NTSB Preliminary Report – UPS Boeing MD-11F Crash [pdf]
104 comments
·November 20, 2025philip1209
PunchyHamster
I think far simpler explanation is "the back part failed first and engine is making thrust so it just flipped over on now-hinge mounting
mrb
Yup. That's exactly what experts said of American Airlines flight 191 which was basically the same engine mount, same failure. Engine flipping over the wing.
cj
There might be some truth in that. But the report doesn't confirm that theory.
rconti
What theory? That the mount failed? Or the rotation of the engine in the photos going up and over the fuselage?
It seems like both are true, but doesn't necessarily prove WHY the mount failed.
scottlamb
Not an aviation expert at all, so take this with a grain of salt, but I think "the spinning engine resists changes to the direction of its spin axis" offers two important insights:
* why it failed at rotation (the first/only sudden change of direction under full throttle) rather than as soon as it was mounted onto the plane, while taxiing, as soon as they throttled up, mid-flight, or on landing. This is important because at rotation is the worst possible time for this failure: no ability to abort take-off, no ability to land safety under no or severely limited power, little time to react at all, full fuel. Knowing these failures are likely to manifest then stresses the importance of avoiding them.
* why it failed in such a way that it damaged the rest of the plane.
Not so much what was wrong with the mounting in the first place, if that's what you're asking. Presumably it was designed to withstand the forces of this moment and clearly has done so many times before.
cj
That the engine was flung into the fuselage due to gyroscopic forces.
philip1209
I'm presenting it "useful not true" - not an RCA.
londons_explore
I assume such forces are calculated and added in when deciding hot thick to make those mounting brackets.
loeg
Yes, obviously; MD-11s aren't flinging engines off the wing every single takeoff. A 34 year old airframe may or may not actually match design strength, though.
shtzvhdx
Aluminum has limited loading cycles
baggy_trough
Yes, but the point is that this moment of the takeoff is when a failure that's been waiting to happen is most likely both because of the thrust and the gyroscopic resistance.
kurtoid
Link doesn't seem to be available now:
> Page not found
> The page you're looking for doesn't exist.
zorgmonkey
I found a link to the PDF that seems to work https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/G...
Also in case that link stops working I got it from this page https://www.ntsb.gov/investigations/Pages/DCA26MA024.aspx
EDIT: nevermind immediately after posting this comment it is now giving a 403 error
greenavocado
Your first link is working fine
zorgmonkey
Yeah working again for me too, they're probably having some sort of server problems
AceyMan
If anyone saved a copy locally, it'd be great if you could share it somewhere. (I, for once, did not, and the tab is gone now :-/ ).
haeberli
Link to page that links to the report, as of now: https://www.ntsb.gov/investigations/Pages/DCA26MA024.aspx
frenchman_in_ny
Adding summary analysis from AVHerald [0]
the-grump
"Your IP address 104.28.103.15 has been used for unauthorized accesses and is therefore blocked! Your IP address belongs to Cloudflare and is being used by many users, some of which are hackers and hide behind the cloud/proxy to avoid being tracked down. Hence the automatic defense closed access from that IP address.
"Make sure to not use a proxy/cloud service for visiting AVH (e.g. Apple Users turn off your private relay) but your native IP address, then access should be possible without a problem again."
No thank you, AV Herald.
kube-system
That's a pretty nice message. Most sites that filter VPNs and proxies just kill the connection, give a generic error, or subject you to endless captchas.
tremon
> 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
If I'm parsing this correctly, they're saying that fatigue cracks should have been visible in the aft pylon mount, and that the forward mount was similarly fatigued but showed no damage on the outside?
pfdietz
It sounds like the aft lug failed first, and then the not quite as compromised forward lug failed in overload.
