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> And at least in theory the MD-11 should be flyable with just two engines Flying with two engines and taking off without an engine in a loaded aircraft are tw

> And at least in theory the MD-11 should be flyable with just two engines Flying with two engines and taking off without an engine in a loaded aircraft are two very different things. A lot more thrust is needed during takeoff than after.

andy99 1y ago
I specifically remember watching a flight test doing an aggressive takeoff and having the voiceover say that aircraft (two engine) need to have enough power to take off full with one engine. And so can take off very steeply empty with two engines. Would that not also be the case for these planes?
- justsid 1y ago
  Yes, planes are designed to be able to take off with a lost engine. Usually this will extend the roll a bit because the speeds are different for engine out operations. This isn't the first MD-11 with an engine out take off, 5 years ago a FedEx MD-11 took off with a failure in the left engine[1]. Slightly different case, obviously, but it's certainly something that is accounted for when designing planes. [1] https://www.avherald.com/h?article=4dfd50b9&opt=0%20 https://www.avherald.com/h?article=4dfd50b9&opt=0%20
  - bobthepanda 1y ago
    That being said, depending on how you lose the engine it can really mess up the takeoff; AA191 was lost when an engine detached from the plane on takeoff and took out part of the wing and hydraulic system with it. https://en.wikipedia.org/wiki/American_Airlines_Flight_191 https://en.wikipedia.org/wiki/American_Airlines_Flight_191
    - anonymars 1y ago
      > when an engine detached from the plane on takeoff... https://imgur.com/a/NYlrLYO https://imgur.com/a/NYlrLYO https://cdn.discordapp.com/attachments/757091156717862935/1435446018098331648/Screenshot_2025-11-04_193907.png?ex=690bfec8&is=690aad48&hm=7a065142e6359edd8e41f00ed0bf70e18c1bdffef825d01ba209a16d893af4d7& https://cdn.discordapp.com/attachments/757091156717862935/14... Source: https://reddit.com/r/flying/comments/1ooms7t/ksdf_accident/nn5wrfh/ https://reddit.com/r/flying/comments/1ooms7t/ksdf_accident/n...
  - rob74 1y ago
    Yes, the takeoff roll will be longer, the climb will be much more shallow, but it is possible to take off with one out of two engines (and obviously also with two out of three). Of course, after successful takeoff, the plane should turn around and land as soon as possible. In this case however, with the wing already on fire (the engine is below the wing, so flames coming out of it would be visible behind and under the wing, not in front), I'm afraid that even if they had managed to take off, the fuel tank would have exploded or burned through the wing before they would have had a chance to land. Actually, this looks similar to the 2000 Concorde crash...
- appreciatorBus 1y ago
  All planes are definitely capable of taking off safely even if they lose an engine at the worst time. Whatever happened here, I would be shocked if lack of thrust in the 2 remaining engines was a significant factor unless someone really screwed up the load calculations and they were overweight for conditions.
  - dboreham 1y ago
    Lack of thrust in the "taken out by debris" sense seems to be the case here.
  - lazide 1y ago
    Single engine planes (GA, and some military planes) don’t handle this condition well at all. In fact, for awhile (maybe still the case), the #1 killer of skydivers was single engine failure on takeoff from the jump plane (and similar aircraft failures), not accidents ‘while skydiving’.
    - appreciatorBus 1y ago
      yes true, I guess I was assuming we were talking about commercial airlines :)
avalys 1y ago
Every multi-engine airliner is designed to be able to take off safely even if an engine fails at a critical moment. What might have happened in this case is that the mechanism of failure of one engine caused damaged or interfered with the operation of another engine (via smoke, debris, etc.), and taking off with two engines degraded is not part of the design criteria.
- HPsquared 1y ago
  Some engine failures can't be contained within the cowling, like turbine disc rupture. Probably something like this happened where fragments punctured the surrounding wing structure and/or fuel tanks.
- pixl97 1y ago
  I do think 'engine fails' and 'engine has left the building' are two different categories of problems. Even if the rear engine was working I'm going to assume this craft would have crashed, probably just farther down range.
filleduchaos 1y ago
Taking off with one engine inoperative (on a multi-engine aircraft, obviously - you aren't going to get anywhere with your only engine gone) is completely normal/within design parameters, albeit undesirable. In fact, it being normal almost certainly contributed to the scale of this accident, since a single engine failure during the takeoff roll isn't considered enough of an emergency to reject the takeoff at high speed (past a certain speed, you only abort if the aircraft is literally unflyable - for everything else, you take the aircraft & emergency into the air and figure it out there). The crew wouldn't have had any way to know that one of their engines had not simply failed, but was straight-up gone with their wing on fire to boot.
- Jtsummers 1y ago
  > The crew wouldn't have had any way to know that one of their engines had not simply failed, but was straight-up gone with their wing on fire to boot. I don't know about the MD-11 itself, but other aircraft from that time period have sensors to detect and report overheat and fire in various parts of the aircraft, including engines and wings.
  - appreciatorBus 1y ago
    I’m sure they knew there was an issue, but I don’t think the sensors can differentiate between “your engine is on fire, but if you can shut it down quickly, everything will be cool.” and “half your entire wing is on fire and your engine is pouring flame out the front/top instead of the back”
  - positron26 1y ago
    This puts an impractical amount of faith in the sensor wiring when the whole pylon and cowling are shredded.
    - Jtsummers 1y ago
      I don't know what the MD-11 would have had, again I didn't work on it. But the systems used for other aircraft would have reported an alarm based on what I saw in the video, at least they were designed to do that. The LRU receiving the sensor inputs wouldn't typically be in the wing and would be able to continue reporting the alarm condition even if the sensors fail. In fact, the lack of current from the sensor (for the systems I worked on) would have been enough to trigger the alarm if the sensor were completely eliminated.

