Quite an uncontained engine failure

[Mike-Bracknell]

https://twitter.com/raulcanelos/status/769568674420297728

Kudos to the crew for bringing it down safely. :ok:

[Luther Sebastian]

Is it just me, or does it look as though all the actual engine-y parts are still intact? Like the fan and everything behind it?

[Enos]

Certainly looks like the N1 is intact, how'd they do it ? It's normally the back end that let's go not the front.

[barit1]

Quite an uncontained engine failure


The failure for all appearances is the inlet duct, not the engine proper. The engine might have continued running albeit at lower thrust. Boeing will truck in a new inlet, the engine will be changed for an overall performance check, and someone in a farm field will collect some scrap aluminum for recycling.

That's why there's another donk on the other wing.

BTW, the absurd dialogue in that link is the reason I never signed up for Twitter.

[flt001]

https://pbs.twimg.com/media/Cq40IDpUAAAcrqn.jpg:orig

Hi-res pic of damage to wing root and more scarily just below the windows.

Source: https://twitter.com/jonostrower/status/769610419988074496/photo/1

[Skyjob]

Cowling separated...?
Interesting to find out how...

[Tempsford]

It appears that The Inlet Cowl has failed structurally as the remaining part of the assembly is still attached to the Engine Fan Case. The failure appears to have gone into the Wing Leading Edge and Fuselage then left an Oval shaped impact on the Stabilizer Leading Edge.

[Safe-T]

And possible loss of cabin pressure too as pax & crew were on oxygen: https://aviation-safety.net/database/record.php?id=20160827-0

[cod liver oil]

Safely parked at the stand too :D.

[lomapaseo]

It seem that we're missing the critical evidence in the cropped pic of the fan.

Most likely the engine was involved and contained, but the bits spitting forward did the damage.


Let's see what other pics turn up

[Kubarque]

What are those two red levers? just to the left and right of top center of the nacelle and just forward of the pylon? They look like they ought to be pushed down into their slots.

[averow]

Jon Ostrower of Wall Street Journal is doing some fine reporting on this right now..
https://twitter.com/jonostrower/status/769635472205242368

[tdracer]

Some of the links in this thread don't work (at least not for me), but it appears all the fan blades are still there. About the only thing that could go wrong with the engine itself that could cause the inlet to separate would be a fan blade release and I don't see any evidence of that.
I'd wonder about a malfunction of the inlet anti-ice :confused:

[number0009]

What are those two red levers? just to the left and right of top center of the nacelle and just forward of the pylon? They look like they ought to be pushed down into their slots. I believe those just "appear" to be latches and we likely see some stress induced seam separation of the pylon or fan cowl assys. Nose/inlet cowl isn't attached using just quick release latches.
......

[johnhb]

Could this be a de ice valve stuck open overheating cowl structure?

[Ranger One]

That's a head scratcher! Never seen one do that before. Maybe took a combination... bleed air duct separation pressurizing inlet cowl and also precipitating especially violent compressor stall?

[CONSO]

from comments in
WSJ

Kathryn's Report: Southwest Airlines, Boeing 737-7H4, N766SW: Incident occurred August 27, 2016 at Pensacola International Airport (KPNS), Escambia County, Florida (http://www.kathrynsreport.com/2016/08/southwest-airlines-boeing-737-incident_27.html)

careful look at one shows minor damage to winglet !

[lomapaseo]

How many fan blades should we expect to count ?

Are we missing one complete blade?

Any large holes out of view like the bottom of the nacelle behind the fan?

I sure don't understand the passenger masks deployment if true

[Passenger 389]

I sure don't understand the passenger masks deployment if true

Have you seen the picture showing damage to the fuselage, a little below and between two cabin windows? Looks as though it may have punctured the pressure vessel. Perhaps that is why masks deployed, and flight crew commenced an immediate descent to FL100.

(Will defer to those more knowledgeable.)

[CONSO]

Have you seen the picture showing damage to the fuselage, a little below and between two cabin windows? Looks as though it may have punctured the pressure vessel. Perhaps that is why masks deployed, and flight crew commenced an immediate descent to FL100.

