Comment by Jtsummers
1 day 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.
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.
> 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?
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.
4 replies →
A good example of the difference it can make was the Flight 191 crash in Chicago in in 1979, which had an engine come off on takeoff: https://en.wikipedia.org/wiki/American_Airlines_Flight_191
The engine coming completely off tore through hydraulic lines, which were need to keep the slats extended. Airflow forced the slats to retract.
Here's what then happened:
> As the aircraft had reached V1, the crew was committed to takeoff, so they followed standard procedures for an engine-out situation. This procedure is to climb at the takeoff safety airspeed (V2) and attitude (angle), as directed by the flight director. The partial electrical power failure, produced by the separation of the left engine, meant that neither the stall warning nor the slat retraction indicator was operative. Therefore, the crew did not know that the slats on the left wing were retracting. This retraction significantly raised the stall speed of the left wing. Thus, flying at the takeoff safety airspeed caused the left wing to stall while the right wing was still producing lift, so the aircraft banked sharply and uncontrollably to the left. Simulator recreations after the accident determined that "had the pilot maintained excess airspeed the accident may not have occurred.
It's the difference between "I can't walk because my leg fell asleep"
and
"I can't walk because I have no legs"
>What is the difference?
Wanting to be in the air vs wanting to over-run the end of the runway.
Hydraulic pressure
Could they add cameras to solve this issue?
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.
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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.
1 reply →
I think too many of us are used to movies and TV (and Star-Trek-like scifi) that gives the incorrect view that extremely detailed information about the state of things is available.
The notification in the cockpit is likely nothing more than "ENG 2 FIRE" or similar. That could mean anything from "the fire is minor enough and we're at high enough speed that it's significantly safer to take off and then make an emergency landing", to "the engine has exploded and the wing is on fire and catastrophically damaged, so even though aborting takeoff now is dangerous and will likely cause us to overrun the runway, trying to continue would be worse".
It's a judgment call by the pilot to guess which of these is the case (or any possibility in between), and given the probabilities of various failure modes, I think it's fair for a pilot to assume it's something closer to the former than the latter.
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”
This puts an impractical amount of faith in the sensor wiring when the whole pylon and cowling are shredded.
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...
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.
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.