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SWA1380 - diversion to KPHL after engine event

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SWA1380 - diversion to KPHL after engine event

Old 22nd Apr 2018, 23:20
  #381 (permalink)  
 
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Originally Posted by RAT 5 View Post
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 suspect also, as alluded to by Gums, that the effect on L/D of the nose cowl being shredded and subsequently departing was a significant factor contributing to the degree of uncommanded roll, compared to an everyday engine failure.
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Old 23rd Apr 2018, 13:41
  #382 (permalink)  
 
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Article about ADs and SBs in MRO:

EASA, FAA Issue Emergency ADs For CFM56-7B Inspections | MRO Network
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Old 23rd Apr 2018, 17:56
  #383 (permalink)  
 
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https://dynaimage.cdn.cnn.com/cnn/li...ef66c7bbdf.jpg

From the peeling forward of the lapped inner skin of the inlet and the clean departure of the honeycomb in circumferential and crisp fashion, I would think the structures were “blown out” forward. That would make a blade separation a result of, and not the cause of the severe damage....
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Old 23rd Apr 2018, 19:17
  #384 (permalink)  
 
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Originally Posted by Concours77 View Post
From the peeling forward of the lapped inner skin of the inlet and the clean departure of the honeycomb in circumferential and crisp fashion, I would think the structures were “blown out” forward. That would make a blade separation a result of, and not the cause of the severe damage....
How does the evidence of fatigue at the root of the departed blade fit in with that scenario ?
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Old 23rd Apr 2018, 19:40
  #385 (permalink)  
 
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Originally Posted by Concours77 View Post
https://dynaimage.cdn.cnn.com/cnn/li...ef66c7bbdf.jpg

From the peeling forward of the lapped inner skin of the inlet and the clean departure of the honeycomb in circumferential and crisp fashion, I would think the structures were “blown out” forward. That would make a blade separation a result of, and not the cause of the severe damage....
Originally Posted by DaveReidUK View Post
How does the evidence of fatigue at the root of the departed blade fit in with that scenario ?
Also, Concours77, what do you think could "blow out" the front of the engine in such a way that it only damages part of the cowling, which is a relatively weak material, but then is also powerful enough to snap off a fan blade, which is very strong indeed unless there already is a fatigue crack.

The only think I know which "blows out" of the front of the engine would be a surge, but these rarely damage the engine, although they can be spectacular. I can't imagine that one would ever blow out a fan blade.

Bernd
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Old 23rd Apr 2018, 19:55
  #386 (permalink)  
 
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Originally Posted by OddballM4 View Post
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.
Just to clarify, Ms Grant has been in the Engine and Propeller Standards branch of the FAA for 15 plus years. She appears to have assumed the duties of acting Director after the death of the previous manager in 2015.

Climber314 seemed to imply that her "acting" status may have been due to fallout from the SW accident and I was just pointing out that most of the FAA senior management is in acting positions.
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Old 23rd Apr 2018, 20:47
  #387 (permalink)  
 
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Originally Posted by DaveReidUK View Post
How does the evidence of fatigue at the root of the departed blade fit in with that scenario ?
It makes the surge theory case; a surge causes a loss of, and an instantaneous reaction to the peak thrust at top of climb....

IF the blade is compromised by patent fatigue, it suggests the rapid and emphatic change in gas path could cause sufficient failure to further crack the flaw, and exacerbate the separation.
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Old 23rd Apr 2018, 20:51
  #388 (permalink)  
 
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Originally Posted by bsieker View Post
Also, Concours77, what do you think could "blow out" the front of the engine in such a way that it only damages part of the cowling, which is a relatively weak material, but then is also powerful enough to snap off a fan blade, which is very strong indeed unless there already is a fatigue crack.

The only think I know which "blows out" of the front of the engine would be a surge, but these rarely damage the engine, although they can be spectacular. I can't imagine that one would ever blow out a fan blade.

