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Boeing 777 Engine blade / failure Crew management & technical

Yup, pretty serious

Unfortunately the people that knew the trade and cared have been retired or kicked out in favor of corporate greed.

Hopefully the corporate people and their stock holders will be flying these crates

Who is John Galt?
 
This might be of some interest regarding a previous blade failure on a B777. Aircraft suffered engine failure and was forced to return to Hawaii.

Very serious situation with aircraft control.

Some very good info regarding cockpit automation and crew management/human factors. The Captain is being interviewed by a current B777 first officer.

Capt. Behnam UAL#1175 Fan Blade Out Event INTERVIEW - YouTube


Thanks, very interesting interview.

He has a very good recommendation at 46:00, also the reason why there will never be pilotless passenger flights...
 
I didn't have the time to watch the video but I thought that incident was an amazing example of just how safe those engines actually are. The facts show the engine tossed a blade out and the whole thing was completely contained and the plane made it safely back and no one was hurt.

Years back I interviewed in the test group of Pratt and Whitney in Middletown Connecticut. One of the tests that my role would have been responsible for was a test where they mount an explosive charge on the root of a fan blade running at max takeoff speed. The explosion breaks the blade free and then the entire structure needs to contain all debris and keep them from entering the cabin. They showed me some videos of the test being run and it was really cool. Talk about containing a lot of energy! The fact that that aircraft returned to the ground safely was no accident but rather the result of a great crew and a lot of hard working engineers. If memory serves me correctly GE had a similar incident not long ago on a CFM-56 and the blade pierced the cabin and a passenger was sucked out to her death.

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This is all al fine example of "boy things are really good, but they're far from perfect"

In the Benham episode, the engine event was NOT completely contained - some fragment smacked the fuselage - but in a place that didn't rupture a window or the skin, and didn't destroy a stringer or longeron. Had it hit higher, or lower, would have been much worse. Had it hit any part of the tail would have been much worse.

There was a crash of prop cargo plane (I wanna say an HC130) where they lost a prop blade. That alone wasn't a problem, except it made so much vibration that other engine parts failed, and one of them destory a longeron, and the airplane came apart. So the Benham accident was maybe closer to utter disaster than it may appear - which is chilling given how difficult it was for a very well prepared crew to deal with the incident.

The Benham accident was over open ocean - very low odds of hitting anything. The Denver incident (just a couple weeks ago) dropped heavy objects all over populated areas, and by great luck no one on the ground was killed, but vehicles were destroyed, etc.

And on 22 Feb in the netherlands a 747 engine failed, dropped some debris, and people in the ground were injured.

Yes, all of these jet failures were "good" in the sense that they caused far far fewer fatalities than crashing the plane into a large crowd, but they were all super perilous. And the SWA accident killed a passenger (sucked out the window) - zilch the crew could do.

So just because something has become very good does NOT mean it should not be subject to constant vigilance, or it that it cannot be even better.
 
At full RPM I would imagine the centrifugal force at the root of the blade has to be tens of thousands of pounds. Anyone know the actual engine RPMs, blade weights and forces involved?
 
At full RPM I would imagine the centrifugal force at the root of the blade has to be tens of thousands of pounds. Anyone know the actual engine RPMs, blade weights and forces involved?
I think that was the big PW4000 so it would base 112in dia of total fan blades. A quick googling shows people discussing that they spin somewhere between 3-4000rpm so yea a lot of energy. Here's a video of the test that they do with throwing a blade.
https://youtu.be/wcALjMJbAvU

It makes one wonder if the tests they do with a stationary engine on a stand is really equal to one flying forward at a few 100mph as the lateral forces one would think may be higher. But then again even on a pad that engine is still going to be moving a lot of air.

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At full RPM I would imagine the centrifugal force at the root of the blade has to be tens of thousands of pounds. Anyone know the actual engine RPMs, blade weights and forces involved?

Fan section normal operating range RPM is ~3,000 RPM.
Fan blade weight is in the 50# ballpark.
Centripetal force is in the 50-100T ballpark.

Regards.

Mike
 
His account of the roll/yaw/vibration is hard to imagine and probably a gross understatement.

We had a compressor stall in a 767 at climb thrust and the airplane immediately yawed 30*, my first thought was that we hit a small airplane.
 
