[HN Gopher] NTSB Preliminary Report - UPS Boeing MD-11F Crash [pdf]
___________________________________________________________________
NTSB Preliminary Report - UPS Boeing MD-11F Crash [pdf]
Author : gregsadetsky
Score : 204 points
Date : 2025-11-20 18:20 UTC (1 days 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.
| toast0 wrote:
| > 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?
|
| If you can get to the report, Figure 7 shows the left pylon,
| with the forward and aft lug enlarged in the inset. Both lugs
| cracked on two sides. They're saying both cracks on the aft
| lug as well as the inboard crack on the forward lug were
| observed to be fatigue cracks, but the forward lug outboard
| fracture was observed to be entirely a stress crack.
|
| Outboard and inboard are just away from and towards the
| center of the plane. On the left pylon, that's left and
| right, respectively. So, it looks like the left side crack in
| the forward lug developed from overstress, but the other
| three cracks were from fatigue. My expectation is that
| fatigue should be apparent upon the right kind of inspection,
| if timely, even if the metal has yet to fracture.
| 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.
| trollbridge wrote:
| They're pretty upfront about their ranges:
|
| https://www.cloudflare.com/en-au/ips/
|
| Or if you prefer:
|
| https://www.cloudflare.com/ips-v4/#
| worewood wrote:
| They could've blocked just the comments, allowing at least
| read-only access to the site, instead of blocking it off
| entirely
| kube-system wrote:
| So could everyone that blocks network traffic for various
| reasons, but usually they don't because they're not doing
| it in the primary application layer, but using a WAF or
| reverse proxy or something else in front of their
| application... and also most DGAF to cater specifically
| to the users they block.
|
| Again, you're usually lucky to even get a return packet.
| 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.
| JumpCrisscross wrote:
| > _Knowing that the engine rotates CCW, there are not
| many candidates_
|
| There are _lots_ of candidates for a failing engine
| yeeting itself in any direction.
| inejge wrote:
| > There are lots of candidates for a failing engine
| yeeting itself in any direction.
|
| For the precise trajectory, certainly; for the general
| direction, not so much. Could you describe a combination
| of forces that would have thrown that engine to the left
| of the direction of travel? (We're talking about this
| accident, not any engine anywhere.)
| JumpCrisscross wrote:
| > _Could you describe a combination of forces that would
| have thrown that engine to the left of the direction of
| travel?_
|
| Foreign object gets yeeted to the right. Internal
| component gets yeeted to the right. Engine exploded on
| its right side.
|
| I think each of those is more likely than gyroscopics
| since the engine went to the left. Not left and up.
| inejge wrote:
| > [...] the engine went to the left. Not left and up.
|
| Whatever you're describing, it's not this accident. Over
| and out.
| JumpCrisscross wrote:
| You're correct-I didn't look at the photos.
|
| My broad comment is that gyroscopic precession having any
| critical role in this is incredibly far fetched. That
| said, I've never flown or worked on a turbofan so
| -\\_(tsu)_/-.
| sandworm101 wrote:
| Gyroscopic forces might have changed the direction of
| travel a few degrees, but the motive force comes from the
| engine's thrust, the power of its spinning blades pushing
| air. An engine cut loose at full power moves forward like
| a missile.
| 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.
| psunavy03 wrote:
| > Presumably it was designed to withstand the forces of
| this moment and clearly has done so many times before.
|
| The report seems to suggest metal fatigue in the motor
| mount may be a possible culprit.
| magicalhippo wrote:
| Not the motor mount but the pylon mount. The pylon was
| found attatched to the engine with both engine mounts
| attached.
|
| But yes, the report mentions stress factures where the
| aft pylon mount failed.
| stackghost wrote:
| This is a preliminary report. Its purpose is to present
| initial evidence/information.
|
| The final reports are always much more comprehensive.
| 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.
| CoastalCoder wrote:
| Wouldn't that be true of all cast metal objects?