(Will defer to those more knowledgeable.)
That sized hole/tear would probably be enough to trigger a mask drop- even though one engine would normally be enough to maintain a relatively slow decompression to perhaps 10K feet equivalent altitude. I'm sure the eventual report will be definitive in the actual cabin pressure rate of decompression versus altitude as the plane was descending.

[ILUVHOKE]

How many fan blades should we expect to count ?

Are we missing one complete blade?

Any large holes out of view like the bottom of the nacelle behind the fan?

I sure don't understand the passenger masks deployment if true
Word I'm hearing is one fan blade completely missing.

[Riverman]

One AME's opinion making the rounds:

From what I can see, no significant portion of fan is missing, all components affected are forward of the fan. We've seen early indications of this sort of thing and it is something I've been watching for for some time but until now have yet to see it this bad.

When metal work ie. repairs/patches, are done on the nose cowl, frequently rivet ends, tails and other swarf are left behind, inside the nose cowl. The nose cowl anti-ice air swirls these bits around abrading the inside surface of the cowl - counter clockwise when viewed from the front looking back, from about the 8:00 position. The worst damage is from about the 7:00 to about the 1:00 position.

I have seen where all the rivet bucks and a significant portion of the skin have been eroded away...to a significant percentage of skin thickness. There is no external indication until a lot of the rivets at the aft end of the nose cowl are loose/smoking. Any cowl that has been repaired with blind fasteners, particularly repeatedly, could potentially have very hard cherry pulls (blind fastener components) left inside the cowl. When a nose cowl is removed/replaced, the interior is still not visible and it would be unusual (until this) to look in the locations I'm talking about. These locations are only visible when the cowl itself is disassembled. In my opinion an over-pressure of the nose cowl is highly unlikely due the size of the vent for that air.

[pattern_is_full]

My gut says this is a cowl failure due to fatigue or other wear and tear (thanks, Riverman), with an engine surge as a secondary effect (disruption of intake air after the cowl departed, or ingestion of inlet shards).

But since the NTSB has not made my gut a job offer - I'll be happy to see what the real engine detectives find out.

Certainly an - interesting - failure mode. Outer cowl separated cleanly at the bulkhead; inner cowl ripped to shreds, except where there are a couple of reinforcement struts.

[A320FOX]

The hole in the fuselage is big enough to decompress the cabin. The cabin altitude was high (aprox 6000 feet) and climbing before the failure and when the pilots started the emergency descent the auto throttles command flight idle on the #2 engine and it is then that the engine does not produce enough bleed air to keep the cabin pressurised even if the outflow valve closes completely. Then the masks fall automatically.

[number0009]

Quote:
What are those two red levers? just to the left and right of top center of the nacelle and just forward of the pylon? They look like they ought to be pushed down into their slots.
I believe those just "appear" to be latches and we likely see some stress induced seam separation of the pylon or fan cowl assys. Nose/inlet cowl isn't attached using just quick release latches.Apologize, after viewing photos in recent post must admit I was wrong.

Kathryn's Report: Southwest Airlines, Boeing 737-7H4, N766SW: Incident occurred August 27, 2016 at Pensacola International Airport (KPNS), Escambia County, Florida (http://www.kathrynsreport.com/2016/08/southwest-airlines-boeing-737-incident_27.html)

Likely fan cowl latches? Cause or effect? Doubt cause and if adjusted properly should not have released and popped up after inlet cowl separation. Will be interesting to get the answers.
......

[GoldwingSpain]

Strange in newspapers, PAX taking selfies in masks.

Southwest Airlines flight forced to divert after part of an engine was 'torn away' | Daily Mail Online (http://www.dailymail.co.uk/news/article-3761748/Southwest-Airlines-flight-Florida-forced-divert-loud-explosion-caused-engine-torn-away.html)

Oh, were all going to die, lets take a selfie !

[The Dominican]

Cowling separated...?
Interesting to find

Look up all the fines that they have paid to the FAA over the years for improper maintenance and you would be on the right track.....!