Aman_Kalwar
Appreciate the transparency in these reports. The technical breakdowns always highlight how complex aviation safety is.
rft
Grounding all MD-11s and DC-10s is a major move. I guess it makes sense as a big factor was the fatigue cracks on the pylon (lugs), despite the pylon not being behind on inspections. I am wondering what the inspections of pylons in other planes will yield, likely that will determine whether the grounding will continue.
But beyond figuring out why the engine mount failed, I am very interested in what caused the actual crash. "Just" losing thrust in a single engine is usually not enough to cause a crash, the remaining engine(s) have enough margin to get the plane airborne. Of course this was a major structural failure and might have caused additional damage.
EDIT: It seems there was damage to the engine in the tail, even though this was not specified in the preliminary report, likely because it has not been sufficiently confirmed yet.
PunchyHamster
It wasn't just one engine off, aside from possibly damaging tail engine you also have damage to the wings and control surfaces that might've just not got enough lift because of that.
bunderbunder
And if the failure of a wing engine can cause the rear engine to fail, that would raise concerns about all "two in front one in back" trijets. Similar to how putting the Space Shuttle orbiter's heat shield directly in the line of fire for debris that comes off he rocket during launch turned out to be a bit of a problem.
ralph84
At this point there aren’t any trijet designs like that being built, and it’s unlikely we’ll ever see a new trijet design. It served a role in the transition from four engines to two, but now with ETOPS-370 there’s no commercially viable route that can’t be served with an appropriate twinjet.
buildsjets
And the failure of an inboard wing mounted engine can cause the failure of an outboard wing mounted engine on the same side, as in the case of El Al 1862. https://www.faa.gov/lessons_learned/transport_airplane/accid...
And the failure of an engine mounted on the left wing can cause debris to cross through the fuselage structure and cause a failure of the engine mounted on the right wing, or to fly thousands of feet in any particular direction, as happened to American Airlines in both a ground run incident, and in their Flight 883 accident.
https://www.dauntless-soft.com/PRODUCTS/Freebies/AAEngine/
https://aerossurance.com/safety-management/uncontained-cf6-a...
bunderbunder
The industry also responded to those crashes. For example, the El Al 1862 incident prompted a redesign of the engine strut that was subsequently mandated as a retrofit for all 747s.
And here's a more detailed description of that ground run incident. It also found that the failure was related to a design flaw, and mandated that aircraft be grounded for inspection and rework. https://skybrary.aero/accidents-and-incidents/b762-los-angel...
I'm not a regulator or aerospace engineer or anything like that so I can't really say which actions are or are not appropriate. But I do want to observe that these are all unique failures with unique risk profiles that can't all be painted with a single broad brush. All I was trying to do in the previous post was speculate on why a MD-11 failure could result in a grounding of the DC-10 and KC-10A as well. The first thing that came to mind is that I think those are the only remaining trijets of that general shape that are still around. Though I suppose another possibility is that they all share an identical pylon design or something like that.
loeg
Yeah, the trijet design seems failed in general. Unless you can design it to tolerate any wing+tail dual engine failure -- in which case, why have the tail engine at all?
rft
At some point it comes down to probabilities. With so many flights going on, one in a million incidents become a certainty. For example UA232 [1] suffered failure in all 3 redundant hydraulic systems due to an uncontained engine failure. Any of the 3 systems would have been enough to retain control of the aircraft. Of course this lead to some investigations on why all 3 systems could be impacted at the same time and what can be done to limit failures.
Besides the technical aspects that flight is an impressive example of resilience and skill. Bringing that plane down to the ground in nearly one piece was essentially impossible and a one in a million chance in itself.
[1] https://en.wikipedia.org/wiki/United_Airlines_Flight_232
wat10000
Airlines operate to a much stricter standard than one in a million. If one in a million flights ended in a fatal crash, the US alone would see about 3 airline passenger deaths per day on average. The actual average over the past 10 years is under 0.02 deaths per day.
