Lawyer speak

"had it not been for..."

But in aviation we work in balancing risks so the regulatory aspects recognize that nothing is perfect among all the systems including their human maintenance and operation.

Thus the operating words are "in spite of"

precautions need be taken to etc. etc.

See the /s?

Thank you for your comment, my thoughts as well.

Assuming it passes, the complete engine fan blade out test is only run once - the test is horribly expensive (it basically destroys the test engine, plus it's heavily instrumented with much of the instrumentation also effectively written off, plus all the 'normal' costs of doing an engine test). They often do rig tests - basically an isolated fan - to test out certain aspects to make sure it'll work when they do the whole engine test. The test is done at redline N1, which is normally considered to be the worst case condition.
The only time I know of where they repeated the test was on the original GE90 - although the blade was contained, the resultant vibrations caused a bunch of other stuff to fail (including the inlet coming off at the attachment flange). Although they tried to convince the Feds that they could show analytically that they'd fixed all the failures, the FAA made them repeat it. Scuttlebut was the cost of repeating the test was north of $40 million.

All that being said, I've not seen anything that says the fan blade was uncontained. Clearly the inlet structurally failed, but the why is unclear.

hey tdracer
.

Suggest you check post by silverstrata

https://www.pprune.org/10122411-post125.html

for a plausible explanation as to path of missing blade

which would probably be enough to whack a chunk off of cowl/inlet

I'll be flying up to Reagan Airport next month on Southwest, with the Missus. I advised her that as usual, she can have the window seat.

If looks could maim, they'd have to put me into a laundry basket. This news story has quite unnerved her.

Me, understanding reliability and probability, am now the proud window sitting passenger of we two on a trip for the first time in years.

The only force that kept the blade continuing its circular path around the shaft was the 'inward' centripetal acceleration force while it was still attached.

Once the blade has failed at the root, that centripetal force has gone, there is no further acceleration force acting on the blade, and its trajectory immediately becomes linear, directly tangential at the moment of release.

Of course, the swirl of air, as well as possible impact by the other blades which are still rotating might well cause it to have some rotational path, and the momentary residual forward force on the blade as well as the 'pitot' force of incoming air will complicate the picture further.

In any case, my main point is that there is no inherent mechanical force or tendency for the liberated blade causing "this radial trajectory [to] sustain after root failure" as you seem to suggest.

pm

The role of the containment ring is to prevent a detached fan blade from flying straight off. To illustrate the damage potential, recall the DC-6 accident at Burbank where a departed prop blade passed through the fuselage and hydraulic lines before damaging the number 2 engine which failed not long after. https://aviation-safety.net/database...?id=19760208-0

The errant blade will lose energy contacting the containment ring, possibly more than once, but may gain energy from the remaining fan blades - all within a fraction of a second before it exits the cowl in whichever direction not blocked by the containment ring.

Blade departure path; hydraulics
 

[QUOTE=pilotmike;10123195]The only force that kept the blade continuing its circular path around the shaft was the 'inward' centripetal acceleration force while it was still attached.
Once the blade has failed at the root, that centripetal force has gone, there is no further acceleration force acting on the blade, and its trajectory immediately becomes linear, directly tangential at the moment of release.

Yes, but:

1. We need to be clear this is happening in airframe co-ordinates.

2. At the moment of blade departure, there will be a significant pressure drop (as before, when the blade was attached) from the back to the front of the blade. Thus, I'd expect the blade's departure path to somewhat behind tangential, opposite the direction of rotation and somewhat towards the nose. That's likely how the blade got around the cowl leading edge to smash the window.

On a different topic, I see reports of a hydraulic failure but evidence of that in the ATC recording. Surely the crew would have reported that to ATC if it did happen?

Well done, crew!

Exactly this....took me a while to wrap my head around this. The percentage of oxygen in air does NOT change with altitude, but the amount does. Air at sea level has the same percentage of oxygen at 20k feet, 30k feet etc. However air pressure drops with altitude, as do the absolute numbers of molecules on nitrogen, oxygen, argon, etc. The concept of "partial pressure" explains this more scientifically but is not terribly intuitive. There are two ways to fix this: increase the inspired fraction of oxygen above 21%, thereby making more molecules of oxygen available, OR force air at higher pressure into the lungs making the pressure (and amount) of oxygen more like breathing at sea level. The first method can help up to a certain altitude and is what happens with the loosely fitting masks that drop down for passengers. Certainly OK for a short period, say to go from 30K feet down to 10K. For the pilots it makes more sense to have tightly fitted masks connected to pressurized air (or air enriched with additional O2) of unlimited supply. That way they can maintain near normal intake of oxygen while flying the plane. Interestingly enough climbers in the Himalayas suffering from altitude sickness can be supported by pressurizing them in a Gamov bag: basically a foot pressurized habitat that is pumped full of ambient air so that the patient receives 21% O2 at higher than ambient pressure.

