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777 Loses Engine Parts Over Denver

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I think it was this incident where one of the blades penetrated the roof of a red car...


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8 hours ago, martin-w said:

New information is emerging. Seems TWO of the engines fan blades were ripped off.

Losing one fan blade is understandable, but losing two of them, that's just carelessness. 🤣


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Perhaps they need to add an autobrake to the shaft after blade separation to stop the uncontrolled wobble of the remaining parts...


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12 hours ago, martin-w said:

New information is emerging. Seems TWO of the engines fan blades were ripped off. Both showed signs of metal fatigue.

 

New Details Emerge About Boeing 777 Explosion Ove…: https://youtu.be/Mhm0_rYsy-Y

Yes you can see that on this image, one fan blade broke and that took out a portion of the fan blade next to it, probably more then just those two had metal fatigue but it was just the one that set off a chain reaction:
800px-United_Airlines_Flight_328_damage_

Edited by Matthew Kane

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3 hours ago, n4gix said:

Perhaps they need to add an autobrake to the shaft after blade separation to stop the uncontrolled wobble of the remaining parts...

To be honest it is just windmilling, as the wobble looks bad it isn't  really doing too much. There is video of when they tested fan blade breaks for certification and the wobble was known back then. This incident is considered contained and as designed

Edited by Matthew Kane

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6 hours ago, Chock said:

Losing one fan blade is understandable, but losing two of them, that's just carelessness. 🤣

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17 hours ago, Matthew Kane said:

To be honest it is just windmilling, as the wobble looks bad it isn't  really doing too much.

I am more concerned with the additional stress being placed on the pylon mounting bolts. 

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4 hours ago, n4gix said:

I am more concerned with the additional stress being placed on the pylon mounting bolts. 

 

I understand that engines mounted beneath wings have bolts that are designed to sheer off if the torque becomes excessive. Thus protecting the wing. 

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If the engine was throttled at takeoff thrust absolutely it would have torn right off, from what I have been understanding from a few mechanics talking about it, this was windmilling at low RPM and contained.

Also best line I've heard so far was the parts that fell off and rained all over the town were airplane parts, and not engine parts, the engine was completely contained except for the one and a half fan blades that were torn off, other then that fully contained, the rest of those parts were airplane parts. 

This guy explains it well 

 

Edited by Matthew Kane

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Also at this point you can change the title of the thread to 777 Loses Airplane Parts Over Denver instead or 'Engine Parts', no engine parts fell off this aircraft 🤣


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1 hour ago, Matthew Kane said:

If the engine was throttled at takeoff thrust absolutely it would have torn right off, from what I have been understanding from a few mechanics talking about it, this was windmilling at low RPM and contained.

I suspect what n4gix what was alluding to, was the fact that whilst from the phone camera footage we saw, yes at that point the engine was windmilling at low RPM, but that was after the incident where the engine fan blades let go. That low windmilling RPM would not have been the case when the engine let go, as evidenced by the bits which flew off and were not contained by the ballistic protection ring on the cowling, damaging the wing and the fuselage as a result of that. This demonstrates that the engine was not windmilling at the point of failure, since there is of course no reason it would be doing prior to a failure, and so it  certainly would have been imparting a lot of stress on those mounting bolts at that point.

From what I understand, there have been instances where a Triple Seven has had an engine let go owing to fractured fan blades, and the asymmetric thrust has caused the aeroplane to roll to almost a 90 degree bank angle before the PIC has got the thing under control. In those circumstances, you would have an unbalanced engine wobbling around with a lot of sideways airflow force on it too, which is not going to do those retaining bolts any favours at all. I wouldn't mind betting the bolts on this particular Triple Seven, and bearings in the holes those bolts go through copped for some pretty serious stresses, and so when that engine was wobbling around afterward, it potentially could have been a very serious cause for concern. I'm no expert on the Triple Seven, but I'm fairly sure an engine is not really meant to shake around as much as that one we saw in that footage, although the fact that it could do so and stay put with a 250+ mph wind battering it, is pretty impressive from an engineering standpoint.