Bernd
It wouldn’t have to be powerful enough to blow out an (undamaged) fan blade, only sufficiently robust to snap an already cracked one. An important piece of evidence is the character of the “bang”. Never present at an actual blade separation, but I have experienced a very impressive surge in a DC-10 (Mexicana, forty years ago). Number two. A LOT of flame, and a very loud “boom”.
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Old 23rd Apr 2018, 21:21
  #389 (permalink)  
 
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Concours, losing a fan blade will invariable cause a surge (go look at the videos of fan blade out testing a few pages back).
Cause and effect is 99.99% that the surge was a result of the blade release, not the other way around...
Also, healthy CFM56 engines very seldom surge. Oh, and the number 2 engine on the DC-10 was notorious for surging during climb - flow distortion from the fuselage at higher angles of attack.
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Old 23rd Apr 2018, 21:36
  #390 (permalink)  
 
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Originally Posted by tdracer View Post
Concours, losing a fan blade will invariable cause a surge (go look at the videos of fan blade out testing a few pages back).
Cause and effect is 99.99% that the surge was a result of the blade release, not the other way around...
Also, healthy CFM56 engines very seldom surge. Oh, and the number 2 engine on the DC-10 was notorious for surging during climb - flow distortion from the fuselage at higher angles of attack.
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Old 23rd Apr 2018, 22:03
  #391 (permalink)  
 
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Originally Posted by Concours77 View Post
It makes the surge theory case; a surge causes a loss of, and an instantaneous reaction to the peak thrust at top of climb....

IF the blade is compromised by patent fatigue, it suggests the rapid and emphatic change in gas path could cause sufficient failure to further crack the flaw, and exacerbate the separation.
Interesting theory, could be true, but Occam's Razor points to a more obvious sequence of events starting with failure of a weakened blade.
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Old 23rd Apr 2018, 23:43
  #392 (permalink)  
 
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Furthering Councours77's musing:
Evidence of pre-existing fatigue damage does not *necessarily* mean that the fatigue failure was primary. It's entirely plausible that some external factor caused loading to the blade in excess of what the remaining material could support, at which time it would fail at the fatigue site and expose the defect.

You'd want to do some analysis -- normally you can tell what part of a fracture face was progressive and what part was sudden, assuming it's not too bashed up by subsequent events. In the state the blade existed in just before the failure, was the remaining strength enough to withstand the normal operating forces (within some reasonable tolerance)? This is a fairly simple calculation.

If it's near the margin, then the most likely scenario is indeed that the fatigue fault grew until time ran out and the blade snapped off under normal (-ish) loads. If it should have still held under normal conditions, even in its degraded state, then you'd need to look for additional precipitating conditions.

What those conditions might be goes into pure uninformed speculation (on my part at least). A whopping surge prematurely disassembles part of the inlet, say, and re-ingested debris whacks the weakest blade?

I understand the general thinking is that a surge should not fracture a blade -- but what if it were approaching the point where it was going to come off soon? Here's a question: is a surge symmetrical (or maybe I should say circumferentially uniform)? During a surge event, does a given blade rotate through drastically different aerodynamic conditions as it spins around? How many revs are made during the typical duration of the upset flow? I think I've seen in the FBO test videos I've watched that sometimes the visible exit of combustion gases through the fan is asymmetrical, at least for part of the event. That would create a cyclic load that is (probably) much different than the design loads.

For that matter, under normal operating conditions, is the pressure/velocity uniform circumferentially around the fan? I can imagine it might not be, especially under large AOA (thinking about a simple prop clawing through the air in climb attitude).

I agree that the simplest and cleanest scenario is that the blade failure was primary, but there are things about that which nag at me. Not the least of which being that this event doesn't seem to conform to what is seen in static blade-off testing. Relying on a testing regime that *may* not accurately capture real-world failure scenarios is not a comfortable place to be.

For the record, I'm neither a pro pilot nor an aviation engineer, but I am a mechanical engineer who has too many years of this sort of failure analysis under my belt. And because of that I am still in awe of the detail and quality of the investigations the NTSB does!

Looking forward to what the professionals say when it's all wrapped up. Back to lurking and learning.
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Old 24th Apr 2018, 02:11
  #393 (permalink)  
 
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I see a lot of bubble and boil going on here, so I'll drop another onion into the soup.
Blades that fail in fatigue do so under the loads of combined stress between tensile-bending and cyclic high frequency fatigue (Goodman's diagram).

As such any pertubation in the rotating arc of the blade, e.g. probes in the case add just a tiny bit of stress which while not being causal of the fracture does statistically pick the clock location where it does fracture. Thus for a given fleet problem, statistically most blade fractures will occur at the same clock location
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Old 24th Apr 2018, 18:48
  #394 (permalink)  
 
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Originally Posted by lomapaseo View Post
Thus for a given fleet problem, statistically most blade fractures will occur at the same clock location
I must be missing something. Every fan blade is at every clock location when the engine is running. Help me out here, what am I missing?
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Old 24th Apr 2018, 18:56
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I must be missing something. Every fan blade is at every clock location when the engine is running. Help me out here, what am I missing?
clock position refers to the stationary bits of the engine relative to the top of the engine looking from the rear.
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Old 24th Apr 2018, 19:14
  #396 (permalink)  
 