|
| Or are some metals impervious?
| harshreality wrote:
| No; roughly, yes. Based on the crystal structure of the
| metal, fatigue works differently.
|
| > The fatigue limit or endurance limit is the stress
| level below which an infinite number of loading cycles
| can be applied to a material without causing fatigue
| failure.[1] Some metals such as ferrous alloys and
| titanium alloys have a distinct limit,[2] whereas others
| such as aluminium and copper do not and will eventually
| fail even from small stress amplitudes.
|
| https://en.wikipedia.org/wiki/Fatigue_limit
| hnuser123456 wrote:
| I know Veritasium gets posted here a lot, but a few days
| ago he posted a deep-dive into the the engineering of jet
| engine turbine blades. Turns out they're made from a
| single crystal of a superalloy that entangles itself at a
| molecular level such that it actually gains strength as
| it's heated, only losing strength above 1200 degrees C /
| 2200 degrees F. Below that temperature, as long as the
| strain on the part is below the plastic deformation
| threshold, it's not really losing any strength at all
| over time.
|
| https://www.youtube.com/watch?v=QtxVdC7pBQM
| 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.
| phire wrote:
| _" 7k cycles at four flights/day"_
|
| It wasn't doing four flights per day. As a long-distance
| cargo aircraft it was doing two flights per day, and I
| doubt it was flying every single day of the week.
|
| So we are talking about at least 10 years before that
| inspection was due.
| 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...
| jacobgkau wrote:
| > The crew chief of the 191 maintenance incident died by
| suicide before he could testify.
|
| To be clear, _a_ crew chief (Earl Russell Marshall) did.
| But he wasn 't directly involved in maintenance of the
| specific DC-10 that crashed. Or at least, I haven't found
| a source saying he was, and some sources say he wasn't.
| https://www.upi.com/Archives/1981/03/26/The-wife-of-an-
| airli...
| 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.
| jacquesm wrote:
| A more likely metric for this particular inspection would
| be hours or cycles, in other words starts and landings,
| not 'miles'.
| masklinn wrote:
| According to various comments the plane was nowhere near
| the cycling for a special detailed inspection of the aft
| pylon mount lugs: SDI is at 29200 cycles and the plane
| had 21043.
|
| There was a lubrication task in October, but according to
| tech comments that would just in greasing the zero
| fittings, no taking apart anything.
| jacquesm wrote:
| Those pictures of that torn up part are pretty hefty,
| that's a clean break, no stretching as far as I can see
| it just tore the material in half, you can see the grain.
| There does not seem to be any torsion either so most
| likely that was the first part to go, if the problem had
| been in the engine then I would expect this part to be
| mangled, not pulled apart. What stress damage there is
| occurred shortly after that first break. A valid question
| would be whether or not that crack was there before take-
| off or not.
|
| I'm very curious what the metallurgic analysis of the
| mirror part on the other wing will come up with,
| especially whether there are any signs of stress
| fractures in there. If there are that will have
| substantial consequences for the rest of the still flying
| MD11's, about 50 or so are still in service.
| masklinn wrote:
| The preliminary report mentions fatigue cracks on both
| sides of the aft lug, and one side of the forward lug,
| with the other showing no trace of fatigue, only
| overstress.
|
| From this it seems like the aft lug was way fucked, and
| the forward lug was hanging on for dear life, until it
| could not.
| jacquesm wrote:
| Yes, that's exactly how I read it. The aft lug was the
| first to go, the forward lug shows signs of stress so it
| held on longer.
|
| I don't think they're going to be skimpy on the
| metallurgy report so looking forward to the analysis of
| the mirror parts on the other wing. Those will tell
| without a doubt whether it was maintenance related or age
| related fatigue. Right now I would bet on the latter but
| the former could also still be a factor, for instance,
| that bearing might not have had enough lubricant.
| masklinn wrote:
| Zer _k_ fittings, not zero (stupid autocorrect), the
| grease fittings.
