[HN Gopher] NTSB Preliminary Report - UPS Boeing MD-11F Crash [pdf]
___________________________________________________________________
NTSB Preliminary Report - UPS Boeing MD-11F Crash [pdf]
Author : gregsadetsky
Score : 107 points
Date : 2025-11-20 18:20 UTC (4 hours ago)
(HTM) web link (www.ntsb.gov)
(TXT) w3m dump (www.ntsb.gov)
| frenchman_in_ny wrote:
| Adding summary analysis from AVHerald [0]
|
| [0] https://avherald.com/h?article=52f5748f&opt=0
| tremon wrote:
| > 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 wrote:
| It sounds like the aft lug failed first, and then the not
| quite as compromised forward lug failed in overload.
| the-grump wrote:
| "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 wrote:
| 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.
| ErroneousBosh wrote:
| I block all traffic from Cloudflare outright on my servers.
|
| Every so often they sneak in new blocks of IP addresses
| though so you're playing whack-a-mole with a particularly
| scummy opponent.
| Aman_Kalwar wrote:
| Appreciate the transparency in these reports. The technical
| breakdowns always highlight how complex aviation safety is.
| philip1209 wrote:
| 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.
| cj wrote:
| There might be some truth in that. But the report doesn't
| confirm that theory.
| philip1209 wrote:
| I'm presenting it "useful not true" - not an RCA.
| rconti wrote:
| 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.
| cj wrote:
| That the engine was flung into the fuselage due to
| gyroscopic forces.
| inejge wrote:
| Well, _some_ force flung it inboard and above the
| fuselage (gods, that CCTV stills sequence.) Knowing that
| the engine rotates CCW, there are not many candidates.
| scottlamb wrote:
| 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.
| londons_explore wrote:
| I assume such forces are calculated and added in when deciding
| hot thick to make those mounting brackets.
| baggy_trough wrote:
| 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.
| loeg wrote:
| 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 wrote:
| Aluminum has limited loading cycles
| dreamcompiler wrote:
| I'd be very surprised to read that the aft lug that cracked
| (and the bearing it contained) were made of aluminum. They
| were almost certainly steel or Inconel.
| HumblyTossed wrote:
| Yep. Now do 3 decades of metal fatigue.
| supportengineer wrote:
| Did I understand the report correctly that the part was
| scheduled to be replaced in the future after a certain
| number of hours, it just hadn't hit the threshold yet ?
| tremon wrote:
| If you're referring to this quote (excerpted from the
| AVHerald article linked elsewhere in the thread), I don't
| think so:
|
| > At the time of the accident, N259UP had accumulated a
| total time of about 92,992 hours and 21,043 cycles [..] A
| special detailed inspection (SDI) of the left pylon aft
| mount lugs would have been due at 29,200 cycles and of
| the left wing clevis support would have been due at
| 28,000 cycles
|
| This isn't talking about replacement, only inspection;
| and it wasn't going to happen in the near future: 7k
| cycles at four flights/day means inspection is due in 5
| years.
| PunchyHamster wrote:
| 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 wrote:
| 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.
| dreamcompiler wrote:
| American 191's engine mount failed because of improper
| maintenance. It remains to be seen whether this failure had
| the same cause or if it was something else, such as metal
| fatigue.
| jacobgkau wrote:
| A failure due to metal fatigue would still be a failure
| to properly maintain the aircraft, right? I know by
| "improper maintenance," you're referring to actual
| improper things being done during maintenance, and not
| simply a lack of maintenance. But I'm reading things like
| "the next check would've occurred at X miles," and,
| well... it seems like the schedule for that might need to
| be adjusted, since this happened.
| dreamcompiler wrote:
| Yes, when I said "improper" I meant the American 191
| maintenance crew took shortcuts. The manual basically
| said "When removing the engine, first remove the engine
| from the pylon, then remove the pylon from the wing. When
| reattaching, do those things in reverse order." But the
| crew (more likely their management) wanted to save time
| so they just removed the pylon while the engine was still
| attached to it. They used a forklift to reattach the
| engine/pylon assembly and its lack of precision damaged
| the wing.[0]
|
| Fatigue cracking would be a maintenance issue too but
| that's more like passive negligence while the 191
| situation was actively disregarding the manual to cut
| corners. The crew chief of the 191 maintenance incident
| died by suicide before he could testify.
|
| [0] https://en.wikipedia.org/wiki/American_Airlines_Fligh
| t_191#E...
| tremon wrote:
| If the (FAA-approved) maintenance schedule says "the next
| check should occur at X miles" and X miles hasn't
| happened yet, then it's not going to be classified as
| improper maintenance -- it's going to be classified as an
| incomplete/faulty manual.
|
| Now, of course, if that maintenance schedule was not FAA-
| approved or if the check was not performed at X miles,
| that's going to be classified as improper maintenance.