We know for sure that engines can certainly shear off in extreme roll maneuvers, this happened a few times with Boeing 707s when how to recover from Dutch roll was being demonstrated to new crews. That exact circumstance resulted in the well-known crash of a brand-new pre-delivery Branif 707-227 - N7071 - which rolled up to approximately 90 degrees of bank and lost three engines off its pylons as a result of shear forces on the engine pylon bolts, when on a training flight for a new Branif 707 crew, whilst demonstrating a recovery from a Dutch roll where the crew gave it a bit too much aileron and rolled it up to 90 degrees. This left both its wings on fire and with only one engine left still attached to the aeroplane, which had to be shut down anyway because it was delivering too much asymmetric thrust whilst throttled back. The aeroplane's Boeing test pilot subsequently attempted a belly landing, unfortunately striking trees on a river bank when nearing touchdown and breaking up as a result of that, with only those seated in the tail section surviving the crash.

I guess we'll find out from what the NTSB reports eventually, but I for one would certainly be interested to see some pictures of the condition of the retaining bolts and the mounting holes for that engine, and some x-rays of the things too.

 

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2 hours ago, Chock said:

I guess we'll find out from what the NTSB reports eventually, but I for one would certainly be interested to see some pictures of the condition of the retaining bolts and the mounting holes for that engine, and some x-rays of the things too.

 

Yes it will be great when we can see more of these reports. The initial blast would have been what caused the most significant damage, but that never caused the engine to drop in this incident, which goes to show the design did what it was supposed to do and contained it. This is why I find this fascinating, I love those 777's and this is just another pressure test in what is the greatest airliner ever built in my view. Also those pilots seem to have done a fantastic job but more reports on their actions are yet to come, I get the gut feeling these guys fell back in their training and did things by the book. 

Also fascinating was the claim that this engine is likely not a right off, they could be put it back into service again after a rebuild as the damage (even as bad as it looks) wasn't enough to right it off, or so has been claimed.


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A gaping hole in the side of the fuselage from engine debris, perhaps fan blades is ....Contained?

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No, most of the pieces from UAL328 that landed in the Denver suburb of Broomfield were from the engine--not internal pieces of the engine, but pieces of the cowling and shroud sections that form the engine's outer aerodynamic shell.  When they talk about a "contained" t-wheel disintegration, they mean the broken blades and other high-energy fragments of the disintegrating wheel were prevented from flying at high velocity laterally through the engine casing.  Those wheels turn at tens of thousands of rpm, so any piece flying off the turbine wheel has a LOT of kinetic energy.  Modern engines have Kevlar belts around the compressor and turbine wheel sections that are designed to keep the shrapnel from a disintegrating t-wheel inside the casing, where it is then blown out either through the bypass duct or through the core of the hot section and out the back end. An "uncontained" failure would result in pieces penetrating laterally through the belt and damaging/puncturing the surrounding structures.

The front cowling ring (the cowl diameter on a PW4077 is about the same size as a 737's fuselage) landed intact on a roof, bounced off and and ended up leaning up against a tree next to a pickup truck in the home's front yard.  That picture, which was all over the news here, really gives a sense of scale as to how big those Pratts are.  Large pieces of the shroud were found in a soccer field nearby, as well as other components off the accessory case of the engine.  The fiberglass/composite fairing where the wing meets the fuselage had a pretty good gash in it, most likely made from parts of the engine shroud and/or pylon after they were torn loose from the engine and accelerated by aerodynamic forces.

Back in the good old days, before Kevlar straps became a thing, we had a C-141B down in Richmond Australia taking off heavy when a t-wheel on the #3 engine cut loose just after liftoff.  The shrapnel took out the #4 engine and punctured the fuselage in multiple places, starting a fire in the cargo compartment.  Heavyweight with two engines out on one side at low altitude and a cargo compartment on fire is a bad way to fly.  A RAAF C-130 in the pattern first told the C-141 pilot to put it in the river off the end of the runway, and then after he managed to clear the trees and get some altitude (just a few hundred feet), the C-130 stayed overhead and called the C-141's turns to get him back to the field, as he was so low he couldn't see the field over the trees.  The shroud on one side of the #3 engine was pulled up almost vertical and embedded in the wing's leading edge above it, and the turbine and combustion chamber sections were hanging out the back end of the engine pod and drooping like the abdomen of a wasp. The investigators asked the pilot (an Air Force Reserve instructor pilot) why he pushed the two good throttles up so far (he overboosted the crap out of the #1 and #2 engines, necessitating a quadruple engine change before the plane could be recovered back to the US)--his answer: "because they wouldn't go any further."  He won the Air Medal for his actions that day.

 


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2:10 in the video. Airbus not Boeing but interesting all the same.

 

 

Edited by martin-w

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