| myself248 wrote:
| Grease nipples. They had a perfectly fine name already,
| which autocarrot was perfectly happy to spell.
| class3shock wrote:
| It depends. This aircraft was made near the beginning of
| the MD-11 production and if the original analysis for the
| fatigue life of this location was wrong, then you would
| expect to see that appear in older aircraft first. If
| that ends up being the case then it's not an inspection
| or maintenance issue, it's an engineering failure. Given
| aerospace accident history I would say that is less
| likely than some maintenance issue but we won't know for
| sure for a bit.
| jacquesm wrote:
| Even if it _was_ an inspection or maintenance issue
| (which given the kind of failure and available data looks
| increasingly doubtful, though it can not yet be ruled
| out) this part failed in a catastrophic way when it
| should have had _ample_ engineering reserve over and
| beyond the load to which it was subjected. It just
| snapped clear in half those breaks are indicative of a
| material that has become brittle rather than that the
| part deformed first and then broke due to excess stress.
|
| In other words, a slow motion video of a camera aimed at
| that part during the accident would have shown one of the
| four connections giving way due to fatigue cracks and
| then the other three got overstressed and let go as well,
| in the process damaging the housing of the spherical
| bearing.
|
| The part at the bottom of page 9 is the key bit. Now I
| very much want to see the state of the mirror part on the
| other wing, that will show beyond a doubt whether it was
| maintenance or an over-estimation of the design life of
| that part.
|
| It would also be interesting to have a couple of these
| pulled from the fleet and tested to destruction to
| determine how much reserve they still have compared to
| the originally engineered reserve.
| lazide wrote:
| According to the preliminary report, 3 of the 4 showed
| fatigue cracks, and the 4th overstressed. So yes, agree a
| random sample of these parts should be pulled from the
| fleet and tested - but something pretty crazy was
| happening here re: fatigue.
|
| That it was so far from the maintenance schedule to be
| inspected AND that the fatigue cracks seem to have formed
| in areas that would be hard to visually inspect anyway
| points to either a engineering problem (especially bad,
| since the DC10 problem of a similar nature happened in
| roughly the same parts, albeit due to different abuse -
| you'd think the engineers would overdo it there, if
| nothing else), or some specific type of repeated abuse
| that particular pylon received, which is pointing more to
| a design problem.
| jacquesm wrote:
| > you'd think the engineers would overdo it there, if
| nothing else
|
| No kidding, especially given the lack of redundancy in
| the design.
| dboreham wrote:
| Re-reading the 1979 report might be helpful here. This
| isn't my field, but it seems that the engine is attached
| "hard" to the pylon, then the pylon is attached via a
| bearing mount system to the wing frame. The bearings wear
| out, and hence have to be replaced (not sure how often,
| but they were doing it on the entire fleet prior to the
| 1979 crash). The 1979 investigators thought that the
| fatigue cracks were caused by removal of the entire
| pylon/engine assembly as one unit (because that put
| excess stress on the aft bearing, they suspected due to
| support being provided from below by a fork lift). After
| the 1979 accident engines had to be removed first, then
| pylon, supposedly removing that cause for mount cracking.
| Perhaps there was another cause.
| sokoloff wrote:
| Before the 1979 accident, engines _also_ had to be
| removed first.
|
| Airlines have to follow the approved maintenance manual
| procedures; that manual called for engine removal and
| installation from a pylon that was on the wing. American
| was improvising a maintenance procedure without the legal
| authority to do so, resulting in 191.
| jacquesm wrote:
| The picture of that part that is torn into two pieces
| certainly seems to suggest so, that's a clean break, not
| an overstressed part deforming and then breaking.
| dboreham wrote:
| If you read the original 1979 report in full, I think
| you'll begin to realize that this "improper maintenance"
| thing was a cover-up. Actually quite similar to the
| 737MAX -- find someone or something to blame other than
| the design of the aircraft, then move on.