| inferiorhuman wrote:
| Flipping backwards is what caused the engine to fly to the
| right and land to the right of the takeoff runway. The stills
| in the NTSB preliminary report clearly show the engine flying
| over the aircraft, to the right, and then heading straight
| down.
| albert_e wrote:
| The surveillance video mentioned in page 2 -- from which the
| series of still images are shown -- is that available publicly?
| rft wrote:
| I haven't seen that one, this video [1] includes a different
| angle taken from a vehicle on the airport.
|
| [1] https://youtu.be/POKJUJk_2xs?t=342
| sosodev wrote:
| 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.
| lotsofpulp wrote:
| 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 wrote:
| 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 wrote:
| 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.
| mrguyorama wrote:
| >rectified a long time ago.
|
| There's no such thing as "This is fixed forever". If lax
| maintenance oversight has led to companies re-introducing
| known dangerous maintenance procedures or departing from
| known good ones, then we will be back in the 70s in terms
| of airplane safety and people will have to die again to
| relearn those lessons.
|
| Someone's always trying to claw you in the less safe
| direction. It's a constant battle to not regress.
|
| But IDK, hopefully this plane just got some sort of
| "unlucky" about fatigue somehow, and it doesn't have far
| reaching consequences.
| jeffbee wrote:
| I don't know if it's "sliding back" as much as it is that this
| plane is also fundamentally from the 1970s.
| sosodev wrote:
| The MD-11 was developed after that crash. Shouldn't its
| design and maintenance procedures have been informed by the
| incident?
| buildsjets wrote:
| 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 wrote:
| 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 wrote:
| Aside from the engine detaching, it doesn't appear that
| this incident is in any way similar to the previous
| incident.
| sosodev wrote:
| How do you figure? They're very similar planes. The left
| engine and its pylon detached in both cases during
| takeoff rotation. Both incident reports stated that
| proper maintenance would have prevented the detachment.
|
| The way the situation played out is different but the
| failure mode seems to be very similar if not the same.
|
| The NTSB report itself even references AA-191 as the only
| "similar event".
| ocf wrote:
| The root cause does not appear (at this stage) to be the
| same: incorrect maintenance in AA191 as opposed to
| fatigue cracking here.
|
| Where does this report say proper maintenance would have
| prevented the incident?
| mrguyorama wrote:
| AA-191 was caused by improper maintenance (dreamed up by
| people who were made to cut corners and was never
| compliant with manufacturer spec) damaging the pylons
| holding the engine.
|
| If someone did the same thing again, that would be rather
| unfortunate. Just more deaths for profit, even though we
| know it was dangerous.
|
| The parts that seem to have fatigued and failed were only
| like 80% of the way through their inspection period. They
| were to be inspected after 28k cycles. They were at 21k
| cycles.
|
| It sure looks the same from "Engine pulled itself off and
| flew away" angle, but if there is any similarity under
| the surface that's very bad. Flying was much much less
| safe in the 70s.
| gosub100 wrote:
| 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
| barbazoo wrote:
| > 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 wrote:
| 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
| londons_explore wrote:
| 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?
| lotsofpulp wrote:
| 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 wrote:
| And also ripped open a giant hole in the fuel tank which
| allowed all of the fuel to be released and ignited.
| baggy_trough wrote:
| 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.
| jeffbee wrote:
| Even if they had the thrust (doubtful) there wouldn't be
| enough lift with a gaping hole in the leading edge of one
| wing.
| sq_ wrote:
| 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_attempte
| d_sho...
| crote wrote:
| An important factor in AA 191 is that the engine leaving
| did significant damage to the hydraulic lines in that
| wing - including those for the leading-edge slats. At the
| time the plane was not equipped with any mechanism to
| keep the slats extended, so after hydraulic pressure was
| lost airflow over the wings caused them to retract, which
| significantly lowered that wing's stall speed.
|
| After AA 191 the DC-10 was equipped with a locking
| system: loss of pressure now results in the slats getting
| stuck in their current position. The MD-11 will
| undoubtedly also have this system, so a direct repeat of
| AA 191 is unlikely.
| sokoloff wrote:
| 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.
| PunchyHamster wrote:
| ..for a moment. If there was sufficient hydraulics damage
| it might've stopped being controllable.
|
| And even if they worked the fire might've damaged the
| plane enough.
|
| For example https://www.faa.gov/lessons_learned/transport
| _airplane/accid...
|
| when they lost tail engine, all of the hydraulics went
| down
| loeg wrote:
| I thought the leading edge of the wing was intact in this
| case? I may be misremembering.
| bunderbunder wrote:
| 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 wrote:
| Debris, or even just smoke from the wing fire.
| bunderbunder wrote:
| It was specifically the distinct, rhythmic puffing. I'm
| not sure you could expect the same pattern from debris or
| a wing fire.
