally done to the Max Differential pressure which is around 9.5 PSI.  9.5psi at that volume would be a pretty drmatic explosion.

 

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The particular test was designed to produce a failure. The article references a differential of 15psi. The concern in this case was the particular way in which the failure occurred. Typical failure is doors being forced open but constrained by the hinges. In this case, the split in fuselage let the entire door assembly break loose. 

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When the test is done the doors are all constrained by VERY heavy netting in the event a door lets go.  It fact a window failure is more likely.

You can actually see the windows bulge out at 9 psi.

15 psi would fit the 150% of tolerance rule but you would never get there in operation.

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