| jsr0 wrote:
| The failure of the pylon appears to be different. On AA
| 191, the pylon rear bulkhead cracked and came apart. In the
| case of UPS flight 2976, the pylon rear bulkhead looks to
| be in one piece, but the mounting lugs at the top of the
| rear bulkhead cracked.
|
| Admiral Cloudberg has a great article on AA 191 that covers
| exactly what happened:
| https://admiralcloudberg.medium.com/rain-of-fire-falling-
| the...
| rob74 wrote:
| Ironically, AA flight 191 could have been salvageable,
| because the engine detaching didn't start a fire. However,
| it led to loss of hydraulic pressure on that wing, which
| led to the flaps/slats retracting on just the left wing,
| which led to the plane becoming uncontrollable. After that
| accident, the DC-10 was retrofitted with hydraulic fuses to
| prevent something like this happening again. Unfortunately,
| that didn't help the UPS crew, because in their case, the
| detachment caused more damage to the wing...
| 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.
| loeg wrote:
| That's why it flipped upwards, but not why it flipped towards
| the body of the plane / to the right.
| kijin wrote:
| Yes, and that lateral movement is very important since the
| debris seems to have caused at least one other engine to
| the right to fail as well.
| jacquesm wrote:
| From a failure analysis perspective that is much less
| relevant though. The first failure was the rear engine
| mount if it had been a secondary failure it would have
| been deformed first and then broken, and it clearly is
| not. It just tore in half on one of the four connections
| and then the rest deformed slightly due to overstress.
| rob74 wrote:
| It was however relevant to the survivability of the
| accident: if the left engine wouldn't have detached, or
| would have detached in a more "manageable" way, the other
| engine (probably the tail engine from how it looks)
| wouldn't have been affected too, and the pilots would
| have had a better chance to take off. Plus the whole
| "when an engine detaches, it shouldn't start a fire in
| the wing it was attached to" part of course...
| jacquesm wrote:
| Yes, agreed, the secondary safety wasn't there either.
| There was a Boeing accident near Amsterdam with the plane
| crashing into an inhabited area, it had dropped two
| engines but kept flying, at least for a while...
|
| https://en.wikipedia.org/wiki/El_Al_Flight_1862
|
| Pictures of that accident are not for the faint of heart
| so think twice before clicking.
| arcfour wrote:
| A 747 with 2 engines out that's already got some altitude
| and speed is much more "survivable" (still
| extraordinarily difficult) than a trijet trying to take
| off on 1 engine, which is impossible.
|
| Planes can safely land with 0 engines, though this is
| obviously "not ideal." See: Gimli Glider.
|
| (Mostly putting that out there for others.)
| testplzignore wrote:
| Maybe stupid question: Why not have the #1 engine spin in the
| opposite direction so that it doesn't go towards the fuselage?
| captaincrowbar wrote:
| Because making every jet engine in two different models would
| make them a lot more expensive. It would also cause
| maintenance issues because of non-interchangeable parts.
| 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?
| sosodev wrote:
| The report doesn't say that because it's just reporting
| the facts not drawing conclusions. In my opinion, if a
| catastrophic failure happens that is a maintenance
| failure. Either the inspections failed to notice the
| fatigue or the inspection guidelines were too optimistic.
| 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.
| AceyMan wrote:
| > significantly _raised_ the stall speed
|
| (yeah, it's one of those weird metrics where "bigger is
| worse", so you're absolved)
| 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:
| To be clear, we don't yet know if the UPS flight lost
| hydraulics or not. There are several somewhat redundant
| hydraulic systems.
|
| (Also, as a result of the Sioux City crash you linked,
| there were several ADs issued requiring changes to
| hydraulics in these airframes.)
| 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.
| pixl97 wrote:
| Also it prevents redactions from being disclosed.
| 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
| m2fkxy wrote:
| Mad dogs are MD-80s.
| 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?