| mlyle wrote:
| I think they were saying that smoke/particulates could be
| sufficient to upset the rear engine-- things short of
| what we ordinarily call "debris".
| loeg wrote:
| I'm just saying that smoke alone can cause a compressor
| stall -- it doesn't necessarily require larger debris.
| bunderbunder wrote:
| Ah, gotcha. My bad.
| jpk2f2 wrote:
| 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.
| yuvadam wrote:
| 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.
|
| [1] - https://en.wikipedia.org/wiki/El_Al_Flight_1862
| Bender wrote:
| 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_.
| loeg wrote:
| 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.
| LPisGood wrote:
| This engine didn't just fail, it failed catastrophically and
| took out another engine with it.
| HumblyTossed wrote:
| It nuked the tail engine so actually TWO engines failed.
| chimpontherun wrote:
| surprised to see typos in aviation terms and acronyms: ADS-8
| (page 3) and 747-BF (page 5)
| ynniv wrote:
| pretty weird... NATIONAL TRANSPORTATION
| SAFEN'BOAFID :J11...:i= of ArutiOn SMel@LA5 301
| A.,r Tral1C.IYU';UQlt-Ort!! NTS,B ri@ss @at.Joo JurtJer
| DCA26 22\C2<
| maxbond wrote:
| 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?
| ynniv wrote:
| it would seem so. so the question is why they would
| maintain an air gap for a safety report
| toast0 wrote:
| It's a good policy. Document formats like to include lots
| of random junk, better to be safe.
| Denvercoder9 wrote:
| Swapping B and 8 in both cases, which is typically something
| that happens with OCR. Weird.
| Grollicus wrote:
| 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 wrote:
| With many eyes, all typos are embarrassing.
|
| The new document is an image.
| rft wrote:
| 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.
| SteveNuts wrote:
| 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 wrote:
| 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 wrote:
| The airforce retired the KC-10 in 2021.
| buildsjets wrote:
| The KC-10 went out of service last year. None are
| operating.
| loeg wrote:
| Yeah, but DC-10 based tankers for wildfire fighting were
| still flying until the recent grounding:
| https://en.wikipedia.org/wiki/DC-10_Air_Tanker
|
| (Blancolirio points out that the DC-10 tanker is what
| they modernized to relatively recently -- before that
| they were flying even more dangerous WW2 airframes for
| firefighting.)
| mandevil wrote:
| Damnit, I knew that! Just forgot it in the moment.
| inferiorhuman wrote:
| Most of the DC-10s in service in the US are used for fire
| fighting.
| dingaling wrote:
| And with Omega Air, for contracted air refuelling
|
| https://www.omegaairrefueling.com/
| mandevil wrote:
| Yes, but there are many MD-11's still flying as
| freighters. There are four fire-fighting DC10's out of ~8
| still flying, but there are 25 Mad Dogs (MD-11) at UPS,
| 38 with FedEx, and Western Global has 4, so there are
| plenty of MD-11F's around.
| dreamcompiler wrote:
| Here are 4 of them. All grounded now.
|
| https://www.10tanker.com/gallery
| rft wrote:
| 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 wrote:
| One other accident that was similiar, but these planes have
| had a ton of crashes for other reason.
| rft wrote:
| I managed to find some statistics on hull losses per
| million departures [1, p. 13]. Seems like indeed MD-11s
| have a highish rate of incidents by that metric compared
| to other types, even if they are not catastrophically
| less safe than other planes. That metric stacks the
| statistics a bit against cargo planes, which most (all?)
| MD-11s are now. These planes tend to fly longer haul
| instead of short hop, so you get more flight time/miles
| but less departures. There are also likely some other
| confounding factors like mostly night operations
| (visibility and crew fatigue) and the tendency to write
| off older planes instead of returning them to service
| after an incident. Plus these aircraft have been in
| operation long enough that improvements in procedures and
| training would impact them less than more modern types,
| as in they already had more accidents before these
| improvements.
|
| [1] https://www.boeing.com/content/dam/boeing/boeingdotco
| m/compa...
| inferiorhuman wrote:
| The DC-10 had a number of other problems, but the MD-11
| has always had a reputation of being an unforgiving
| aircraft especially when compared to the DC-10. It's less
| about training and more that the MD-11 was simply too
| many design compromises piled on to an old design.
|
| The MD-11 had a pretty short service life as a passenger
| aircraft because it simply wasn't very fuel efficient
| compared to the competition, safety wasn't really the
| motivating factor. However fuel consumption was behind
| some of the poor design choices McDonnell/Boeing made. In
| broad strokes: McDonnell/Boeing shrunk the control
| surfaces to improve fuel consumption "necessitating"
| poorly designed software to mask the dodgy handling and
| higher landing speeds. This exacerbated a DC-10 design
| "quirk" where hard landings got out of hand very quickly
| and main landing gear failure would tend to flip the
| plane.