[PersonFromPorlock]

My only experience with a thrown fan blade was on a B-52H, and there the sound was a very loud 'honk', like an organ note.

[deutschemark]

The latches on top of the pylon (which is where the bleed/anti-ice duct supplies the hot air to the intake piccolo tube) are access panels, but they also act as blow-out panels (the latches unlatch and the panel) incase of overpressure in the pylon area.
The excess pressure was probably what caused the Engine Inlet to separate. Maybe due to a failed bleed valve or engine compressor surge.

[glad rag]

I'm sure there was a previous 737 th engine failure where the damage was on the rh fuselage BUT there was also damage to the left had fuselage side as well.
when it goes wrong as speed had altitude sometimes WEIRD things happen.

[Carbon Bootprint]

My only experience with a thrown fan blade was on a B-52H, and there the sound was a very loud 'honk', like an organ note.Oh my gosh, so you had to do the dreaded seven-engine approach? :E

[cooperplace]

My only experience with a thrown fan blade was on a B-52H, and there the sound was a very loud 'honk', like an organ note.

must have been loud if you could hear it in a B52!

[PersonFromPorlock]

Oh my gosh, so you had to do the dreaded seven-engine approach? http://cdn.pprune.org/images/smilies/evil.gifLife at the sharp end can be hard. :p

[PersonFromPorlock]

must have been loud if you could hear it in a B52! Loud? It woke up the gunner!

[underfire]

Quite the 'problem' I would say!

http://i65.tinypic.com/5mx30g.jpg

http://i65.tinypic.com/2z84xma.jpg



https://img.rt.com/files/2016.08/original/57c1f149c36188b95a8b45d8.jpg
Florida-bound Boeing plane diverted after engine problem | KING5.com (http://www.king5.com/tech/science/aerospace/florida-bound-boeing-plane-diverted-after-engine-problem/309665415)

[DaveReidUK]

http://www.pprune.org/rumours-news/583559-quite-uncontained-engine-failure.html

[lomapaseo]

It doesn't look like a fan blade even hit the fuselage. Looking at past southwest photos the inlet looks the worst when an engine fails.

[underfire]

Couple of good dents there...

http://www.aviationgazette.com/wp-content/uploads/2016/08/southwest_b737_n766sw_pensacola_160827_2.jpg

[hoss183]

Agreed, i dont think the blade (if there is one missing) hit the fuselage, My guess is it was was the end of the (anti-ice?) pipe which is bent back in that direction.
To me it doesn't seem to be an uncontaminated failure, rather a surge that has damaged the cowl enough for it to disintegrate.

[Terry McCassey]

Fan blades don't come off on their own - they tend to take some of their mates with them ! I can see no evidence at all of a fan set distress in the pictures I have seen.

[Hi_Tech]

This is a clear case of inner barrel of nose cowl (usually carbon fiber) failure. I have seen such a failure on RR engine. It occurs during takeoff thrust when the engine suction is highest. Once a small portion liberates from inner barrel, within no time the rest of the inner barrel and outer barrel fails due high suction produced by fan. On most aircraft it is a turnaround inspection item, to check inner barrel for any surface damage. Engineers are not supposed to stand or sit on the inner barrel for any maintenance work without a protective mat. This is applicable to most modern engines that have carbon fiber honey comb panels in the intake. Just an observation from my experience. Could be other reasons as well,

[Loose rivets]

Interesting. In all these years I've not pondered the differential pressure across the sides of the intake.

They were perhaps still in the climb at 30k' before maximum ram air.

Given the 777 gulps a tonne of air a second in the cruise, I'd not be surprised if this wasn't a major factor.

So, all those pretty girls standing in engines for promotional photos have heel protectors?.

[Yamagata ken]

Recent flight on a humid day I was sitting just forward of the intake. It was fascinating to see a low pressure condensation cloud form just in front of- and around the intake. That included a mini-spiral tornado reaching from the ground. Physics is a wonderful subject. I wish I were better at maths.

