UPS cargo plane crash. Louisville Kentucky

[Reynard]

MD11s now grounded by FAA pending inspections. 

[onetrack]

The interesting part of the whole deal is the engine pylon pulling right out of the wing structure. The engine and pylon left the airframe complete, but the pylon only separated from the engine after the engine hit the ground.

All the previous reinforcement instructions for the MD-11 engine mount area were to strengthen the section of the wing structure where the pylon attached.

 

It was jiggling and pressure from the forklift operator as the maintainers reinstalled an engine complete with pylon (against manufacturer advice) that caused stress fractures in the wing structure where the pylon mounts were attached, was what caused the Chicago Flight 191 crash.

 

This UPS MD-11 was fully stripped and rebuilt from the ground up in 2006, in its conversion from a passenger aircraft to a freighter. The airline industry calls it a D-check, and not a single item in the aircraft is left unchecked.

However this aircraft recently underwent a major fuel tank crack repair job, that took 6 weeks to carry out. The fact that the job took such a long time, indicates some very major work was required, and no doubt investigators will be poring over the crack repair records.

The major factor in the crash is simply that the aircraft was well and truly on fire, before the engine departed the airframe. This appears to indicate a wing tank structural failure of some kind, as the level of fire is major and it would've had to have been fed by a large volume of fuel that could only come from a fuel tank rupture.

 

[facthunter]

No, a fuel TANK rupture would entail Major wing deformation and would just stream out and Possibly not even  catch fire. More likely the fuel Manifolding  damaged with fuel pump pressure applying, RAPID flowrate. Fuel tanks are not pressured. Nev

[Blueadventures]

[facthunter]

Big fire there right at  the worst time with Likely uncommanded LE devices retracting with loss of hydraulics on the left wing, Big loss of Lift. as well as the Loss of thrust. very dramatic and No hope of recovery.. They are right to ground these Planes at this Point. We will see if it was a faulty Engine  changing process. . Nev

[jackc]

Never liked those machines, in 1979 I was due to fly Air New Zealand on one. I cancelled the flight and changed to Qantas 747.

Based on  published incidents about ‘78, ‘79? 
 

[facthunter]

The Air New Zealand crash was not caused by any fault in the Plane. The Chicago one was faulty Maintenance. Cargo door was an issue on one in Europe.. Nev

[onetrack]

I erred in my previous opinion that the aircraft was on fire before the engine departed the airframe (based on the previously-available limited video footage). Blueadventures photos show the engine departing the airframe first, followed by a rapid outbreak of fire.

 

However, I stick by my original opinion, that major structural failure of the wing fuel tank, caused by the engine departure, resulted in the huge fire. It's amazing to see how instantly the major fire erupted, which could only have been caused by the hot engine exhaust gases at full throttle, penetrating a wide gash in the fuel tank.

 

Edited November 21 by onetrack

[facthunter]

The fuel manifolds for X feed etc are all there and are pressurised by the Boost Pumps. Large DIA Pipes'  The tanks are Behind the Mainspar. The engines normally go UP and over the wing when the rear pin fails. The Pylon is Mounted in 3 Places. 2 at the front. They are designed to fail  there if something violent happens. Engine vibration/ seizure, Large "G" force etc. Nev

[jackc]

2 hours ago, facthunter said:

The Air New Zealand crash was not caused by any fault in the Plane. The Chicago one was faulty Maintenance. Cargo door was an issue on one in Europe.. Nev

One lost a motor, and crashed not long before I was due to take my trip, killed all on board.  I never liked the look of the design, that crash was simply a decider for me.

 

[danny_galaga]

1 hour ago, facthunter said:

The fuel manifolds for X feed etc are all there and are pressurised by the Boost Pumps. Large DIA Pipes'  The tanks are Behind the Mainspar. The engines normally go UP and over the wing when the rear pin fails. The Pylon is Mounted in 3 Places. 2 at the front. They are designed to fail  there if something violent happens. Engine vibration/ seizure, Large "G" force etc. Nev

Totally. How many litres a minute would it be pumping? It's going to be an instant fireball with no damage to the tank. 

[onetrack]

Blanco Lirio is dissecting the preliminary NTSB report, released 20 Nov.

 

 

[KRviator]

1 hour ago, danny_galaga said:

Totally. How many litres a minute would it be pumping? It's going to be an instant fireball with no damage to the tank. 