Yes that was the bad part how hard the plane was to fly with all that drag on one side
Once it came apart it became even more of a drag, there wasn’t a smooth nacelle there any more.
One has to wonder if they actually test flew it with a completely dead engine, not just at idle.

Probably not just a Boeing problem either, more of the large fan jet power twins.
Might should be rethinking the more than 2 engine rule over water.
 
On steam turbine blades, the fir tree roots (where still used) are milled. Pinned roots are actually more reliably and stronger for most blades, but the large blades still need fir tree roots because the roots are curved and the blades have to be driven in 'around the bend'

Coincidentally, on our 42" last row blades, which were the largest steel blades we did before going to titanium alloys, the centripetal force at 3000rpm was 1000 long tons per blade...
 
Coincidentally, on our 42" last row blades, which were the largest steel blades we did before going to titanium alloys, the centripetal force at 3000rpm was 1000 long tons per blade...

Mark, how did your engineers deal with stress life calculations when going from steels to Ti blades? My "fake engineer" understanding is that below a certain stress level, steels have a near-infinite fatigue life, but Ti does not, and so must be monitored much more carefully for the onset of cracks.
 
Mark, how did your engineers deal with stress life calculations when going from steels to Ti blades? My "fake engineer" understanding is that below a certain stress level, steels have a near-infinite fatigue life, but Ti does not, and so must be monitored much more carefully for the onset of cracks.

Even though the Ti does not have an infinite fatigue life, the stress-life curve flattens out as you get towards infinite number of cycles. Therefore the allowable stress for a Ti blade at 10^8 cycles is only going to be a bit higher than at 10^9 cycles which will only be a bit higher than 10^10 cycles. You can do some testing on a bunch of coupons at different stress levels and get the curve shape, then do some statistical reductions on it and get a stress level that will not fail at 10^10 cycles (roughly the number a fan blade will see). The testing is very expensive though as it takes a long time to accumulate that number of cycles and you need to test alot of different configurations.
 
I’m not referring to the P&W fan blade failure here, but rather to the comments about fatigue cycles. In the broad context of turbomachinery, the chief killer of blades is fatigue under conditions of resonant vibration.

Any turbo-machine blade has a number of natural vibration frequencies, corresponding to various modes of vibration. The first mode is usually simple bending. Think of the blade as a vibrating tuning fork. Higher modes involve higher frequencies, but with lower amplitudes of vibration.

In the case of a steam turbine, for example, the natural frequency of short blades in the high pressure stages in the first mode will be several thousand Hz. For the long last stage blades, the natural frequencies in the first few modes may be of the order of a few hundred Hz.

If a blade happens to be excited at one of its resonant frequencies by periodic steam or gas forces, it won’t take long to accumulate 10^8 or more cycles. If the excitation force at a critical resonant frequency is high, then the alternating stress may be above the endurance limit, leading to failure. If the alternating stress (actually the combination of alternating and mean stress) is high enough, then failure may occur at a very much lower number of cycles.
 
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Given the 2 incidences of the fan blade failures it might be that there needs to be
An absolute max life less than that of the 2 recent failures.
It would appear that the current inspection regiment isn’t adequate.
Quite a bit of stuff that needs to be looked at
 
Given the 2 incidences of the fan blade failures it might be that there needs to be
An absolute max life less than that of the 2 recent failures.
It would appear that the current inspection regiment isn’t adequate.
Quite a bit of stuff that needs to be looked at

Perhaps a mandatory blade replacement, then each of the removed blades undergoes a thorough NDT procedure, anything at all questionable is rejected, and ones that pass go into the next swap pile?

I also wonder if the blades can be redesigned to strengthen the area above the root, where the latest blade broke. More mass, but close enough to the center of rotation to not contribute enormously to centrifugal stress?
 
It's not even just having two engines, it's having a damaged (and out of balance) engine freewheeling and setting up massive stresses in the wing.

My understanding is that the engine/pylon mounting system is supposed to be "brittle", and if vibrations are at a level when structural damage to the wing can occur the engine's supposed to separate, but I'm not sure how much I trust this.

I wonder if something like a shot pin or other locking mechanism could be used to stop the turbines from rotating and creating the OOB stress. But it would have to be foolproof to prevent inadvertent activation.
 

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