|
| Yeah you can train around this but when something else
| goes tits up you've got a lot less leeway to actually
| recover safely.
| loeg wrote:
| Airlines haven't been using them, or at least not 1st world
| airlines. Just freight and wilderness fire fighters.
| mrpippy wrote:
| UPS and FedEx each have around 25 MD-11s, Western Global has
| 2 I think, the Orbis Flying Eye Hospital is an MD-10, some
| cargo airline in Botswana has one, and 10 Tanker has some
| DC-10 firefighting tankers.
|
| That's the entire worldwide fleet.
| virtue3 wrote:
| Most of them are used as cargo planes. Which have
| dramatically lower usage rates than passenger planes (and
| they are retired passenger planes)
|
| Sucks for the pilots flying them for sure tho.
| bunderbunder wrote:
| 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.
| loeg wrote:
| 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?
| potato3732842 wrote:
| > in which case, why have the tail engine at all?
|
| "you know what this motorized piece of anything needs, less
| power"
|
| -nobody, ever
| loeg wrote:
| You know you can just make the wing engines 50% more
| powerful, right?
| MBCook wrote:
| It wasn't failed. It was designed for a very specific
| reason and served that purpose well.
|
| Once the reason went away, better designs took over.
|
| They were designed to allow smaller jets to fly over the
| ocean further than a two engine jet was allowed (at the
| time). Airlines didn't want to waste all the fuel and
| expense of a huge 4 engine jet, but 2 wouldn't do. Thus:
| the trijet.
|
| The rules eventually changed and two engine jets were
| determined to be safe enough for the routes the trijets
| were flying.
|
| Using two engines that were rated safe enough used less
| fuel, so that's what airlines preferred.
|
| It was never designed to be used anywhere else as a general
| design. Two engines did that better.
| inferiorhuman wrote:
| In the case of the quad jets, Boeing tried the 747-SP and
| had minimal marketing success.
|
| In the case of the trijets the MD-11 lived on as a
| freighter because it had a much higher capacity than
| anything else smaller than a 747. It was
| never designed to be used anywhere else as a
| general design. Two engines did that better.
|
| Not quite. Dassault still makes a three engined bizjet
| and in theory the Chinese fly a three engined stealth
| jet.
| buildsjets wrote:
| 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/lesso
| ns_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 wrote:
| 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.
| rft wrote:
| 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 wrote:
| 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.
| 16bytes wrote:
| > 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.
|
| I think you conflated flights (several 10Ks per day) with
| passengers (several million per day).
|
| One in a million flights is one accident every few
| decades.
|
| > at least in the US. Engines will fail
|
| As per the report, this appears to be a structural
| failure, not an engine failure.
| wat10000 wrote:
| If randomly distributed, one in a million flights
| crashing and killing all passengers means that one in a
| million passengers dies.
|
| The US sees about 25,000 airline flights per day, or
| around 9 million per year. So with one in a million
| flights crashing, we'd expect roughly 9 crashes per year.
| ralph84 wrote:
| 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.
| lazide wrote:
| 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 wrote:
| > 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 wrote:
| 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.
| inferiorhuman wrote:
| Fully functioning engines departing from aircraft isn't
| common but it's not unheard of either. Off the top of my
| head it's happened a few times on the 747 and 737.
| cyberax wrote:
| > 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.
| PunchyHamster wrote:
| 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.
| dzonga wrote:
| McDonnell-Douglass right there that's where the problems start.
| GiorgioG wrote:
| It's just time to kill the MD-11 entirely. These 3-engine
| aircraft are too risky to continue flying.
| LinuxAmbulance wrote:
| 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?
| LPisGood wrote:
| I'm seeing 2021 on page 10 - an I missing something?
| loeg wrote:
| 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.
| serhack_ wrote:
| Not an aviation expert, nor I want to be one, but the images look
| pretty intense.
| pseudosavant wrote:
| It is incredible to me how quickly some lives can go from
| "another day as usual" to "gone" in a matter of seconds.
| kurtoid wrote:
| Link doesn't seem to be available now:
|
| > Page not found
|
| > The page you're looking for doesn't exist.
| zorgmonkey wrote:
| 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 wrote:
| Your first link is working fine
| zorgmonkey wrote:
| Yeah working again for me too, they're probably having some
| sort of server problems
| AceyMan wrote:
| 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 wrote:
| Link to page that links to the report, as of now:
| https://www.ntsb.gov/investigations/Pages/DCA26MA024.aspx
| waiwai933 wrote:
| Looks like it's been moved to
| https://www.ntsb.gov/investigations/Documents/DCA26MA024%20P...
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(page generated 2025-11-20 23:00 UTC)