There is no evidence that it was the blade that smashed the window - you are jumping to assumptions.

Seems reasonable, trajectory after separation would certainly be chaotic.

But this does also assume instantaneous separation under tension (typical fatigue failure).
However the blade in operation is subject to considerable bending and twisting moment, cyclic with every engine power change or every time that the load on the blade changes. This could (is likely) to see crack propagation originating along the trailing edge surface, the surface under tension when the blade is bent forward.
It is conceivable that the final failure is not instantaneous, no matter how quickly it occurs, but occurs over the course of some part of rotation or full rotations of the fan.

Possible that final separation might occur progressively with the leading edge surface failing under combined bending / tensile load, at which time the tip of the blade could well be "hinged forward" to some extent.

Such a failure would be evidenced by plastic deformation along the leading edge fracture zone.

In routine inspection, is the focus on the trailing edge root area?

Conso, while there is a first time for everything, we did a lot of investigations of fan blade releases over the years. In some of the events, there was some low energy debris that did damage forward and aft of the fan containment ring (in most cases it didn't penetrate the acoustic lining), but never any indication of high energy debris missing or penetrating the containment ring.
Again, I've seen no evidence that the fan blade was uncontained or that was what took out the window. My personal theory is it was a large chunk of the disintegrating inlet that hit the fuselage. The question remains why the inlet broke up. The inlet is designed to withstand the aero loads inflight, and it's designed to withstand the forces (mainly vibration) from a fan blade out. It appears that perhaps the combination of those two loads was not adequately accounted for.

WN60, I think I sort of remember balancing a blade so that the SLIGHTLY offset CofG counteracted the aero forces, at a specific speed, etc., but it's all a very long time ago.

TDR, thanks for your measured, informed and intelligent contributions.

tdracer: >"I've seen no evidence that the fan blade was uncontained"

The NTSB has stated that fan blade 13 is missing. That's not simply missing from the hub, it's gone and they cannot find it. To me, that's uncontained.

Did you mean "no evidence of high kinetic energy blade departure"?

Re: Liberated Fan Blade
 

@WingNut60:

>>> It is conceivable that the final failure is not instantaneous, no matter how quickly it occurs, but occurs over the course of some part of rotation or full rotations of the fan.

[. . .]

>>> Possible that final separation might occur progressively. . .

Yes. In fact, however fast it may occur, it almost certainly is progressive. Very short time periods are still time periods.

Also, as has been pointed out, this failure didn't occur in a vacuum or on a fan that was motionless (except for rotation) with respect to surrounding structures. It took place at speed, on an aircraft engine moving, to various degrees, along multiple axes.

Taken together all of the forces likely to have been in play would presumably have resulted in the separated blade moving forward and along a(n at least somewhat) radial path.

Regardless of the above, it certainly seems that serious consideration should be given to the containment capability of the inlet cowl.

Double emergency at the same time
 

I must give my props to the crew for their handling of the situation. But I have a few questions.

1) As the story has unfolded, I can assume that the crew first received the Engine Fire indications with Fire Warning going off. As they were still climbing (or maybe cruising), first thing they would be doing is Engine Fire or Engine Sever Damage or Separation Checklist memory items. But the cabin was punctured and they had a rapid depressuzation coming. If the cabin altitude warning horn sounded while they were doing the Engine Severe Damage memory items, does that mean that they have to hold checklist and continue with the Rapid Depressuzation memory items?

2) We didn't have the option of choosing between Flaps 15 and any other Flap setting on our QRH in the One Engine Inoperative Landing Checklist. Does planning a Flaps 5 landing raise the question of legality in terms of crew training?

I'm just curious.

Which was one of the smartest decisions made by the crew. Remember the ELAL1862 incident where slats were damaged by the engines being ripped off. This may very well have produced a similar scenario of uncontrollability at lower speeds while deploying flaps/slats.

Excellent crew (both flight and cabin), and soooo sad about the loss of life.

But that isn't what the design designation means. The containment ring did its job and prevented the separated blade from exiting the engine at 90 degrees. The investigation now is to discover why there was a catastrophic failures of the nose cowl assy.

Given that there were NO reports of incapacitations or fatalities caused by the incorrect wearing of the O2 masks, maybe it's time to just let it go.