A very quick Google suggests a takeoff fuel flow of around 15,000lbs an hour. That's consumption not what the pumps can actually put out through a system that now has no restrictions in it and is open to atmosphere.. And given this is on rotation, there's no memory items for closing the spar valve or pulling the fire handle that early in the takeoff sequence, so the boost pumps will continue to run, the spar valve will remain open, yadda yadda. 

[onetrack]

There is no wing tank fracture as I presumed, Facthunter is on the money, the fire was obviously fed by the fuel manifolds.

 

The engine aft pylon lugs simply failed, they just broke right through the lugs, and with that support gone, there was absolutely nothing to stop the engine departing the airframe.

A very simple, single point of failure, that should not ever have been allowed to pass certification. The lugs had been cracked for some time, and the cracks simply progressed to total failure of the lugs.

 

The airframe was high hours, in excess of 92,000 hrs, and the mandated pylon inspection was determined to be at 28,000 cycles, but this aircraft had only done just over 21,000 cycles, so, as Blanco Lirio says, this inspection period is almost certainly going to change.

 

The interesting point that Blanco Lirio raised, is how gyroscopic procession from the engines rotating components produces increased forces on the engine mountings, right at rotation. The greatest forces applied to the mountings, right at the worst possible moment.

 

Edited November 21 by onetrack

[Thruster88]

I do not understand why the bulkhead bearing lug is in two pieces. Moisture ingress, extra fatigue crack propagation sites?  The bearing is replaced in the field using an enerpac hydraulic press tool.

[onetrack]

The reason it's in two pieces could be because that style of design sped up the manufacturing process. The bottom line is, no aircraft engine should depart the airframe, ever. There's just no redundancy when that lug fails, and the lug design obviously has minimal reserve strength.

American built machines usually have massive reserves of strength in critical areas, it seems the engineers calculations on the forces applied to that lug under all potentially-foreseeable conditions, were just simply wrong.

And they could have engineered some other form of redundancy into the design, such as a safety strap, similar to driveshaft safety straps, which prevent driveshafts that fall off, from flailing about.

[facthunter]

Mount Points are designed to fail when extreme circumstances exist to save other Parts of the structure. Most big Turbo Fans are Pylon Mounted under the Wing. Nev

[Blueadventures]

Maybe the two pieces are not halves just a form of double up of attachment?

[facthunter]

It can't be designed to fail and also Have redundancy. There's NO Logic in that. Nev

[pmccarthy]

They are designed to fail under excessive vibration, but it is hard to understand. A dead engine would fall away, but one producing thrust will go ahead and then back into the aircraft, as has happened I other cases.

[facthunter]

Why would a dead engine fall away? That's NOT how it works. It's an extreme situation of stress/load for an engine to detach. There could be Maintenance Procedure Issues involved Metal fatigue Violent engine failure  where the rotational Inertia of the engines internals is involved. "Flywheel effect", when an engine seizes involves LARGE forces. Nev

[jackc]

Those things are a crap aircraft, the moment I first saw one…….was enough for me. Yes, a crap design that flies BUT ??

[facthunter]

You have the ability to "sense" these things by how they LOOK do you? Amazing. ! You have to be kidding.  ALL planes have faults. Proper Inspection and Maintenance Keeps them safe especially WHEN they have been flying for a Long time. The Comet looked Pretty but was Fatally weak in the structure particularly the forward  Part of the fuselage..  Nev

[jackc]

When I first saw that the rear engine was mounted on the vertical stabiliser, that was the start. I knew nothing about aircraft back then, and I don’t know much more now.  I had visions of what could go wrong but millions of flight hours later, between Wing pylons and cargo doors, they have been reasonably reliable BUT, when it goes wrong it seems to result in a major disaster. 
I still have visions of major real engine failure, destroying the aircraft.  I have seen too many instances  of poor engineering,  in my life.  
My 24 reg Jabiru has one, and I am not allowed to fix it. 🤢
 

[danny_galaga]

15 hours ago, pmccarthy said:

They are designed to fail under excessive vibration, but it is hard to understand. A dead engine would fall away, but one producing thrust will go ahead and then back into the aircraft, as has happened I other cases.

I think the gist of it is that it's better those parts fail, than the whole wing snaps in half. Clearly, in this case it still ended in disaster but in general the idea makes sense. There's only so much you can plan for