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Author Topic: Russian Jet Carrying Hockey Team Crashes, 43 Dead  (Read 10474 times)
NoMad
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« Reply #15 on: November 06, 2011, 09:49:42 PM »

One thing I don't quite understand is the following: Had the crew rejected takeoff even above V1, with about 1000 meters of runway remaining available after the failed first attempt to rotate the aircraft, an accident would have been averted.

This doesn't make sense to me because V1, by definition, means that you can not stop the plane safely with the amount of runway remaining, and V1 calculations take into account runway length, weather conditions, plane weight and so forth. Any ideas?

Because that is not what V1 means at all.  V1 is the speed at which you decided to takeoff or reject and should be within the accelerate to stop distance.  It does not mean it is the end of your accelerate to stop distance, completely the opposite actually.  Consequently it also is the minimum speed required to take off if you lose an engine.
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derekjackson
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« Reply #16 on: November 07, 2011, 08:37:43 AM »

One thing I don't quite understand is the following: Had the crew rejected takeoff even above V1, with about 1000 meters of runway remaining available after the failed first attempt to rotate the aircraft, an accident would have been averted.

This doesn't make sense to me because V1, by definition, means that you can not stop the plane safely with the amount of runway remaining, and V1 calculations take into account runway length, weather conditions, plane weight and so forth. Any ideas?

Because that is not what V1 means at all.  V1 is the speed at which you decided to takeoff or reject and should be within the accelerate to stop distance.  It does not mean it is the end of your accelerate to stop distance, completely the opposite actually.  Consequently it also is the minimum speed required to take off if you lose an engine.

I'm sorry but could you please go over that again? It didn't make sense to me. Yes, I understand V1 is the decision speed beyond which you can not reject the takeoff with the amount of runway remaining. So how can in this case rejecting takeoff above V1 avert an accident? Could you also please go over what you mean by the "end of accelerate to stop distance?
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NoMad
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« Reply #17 on: November 07, 2011, 09:13:30 AM »

One thing I don't quite understand is the following: Had the crew rejected takeoff even above V1, with about 1000 meters of runway remaining available after the failed first attempt to rotate the aircraft, an accident would have been averted.

This doesn't make sense to me because V1, by definition, means that you can not stop the plane safely with the amount of runway remaining, and V1 calculations take into account runway length, weather conditions, plane weight and so forth. Any ideas?

Because that is not what V1 means at all.  V1 is the speed at which you decided to takeoff or reject and should be within the accelerate to stop distance.  It does not mean it is the end of your accelerate to stop distance, completely the opposite actually.  Consequently it also is the minimum speed required to take off if you lose an engine.

I'm sorry but could you please go over that again? It didn't make sense to me. Yes, I understand V1 is the decision speed beyond which you can not reject the takeoff with the amount of runway remaining. So how can in this case rejecting takeoff above V1 avert an accident? Could you also please go over what you mean by the "end of accelerate to stop distance?


Because once again, that is is NOT what V1 means at all.  Remove that thought from your head.

V1 is the speed at which the crew makes the decision to continue the takeoff or reject the takeoff.  It is the speed at which the aircraft must reach to continue the takeoff with an engine failure.  This speed should be reached within the accelerate-to-stop distance.  It does NOT mean that going faster or further puts you outside the accelerate-to-stop distance.
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derekjackson
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« Reply #18 on: November 07, 2011, 11:23:43 AM »

Okay so if I'm understanding this correctly, then the "guaranteed runway overrun" past V1 is a misconception and TV shows like Mayday are getting it wrong (either as an oversimplification or by not understanding it themselves).

But if that's the case, then what you're saying is that in some cases it is possible to reject takeoff with runway remaining past V1. If that's so, then why continue with takeoff if an engine goes out? I know that airplanes can takeoff and climb with an engine out and return and land safely but if there's enough runway left, wouldn't rejecting the takeoff still be preferable? Sorry for the barrage of questions.
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notaperfectpilot
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« Reply #19 on: November 07, 2011, 11:28:21 AM »

"V1 is the critical engine failure recognition speed or takeoff decision speed. It is the decision speed nominated by the pilot which satisfies all safety rules, and above which the takeoff will continue even if an engine fails. The speed will vary between aircraft types and also due to aircraft weight, runway length, wing flap setting, engine thrust used, runway surface contamination and other factors.

V1 is defined differently in different jurisdictions:
The US Federal Aviation Administration defines it as: V1 means the maximum speed in the takeoff at which the pilot must take the first action (e.g., apply brakes, reduce thrust, deploy speed brakes) to stop the airplane within the accelerate-stop distance. V1 also means the minimum speed in the takeoff, following a failure of the critical engine at VEF, at which the pilot can continue the takeoff and achieve the required height above the takeoff surface within the takeoff distance.