| psunavy03 wrote:
| > just make the wing engines 50% more powerful
|
| You realize this is not quite how aerospace engineering
| works, right?
| loeg wrote:
| Essentially every new design is a twinjet, so it's
| clearly possible to make appropriate decisions in that
| design space. And both Boeing and Airbus have given up on
| quadjets.
| lazide wrote:
| Now it is, yes. At the time, it would have required 4
| total engines, which is a different matter altogether.
| db48x wrote:
| It would be way cheaper to replace the airplane with a
| modern twin-engine plane than to retrofit new engines
| onto an old plane.
| inferiorhuman wrote:
| The MD-11 isn't a new design. It's a stretched version of
| a first generation widebody whose design dates back to
| the mid-1960s. Before the MD-11 was developed, McDonnell-
| Douglas toyed with the idea of a dual engine variant
| before settling on a three engine version of the DC-10.
| Trijets in general came about because the engines of the
| day were too unreliable and too small to work in twin
| engine configuration at that scale.
|
| The plane which ended up being the final nail in the
| MD-11's coffin, the 777, didn't start development until
| the 90s. Of its three initial engine choices, two were
| derivatives of engines that were around when the trijets
| came to be. The initial version of that Rolls Royce
| engine was so late (and so unreliable) that it
| essentially killed the Lockheed trijet. The third option,
| the GE90, was the largest turbofan engine at its
| introduction until it was succeeded in 2020 by the GE9X.
|
| Scaling these earlier engines up to fit an MD-11 sized
| twin was never an option.
| 542354234235 wrote:
| >both Boeing and Airbus have given up on quadjets.
|
| It is possible "to make appropriate decisions" up to a
| certain size. They didn't stop making new quadjets
| because the design doesn't work as well as a twin engine,
| but because airlines don't need/want aircraft that large.
| You wouldn't build a successor to the A380 as a twin
| engine.
| toast0 wrote:
| Look at thrust on the 737 Max vs thrust on the original
| 737.
|
| There's a lot of other changes, of course, but more
| powerful wing engines let you build a bigger plane in the
| same kind of shape. Changes in flight rules are also
| significant; if twin jets can't serve all your routes,
| you most likely want trijets to cover the routes that
| can't be served by twins and don't demand a quad ... with
| current flight rules and current engines, twin engine
| covers pretty much everything.
| inferiorhuman wrote:
| No, you really can't. Even if it were the same size a
| dramatically more powerful engine would need a larger
| "tail" to maintain control in case of an engine out
| scenario. But a 50% more powerful engine is also likely
| to be _much_ bigger meaning that major components like
| the landing gear (and everything around them). A 50% more
| powerful engine is also likely to be much heavier
| necessitating its support structures (a.k.a. the wing or
| tail) be redesigned.
|
| The 737 MAX suffered a number of bad design decisions to
| accommodate its newer, more powerful engines. Its engines
| topped out at about _8%_ more powerful than the 737 NG
| engines.
| rangestransform wrote:
| It wasn't about the engines being powerful but about the
| fan being bigger and therefore more efficient
| 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.
| MBCook wrote:
| I didn't know there was a three engine business jet, my
| knowledge is mostly passenger airliners and even then
| just from an amateur perspective.
|
| Other than being able to identify a couple of famous ones
| I don't know a ton about military airplanes either.
|
| Thanks!
| loeg wrote:
| You've framed this as disagreeing with me, but I don't
| think you are. I agree the design made sense in the
| 1960s, when we didn't know any better and requirements
| were different.
| harpiaharpyja wrote:
| A design that was once useful but no longer has a use is
| not the same thing as a failed design. Which is what the
| disagreement seems to be about.
| 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.
| jefftk wrote:
| _> Though I suppose another possibility is that they all
| share an identical pylon design or something like that._
|
| They're very closely related planes (MD-11 is an upgraded
| DC-10; KC-10A is a military version of the DC-10), so
| that wouldn't be surprising. Likely the KC-10A has the
| same pylon, and the MD-11 has one that's similar enough
| that it's worth being cautious.
