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0 pointsazalemeth4y ago0 comments

It depends on exactly what has happened to cause a lack of control. Essentially all fixed-wing aircraft other than high-performance military fighter jets are built to be aerodynamically stable: if you do nothing, they go in a straight line and if they are in an established turn, they tend to continue in that turn. There are plenty of examples of "famous" not-as-bad-as-they-could-have-been crashes where control was effected unconventionally in aircraft made otherwise uncontrollable by mechanical failure -- for example, using throttle control to land aircraft experiencing their phugoid nose up / nose down inherent dynamic stability mode [1, 2].

Full blown nose down is rare unless controlled flight into terrain. The obvious armchair speculation I would make here is that a total separation of the tailplane / stabilator or empennage of the aircraft could cause something approximating that -- the tailplane provides negative lift and without it the aircraft would pitch up until it stalled, and then a series of exponentially growing oscillations would likewise result.

It's far better to wait for the NTSB accident report and deliver sympathy and aid to those affected, however -- we don't have the facts and I am sure that they will be determined in the fullness of time.

[1] https://en.wikipedia.org/wiki/United_Airlines_Flight_232 [2] https://en.wikipedia.org/wiki/2003_Baghdad_DHL_attempted_sho...

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mannykannot4y ago

I am not going to speculate about this crash, but the claim made here about stability is missing one very important fact: just about every airframe exhibits spiral instability and will eventually undergo spiral divergence unless controlled by a pilot or automatic system. This results in an airplane descending in a steeply nose-down spiral even though it is trimmed for level flight. As a result, most spatial-disorientation crashes end in a steep nose-down impact with the surface, as in the case of JFK jr.

Such accidents are way too common - Informally, I get the impression that there may be up to one a month in the US alone - but they are rare in airline operations and I am not suggesting that this is likely here.

azalemethOP4y ago

This is true -- and I forgot to mention it (although I was perhaps obliquely alluding to such things with the CIFT comment). My brain meant the more the conventional dutch roll / longitudinal static stability concerns that are perhaps more actively considered in airframe design and aerodynamics. Thank you for pointing this out.

sbierwagen4y ago

>other than high-performance military fighter jets

Recent, computer controlled jets, rather. Older jets were aerodynamically stable, probably because otherwise they would have been very fatiguing to fly. There are at least two well known instances of pilots ejecting from fighter jets that then recovered to normal flight: https://en.wikipedia.org/wiki/Cornfield_Bomber and https://en.wikipedia.org/wiki/1989_Belgium_MiG-23_crash

>On 4 July 1989, a pilotless MiG-23 jet fighter of the Soviet Air Forces crashed into a house in Kortrijk, Belgium, killing one person. The pilot had ejected over an hour earlier near Kołobrzeg, Poland, after experiencing technical problems, but the aircraft continued flying for around 900 km (600 mi) before running out of fuel and descending into the ground. [Where it killed a Belgian citizen on impact.]

krisoft4y ago

> Full blown nose down is rare unless controlled flight into terrain.

I agree with you that full nose down attitude is rare in accidents. It is rare even in controlled flight into terrain. The typical CFIT scenario is one where the airplane is flying straight or close to in bad visibility and they hit the side of a hill or mountain because of a navigational error.

throwaway0a5e4y ago

>It's far better to wait for the NTSB accident report...

You seem to be measuring "better" in terms of "not saying things that may become obviously false as more information becomes available with time".

Many internet commenters measure better in terms of how many internet virtue points they get, hence all the completely baseless speculation you get on literally any developing news story. I'm sure those people disagree with my assessment but their actions tell a different story.

InCityDreams4y ago

I enjoy 'completely baseless speculation'. To me, it's especially interesting regarding subjects i know nothing about. I understand plane enquires may take years, so its always interesting to see who was most correct, as well as the more immediate satisfaction of another speculator negating a proposition, and proposing another.

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