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SWA1380 - diversion to KPHL after engine event

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SWA1380 - diversion to KPHL after engine event

Old 21st Apr 2018, 22:31
  #361 (permalink)  
 
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Wound down sure. Absent a shaft brake or lock, what does windmilling do in such a circumstance?
The windmilling vibration loads are still tremendous - the FAA has made Boeing show that the rest of the aircraft can readily handle the blade out vibrations for an extended ETOPS diversion - it wasn't trivial.
One story was that after a blade out event on a 747, the aircraft vibrations were so severe the crew had difficulty reading the flight deck gauges (one variation of the story - perhaps antidotal - was that there was a Boeing exec on the flight - after the flight he promptly asked engineering to go make sure the aircraft could handle that level of vibration..)
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Old 21st Apr 2018, 23:46
  #362 (permalink)  
 
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The windmilling vibration loads are still tremendous - the FAA has made Boeing show that the rest of the aircraft can readily handle the blade out vibrations for an extended ETOPS diversion - it wasn't trivial.
The load on engine mounts and wing structure can be significant. For an extreme case- check out whirl mode on the Electra problem/flutter due to 'engine mount ' failures. Sufficient to tear off a wing in a few seconds. Granted the current problem was different in many respects- but the point of high frequency vibrations on structure is real . For low frequency vibrations caused by simple aero loading and what they can do without damping - google galloping gertie.
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Old 22nd Apr 2018, 00:01
  #363 (permalink)  
 
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Originally Posted by Concours77 View Post
PineappleFrenzy.

Wound down sure. Absent a shaft brake or lock, what does windmilling do in such a circumstance?
Windmilling simply adds more opportunity for parts to shake loose. It also stresses the airframe.

Given the lack of vibration depicted in video of the SW1380 incident, I'd say the engine wasn't windmilling at all. The first two videos below show what it's like inside an airplane with a windmilling but unbalanced engine.

As seen in previous catastrophic engine failure events, often the initial shaking caused by an unbalanced high speed rotating mass is so strong that the engine simply sheds its exterior components (see the third video), if it isn't ripped from the pylon altogether. Even when blades remain within the containment ring, and even if friction prevents the engine from windmilling, it certainly seems possible for a piece of the cowling to catch the airflow at just the right angle to lead it directly into the side of the plane and damage a window as the engine winds down.

AirAsia X D7237:

United 1175:

Exterior shot of United 1175:

Last edited by PineappleFrenzy; 22nd Apr 2018 at 00:36.
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Old 22nd Apr 2018, 01:45
  #364 (permalink)  
 
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tdracer

the FAA has made Boeing show that the rest of the aircraft can readily handle the blade out vibrations for an extended ETOPS diversion - it wasn't trivial.
One story was that after a blade out event on a 747, the aircraft vibrations were so severe the crew had difficulty reading the flight deck gauges (one variation of the story - perhaps antidotal - was that there was a Boeing exec on the flight - after the flight he promptly asked engineering to go make sure the aircraft could handle that level of vibration..)
The FAA also included all other plane manufacturers as well in the assessment. Tis true some interesting windmill events did occur but they were all associated with the loss of the engine front shaft support and did not otherwise degrade other critical structures or the ability to fly the aircraft.. Nevertheless the loads developed were well within the design loads for manuever and gust loading in the aircraft certification base.

The worst part of it was that the passengers were not happy as the aircraft went through a critical windmill speed range while landing.

As for reading the flight deck instrumentation we confirmed that the crews could fly the aircraft with no problem. We got one famous chap to sit on a laboratory shake table and cranked it up to the expected frequency and amplitude for a time and he had no complaints and slept for days afterwards.
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Old 22nd Apr 2018, 02:39
  #365 (permalink)  
 
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Insight on Acting Gov Managers...

Originally Posted by MarkerInbound View Post
The FAA has an "acting" -

Administrator
Deputy Administrator
Chief of Staff
Associate Administrator Airports
Assistant Administrator Finance and Management
Assistant Administrator Next Gen

And on and on. The previous manager for Engines and Propeller Standards died a couple years ago. Ms Grant has been in that office all this century. They probably don't want to make her position official as she'd go up a notch in pay.
Not really germane to the rampant speculation on this event; but...

Gov employee here (not FAA or NTSB, but another federal safety regulator). While 17+ years seems kind of long in my experience (has she really been an actor in that role for that length of time, or are you extrapolating her time in service with the FAA to that one position - people do move around a lot in Fed agencies), acting managers are a fact of life in government service. It takes time to post, interview, hire (most often from within) for a management position in a Fed agency. Also, there are generally time limits on how long one can act in a higher-graded position without receiving the higher-grade pay.

Most of us - even the managers - are competent professionals just trying to do our part to serve the public. This even applies to the political appointees (although I'll grant it 's become more of an exception in the last year or so ). I thought Chairman Sumwalt did a fine job in the media briefing posted earlier.