It's true that you can never get to zero. There's always a chance of some catastrophic failure. The lesson of modern airline safety is that you can get extremely close to zero by carefully analyzing and learning from the failures, which is exactly why these thorough investigations are done. The lesson from UA232 was to make sure one failure can't take out all of the hydraulic systems.
In this specific instance, "the engine fell off and took out another engine, leaving the aircraft with insufficient power to climb" is definitely not in the realm of "probabilities will get you eventually." It's very much in the realm of a mechanical failure that should not happen, combined with a bad design flaw that turns that failure from a mere emergency into pretty much guaranteed death.
Cargo is held to a lower standard than passenger service, but I suspect this will still spell the end of the DC-10 and MD-11, at least in the US. Engines will fail, and for an aircraft of this size, that needs to be survivable in all phases of flight just for the safety of people on the ground.
SteveNuts
Even if they end the grounding of the MD-11/DC-10 I'd be shocked if any airlines still using them will continue to use them.
Seems like the risk/reward just isn't really there for the few of them still in service, and if anything happened it would be a PR nightmare on top of a tragedy.
Definitely an end of an era!
mandevil
I think that the Mad Dogs only exist as freighters (~or their derivative KC-10 tankers~-Edited to correct that they retired last year) these days. I think the last pax service for any of them was over a decade ago.
And air freight just gets a lot less public attention, I think they are going to keep flying them if they don't get grounded.
joleyj
The airforce retired the KC-10 in 2021.
buildsjets
The KC-10 went out of service last year. None are operating.
inferiorhuman
Most of the DC-10s in service in the US are used for fire fighting.
rft
Given that the report only mentioned a single other seemingly related accident in 1979 I am not sure that objectively this is a reason to discontinue flying these planes. The fact that these planes have been in service since the early 70s is a testament to their safety and reliability in itself. Of course public perception, especially with the videos of huge fireballs from hitting one of the worst possible locations, might put enough pressure on airlines to retire the planes anyway.
I agree on the end of an era. Hearing something else besides just Airbus- or Boeing-something always gives me a bit of joy. Even though MDs and DCs are of course Boeings in a sense now as well.
TinkersW
One other accident that was similiar, but these planes have had a ton of crashes for other reason.
loeg
Airlines haven't been using them, or at least not 1st world airlines. Just freight and wilderness fire fighters.
cyberax
> EDIT: It seems there was damage to the engine in the tail, even though this was not specified in the preliminary report, likely because it has not been sufficiently confirmed yet.
Yes, the initial videos were showing the tail engine flaming out. And in the 1979 crash, the engine also severed hydraulic lines that hold the slats extended. So they folded in due to the aerodynamic pressure, essentially stalling the wing.
lazide
Based on the original descriptions of the crash, I assumed the engine fell off.
From the photos, it’s clear it went up over the wing and impacted the fuselage with a (at least) minor explosion, which would have thrown foreign objects into the third engine in the tail for sure.
Losing 2/3 of the engines isn’t survivable on takeoff for this class of plane, at the weights they were at.
crote
> I assumed the engine fell off
It's an engine - the thing pushing the entire plane forwards. Provided it is running (and at takeoff that's definitely the case), an engine being liberated from its plane suddenly has a lot less mass holding it back, so the logical thing to do is to shoot forwards. And because the wing is attached to the upper side of the engine, anything short of an immediate failure of all mounting points is probably also going to give it an upwards trajectory.
Add in air resistance, and you get the "swing across the wing and back" seen in the photos.
lazide
Sure, but if the engine grenades it can take it’s mounts with it and not shoot off like a bottle rocket in front of and over the plane, dropping down and under the plane instead (or even just sit there). Same with a compressor stall, or whatever.
It’s clear from the photos this wasn’t the engine failing at all, and in fact the engine kept producing a ton of thrust (probably until it ran out of fuel as it pulled it’s fuel line apart while departing the wing), and instead the thing that is supposed to be so incredibly strong that it restrains all this chaos failed.
Which is a pattern in this family of aircraft, but definitely not a common or normal thing in general eh?
