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[LC0112G]

Sorry - that first sentence should have been....

"#3 is the tail engine? Anything departing #1 with enough energy to penetrate the fuselage is going to miss the tail engine."

Point is, I can't find any instances of an engine on one wing causing damage to an engine on t'other wing. Yes there have been instances (on both B-707's and B-747's) where one engine has failed and knocked the other one on the same wing off, but never on the opposite wing.

[Kevin Wood]

No.3 would be the engine on the starboard wing. They are counted from port to starboard.

I think the cowling of the departed no.1 engine ended up the other side of the runway so quite possible it killed no.3.

However, one of the videos shows no. 2 at the back spitting out sparks just after rotation. It quite possibly ingested fire from the burning port wing at that point.

[TheBoy]

Yes, to clarify, it is the starboard engine I'm talking about the rumours of it flaming out as the nose lifts. Which as Kevin Wood says, is called No3.

Additionally, there is also talk of there being a direct line of sight between the No1 and No3, under the fuselage, so maybe it didn't penetrate the fuselage.

As a cargo plane, my thoughts were how likely would it be for engine debris, admittedly at high speed with a lot of spin, to penetrate the fuselage (easy, thin aluminium) and the cargo (less likely?)

[LC0112G]

As a cargo plane, my thoughts were how likely would it be for engine debris, admittedly at high speed with a lot of spin, to penetrate the fuselage (easy, thin aluminium) and the cargo (less likely?)

There is no real difference between a cargo and a passenger planes construction. Some cargo planes do have a strengthened floor to take the weight of pallets and extra loading doors, but the wings, skins and bulkheads are the same. I don't think the cargo has any bearing on this, because for parts of an engine to hit the cargo they have to travel up, so they will miss the other engine if they emerge out the other side of the fuselage.

AIUI there are contained and uncontained engine failures. Smaller things like individual engine blades are supposed to be contained within the engine cowling if they break off. The engine will be destroyed, but things shouldn't fly out of the sides. This is tested during engine certification, and is often implemented by having kevlar bands around the engine. Larger parts - like rotor disks (either whole or segments) are considered to have infinite energy and cannot be contained. If they do break off, they will go through virtually anything. The safety mitigation for these is simply to route critical wiring and hydraulics out of being in direct line with the high energy rotating parts. Engines are also mounted forwards of the front wing spar, so if anything does fly off it doesn't puncture fuel tanks.

If some high energy part of #1 did escape and somehow hit #3 it will be the first known incident of this happening. It will have very serious consequences for air travel. Aircraft are certified to be able to takeoff, fly and land on n-1 engines on the basis that it's highly unlikely that two engines can be damaged by the same event. If that assumption proves to be false then it opens a huge can of worms. n-2 isn't possible on any aircraft, and since almost all are now twins (B-737,767,777,787,A-319,320,330,350) n-1 means zero.

[TheBoy]

As a cargo plane, my thoughts were how likely would it be for engine debris, admittedly at high speed with a lot of spin, to penetrate the fuselage (easy, thin aluminium) and the cargo (less likely?)

There is no real difference between a cargo and a passenger planes construction.

Yes, the bit I was wondering is if debris would penetrate the cargo easier than it would penetrate the organic matter in a passenger jet....

[LC0112G]

As a cargo plane, my thoughts were how likely would it be for engine debris, admittedly at high speed with a lot of spin, to penetrate the fuselage (easy, thin aluminium) and the cargo (less likely?)

There is no real difference between a cargo and a passenger planes construction.

Yes, the bit I was wondering is if debris would penetrate the cargo easier than it would penetrate the organic matter in a passenger jet....

Pax planes are usually full of seats, which are partly made of metal. I've got a memory of one incident where engine bits were discovered embedded in the seats, but can't remember which accident that was. It's simply pot luck if an engine fragment hits something soft and squishy or hard and resilient. Heavy/dense cargo is likely to be placed close to the centre of lift/gravity, so over the wings and behind the line of the engines. However, no way of knowing if this plane was carrying a load of light teddybears or the lead lining for a nuclear reactor.

[Doctor Gollum]

Rotation puts the tail engine at or below the Centre of Gravity, ie about level with the front wing spar and therefore in the firing line of any debris.

Pretty sure the tail engine is actually #2.

No mention yet that I have seen of a bird strike but there was report of increased bird activity before the crash.

[Viral_Jim]

NTSB preliminary report is out. 

https://www.ntsb.gov/investigations/Pages/DCA26MA024.aspx

[Kevin Wood]

NTSB preliminary report is out. 

https://www.ntsb.gov/investigations/Pages/DCA26MA024.aspx

Wow. That series of still images is quite chilling.

