Comment by filleduchaos

Comment by filleduchaos 11 hours ago

25 replies

View on Hacker News

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 11 hours 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.

Reply View 24 replies
  • filleduchaos 9 hours ago

    Well, there's a very big difference between "Engine fire: some of the combustion chamber's heat and flame has breached containment" and, say, "Engine fire: the engine has exploded, catastrophically damaging your wing which is now visibly on fire". However, both things are reported in the cockpit as ENG FIRE.

    There's also a very big difference between "Engine failure: something has damaged or jammed enough components that the turbines are no longer spinning fast enough to produce thrust or drive the generators" and "Engine failure: the engine is no longer attached to the aircraft, which is why it is no longer producing thrust". However, both things are reported in the cockpit as ENG FAIL.

    (Un)fortunately, cockpit warnings prioritise the what (so to speak) and not the how or why. On one hand, this makes decision-making a lot simpler for the crew, but on the other...well, in rare cases the lack of insight can exacerbate a disaster. Depending on when exactly the engine gave out, this poor crew might have been doomed either way, but they might have been able to minimise collateral damage if they knew just how badly crippled the aircraft was. And there was a very similar accident to this one (actually involving the predecessor of the MD-11, the DC-10), American Airlines 191 - one of the engines detached from the aircraft, damaging the leading edge of its wing in the process, causing that wing to stall when the crew slowed down below the stall speed of the damaged wing in a bid to climb. If they could have somehow known about the damage, the accident might have been avoided entirely as the crew might have known to keep their speed up.

    Reply View 18 replies
    • ragazzina 3 hours ago

      > There's also a very big difference between "Engine failure: something has damaged or jammed enough components that the turbines are no longer spinning fast enough to produce thrust or drive the generators" and "Engine failure: the engine is no longer attached to the aircraft, which is why it is no longer producing thrust". However, both things are reported in the cockpit as ENG FAIL.

      What is the difference?

      Reply View 5 replies
      • HPsquared 3 hours ago

        Wider effects like damage to the wing or changes to aerodynamics.

        Edit: and damage to other engines, possibly engine #2 in the tail ingesting debris in this instance.

        Reply View 2 replies
      • potato3732842 an hour ago

        >What is the difference?

        Wanting to be in the air vs wanting to over-run the end of the runway.

        Reply View 0 replies
    • eternityforest 5 hours ago

      Could they add cameras to solve this issue?

      Reply View 11 replies
      • roryirvine 5 hours ago

        During engine failure / fire situations, I would expect that pilots are likely to be too busy to have any time left over for peering at a video feed, trying to assess the state of the wing.

        In emergencies, information overload tends to make things worse, not better.

        Reply View 8 replies
      • zuppy 3 hours ago

        They surely can and this has been done. On one the flights that I took with Turkish Airlines they had a few video streams from different sides of the airplane. One was from the top of the tail and you could see the entire plane.

        Now... not sure how much that is helpful in this kind of emergency, they really didn't have time to do much.

        Reply View 1 reply
        • fredoralive 3 hours ago

          I'm not sure they usually have the views on screen in the cockpit in flight, even if available (and an old MD-11 freighter won't have the cameras in the first place). The picture of an A380 cockpit (on the ground) on Wikipedia does show the tail view on a screen, but its on the screen normally used for main instruments. With an A380 that had an uncontained engine failure causing various bits of havok (Qantas 32?) IIRC the passengers could see a fuel leak on the in flight entertainment screens, but they had to tell the crew as AFAIK they didn't have access to the view in the cockpit in flight.

          Reply View 0 replies
  • appreciatorBus 11 hours 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”

    Reply View 0 replies
  • positron26 11 hours ago

    This puts an impractical amount of faith in the sensor wiring when the whole pylon and cowling are shredded.

    Reply View 3 replies
    • krisoft an hour ago

      It is a very practical amount of fait.

      There are two fire detection loops for each engine.[1] Even if both fails (because they get shredded as you say it) the system will report an engine fire if the two loops fail within 5s of each other. (Or FIRE DET (1,2,3,or APU) FAIL, if they got shredded with more than 5s in between without any fire indications in between.)

      The detection logic is implemented directly below the cockpit. So that unlikely to have shredded at the same time. But even if the detection logic would have died that would also result in a fire alarm. (as we learned from the March 31, 2002 Charlotte incident.)[2]

      In other words it is a very reliable system.

      1: page 393 https://randomflightdatabase.fr/Documents/Manuel%20Aviation/...

      2: https://www.fss.aero/accident-reports/dvdfiles/US/2002-03-31...

      Reply View 0 replies
    • Jtsummers 10 hours 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.

      Reply View 1 reply
      • positron26 10 hours ago

        No reading is not quite the same as "hot", but I'm sure it did contribute to discerning simple compressor stall to whatever this was.

        Reply View 0 replies