[hunbet]

In the first picture it is an L1011 and you can't see the intake and the second you can see the protective mat !

[Chris2303]

Did they find any debris on the ground?

[TriStar_drvr]

Did they find any debris on the ground?

It was over the Gulf of Mexico.

[Hi_Tech]

Here is the example of what can happen when intake fails. This one did not disintegrate completely like south west B737. But engine ingested enough debris to cause severe damage. Damage to intake are rare and are usually spotted during turnaround inspection.

http://www.pprune.org/attachment.php?attachmentid=865&stc=1&d=1472550670

[waggie]

Looking at the numbering on the Fan Blades the Engine can still be Rotated, which if there was any sort of Blade Failure would be impossible.

[sockfocksAP]

I'm thinking a compressor surge as a likely candidate for the cause of the inlet failure. It appears most if not all N1 blades appear intact. No sign of breech in the rotational plane of N1 disc. No visible indication of bird strike. What other force could drive the debris to contact the fuselage and winglet?

[pattern_is_full]

sockFAP - "What other force...?" Ram air into the front of the intake. Emphasis on the "RAM."

Like a balloon popping, if the intake loses structural integrity ("comes apart") through fatigue or whatever other fault, the pieces will tend to shoot off in all directions in whatever is the "path of least resistance." With ram air coming in from the front, and a fairly solid chunk of nacelle and engine behind, that path will be mostly sideways.

Think of a plastic or paper cup, mounted at its base onto something solid. Direct a firehose into the open mouth of the cup, and it will fan out sideways as it comes apart.

[barit1]

hunbet:In the first picture it is an L1011 (red uniform)

Nope - Fan rotation is opposite of a RR engine. (EDIT:) MY BAD! I think my eyeballs have optical reversal!

DaveReidUK below is correct!

[DaveReidUK]

Beg to differ, it looks exactly like an RB211-22B to me.

Or if that PSA girl is standing in a 727 or DC-9 intake, she's extremely short. :O

[lomapaseo]

You're both confused, those are turbines not fans

You can tell because you're looking at rear ends :)

[barit1]

lomapaseo: Agreed!

[TURIN]

What engine? ;)

[Longtimer]

A classic "Chicken and Egg" puzzle. Which came first, the blade separation causing the cowling failure or ..... the cowling failure causing the blade separation?

Investigative Update Provides Initial Findings in Investigation of Uncontained Engine Failure http://www.ntsb.gov/news/press-releases/Pages/PR20160912.aspx
________________________________________

September 12, 2016
WASHINGTON — As part of its ongoing investigation of an Aug. 27, 2016, uncontained engine failure on Southwest Airlines flight 3472, the National Transportation Safety Board issued an investigative update Monday.

The uncontained engine failure happened on a Boeing 737-700 enroute from New Orleans, Louisiana, to Orlando, Florida. The airplane was diverted to Pensacola International Airport, Pensacola, Florida, and safely landed without further incident.
The investigative update details the NTSB’s initial findings from the examination of the airplane and the engine, and a metallurgical examination.
Initial findings from the examination of the airplane include:
o The left engine inlet separated from the engine during the flight. Debris from the engine inlet damaged the airplane fuselage, wing and empennage,
o A 5-inch by 16-inch hole was found in the left fuselage just above the left wing,
o No fan blade or inlet material was found in the hole and the passenger interior compartment was not penetrated, and
o During the accident sequence, the airplane experienced a cabin depressurization.
o The aircraft maintenance records are being reviewed.

Initial findings from the engine examination include:
o One fan blade separated from the fan disk during the accident flight and
o The root of the separated fan blade remained in the fan hub; however, the remainder of the blade was not recovered.

Initial findings from the metallurgical examination conducted in the NTSB Materials Laboratory include:
o The fracture surface of the missing blade showed curving crack arrest lines consistent with fatigue crack growth. The fatigue crack region was 1.14-inches long and 0.217-inch deep,
o The center of the fatigue origin area was about 2.1 inches aft of the forward face of the blade root. No surface or material anomalies were noted during an examination of the fatigue crack origin using scanning electron microscopy and energy-dispersive x-ray spectroscopy, and
o The blades are manufactured of a titanium alloy and the root contact face is coated with a copper-nickel-indium alloy.

