Originally posted by Evan
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MD-87 hits fence after takeoff from TME. All passengers survive the crash.
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Originally posted by Evan View Post
Dunno... Determining the state of those geared links would take the NTSB about ten minutes since the tail is perfectly intact. So why no announcement, especially no emergency AD? And is that puff of white smoke and assymetrical burn marks in the grass merely coincidental?
Rather disturbing to learn that there is no way to check elevator function during preflight. How did that get past certification?
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Originally posted by Gabriel View Post
Rather disturbing to learn that there is no way to check elevator function during preflight. How did that get past certification?
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Originally posted by Gabriel View PostWell, you are assuming that one engine was significantly underperforming. Although I am totally open to that possibility, I am not ready to discard other options yet.
A normal acceleration to Vr plus a few seconds between that and aborting when they realized that plane would not rotate would put the plane very close to the end of the runway, perhaps more or less about where the skid marks start? Again, not saying that I believe this happened. It is just an alternate possible scenario. One that happened in this type of plane not so many years ago also with everybody surviving the high-speed overrun.LINKS: UPDATE NYSB PRELIMINAEY REPORT! https://www.ntsb.gov/investigations/Pages/DCA22MA009.aspx?fbclid=IwAR0lNd7851UwCE6xyu0mhVAbR4peYVXB5y6qWDxqoqCionzOJe-...
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Originally posted by Evan View Post
The Horse That Wouldn’t DieI realize that you are being academic here but as I pointed out at the beginning, a private MD-87 with 18 souls aboard is probably not overweight (or an underweight weight calc error).
That said, few souls but probably lots of fuel since it was a quite long flight, and a short-ish runway.
I can’t fathom any other reason for them not stopping safely at low speed.
A normal acceleration to Vr plus a few seconds between that and aborting when they realized that plane would not rotate would put the plane very close to the end of the runway, perhaps more or less about where the skid marks start? Again, not saying that I believe this happened. It is just an alternate possible scenario. One that happened in this type of plane not so many years ago also with everybody surviving the high-speed overrun. And in this case TOPMS would have nothing to do with it.
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The only thing missing from this discussion is our German friends explanation of how Randazos flight sim reacts to the infamous V1 cut.
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Originally posted by Gabriel View PostThat's not the main problem. V1 is only relevant in an engine failure scenario (ok, some other rejected take-off scenarios too.
I realize that you are being academic here but as I pointed out at the beginning, a private MD-87 with 18 souls aboard is probably not overweight (or an underweight weight calc error). Also, a good indicator of degraded acceleration is found on the engine instruments which almost certainly were complaining about the #1 parameters. It’s possible that these were not being monitored (and there’s your pilot error) and perhaps the yaw isn’t very noticeable on fuselage-mounted engines. I can’t fathom any other reason for them not stopping safely at low speed.
I think V3bs is irrelevant here. The old argument about when to give up when you decide to continue at V1 but she won’t rotate at Vr doesn't matter if you never make it to Vr.
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Originally posted by gurrit View PostFiiiinnnnneee, "W-E" do not talk anymore about V...
It appears to have worked well in this incident.
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Guest repliedOriginally posted by Gabriel View PostThat's not the main problem. V1 is only relevant in an engine failure scenario (ok, some other rejected take-off scenarios too).
The REAL problem we discussed while beating this dead horse dead again and again is what happens when you DO NOT reject the take off, which is what (almost) ALWAYS happens in the accidents and incidents involving a sub-par take-off scenario. So Vr is the problem.
So say for example that you mixed up 2 numbers and instead of calculating the take off with your actual weight of 53000 lb you input 35000 lb.
Now you get a given Vr and a given distance, and with that Vr comes a Vlo (lift-off) which is not shown to the pilot but is part of the "internal" algorithm.
Is your filed length is more than the minimum needed, V1 is selectable within a range that ensures that you can reject at V1 and stop, or lose an engine at V1 and lift off, both within the the runway length (which is why Vlo is part of the internal algorithm).
Vr is NOT selectable. Is unique for each scenario. And a unique Vlo and lift-off distance comes with it.
But the acceleration will be 35/53=66% of the assumed one.
And, to make things worse, to generate a lift equal to the increased weight you will need a speed sqrt(53/35)= 1.23 the calculated speed
Since the distance needed to achieve a given speed is given by D = V^2 / 2A, we can write the assumed and real scenarios as
Assumed: D1 = V1^2 /2A1
Real: D2 = V2^2 / 2A2 = (1.23V1)^2 / 2(0.66A1) = 2.29 * V1^2 / 2A1 = 2.3 D1
The real distance you will need to get the plane in the air is more than twice what you thought it would take.
And there is NOTHING to alert you that you are accelerating less than expected and will need more speed and much more distance than expected.
Good luck.
Fiiiinnnnneee, "W-E" do not talk anymore about V...
Happy?
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Originally posted by Gabriel View Post
***there is NOTHING to alert you that you are accelerating less than expected and will need more speed and much more distance than expected.***
*Left and right buttocks, (and many takeoffs resulting in a good, albeit fallible, system of checks…)
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