andy99 1y ago

I specifically remember watching a flight test doing an aggressive takeoff and having the voiceover say that aircraft (two engine) need to have enough power to take off full with one engine. And so can take off very steeply empty with two engines. Would that not also be the case for these planes?

justsid 1y ago
Yes, planes are designed to be able to take off with a lost engine. Usually this will extend the roll a bit because the speeds are different for engine out operations. This isn't the first MD-11 with an engine out take off, 5 years ago a FedEx MD-11 took off with a failure in the left engine[1]. Slightly different case, obviously, but it's certainly something that is accounted for when designing planes. [1] https://www.avherald.com/h?article=4dfd50b9&opt=0%20 https://www.avherald.com/h?article=4dfd50b9&opt=0%20
- bobthepanda 1y ago
  That being said, depending on how you lose the engine it can really mess up the takeoff; AA191 was lost when an engine detached from the plane on takeoff and took out part of the wing and hydraulic system with it. https://en.wikipedia.org/wiki/American_Airlines_Flight_191 https://en.wikipedia.org/wiki/American_Airlines_Flight_191
  - anonymars 1y ago
    > when an engine detached from the plane on takeoff... https://imgur.com/a/NYlrLYO https://imgur.com/a/NYlrLYO https://cdn.discordapp.com/attachments/757091156717862935/1435446018098331648/Screenshot_2025-11-04_193907.png?ex=690bfec8&is=690aad48&hm=7a065142e6359edd8e41f00ed0bf70e18c1bdffef825d01ba209a16d893af4d7& https://cdn.discordapp.com/attachments/757091156717862935/14... Source: https://reddit.com/r/flying/comments/1ooms7t/ksdf_accident/nn5wrfh/ https://reddit.com/r/flying/comments/1ooms7t/ksdf_accident/n...
- rob74 1y ago
  Yes, the takeoff roll will be longer, the climb will be much more shallow, but it is possible to take off with one out of two engines (and obviously also with two out of three). Of course, after successful takeoff, the plane should turn around and land as soon as possible. In this case however, with the wing already on fire (the engine is below the wing, so flames coming out of it would be visible behind and under the wing, not in front), I'm afraid that even if they had managed to take off, the fuel tank would have exploded or burned through the wing before they would have had a chance to land. Actually, this looks similar to the 2000 Concorde crash...
appreciatorBus 1y ago
All planes are definitely capable of taking off safely even if they lose an engine at the worst time. Whatever happened here, I would be shocked if lack of thrust in the 2 remaining engines was a significant factor unless someone really screwed up the load calculations and they were overweight for conditions.
- dboreham 1y ago
  Lack of thrust in the "taken out by debris" sense seems to be the case here.
- lazide 1y ago
  Single engine planes (GA, and some military planes) don’t handle this condition well at all. In fact, for awhile (maybe still the case), the #1 killer of skydivers was single engine failure on takeoff from the jump plane (and similar aircraft failures), not accidents ‘while skydiving’.
  - appreciatorBus 1y ago
    yes true, I guess I was assuming we were talking about commercial airlines :)

avalys 1y ago

Every multi-engine airliner is designed to be able to take off safely even if an engine fails at a critical moment. What might have happened in this case is that the mechanism of failure of one engine caused damaged or interfered with the operation of another engine (via smoke, debris, etc.), and taking off with two engines degraded is not part of the design criteria.

HPsquared 1y ago
Some engine failures can't be contained within the cowling, like turbine disc rupture. Probably something like this happened where fragments punctured the surrounding wing structure and/or fuel tanks.
pixl97 1y ago
I do think 'engine fails' and 'engine has left the building' are two different categories of problems. Even if the rear engine was working I'm going to assume this craft would have crashed, probably just farther down range.

filleduchaos 1y ago

Taking off with one engine inoperative (on a multi-engine aircraft, obviously - you aren't going to get anywhere with your only engine gone) is completely normal/within design parameters, albeit undesirable. In fact, it being normal almost certainly contributed to the scale of this accident, since a single engine failure during the takeoff roll isn't considered enough of an emergency to reject the takeoff at high speed (past a certain speed, you only abort if the aircraft is literally unflyable - for everything else, you take the aircraft & emergency into the air and figure it out there). The crew wouldn't have had any way to know that one of their engines had not simply failed, but was straight-up gone with their wing on fire to boot.

Jtsummers 1y ago
> The crew wouldn't have had any way to know that one of their engines had not simply failed, but was straight-up gone with their wing on fire to boot. I don't know about the MD-11 itself, but other aircraft from that time period have sensors to detect and report overheat and fire in various parts of the aircraft, including engines and wings.
- appreciatorBus 1y ago
  I’m sure they knew there was an issue, but I don’t think the sensors can differentiate between “your engine is on fire, but if you can shut it down quickly, everything will be cool.” and “half your entire wing is on fire and your engine is pouring flame out the front/top instead of the back”
- positron26 1y ago
  This puts an impractical amount of faith in the sensor wiring when the whole pylon and cowling are shredded.
  - Jtsummers 1y ago
    I don't know what the MD-11 would have had, again I didn't work on it. But the systems used for other aircraft would have reported an alarm based on what I saw in the video, at least they were designed to do that. The LRU receiving the sensor inputs wouldn't typically be in the wing and would be able to continue reporting the alarm condition even if the sensors fail. In fact, the lack of current from the sensor (for the systems I worked on) would have been enough to trigger the alarm if the sensor were completely eliminated.