Back to lurking. Thanks to the many professionals who make this site such an engaging read for this wanna-be aviator.
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Old 22nd Apr 2018, 05:33
  #366 (permalink)  
 
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Originally Posted by Concours77 View Post
PineappleFrenzy.

“Given the delay between the initial blade failure and the window failure, I think the evidence available supports the hypothesis that pieces of the cowl, or other secondary debris struck the window as the unbalanced engine wound down...”

Wound down sure. Absent a shaft brake or lock, what does windmilling do in such a circumstance?
I don't think we really know how much of a delay there was between the blade failure and the window failure. Passengers have stated that there was some delay between the initial explosion and the masks dropping, and another delay between the masks dropping and the passenger being sucked out, but how reliable are those accounts, and how much of a delay? Even if that is an accurate chain of events, and a short span elapsed between each, I don't think that eliminates the possibility of something (partial fan blade or other material) from the initial event hitting the window. It would seem a glancing blow could have caused a crack or small hole, which as it spread caused cabin pressure to go down/masks to drop, before failing completely. Am I wrong? Unless they find the pieces (highly unlikely), I doubt if they will ever determine exactly what caused the damage.
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Old 22nd Apr 2018, 05:48
  #367 (permalink)  
 
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Unless they find the pieces (highly unlikely), I doubt if they will ever determine exactly what caused the damage.
They found paint transfer marks on the fuselage, so it's pretty much established that parts of the nacelle impacted the fuselage.
It should be fairly straightforward to determine if the damage around the paint marks correlates with the window failing.
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Old 22nd Apr 2018, 06:01
  #368 (permalink)  
 
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Originally Posted by DaveReidUK View Post
I don't see many posters maintaining that the departing blade struck the window, particularly in view of the NTSB's early finding that no window fragments were found inside the cabin.
Well I have responded to several - it does seem to be a common assumption. Not sure what the relevance of window fragments would be as they wouldn't confirm blade impact or impact by parts of the nose or fan cowl.

FWIW my money is still on the fan cowl..
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Old 22nd Apr 2018, 08:09
  #369 (permalink)  
 
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Originally Posted by PineappleFrenzy View Post
Given the lack of vibration depicted in video of the SW1380 incident, I'd say the engine wasn't windmilling at all. The first two videos below show what it's like inside an airplane with a windmilling but unbalanced engine.

AirAsia X D7237:
https://www.youtube.com/watch?v=_J5QsbA_QzQ

United 1175:
https://www.youtube.com/watch?v=f2TEJbm-HE4
I'm not sure you can make a direct comparison between the out-of-balance forces produced by a windmilling Trent or PW4xxx compared to a CFM56.
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Old 22nd Apr 2018, 08:23
  #370 (permalink)  
 
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Originally Posted by lomapaseo View Post
PineappleFrenzy



yes it's hard to believe

The blade loss video show large motions at the inlet, but motion alone is not enough. You have to couple it with mass and rate of change.

The even more challenging forces are gust loads in extreme turbulence or aircraft upsets and these don't end up like what you see in the pictures. As long as the inlet remains a box structure designed to aircraft principals it will hold up through all types of loadings.
You get some interesting aeroelastic effects at higher IAS. So it's not just about the structure witholding the fan when it fails. Those blade off tests don't show incoming air at around 250-270kts IAS. Only takes a part to become partially detached into the airflow and it will start to tear apart. Even if it witholding the fan, the weakened structure may struggle to stay attached. Be more concerned what could happen if the cowl, accelerated in the air flow, were to impact the vertical or horizontal stab.
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Old 22nd Apr 2018, 10:13
  #371 (permalink)  
 
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In this news article http://www.bbc.com/news/world-us-canada-43804253
I saw this quote:
For a few seconds, the aircraft rolled to an angle of 41 degrees before levelling out and starting an emergency descent, federal investigators said on Wednesday.
Does that sound right? Haven't seen it mentioned in this thread or anywhere else. If true it seems like quite a significant roll. What would cause that?
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Old 22nd Apr 2018, 10:16
  #372 (permalink)  
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Yaw.
......
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Old 22nd Apr 2018, 10:46
  #373 (permalink)  
 
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Originally Posted by Chesty Morgan View Post
Yaw.
NTSB board member Robert Sumwalt said during one of the briefings that the bank angle reached 41.3 degrees (or was it 41.5?). He then proceeded to say that your first reaction would be to grab the yoke and correct it. Since he was an airline pilot for 24 years, I doubt he would have confused bank angle with yaw. Certainly one of the staffers may have given him misinformation, but it doesn't sound like it. (Edit: I misunderstood Chesty's terse answer. My apologies.)

