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Turkish A320 very hard landing+go around+crash landing
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Originally posted by Gabriel View PostMaybe the gear didn't collapse in the first landing but some strut got bent (or there was other damage) that, once the gear was retracted during the go-around, prevented the full retraction first, and the full extension and locking later. If the gear is not locked down, it will collapse no matter how smooth the second landing.
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Originally posted by Evan View PostI just can't see how this plane could strike an engine (and hard enough to cause engine damage) with full main gear deployment. Take a look at the photo of the LH wing strike and notice the ground clearance on the engine (and that's the larger CFM version, This was the IAE version, which has more clearance). Maybe the right main partially collapsed on the first landing? Maybe the tires were still rolling on the sidewalls? I can't figure this one out. But lift-off after a gear collapse dragging on one (inoperative) engine, that I'd like to see.
All that being said, let's use some Newton here.
The friction drag force is drag coefficient times the normal force in the contact point. In an airplane, that normal force would be weight minus lift, divided (evenly or unevenly) among the different contact points.
If the go-around was initiated before the actual touch down due to a high sink rate and bank angle, the pilots very likely pulled up before touchdown but, despite the positive load factor greater than one, the sink rate didn't reduce enough to change from a sink rate to a climb rate (but it was still a diminishing sink rate). This means that lift was greater than weight. The moment that the landing gear / wingtip /engine touched the ground and did what the pilots were not able to do until then (that is, fully arrest the sink rate), the lift could have very well still been higher than the weight. In that case the plane goes up again "by itself" and there is no friction but during the brief contact of the plane with the runway. Actually, that's how most of the "bounces" happen, it's not just that the plane hits hard and the "spring" effect in the dampers make it "bounce" off the runway, dampers are designed with a good viscous damping effect to prevent that. in most cases, it's the pilot seeing that they will hit hard and pulling up to slow down the sink rate. Slow down the sink rate means lift > wight and, after the ground completed our job of arresting the sink rate, up we go.
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Originally posted by 3WE View PostIndeed.
Most procedures frown upon go arounds after touch down, except maybe to avoid school buses full of nuns blowing their hold-short instructions.
--- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
--- Defend what you say with arguments, not by imposing your credentials ---
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Originally posted by Gabriel View PostI am not sure that the tires in this photo are actually touching the ground, not to mention that the tires are compressed to the rim and the strut compressed to the stop, what is actually what tends to happen in really hard landings before the gear gets structurally damaged. From looking at a 3-view of the A320, it looks to me that the engine would be a bunch of engines below the ground line if you put the wingtip (less the lower tip of the winglet) and the main gear on the ground at the same place, and even more if you compress the tire and strut.
So if the tire failed with full strut compression and no gear collapse, maaaybe you would get an engine contact on the runway, maybe enough to take out the accessories, the starter, the generator, but enough to disable it? I think it would have to be a pretty solid hit, not just a scrape.
Or the alternate theory...
All that being said, let's use some Newton here.
The friction drag force is drag coefficient times the normal force in the contact point. In an airplane, that normal force would be weight minus lift, divided (evenly or unevenly) among the different contact points.
This means that lift was greater than weight. The moment that the landing gear / wingtip /engine touched the ground and did what the pilots were not able to do until then (that is, fully arrest the sink rate), the lift could have very well still been higher than the weight. In that case the plane goes up again "by itself" and there is no friction but during the brief contact of the plane with the runway.
I'm not saying it's impossible, I just would have to see it to believe it.
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Originally posted by Evan View PostRight, well, here are the numbers. See the attached chart. The red line is the ground angle between the main gear and the wingtip. Let's assume that in this drawing the gear strut is compressed only for the weight of the a/c somewhere between MTOW and empty weight. The A320 had 16.5" of total main gear suspension travel. We can also assume the tire failed so there's another, I don't know, 10"? But now also note that the chart shows the CFM configuration. The blue area on the chart is CFM clearances and the yellow is IAE. There's a bit more clearance we get back for the IAE's. And the LW? Maybe somewhere between the 41T and the 78T columns. CG doesn't make a huge difference.
So if the tire failed with full strut compression and no gear collapse, maaaybe you would get an engine contact on the runway, maybe enough to take out the accessories, the starter, the generator, but enough to disable it? I think it would have to be a pretty solid hit, not just a scrape.
