737 engine departs aircraft!

[tgrayson]

Originally Posted by Minnesota_Flyer

I only know that the pylon attach points (fuse pins, I think?) generally are designed to fail in a specific way to protect the wing.

I googled on "fuse pin":

Pylon fuse pin (Pylon is the structural component connecting the jet engine to the main wing. The role of the fuse pin is to allow the engine to separate from the wing under the strong impact load that occurs in the event of a crash or hard landing in order to protect the fuselage from engine fire.)

Although I don't consider the above quote authoritative, it does seem that the fuse pin is intended for a particular purpose, so there is something here. I don't presently accept that purpose is for sudden engine stoppage, since the regs say that the structures must withstand that.

I'm going to keep looking because now I'm curious.

Cool. Please report what you find.

[tgrayson]

Originally Posted by Minnesota_Flyer

Edit: El Al 1862 involved damaged fuse pins. The final report discusses the fuse pin design (see section 1.6.3.1) a little. Doesn't cite any design regs, though: http://verkeerenwaterstaat.nl/kennis...light_1862.pdf

Good stuff:

1 .6 .3 .1 Pylon to Wing Attachment Desigin

The design of the engine nacelle and pylon incorporates
provisions that preclude a wing fuel cell rupture in case of engine
separation, by means of structural fuses . A clean breakaway of the
nacelle and/or pylon from the wing is ensured when the shearloading
of the fuse pins exceeds the design load conditions.

The structural fuse concept utilizes hollow shear pins at the four wing
attachment fittings between pylon and wing . The wing support structure
and fittings have been designed sufficiently stronger than the
fuse pins thus safeguarding the wing from structural damage in case
of an overload condition.

The nacelle and engine are attached to the pylon bulkheads through
forward and aft engine mount fittings.

The pylon is essentially a two cell torque box containing thre e
bulkheads: a forward engine mount bulkhead, an aft engine mount
bulkhead and a rear closure bulkhead . Pylon to wing attachments are
made at the aft end of the upper link, the aft end of the diagonal brace
and at the two pylon midspar fittings.

The fuse pin at the forward end of the upper link, the aft end of the
diagonal brace and at both midspar fittings are the primary fuse pins.
The fuse pins at the forward end of the upper link and the aft end of
the diagonal brace are designed to fail at a slightly lower load than
the fuse pins at the other ends in order to assure a controlled separation
of the pylon from the wing.

Nacelle load components in the vertical and side directions are absorbed
by the forward pylon bulkhead while vertical, side, torque and
drag components are reacted at the aft mount bulkhead. These pylon
loads go to the four wing attachment fittings through the pylon front
spar and lower spar, the midspar and the pylon skin . Primary drag
loads go through a thrust link into the diagonal brace . An additional
side brace from the pylon midspar to the wingbox takes pylon side
shear into the wing. A schematic of the pylon to wing attachments
fittings is given in figure 1.

[ready2fly]

Originally Posted by MQAAord

Ah, but you'll notice the airplane didn't fall out of the sky!

Scary, sure. But every scary thing that happens on a plane doesn't necessarily mean demise is imminent.

My sister-in-law (Bill's sister) used to be completely freaked out by flying. Afraid of every little thing that could happen. Then Bill took her up in a Seneca and showed her what happens when pilots do "things", what the gear sounds like, putting out flaps and what that does, and just sitting where she could SEE what was going on and be able to talk & ask questions made a huge difference to her.

Funny.

My wife used to be fine with flying until I took her up and did the same thing.....now she's terrified.














.... seriously.

[tonyw]

Originally Posted by Minnesota_Flyer

AA 191: an engine came off during take-off and damaged the the wing causing a crash. Damage was found in the pylon structure (caused by improper maintenance procedures) which both caused the breakaway and prevented a clean breakaway.

Wasn't there something in there about using a forklift to mount the engine which contributed to the accident? I don't recall, it's been a while.

[Minnesota_Flyer]

Originally Posted by tgrayson

I don't presently accept that purpose is for sudden engine stoppage, since the regs say that the structures must withstand that.

I don't disagree. It would be more to protect against the severe engine vibrations that might be caused by an engine which sheds a few blades at full torque and does not stop.

[Minnesota_Flyer]

Originally Posted by tonyw

Wasn't there something in there about using a forklift to mount the engine which contributed to the accident? I don't recall, it's been a while.

Yup. It was a maintenance shortcut adopted by AA, but not approved by MD. The investigation determined that the method was causing stress fractures in the pylon structure of many (most?) of AA's DC-10s.