| TylerE wrote:
| No military operates the KC-10 anymore. There are a grand
| total of two remaining in use as aerial firefighters.
| jefftk wrote:
| _> Incorrect. The KC-10 was based on the Boeing 707. No
| connection to the DC-10 at all other than having 10 in
| the name._
|
| I think you're confused? It's nothing like the 707, and
| is a trijet. https://en.wikipedia.org/wiki/McDonnell_Doug
| las_KC-10_Extend...
|
| EDIT re your edit: it's still a military version, even if
| militaries have retired it.
| 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.
| chasil wrote:
| > 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.
|
| I have heard it said that "every air safety rule is
| written in blood."
|
| https://www.cnn.com/2024/01/02/travel/tokyo-plane-crash-
| safe...
| SoftTalker wrote:
| If the engine had just failed, they would very likely
| have been fine. Experienced crew, would likely have
| handled it. But the engine came off the wing, and then
| another engine was damaged. At that point there was no
| recovery possible.
| foldr wrote:
| This is understating it. Any minimally competent crew
| should be able to handle a single engine failure on
| takeoff (in a normal scenario, not this one). It's
| absolutely within the performance envelope of the
| aircraft and is something that crew train for. If pilots
| were not routinely able to handle this kind of failure,
| we'd see a lot more crashes.
| bombcar wrote:
| The pilots did (apparently) exceptionally well keeping
| the plane level even with unbalanced weight and nearly no
| thrust; perhaps they had been over water they'd even have
| been able to ditch successfully.
| ImPostingOnHN wrote:
| This is _still_ understating it. Any _barely_ competent
| crew should be able to handle a single engine failure on
| takeoff (in a normal scenario, not this one).
| 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.
| filleduchaos wrote:
| There are several passenger trijets still existing - they
| are just not commercial airliners. Dassault for one is
| quite fond of the design; the Falcon 900, 7X and 8X are
| trijets, and I'm pretty sure the latter two are still in
| production. I wouldn't be at all surprised to see another
| trijet design from them probably around 2030.
| Gare wrote:
| The Falcons have all three engines tail mounted, so not
| the same "type" of trijet as MD-11.
| secult wrote:
| Don't forget about Tupolev Tu-154. It didn't stop flying
| as a commercial airplane because of safety, rather
| because of noise emission limits.
| 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.
| nicole_express wrote:
| Engine pylons are actually usually designed to fail in a
| particular way to ensure the separation happens as safely
| as possible; obviously that didn't happen here, which
| will probably be something the NTSB will have to
| investigate why.
|
| The up and over is usually actually the safer direction I
| think? But in this case it also moved laterally, which is
| possibly what fouled the tail engine and made it
| unrecoverable. Will be interesting to see the final
| report.
| 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.
| decimalenough wrote:
| > _Grounding all MD-11s and DC-10s is a major move_
|
| Not really. There are zero left in passenger service, they
| pretty much only serve cargo now.
| pixl97 wrote:
| Losing cargo jet capacity right before the holidays may cause
| some issues.
| citbl wrote:
| All cargo companies run a wide fleet of many different
| plane types, particularly to avoid this very problem of
| being grounded by the FAA. But yes, these were still widely
| used in cargo transports. Although newer 2 engine planes
| can haul the same kg and use a lot less fuel.
| sathackr wrote:
| Captain Steeeve thinks it was actually the starboard engine
| that also failed due to evidence of compressor stalls in some
| of the footage
|
| https://youtu.be/CmXLQHhUtv4?t=499
| 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...
| Aloha wrote:
| Revised URL
| -https://www.ntsb.gov/investigations/Documents/DCA26MA024%20P...