On the other hand, some other factors can play against.
- I guess that the drawing depicts an A320 on the ramp, the wing in flight would be a few inches flexed up (especially if they were at more than 1G as I hypothesized), plus there can be more flexing (bending, tearing) when the wingtip contacts the ground.
- I previously mentioned the possibility that there could be some damage/bending of the landing gear and supporting structure that, without making it collapse, prevented it from locking down when they retracted it for the go around and extended it for the second landing, thus causing the collapse in the second landing.
- Any good impact in the cowling can missalign it enough to damage some blades and from there the situation can cascade. Or the damage to the starter, generator, gearbox etc can bend the engine shaft or stuck some mechanism... or a simple a fuel hose can break.
Or... maybe it did collapse in the first landing and we get to...
the alternate theory...
So the lift would have to be greater than the normal force plus the drag of an engine contacting the runway with enough impact (weight, friction) to disable it (plus the wingtip friction), at a moment when the a/c is about 1.3X stall speed, has lost some lift in the roll, has lost further airspeed on the ground and 50% of its available thrust.
I'm not saying it's impossible, I just would have to see it to believe it.
If the lift is bigger than the weight, then there is no normal (except for a very brief moment when the normal provides the acceleration to bring the sink rate to zero, like in anything hitting the ground smoothly or violently). No normal = no friction (except, again, in that brief moment)
If the lift is higher than the weight after the downward motion stopped, the plane WILL go up again no matter the friction that there might have been there until then.
--- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
--- Defend what you say with arguments, not by imposing your credentials ---
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And, gentlemen, let's not forget: the aircraft DID indeed go up again, flew into a successfull go-around, returned to the airport and landed with everybody walking away without injuries.
For me, the more interesting question is: what caused the ground contact on the first attempt? This is where the pilots might have goofed. After the A320 became airborne again, they certainly earned their wages, and their training paid off handsomely.
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Originally posted by Gabriel View PostWhaaaaat????? The lift doesn't have to be greater than the normal but greater than the weight and you can't add there the drag because it acts at 90° of the normal, different axis. Plus, 1.3 Vs is enough to provide a load factor of 2 (or "2 G" as they say even if I don't like it).
If the lift is bigger than the weight, then there is no normal (except for a very brief moment when the normal provides the acceleration to bring the sink rate to zero, like in anything hitting the ground smoothly or violently). No normal = no friction (except, again, in that brief moment)
If the lift is higher than the weight after the downward motion stopped, the plane WILL go up again no matter the friction that there might have been there until then.
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Originally posted by Peter Kesternich View PostAnd, gentlemen, let's not forget: the aircraft DID indeed go up again, flew into a successfull go-around, returned to the airport and landed with everybody walking away without injuries.
For me, the more interesting question is: what caused the ground contact on the first attempt? This is where the pilots might have goofed. After the A320 became airborne again, they certainly earned their wages, and their training paid off handsomely.
--- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
--- Defend what you say with arguments, not by imposing your credentials ---
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Aha! Found this video angle on YouTube. Obviously a damaged, not entirely extended (bent? pushed into the wing?) undercarriage from the first landing. That would explain the engine strike.
Pilot did a nice job of landing on the left main only.
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Originally posted by Evan View PostThey probably tried the alternate gear extension. That will leave the doors open. And you lose the nose wheel steering.
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Originally posted by Peter Kesternich View PostAfter looking at the pictures at avherald, I don't think they ever tried to retract the gear.
In the photo in AvHerald, maybe they had not tried yet, or maybe they had tried but unsuccessfully due to mechanical or hydraulic damage.
Or.... maybe they didn't even try.
--- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
--- Defend what you say with arguments, not by imposing your credentials ---
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Originally posted by Gabriel View PostI'd be surprised if they didn't even try. They had no way to know the damage and in go around with an engine on fire you certainly want as little drag as possible.
In the photo in AvHerald, maybe they had not tried yet, or maybe they had tried but unsuccessfully due to mechanical or hydraulic damage.
Or.... maybe they didn't even try.
From the looks of it (though blurry), I can now imagine how they got both an engine strike and off the runway again.
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