[ERfly]

Originally Posted by Minnesota_Flyer

AA 191: an engine came off during take-off and damaged the the wing causing a crash. Damage was found in the pylon structure (caused by improper maintenance procedures) which both caused the breakaway and prevented a clean breakaway.

They would have survived if just the engine had come off, but now (in my best Paul Harvey voice)....the rest...of the story. The DC-10 lacked shut-off valves on certain hydraulic controls. When the pylon separated, it took the hydraulic pressure with it. The slats on the left wing retracted. As the pilots pitched up to the single engine climb speed and the jet slowed. In addition to that, the #1 electrical system was gone. This provided vital indications. On this DC-10, the CA's airspeed as well as the slat indicators and the stick shaker were all on this system. They had to way of getting the stall information (nothing on the right side). The left wing stalled and thus the disaster.

Urban legend states that there is a good chance the passengers watched themselves die. AA used to have a camera up front that showed all the take-offs on the video system in back. There was no way of knowing if it was on during Flight 191, but who knows.

[JHines]

Originally Posted by tgrayson

Those aren't the only two choices.

The greatest safety risk on the turbofans used in most commercial airliners is fan blade or disk failure - less so for the LP turbine or HP section.

Various means (aramid fiber armor, etc.) are used to prevent ejection of the fan blades from the case.

Large torque loads and unbalanced gyrating forces due to fan failure are often mitigated by means of a "decoupler" installed between the fan and its bearing support.

When unbalanced loads exceed a predetermined limit, the decoupler (a type of mechanical "fuse") will fail and allow the fan to "whirl" and decelerate to a safe speed, without transferring large imbalanced loads to the rest of the engine/pylon/airframe.

[tgrayson]

Originally Posted by JHines

The greatest safety risk on the turbofans used in most commercial airliners is fan blade or disk failure - less so for the LP turbine or HP section.

Various means (aramid fiber armor, etc.) are used to prevent ejection of the fan blades from the case.

Large torque loads and unbalanced gyrating forces due to fan failure are often mitigated by means of a "decoupler" installed between the fan and its bearing support.

When unbalanced loads exceed a predetermined limit, the decoupler (a type of mechanical "fuse") will fail and allow the fan to "whirl" and decelerate to a safe speed, without transferring large imbalanced loads to the rest of the engine/pylon/airframe.

Interesting info, thanks.

[tgrayson]

Originally Posted by Minnesota_Flyer

I don't disagree. It would be more to protect against the severe engine vibrations that might be caused by an engine which sheds a few blades at full torque and does not stop.

Could be. I've come across several references that indicated that the fuse pins were designed for large impacts or severe turbulence, which makes more sense to me. Externally derived loads, rather than from the engine itself. There was one Part 25 reference that indicated the design should handle the loss of a turbine blade(s?). I lost it now, but I'll look again when I have access to my search engine at home.

[mrivc211]

Originally Posted by tgrayson

Those aren't the only two choices.

I think your defense was proved wrong. I don't see how you can continue to argue your point. I see both sides, but I too would rather have an engine break off and have a clean airplane than to have to deal with all that drag and stress put on the airframe.

[tgrayson]

Originally Posted by mrivc211

I think your defense was proved wrong. I don't see how you can continue to argue your point.

Not yet. Argumentation, as long as information is provided, leads to truth and understanding.

The implication that if you have an engine failure of a certain type, the engine falls off, still appears false to me. The regulations appear to call for the structures to withstand any predictable engine failure mode.

I see both sides, but I too would rather have an engine break off and have a clean airplane than to have to deal with all that drag and stress put on the airframe.

The issue is not what you would prefer, but what is most conduicive to safety. As long as the airplane will fly, the engine is better attached to the aircraft.

[Minnesota_Flyer]

Originally Posted by tgrayson

As long as the airplane will fly, the engine is better attached to the aircraft.

While true, it is equally true that if the engine is going to shake itself to death, for whatever reason (imbalance, turbulence, Mothra), it is far better to get it off the airframe before it overstresses the wing.

[Velocipede]

grayson obviously isn't qualified in jet airplanes.

[tgrayson]

Originally Posted by Minnesota_Flyer

it is equally true that if the engine is going to shake itself to death, for whatever reason (imbalance, turbulence, Mothra), it is far better to get it off the airframe before it overstresses the wing.

Yep, but the question is whether it *can* shake itself to death through imbalance.