Link to relevant portion of briefing
The aircraft began a rapid uncommanded left roll of about 41 degrees of bank angle. So usually when you're flying on an airliner you rarely get over about 20-25 degrees of bank. This went over to 41 degrees. The pilots leveled the wings.
Then during the Q&A one of the reporters asked him about the roll and he elaborated:

Last edited by core_dump; 22nd Apr 2018 at 11:01.
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Old 22nd Apr 2018, 10:55
  #374 (permalink)  
 
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[QUOTE= Since he was an airline pilot for 24 years, I doubt he would have confused bank angle with yaw. But certainly one of the staffers may have given him misinformation.
I found that tidbit during the briefing very interesting as well.[/QUOTE]

following the question
"If true it seems like quite a significant roll. What would cause that? "

and answer "yaw"

What Chesty Morgan (of few words) probably meant was that engine failure causes asymmetric loss of thrust which causes yaw towards the failed engine, and the yaw coupled with wing sweepback causes significant ROLL
QED
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Old 22nd Apr 2018, 11:32
  #375 (permalink)  
 
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Originally Posted by jaytee54 View Post
What Chesty Morgan (of few words) probably meant was that engine failure causes asymmetric loss of thrust which causes yaw towards the failed engine, and the yaw coupled with wing sweepback causes significant ROLL
Those considerations apply, of course, to any engine failure in a twin.

How many of those result in rolling almost halfway to the vertical ?

While Chesty's succinct responses are always to be admired, in this case a few more words of explanation might have helped ...
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Old 22nd Apr 2018, 11:59
  #376 (permalink)  
 
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Originally Posted by DaveReidUK View Post
Those considerations apply, of course, to any engine failure in a twin.

How many of those result in rolling almost halfway to the vertical ?

While Chesty's succinct responses are always to be admired, in this case a few more words of explanation might have helped ...
Normally when you have gotten up to the point where you are talking to center (at the higher altitudes), things are fairly relaxed (George, the autopilot is doing its thing) and direct hands-on-the-yoke is several minutes in the past. A bang and shudder takes a few seconds to determine something serious has gone wrong, and may have even gotten both sets of eyes on the engine instruments, attempting to decipher exactly what had happened, with feet not on the rudder peddles.

With those big fat dumpsters out on the wing, the drag, assuming the fan stopped fairly quickly, could be a tremendous yaw/roll.

On takeoff, your concern is complete control if such an event happens at low speed, as the ground is right there waiting, so hands and feet at literally on or near the controls on both sides. At altitude, the crew thought process is much more relaxed.
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Old 22nd Apr 2018, 13:13
  #377 (permalink)  
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I suspect not many happen near top of climb, probably feet up, with a coffee.

15 words! I’m done in
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Old 22nd Apr 2018, 14:31
  #378 (permalink)  
 
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Originally Posted by OddballM4 View Post
This even applies to the political appointees (although I'll grant it 's become more of an exception in the last year or so ). I thought Chairman Sumwalt did a fine job in the media briefing posted earlier.
He is probably the best chairman the NTSB has had. He was elevated to chairman by the present administration. Bob is a former airline pilot and ALPA safety rep. He also has an abundance of common sense and tact.
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Old 22nd Apr 2018, 14:43
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TNX for the education Chesty and others.

I was surprised at the amount of roll, but I guess with the motors at near-full thrust that the lack of thrust on one as well as increased drag from the damage was enuf. Also was prolly a fairly low "q" so aero authority of vertical stab likely low.

Yaw can cause significant roll even in straight wing planes depending on engine alignment with the aerodynamic longitudianl axis and not necessariy the physical. So you can get decent roll even on symmetrical thrust twins, and I flew one that required immediate full rudder and pulling the good engine back from mil thrust. Lost two folks on single engine go arounds because of that, especially if they were pullng back on the stick to get the nose up.

On the bent wing planes, the roll due to yaw can be extreme. Flying some fighters, we used nothing but rudder for roll when at high AoA, with stick locked between your knees. But 41+ degrees of roll within seconds at that stage of flight would sure get my attention, heh heh.

Gums sends...
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Old 22nd Apr 2018, 20:21
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Dangerous, but I'm going to make some assumptions. Engine failure, yaw, roll, autopilot tries to keep wings level with ailerons and control column goes to full scale PDQ. No doubt there was quite a bang. Autopilot lets go and a/c rolls. That would happen in only a few seconds. The startle factor must have been severe.
I wonder who was PF, but if I was captain I think I would have my hands and feet doing their thing. That in itself would be interesting if F/O (as PF) was also doing his thing. Knowing who had control would be essential, quickly.
One engine out FL325 means immediate descent, perhaps at idle to help control the yaw/roll. That needs ATC coordination/communication. A drift down in the scenario was highly unlikely.
Somewhere during the analysis of the engine bang they were then presented with the cabin ALT warning, then emergency descent.
This is worse than a bad hair day, and indeed at Gums says, idle thrust on the live makes life easier. They did have lots of height.
I'll be curious when/if they re-engaged the autopilot to reduce work load. The idle thrust on live + drag on sev damage engine would still give some yaw/roll problems, but rudder trim should have been enough to help the autopilot.
This really would have been a scenario of ANC & priorities.

I was curious, in the NTSB briefing, how he mentioned, and repeated the landing speeds for F30/40 landing; explaining their F5 landing was 30kts faster than normal. Difference between F5 & F15 is 10kts.

Good to hear the CVR/FDR and crew debriefing is underway expeditiously.
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