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Originally Posted by lomapaseo View Post
clock position refers to the stationary bits of the engine relative to the top of the engine looking from the rear.
I understand that part. What I don't understand is blades fractures occurring "at the same clock position." Every blade is at every clock position when the engine is running. You can't say "the blade at 2 o-clock tends to fail more often than the blades at the other clock positions". So what am I missing?
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Old 24th Apr 2018, 19:33
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Originally Posted by KenV View Post
I understand that part. What I don't understand is blades fractures occurring "at the same clock position." Every blade is at every clock position when the engine is running. You can't say "the blade at 2 o-clock tends to fail more often than the blades at the other clock positions". So what am I missing?
Allow to interfere: the numbering is done while the blades don't turn. So the blades have a number as lomapaseo states.
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Old 24th Apr 2018, 19:36
  #398 (permalink)  
 
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Ken, what loma is saying is that the failure would happen at about the same engine clock position - not the fan clock position (which as you noted is constantly changing as the fan rotates).
There a inlet probes in front of the fan for total temp (and on EPR engines, total pressure) - these create turbulence/vortices. The big concern for these has been the fan hitting those vortices makes a lot of noise - hence on new installations those probes have been pushed further forward in the inlet to give the airflow a chance to clean up before it hits the fan. What lomapaseo is pointing out is that those probe vortices also cause a once/rev stress on the individual fan blades as they pass - so if there is a cracked fan blade, it is most likely to fail as it passes through the probe wake.

I saw the report on a real severe case of this once/rev stress. A brand new GE90 (I think, it's been ~20 years) came apart during acceptance testing. Turns out part of one of the fuel nozzles hadn't been installed properly and came loose - it moved through the burner and blocked one of the stage one turbine nozzles. So first stage turbine blades saw a massive once/rev stress as they were totally unloaded then reloaded as the passed the blocked nozzle. It took something line 10 minutes at power before the first turbine blade failed
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Old 24th Apr 2018, 19:39
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Originally Posted by KenV View Post
I understand that part. What I don't understand is blades fractures occurring "at the same clock position." Every blade is at every clock position when the engine is running. You can't say "the blade at 2 o-clock tends to fail more often than the blades at the other clock positions". So what am I missing?
Lets try again-IMHO a particular spot on the fixed ( non rotating ) part of the engine casing/inlet is defined by ' clock position " The comment was made about an instrumentation device (probably a very small protrubence into the surrounding casing such as a magnetic/proximity/ device to measure rpm/temp/pressure ( approx 5000 rpm I believe ) This then could cause a minor disturbence in the airflow or a minor change in tangential/radial stress when each blade passes )

Over a period of time, given a marginally fatigued blade, this change in stress while quite small **COULD** **MAY** be sufficient to cause that blade to depart within a few milliseconds.
The point was that **IF** that is the case, then the first 'impact' point of the broken blade **COULD** be a function on fan speed and direction. so **IF** the fan speed was the same in a few cases, then the first impact point would **PROBABLY** be in the same relative clock position depending on fan direction eg 9 O'clock or 3 O'clock and x o'clock from the protrubence.

Keep in mind- the comment was re statistics and/or probability of such a comparison - NOT a fixed- proven theory.

Just my .000002 based on my injun-ear background

And after I posted this- I found tdracer comment made a few minutes before I hit save of my tome

Last edited by CONSO; 24th Apr 2018 at 19:57. Reason: update re tdracer prior post
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Old 24th Apr 2018, 20:18
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SW Emergency plan details in WSJ

https://www.wsj.com/articles/at-sout...uck-1524586032

At Southwest Airlines, the Minutes After Disaster Struck

How top management, using updates from the cockpit and passengers’ phones, put the emergency-response plan into action in Philadelphia and Dallas



By Scott McCartney

April 24, 2018 12:07 p.m. ET 59 COMMENTS

All Southwest Airlines senior executives were at a Dallas hotel for a day-long meeting on leadership development last week when suddenly phones blared in unison around the room: Flight 1380 was in serious trouble.
The team had a quick conference call with the airline’s operation center, then raced to headquarters nearby. From there they put an emergency-response plan into action.
The plan had gotten a lot of use in the past year: three hurricanes, plus mass shootings in Las Vegas and Sutherland Springs, Texas, near San Antonio. All required extensive coordination and interaction with customers. But nothing prepared executives for the kick in the gut they got when passenger Jennifer Riordan died.

goes on
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