Most aircraft, the engine stays with the airframe even if it turns into a giant burning pile of shrapnel and dead hopes and dreams.
londons_explore
I was under the impression that a plane could deal with an engine failure at any point in flight - including during takeoff.
Dropping an engine entirely is a similar situation to a failure - with the benefit that you now have a substantially lighter if imbalanced aircraft.
Should this plane have been able to fly by design even with an engine fallen off?
yuvadam
El Al 1862 was another flight [1] that had an engine fall off, taking another engine out with it. The pilots managed to fly around for a few minutes and attempt a landing, but there was too much structural damage.
It doesn't seem aircraft are designed to survive these types of catastrophic failures.
loeg
They seem to have lost the tail engine too. Yes, it is a significant problem that engine failures aren't independent, so trijets are kind of a bad design.
Bender
From the wing down I assumed it may have depended if the engine coming out unintentionally means redundant hydraulic lines and mounts are also getting disconnected causing a complete loss of control not that it would have helped much at that point beyond minimizing ground damages.
jpk2f2
Not only did it happen at the worst possible moment, it took out a second engine on it's way out and over the plane. Two engines should've been enough to get off the ground and potentially land the plane, but one engine on a trijet isn't enough.
LPisGood
This engine didn’t just fail, it failed catastrophically and took out another engine with it.
baggy_trough
Yes, but when the engine came off, it also disrupted the third engine in the tail. Can't take off in this model with 2 out of 3 engines gone.
bunderbunder
Yeah, pilots I know saw puffs of flame coming out of the engine, and said that that's a tell-tale sign of a compressor stall. Which could have been caused by debris from the separating left engine striking the turbine.
loeg
Debris, or even just smoke from the wing fire.
jeffbee
Even if they had the thrust (doubtful) there wouldn't be enough lift with a gaping hole in the leading edge of one wing.
sokoloff
The video of the aircraft crossing the road wings level (well after #1 separated) and maintaining relatively controlled flight until too much energy bled off suggests to me the aircraft was likely to be controllable to a landing if sufficient thrust was available.
loeg
I thought the leading edge of the wing was intact in this case? I may be misremembering.
sq_
Yeah, if they had had more altitude, I would guess that this would have looked even more like the AA 191 crash from 1979, with the left wing stalling and causing a roll and pitch down.
That in turn reminds me of the DHL flight out of Baghdad in 2003 that was hit by a missile [0]. Absolutely amazing that they managed to keep it together and land with damage like that.
[0] https://en.wikipedia.org/wiki/2003_Baghdad_DHL_attempted_sho...
lotsofpulp
It didn’t fall off, it flew up and then landed back on the plane.
https://www.reddit.com/r/aviation/comments/1p276xx/ntsb_issu...
buildsjets
And also ripped open a giant hole in the fuel tank which allowed all of the fuel to be released and ignited.
LinuxAmbulance
I'm surprised at how many years the plane went without having that part inspected. It looks like the failure was due to fatigue cracks, but the last time the part was inspected was in 2001?
loeg
I believe the part was at least visually inspected in 2021:
> A review of the inspection tasks for the left pylon aft mount found both a general visual inspection (GVI) and a detailed visual inspection of the left pylon aft mount, required by UPS's maintenance program at a 72-month interval, was last accomplished on October 28, 2021.
null
LPisGood
I’m seeing 2021 on page 10 - an I missing something?
sosodev
A commenter in HN thread covering the initial crash mentioned that the left engine detaching might have been the cause https://news.ycombinator.com/item?id=45821537
The referenced AA Flight 191 is shockingly similar. It makes me wonder if aviation really is back sliding into a dangerous place.
barbazoo
> The referenced AA Flight 191 is shockingly similar. It makes me wonder if aviation really is back sliding into a dangerous place.
