Southwest Flight Lands Safely After Major Engine Malfunction

[allardjd 1,853]

Southwest Flight Lands Safely After Major Engine Malfunction

 

http://www.wsj.com/articles/southwest-airlines-flight-lands-safely-after-major-engine-malfunction-1472320957

 

 

"The Boeing Co. 737-700 was flying from New Orleans to Orlando early Saturday operating as flight 3472"

 

"According to tracking data from FlightAware, the 737 was flying around 30,700 feet and climbing..."

 

"CFM International, a joint venture between General Electric Co. and France’s Safran SA, is the sole supplier of engines to Boeing for the single-aisle 737. Southwest is the single largest operator of the single-aisle workhorse jetliner in the world."

 

Not sure how long the image will be available.  I linked it from the news aggregation site and it does not appear in the linked article.

 

John

[needles 1,010]

After seeing that picture John, I'm really glad it made to the runway.  

Thank goodness everyone is safe. 

It could have been another disaster.

[Jess-b 420]

Looks like the forward cowling has separated. What a weird failure. I don't think I've ever seen a forward cowling come off in flight. 

[Captain Coffee 2,030]

how bizzare...no way a bird hit it at that altitude.

Maybe something struck it at a lower altitude and it gave way later?

Someone left some cowling fasteners undone?

Some idiot on a forum page is wildly speculating?

[allardjd 1,853]

I think most of what came off is cowl, bleed-air ducting for the anti-icing, sensors, etc - there's nothing really structural that far forward in the nacelle.  

 

I think I can see the fan hub (minus the usual cover/nose cone) and even a shadow of rotating blades there, but not sure.  The two fasteners at top center are unlatched but that probably occurred during the event.  Unlikely that would have gone unnoticed.  If I'd have been seated on that side I'd sure have noticed those red latches sticking up and would have told someone long before they got anywhere near the runway.  

 

That kind of loss of parts could hardly have happened without the engine ingesting some of the hardware, so it's doubtful if the engine was completely unaffected, even though it is mostly intact and appears to still be rotating.

 

John

[Captain Coffee 2,030]

Yeah...amazing there are still compressor blades in the front...clearly stuff must have gone into the engine from the look of the shredded pieces bent inward. I bet those blades are just freewheeling in the rush of air...that engine must have flamed out or been shut down ASAP.

 

As far as your average pax noticing or commenting on red levers sticking up from a cowling...doubtful. Most of us on Mutley's would have been yelling foul...not many "normal" people would know the difference.

 

[stu7708 244]

From AVHerald.com 

 

"The airline reported the captain decided to divert the aircraft to Pensacola due to a mechanical issue with the #1 engine"

 

Sorry Matt, but I'm going to have to decline your nomination for understatement of the year you awarded me last week and hand it over to Southwest Airlines.

 

There are three more images available over on AVHerald, including on of the damage done to the main fuselage.

 

http://avherald.com/h?article=49d2d7e3&opt=0

 

 

[brett 2,285]

Wowzer, not something you want to see happen while in the passenger seat or the cockpit, although better than looking out and not see any engine out there. It will be very interesting to see what the NTSB find out as the cause of this malfunction.

[allardjd 1,853]

That scar below the window line appears to compromise the pressurization envelope, though not large enough to cause an explosive decompression.  We'd have heard about that.  Interesting scenario, though with a pressurization leak and 50% of the bleed air supply gone.  I wonder how big a hole would have to be for the other engine not to be able to maintain cabin pressure.

 

I did not hear that it was an "expedited" descent.

 

There's damage to the wing root too, but that looks like it's just bent tin (OK, stainless steel, in that location - "tin" is generic).

 

John

[J G 927]

Interesting, and a bit weird.  My guess is that the cowl separated in one or two bits. If it pealed back then there would be a good chance that it could avoid being ingested into the engine.

 

The above if true would mean that the cowl was not secure and another indicator of this would be the open lugs on the top of the cowl. These would be hard to see from the ground and therefore from a walkround.

 

My guess is that it was not secured properly and the battering the cowl had, perhaps over more than one flight, caused it to break into two or more large bits and these pealed back over and/or under the wing.

[stu7708 244]

On 2016-08-31 at 10:40, J G said:

The above if true would mean that the cowl was not secure and another indicator of this would be the open lugs on the top of the cowl. These would be hard to see from the ground and therefore from a walkround.

 

I'd agree with you if it had been Engine #2, but those locks on engine #1 should be easily spotted from the front entrance, given that there were windows facing towards the rear of the plane on a connected Jetway. So unless checking those aren't part of the SOP for the walk around it should have been spotted in my mind.  