I found an interesting thread on the subject of the forces required to separate a pylon from the wing:

http://www.airdisaster.com/forums/ar...p/t-59099.html

One of the participants is Al Weaver, who is a well-known accident investigator. Among other pertinent comments, he said:

I was on the FAA/JAA committee which reviewed the design standards for engine seizure loads on the pylon and wing structures...

The most limiting factors relate to gust and/or flutter loading and after meeting the aerodynamic loads it is relatively easy to make a quick check to ensure that the engine induced loads do not become limiting.

I read that to say that if the wing can withstand gust and flutter loads, it can handle anything the engine can throw at it.

Read it and see what you think.

[tgrayson]

Originally Posted by Velocipede

grayson obviously isn't qualified in jet airplanes.

Being jet-qualified seems to have granted you no insight into this topic, so I seem to operate with no handicap.

[Mariano]

Originally Posted by Minnesota_Flyer

Yup. It was a maintenance shortcut adopted by AA, but not approved by MD. The investigation determined that the method was causing stress fractures in the pylon structure of many (most?) of AA's DC-10s.

Actually, it was because the procedure called to dismount the engine from the pylon and then remove the pylon from the wing, and the reverse when putting back the engine: pylon then engine. The maintenance crew dismounted the whole pylon-engine assembly to save time. I think that the use of the fork-lift was just a contributing factor (maybe not even that).

I'm talking out of memory, I haven't actually looked it up.

[blakman7]

Originally Posted by athomeinthesky

That sux, do they only get to log single engine time for the remainder of the flight?

It isn't a funny story but that surely did change the mood for the better that I had upon initially reading the post.

[Cruise]

Originally Posted by Minnesota_Flyer

While true, it is equally true that if the engine is going to shake itself to death, for whatever reason (imbalance, turbulence, Mothra), it is far better to get it off the airframe before it overstresses the wing.

Hilarious!

OMG, look over there.....Mothra is destroying our wing. Take evasive action.

BTW, what are the memory items for a 'Mothra attack'.....sadly, I don't think that got covered in ground school.

[tonyw]

Originally Posted by Cruise

Hilarious!

OMG, look over there.....Mothra is destroying our wing. Take evasive action.

BTW, what are the memory items for a 'Mothra attack'.....sadly, I don't think that got covered in ground school.

And to add to it, what do you do if there's a situation like the one which William Shatner encountered in the Twilight Zone?

[Velocipede]

Actually, you do. The original witness heard one loud bang and the engine departed. That's a pretty good description of a hard seizure. Your limited knowledge of jet engines and airframe systems has led you to make numerous erroneous statements on this thread.

But, by all means, go ahead and continue. Its quite amusing.

[tgrayson]

Originally Posted by Velocipede

The original witness heard one loud bang and the engine departed. That's a pretty good description of a hard seizure.

It's probably also a good description of a structural failure due to a number of other reasons.

Your limited knowledge of jet engines and airframe systems has led you to make numerous erroneous statements on this thread.

Fine, then correct them with knowledge and references, rather than snippy comments. Sharing knowledge is what this forum is all about. Many jet pilots I know also have a "limited knowledge of jet engines and airframe systems", so you'll have to demonstrate you're different.

[greaper007]

http://www.ntsb.gov/ntsb/brief.asp?e...10X00187&key=1

This was my Dad's plane. It earned him a night of lobster and Wild Turkey with Herb. The funny thing was that they couldn't get the engine to fall off like it was supposed to.

Apparently they had engineers at Boeing on the phone and they couldn't even come up with a solution. My Dad still has video of this, when they landed the engine was dragging on the ground. It was pretty crazy, I just remember him coming home covered in sweat and having to stop watching Saturday morning cartoons.

[Swen]

Originally Posted by greaper007

http://www.ntsb.gov/ntsb/brief.asp?e...10X00187&key=1

This was my Dad's plane. It earned him a night of lobster and Wild Turkey with Herb. The funny thing was that they couldn't get the engine to fall off like it was supposed to.

Apparently they had engineers at Boeing on the phone and they couldn't even come up with a solution. My Dad still has video of this, when they landed the engine was dragging on the ground. It was pretty crazy, I just remember him coming home covered in sweat and having to stop watching Saturday morning cartoons.

I'm not sure I have ever read a report that wasn't pilot error....

[Duck_Twacy]

Originally Posted by Doug Taylor

Better a 5,000 lbs engine getting dead dropped over Detroit is more agreeable than 400,000 lbs of jet dropping down in a few chunks!

I don't know about that Doug...I mean, we're talking about Detroit after all...