I think it's cut throat capitalism at its best. Surely it was much too safe before, let's see how far back we can scale maintenance on the operations front but also how far back can you scale cost during development and production and then see where it takes us. If that changes the risk for population from 0.005 to 0.010, the shareholders won't care and it's great for profits.
I think we can see both but especially the latter with Boeing.
dingaling
The entire MD-11 project was a budget-limited rush-job to try to capture some market share before the A340 and 777 came into service.
It produced an aircraft that failed to meet its performance targets, was a brute to fly and was obsolete the moment its rivals flew.
Douglas* by the early 1990s was a basket-case of warmed-over 1960s designs without the managerial courage to launch the clean-sheet project they needed to survive.
* as a division of MDC
jeffbee
I don't know if it's "sliding back" as much as it is that this plane is also fundamentally from the 1970s.
sosodev
The MD-11 was developed after that crash. Shouldn't its design and maintenance procedures have been informed by the incident?
buildsjets
The MD-11 is nothing but a re-engined and a re-named DC-10. They share the same type certificate.
https://www.easa.europa.eu/en/document-library/type-certific...
loeg
Maintenance was informed by the earlier incident. It's why we haven't seen even more DC-10/MD-11 failures sooner. Designs too have kinda been informed by this -- it's not like Boeing or Airbus make trijets anymore.
0xffff2
Aside from the engine detaching, it doesn't appear that this incident is in any way similar to the previous incident.
gosub100
40 years between severe accidents is fine in terms of expected failures. It's also not a good comparison because in the 70s maintenance crew were using a forklift to remive engines, improperly stressing the engine pylon. This was done as a shortcut
lotsofpulp
Are you referring to AA 191 in 1979? That seems like low enough frequency event to not be worried about it.
The murder suicides in the last few decades seem more concerning.
crote
Rather the opposite: if the cause is similar to AA 191, why weren't the actions taken after AA 191 to prevent a repeat effective? If we can get a repeat of that incident, what's preventing the industry from repeating the mistakes from all those other incidents from the past decades? Why aren't they learning from their past mistakes - often paid for in blood?
lotsofpulp
I understood the post I responded to to be referring to the cause as the engine detaching from the same type of plane, not the root cause for why the engine detached. Per the “investigation section” in the wikipedia article, I would be surprised if it was the same root cause:
https://en.wikipedia.org/wiki/American_Airlines_Flight_191
I assume the erroneous maintenance procedures that led to the loss of AA191 were rectified a long time ago.
null
chimpontherun
surprised to see typos in aviation terms and acronyms: ADS-8 (page 3) and 747-BF (page 5)
Grollicus
Reminds me of xerox scanner fun, maybe someone scanned it to pdf to publicise?
Nontheless the pdfs have been replaced and the newer ones don't seem contain these errors anymore.
maxbond
With many eyes, all typos are embarrassing.
Denvercoder9
Swapping B and 8 in both cases, which is typically something that happens with OCR. Weird.
ynniv
pretty weird...
NATIONAL TRANSPORTATION SAFEN'BOAFID
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A.,r Tral1C.IYU';UQlt-Ort!!
NTS,B ri@ss @at.Joo JurtJer
DCA26 22\C2<maxbond
These all seem like OCR errors...? Why would there be OCR in this workflow? Did they print this out and then generate a PDF from a scan instead of the original source? To maintain an air gap maybe?
null
ynniv
it would seem so. so the question is why they would maintain an air gap for a safety report
serhack_
Not an aviation expert, nor I want to be one, but the images look pretty intense.
pseudosavant
It is incredible to me how quickly some lives can go from "another day as usual" to "gone" in a matter of seconds.
Originally explained on the blancolirio channel on YouTube -
The timing and manner of the break make a lot more intuitive sense when you consider that the engine is essentially a massive gyroscope. As the plane starts to rotate, the spinning engine resists changes to the direction of its spin axis, putting load on the cowling. When the cowling and mount fail, that angular momentum helps fling the engine toward the fuselage.