[Captain Coffee 2,030]

2 hours ago, stu7708 said:

 should have been spotted

 

 

I think you hit upon the key terms.

 

 

[allardjd 1,853]

I don't think there's any confirmation yet that whether the open latches at the top of the nacelle were cause or effect.  None that I've seen, anyway.  I think either is a possibility.

 

John

[stu7708 244]

You are indeed correct John, there have been no reports on this either ways as far as i've seen...

 

My intention was to include a "if they were indeed open/not properly secured" in my post, but I guess I lost my chain of thought while writing  

[allardjd 1,853]

More from PPRUNE...

 

There is one report of one fan blade completely missing, but it seems to be unconfirmed and others have expressed doubt.  At this point I'd call it doubtful, but since it was reported in PPRUNE I included it here.

 

There is supposedly minor impact damage to the winglet and leading edge of the horizontal stabilizer as well as what we've already seen to the wing root fairing and the ruptured fuselage skin just below the window line.

 

The oxygen masks did deploy, though it's unclear how much decompression occurred.  An immediate descent to 10,000' was begun right after the event.  Some of the pax took selfies with the masks on.

 

This from an AME (Aircraft Maintenance Engineer)

 

"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  [emphasis added] - 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."

 

Interesting...

 

No one there seems to think that cowl latches left open are a cause.

 

John

[hurricanemk1c 195]

NTSB suspect fan blade metal fatigue was part of the process. A 1.14 in long and 0.217 in deep fatigue crack region was found of the blade root of the missing blade

 

http://aviationweek.com/commercial-aviation/ntsb-metal-fatigue-complicit-southwest-engine-fail?NL=AW-05&Issue=AW-05_20160913_AW-05_118&sfvc4enews=42&cl=article_3&utm_rid=CPEN1000001461166&utm_campaign=6993&utm_medium=email&elq2=34b681af6987472c9ba30801666dddc4 (free subscription required. Quite a good e-mail newsletter gets sent out around 1000 UK/Irish time every day)

 

And the NTSB press release - http://www.ntsb.gov/news/press-releases/Pages/PR20160912.aspx

[Captain Coffee 2,030]

OK, how did a fan blade rip the inlet off? Wouldn't a torn off blade suck back into the motor?..or exit the side at high speed??

[allardjd 1,853]

3 hours ago, Captain Coffee said:

OK, how did a fan blade rip the inlet off? Wouldn't a torn off blade suck back into the motor?..or exit the side at high speed??

 

I'm having a hard time coming up with ANY scenario that would account for ripping off that honeycomb panel structure, but obviously SOMETHING did.  As for the blade, its pitch and rotation is trying to make it "screw itself into the air" which is only prevented by being attached to the hub.  If freed from the hub it will initially move outward (from centrifugal force) AND forward (due to it's pitch), until the forward momentum is lost in the airflow or by impact with surrounding structure.  It would not get sucked back into the engine unless that forward momentum was lost while it was still more or less directly in line with the intake.  

 

There has also been some speculation of a violent compressor stall, which momentarily disrupts air flow into the engine and can, I think, even cause a brief reverse flow in the compressor section.

 

The fatigue crack is significant and is very likely the root cause of the whole event.  

 

John

 

EDIT: One thought that occurs to me is that most parts of aircraft are designed to only be loaded in certain directions, and due to weight concerns are relatively fragile.  Usually the overall strength of a structure depends on the structure being intact.  If damaged in such a way that its overall structural integrity is lost, or if loaded by forces from a direction other than that for which it was designed, they can fold up like a cheap tent.  It may well be that the departing blade caused enough loss of integrity to the inlet structure that the ram-air effect of the aircraft speed plus the inlet stream velocity did the rest.  Just conjecture, but seems plausible to me...

 

JDA

[J G 927]

I am fairly sure that a fan blade would explain the damage.  The blades are put under a huge amount of centrifugal force as they turn, and are not actually tightly fixed into the hub, you can hear a clinking sound coming from the engine when the fan is turning slowly, this is the blades moving in their sockets.  They are, however, held tightly in place as the engine is operating by the enormous centrifugal force put upon them. A blade snapping off from its mount will travel outwards a good way before the other forces on it come into effect.This event would be more than enough to wreck the mounts of the engine fairing, which would then rip itself to pieces in the airflow acting upon it. 

 

Given the the blade, when no longer mounted to the hub, would prescribe an arc as the centrifugal and rotational force acted upon it, the passengers and crew were very lucky that the rapidly departing chunk of fan blade didn't scythe into the body of the aircraft like a piece of shrapnel causing rapid decompression, not to mention carving up people in its path.