Transport Canada defines it as: Critical engine failure recognition speed and adds: This definition is not restrictive. An operator may adopt any other definition outlined in the aircraft flight manual (AFM) of TC type-approved aircraft as long as such definition does not compromise operational safety of the aircraft."


from:
http://en.wikipedia.org/wiki/V_speeds
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derekjackson
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« Reply #20 on: November 07, 2011, 11:32:38 AM »

I found this document on the FAA website that is helping. It says the definition of V1 consists of two separate concepts:

1) V1 is the maximum speed at which the rejected takeoff maneuver can be initiated and the airplane stopped within the remaining field length under the conditions and procedures defined in the FARs. It is the latest point in the takeoff roll where a stop can be initiated. (this is how I was understanding it earlier)

2) V1 is also the earliest point from which an engine out takeoff can be continued and the airplane attain a height of 35 feet at the end of the runway. (this is how I think you are explaining it)

The FAA also states that "A No-go" decision after passing V1 will not leave sufficient runway remaining to stop if the takeoff weight is equal to the field length limit weight.

So the "run out of runway" scenario only applies in certain cases. Also, it says Do not attempt an RTO once the airplane has passed V1 ... ... this recommendation should prevail no matter what runway length appears to remain after V1

So perhaps in the case of the Yak crash, they may have had enough runway remaining but the V1 definition was based on an engine-out scenario (which of course was not the cause fo the accident).
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notaperfectpilot
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« Reply #21 on: November 07, 2011, 11:41:29 AM »

Also, it says Do not attempt an RTO once the airplane has passed V1 ... ... this recommendation should prevail no matter what runway length appears to remain after V1

Correct me if I am wrong, but it seems to me from what that says, the crew did the RIGHT thing. Maybe I am not understanding it right. If that is the case, than why do they say that they should have RTO? 
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derekjackson
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« Reply #22 on: November 07, 2011, 12:19:26 PM »

Also, it says Do not attempt an RTO once the airplane has passed V1 ... ... this recommendation should prevail no matter what runway length appears to remain after V1

Correct me if I am wrong, but it seems to me from what that says, the crew did the RIGHT thing. Maybe I am not understanding it right. If that is the case, than why do they say that they should have RTO? 

Hence my confusion.
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NoMad
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« Reply #23 on: November 07, 2011, 12:40:30 PM »

You can't base "right" vs "wrong" on simply whether or not they chose to reject after V1.  You have to evaluate your circumstances and make a decision.  MOST scenarios dictate not bothering to reject after V1 because the act of trying to stop is often more dangerous than continuing the takeoff with the given problem.  Those dangers include but are not limited to overrunning if you're beyond the stopping distance and the brakes catching on fire.  For example an engine failure is a serious problem but the plane can takeoff and fly without it.  The safest thing to do is continue the takeoff.

However, if the problem is such that continuing the takeoff will be more dangerous than trying to stop, than the safest course of action is to reject regardless of V1 or not.  Things such as "the plane is on fire" or perhaps "the plane isn't rotating and will never get off the ground".  Those situations are going to be rejects.  Most runways use by commercial aircraft will be long enough for most aircraft to not overrun anyway.  Maybe it will.  however I would rather slowly overrun and take out an antenna than keep trying to fly a plane that won't fly or that is on fire.
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derekjackson
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« Reply #24 on: November 07, 2011, 12:56:29 PM »

Ok, so in this case they happened to have enough runway remaining to stop and since they couldn't rotate the aircraft (meaning something was very wrong), rejecting takeoff after V1 could have led to a more favourable outcome.
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NoMad
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« Reply #25 on: November 07, 2011, 03:49:59 PM »

Most likely that is correct.  I don't know the stopping distance number.  But look at it this way.  Even if there was not enough runway to stop and an overrun was inevitable, they would have overrun and crashed a slow speed rather than balls to the wall.  Hence the safer outcome would have been rejecting.
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joeyb747
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« Reply #26 on: November 07, 2011, 08:33:37 PM »

"An AVI video showing the reconstructed flight was later released."

From AvHerald.

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Aircraft Mechanic
ORD Don
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« Reply #27 on: November 10, 2011, 12:13:24 PM »





             Very tragic.  Especially considering the fact that this is an accident that should never had happened.

             I was just wondering, not being a pilot, what the mindset is of a pilot who is running out of runway.

             Is it human nature to want to force the issue (get it up), or would any well trained pilot instinctively

             abort the take-off ?    Sorry if it's a stupid question...
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