NTSB Senior Aviation Investigator Tim LeBaron, the Investigator-in-Charge, is leading a team with expertise in the areas of airworthiness, powerplants, and metallurgy. The flight data recorder and the cockpit voice recorder were shipped to the NTSB Recorder Laboratory and the data from each were downloaded.
Parties to the investigation include the Federal Aviation Administration, Southwest Airlines the Southwest Airlines Pilots Association, and CFM International. The French Bureau d’Enquêtes et d’Analyses pour la sécurité de l’aviation civile has appointed an accredited representative who is supported by a technical advisor from Safran Aircraft Engines. CFM International is a joint venture between GE Aviation [US] and Safran Aircraft Engines [France].
Future work will include 3-D measurements of the contact areas of all the blades, a non-destructive examination of the blade surfaces for cracks, and a review of the engine maintenance records.
The accident docket, containing factual group reports and other investigation-related material, will be opened at a future date. Additional information will be released as warranted.

[lomapaseo]

Not much of a puzzle with the scrape marks in the inlet if the fan blade pieces traveled across the fractured edges of the cowl.

It did take quite a bit of time to come out with the fact of a missing blade :)

The rest of the story reverts now to the engine analysis experts and the inlet designers under engine rundown and windmill conditions.

[ILUVHOKE]

See post #21. Officially it did take some time, however, the info was out there:cool:

Will be interesting to hear the detailed analysis.

[lomapaseo]

See post #21. Officially it did take some time, however, the info was out there

Well from day 1 it was obvious from the pics if you counted blades and noted that you could see right though to the vanes behind the fan in one quad. Also the tracks in the inlet cowl were quite evident.

With some sleuthing of pics you could even make out the hole at the bottom of the nacelle.

What gets fixed and how is of the interest now

[RealUlli]

(Disclaimer: SLF here)

I'm not sure if it is of interest here, but I found a transcription of the ATC communication during the event on Youtube. It's not based on real ATC tapes, just LiveATC recordings, but I think it's interesting.

https://www.youtube.com/watch?v=3mJCI-NCxoI

What do you think?

[sandos]

Why the open mic all the time? There is a lot of it?

[KenV]

Why the open mic all the time? There is a lot of it? Probably a case of muscle memory. With aircraft depressurized the pilots are wearing oxygen masks. The only way for them to communicate is to use the crew intercom. The PTT button has two positions. Up to transmit over radio and down to communicate on the intercom. Muscle memory probably caused them to press up to talk to each other, and when they did, they transmitted and ATC recorded it.

[johnhb]

Has anybody heard more about this?

[JW411]

KenV:

"Why the open mike all the time"

I might be able to help. As a TRE/TRI for many years I cannot remember how many "loss of cabin pressure" drills I have run in the simulator. Some crews can make an absolute :mad: of the exercise because they are unable to hear one another properly when wearing oxygen masks especially on emergency flow.

I have spent hundreds of hours teaching pilots to use a high level of discipline in the use of intercom in such circumstances. The background noise created when one of the pilots involved keeps an "open mike" is considerable. So, it is vital to use the intercom/transmit switch in the off position unless you have something vital to say and then, as soon as you have said it, switch off again.

This is particularly essential when reading and responding to checklists.

It should come as no surprise that the ex-military pilots came out tops on this front. They were much more used to wearing oxygen masks and had learned the discipline well. The average civilian pilot only ever used an oxygen mask once in a blue moon and possibly never in anger.

As you might have gathered, I am ex-military and in my day it was not unusual to have five crew members communicating with one another with oxygen masks on.

[lomapaseo]

I have spent hundreds of hours teaching pilots to use a high level of discipline in the use of intercom in such circumstances. The background noise created when one of the pilots involved keeps an "open mike" is considerable. So, it is vital to use the intercom/transmit switch in the off position unless you have something vital to say and then, as soon as you have said it, switch off again.