| decimalenough wrote:
| TIL about this eerily similar DC-10 crash in 2011:
|
| _Shortly after liftoff, 20 feet (6.1 m) above and 7,000 feet
| (2,100 m) down the runway, the No. 2 engine separated from the
| wing and struck the No. 1 engine 's inlet cowling, causing it to
| produce drag and reduced thrust. Even with full right aileron and
| rudder, the plane started to descend and drift to the left. The
| captain lowered the nose and leveled the wings, which was
| followed by the plane making multiple contacts with the runway.
| After touchdown, the plane drifted left and departed the runway,
| crossing a taxiway before coming to rest in a saltwater marsh. A
| fire erupted which consumed the top of the cabin and the cockpit.
| All three crew members survived._
|
| https://en.wikipedia.org/wiki/Omega_Aerial_Refueling_Service...
|
| Obviously the DC-10 is not the MD-11, but the MD-11 is a direct
| descendant, including the trijet configuration.
| filleduchaos wrote:
| ...is this a bot comment? The accident you linked is very
| clearly of a Boeing 707, which has zero relation to a DC-10 and
| is most decidedly not a trijet.
| loeg wrote:
| The article you linked is talking about a 707, not a trijet. In
| particular, engine 2 on the MD-11 is the tail engine, not a
| wing engine.
| stego-tech wrote:
| As I told my friends, this preliminary report _annoys me_. It
| _annoys_ me for the same reason it seemingly _annoys_ the NTSB:
| American 191 is nearly identical on the surface, right down to
| the engine detachment and resultant loss of the aircraft, in
| almost the exact same spot on the airframe, ~45 years later.
|
| Needless to say they're going to be scrutinizing everything to
| determine what the cause is and the sequence of events that
| created the accident, but I also suspect everyone involved is
| just as _annoyed_ at this as I am, given that this exact
| situation _should_ have been fixed already.
|
| * _Annoyed_ = seething rage
| filleduchaos wrote:
| Actually, the two accidents are only superficially similar, and
| there is no basis for saying that "this exact situation" should
| have already been fixed.
|
| And no, this is not just pedantry. A bulkhead fracturing from
| impact damage and its mounting point failing from fatigue
| cracking are nowhere near the same thing, even if they might
| lead to the same outcome.
| BXLE_1-1-BitIs1 wrote:
| Gyroscopic precession took the left engine to the right. In AA
| 191 the right engine departing to the right did not affect the
| center engine. Sadly the engine failure procedure at the time
| mandated slowing down to V2 which was below the stall speed with
| slats retracted. There's now revised procedure and hydraulic
| fuses.
|
| I expect all remaining aircraft will be getting new rear pylon
| lugs with shortened inspection intervals - provided the
| replacement cost is below the value of continued usage.
| Simon_O_Rourke wrote:
| That's terrible. If the NTSB had flagged this flaw before then
| someone failed with an inspection regime or maintenance.
|
| The NTSB doesn't ever accept the "sometimes bad things happen,
| shrug" excuse and kudos to the professionals there.
| anshumankmr wrote:
| Very fast. Quite sad to see it happen. Also quite puzzling is how
| the Air India disaster still does not have a root cause analysis
| done (though supposedly it will be released end of this year)
| objclxt wrote:
| > quite puzzling is how the Air India disaster still does not
| have a root cause analysis done
|
| Not that puzzling: the most likely explanation is pilot suicide
| and the Indian government does not want to acknowledge that.
| anshumankmr wrote:
| The Indian authorities has blamed the pilots in every single
| crash. AND there is not enough evidence to guarantee that was
| the case. It is one of many possibilities.
| fransje26 wrote:
| > Also quite puzzling is how the Air India disaster still does
| not have a root cause analysis done
|
| Nothing puzzling. Straight-up cover-up.
|
| Now, the interesting part would be to know what is being
| covered-up. Pilot error? Pilot suicide? Or a critical system
| malfunction Boeing cannot afford?
___________________________________________________________________
(page generated 2025-11-21 23:02 UTC)