[Doctor Gollum]

NTSB preliminary report is out. 

https://www.ntsb.gov/investigations/Pages/DCA26MA024.aspx

Non of the media content on that page is viewable* 

https://youtu.be/UpUkwzVUs5Y?si=WGyxm3jv-EjiOqu9

This should cover it...

Incidentally, given the proximity to the ground pictures 5 and 6 show a pronounced (for that point in the take off) roll to the left... It was a coin toss as to whether the left wing tip lower scimitar fin hit the ground or not... If it had, the aircraft wouldn't have left the airfield.

* Not in the UK so it could simply be that.

[Doctor Gollum]

This was in January this year, but adds weight to the possible trigger event...

https://youtu.be/npY42pcf1VI?si=BsvkXjaagx3oN-De

[LC0112G]

Page 9 of the initial report states...

After initial cleaning of the fracture surfaces, examination of the left pylon aft mount lug
fractures found evidence of fatigue cracks in addition to areas of overstress failure. On the aft
lug, on both the inboard and outboard fracture surfaces, a fatigue crack was observed where
the aft lug bore met the aft lug forward face. For the forward lug’s inboard fracture surface,
fatigue cracks were observed along the lug bore. For the forward lug’s outboard fracture
surface, the fracture consisted entirely of overstress with no indications of fatigue cracking.
The forward top flange of the aft mount assembly was examined for indications of
deformation or pre-existing fractures, but no indications were found. The spherical bearing
was removed from the wing clevis for further evaluation (see figure 10).

What they're saying is there were pre-accident fatigue cracks in 3 of the 4 mounting lug surfaces for the #1 engine. The engine "fell off" when the 4th lug gave way under the overstress of the take off. Whilst it's possible a bird strike was the straw that broke the camels back, the root cause of the accident is the fatigue cracks. It appears the design can withstand cracks in one and two of the 4 lugs, but if/when the third cracks the fourth isn't strong enough to hold it all together. And you wouldn't expect it to be.

So the report will IMHO concentrate on how/why these cracks occur, and how to inspect them such that the fault is detected when the first crack appears, rather than waiting for the engine to fall off when all 4 become cracked. 

[Kevin Wood]

What they're saying is there were pre-accident fatigue cracks in 3 of the 4 mounting lug surfaces for the #1 engine. The engine "fell off" when the 4th lug gave way under the overstress of the take off. Whilst it's possible a bird strike was the straw that broke the camels back, the root cause of the accident is the fatigue cracks. It appears the design can withstand cracks in one and two of the 4 lugs, but if/when the third cracks the fourth isn't strong enough to hold it all together. And you wouldn't expect it to be.

So the report will IMHO concentrate on how/why these cracks occur, and how to inspect them such that the fault is detected when the first crack appears, rather than waiting for the engine to fall off when all 4 become cracked.

Indeed. Bird strike or not, that aircraft was an accident about to happen when it started its take-off roll, and potentially so is the rest of the remaining  MD-11 / DC10 fleet. Given its obsolete status and the fact that there are relatively few airframes left flying, I wouldn't be surprised if the inevitable inspection and rectification actions that would be required to continue safe flight turn out to be prohibitively expensive.

[Doctor Gollum]

Thing is with the DC10/MD11 it's large enough to be useful but not so large as to be too expensive to operate. If UPS and FedEx suddenly have to scrap them, then there's not much to replace them with. The A330 doesn't age well and all the bigger Boeings are either already converted or have been scrapped 

It's a surprise that this failure hasn't happened more often and it will be interesting to see how many aircraft are about to fail. It also begs the question as to how such a high cycle airframe had yet to reach the inspection threshold. Replacing the parts and dropping the inspection to 2,500 hours might be enough.

The only operators that might not be able to afford it are the flying hospital and the fire tankers which is a bit ironic as they're probably better maintained due to their more specialist uses.

[LC0112G]

There are 60 odd ex USAF KC-10's stored in the boneyard at Davis Monthan/Tuscon. They were only retired about a year ago. They've only ever been operated by the USAF, and were in service from 1979 ish. The last ones were built (tecnically funds were allocated) in 1987. The hours and cycles on these airframes will be well documented.

If I were NTSB I'd be asking the USAF if they wouldn't mind stripping the engines and pylons off a handful of them so they can inspect the parts that broke assuming the KC10 uses the same or similar parts.