This is particularly essential when reading and responding to checklists.


stretching the thread a bit ... but I've seen minor problems turn into major problems when O2 masks interfered with normal communications on an emergency return due to smoke in c0ckpit

[mayam13]

Hi Tech,
Thanks for bringing out bringing out safety points. The differential pressure in Fan cowling is a good point. I suggest the cowling be made of Titanium:
1) With titanium protracted turn around inspection is not required
2) Engineers can stand on the cowling.
3) Engine aerodynamic profile will be less bulky.Less drag is created eventual fuel efficiency improvements
4) When sheet metal is bent it improves stress, whereas Composites weakens.
5) It is alarmng to hear this has occured before on other engine.
6) By employing Composites on fan cowling, a few kilograms of weight may be saved, but using Titanium, passenger lives can be saved.
7) I guess FAA is listening

[Krystal n chips]

Hi Tech,
Thanks for bringing out bringing out safety points. The differential pressure in Fan cowling is a good point. I suggest the cowling be made of Titanium:
1) With titanium protracted turn around inspection is not required
2) Engineers can stand on the cowling.
3) Engine aerodynamic profile will be less bulky.Less drag is created eventual fuel efficiency improvements
4) When sheet metal is bent it improves stress, whereas Composites weakens.
5) It is alarmng to hear this has occured before on other engine.
6) By employing Composites on fan cowling, a few kilograms of weight may be saved, but using Titanium, passenger lives can be saved.
7) I guess FAA is listening

With all due respect, and I am not being critical or disparaging you, I would suggest you read this article please.

https://www.premix.com/why-composites/adv-composites.php

Both Riverman and Hi Tech summate the engineering / maintenance aspects very well, and certainly with regard to possible causes of damage to composites with delamination being the hidden from routine inspections source. By the time you get to see de-lam, it's too late and the damage is done.

Likewise an innocuous dent ( Visible impact damage ) on the surface, but underneath, and invisible until a detailed inspection is carried out using NDT, the damage may be catastrophic.

Titanium is impractical for use in an intake, Kevlar however is, and it's also a time consuming nightmare to work with as any engineer who has been involved with the material will testify.

As for bending metal, no matter how much effort is applied to alleviate the problem, stress corrosion will be induced from the onset of the manufacturing process.

I formerly trained engineers in corrosion inspections and rectification techniques, both metal and composites, so my reply to you is not purely theory based and is intended to help remedy the misunderstanding within your summary.

[mayam13]

Thank you. Titanium is costly hence designers are reluctant to use it. However to arrest flying debris from high speed compressor and turbine discs composites is a poor choice, the incident proves it.

[KenV]

Thank you. Titanium is costly hence designers are reluctant to use it. However to arrest flying debris from high speed compressor and turbine discs composites is a poor choice, the incident proves it.Nonsense, on three counts.

1. While pricey, titanium has many unique properties. If those properties are desirable or necessary in a design, aircraft designers will not hesitate to use titanium.

2. Nacelle cowlings are NOT intended nor designed to "arrest flying debris from high speed compressor and turbine discs." The engine's fan and turbine case are so intended and so designed.

3. Composite fibers are an ideal ballistic material. Consider that ALL bullet proof vests are made of composite fibers, and essentially ALL armored vehicles have spall liners made of composite fibers.

[Intruder]

Why the open mic all the time? There is a lot of it?
Another possibility: In some airplanes (e.g., 747 Classic) a switch must be thrown to switch from boom mike to the mike in the mask. If this airplane was not equipped with the newer masks with automatic switching (switch is in the cover of the mask compartment, and activates when the mask is pulled out), she might have forgotten this step in the fray. I've been there, done that!

I noted that as soon as the controller said that he was only getting static, the next transmission from the airplane was clear. Either he jogged her memory or she finished doing the other stuff she had to do - like FLY THE AIRPLANE. Don't forget the priorities: Aviate, Navigate, Communicate, in that order.

[Redlands]

>Titanium is costly

Graphene.