Rejecting A Takeoff After V1…why Does It (still) Happen?
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John you have to go apples to apple....whether you abort at V1 or you abort 5 knots past...all the factors are the same...
If you want to chase down the over run argument again...then it's simple.....when you calculated balanced field and notice that you had 5000 feet left over...that tidbit of info goes into the back of your head...
If you purposefully plan out that extra 5000 feet..then again...your simply giving your self less options ON PURPOSE...which is a variable I am not willing to accept with passengers in back....by myself...sure.....
I plan for the most layers of safety, not purposefully take out all the buffers, back up systems, fudge factor and safety pillows because financial thift and corporate policy direct that I do so.
If you want to chase down the over run argument again...then it's simple.....when you calculated balanced field and notice that you had 5000 feet left over...that tidbit of info goes into the back of your head...
If you purposefully plan out that extra 5000 feet..then again...your simply giving your self less options ON PURPOSE...which is a variable I am not willing to accept with passengers in back....by myself...sure.....
I plan for the most layers of safety, not purposefully take out all the buffers, back up systems, fudge factor and safety pillows because financial thift and corporate policy direct that I do so.
Johns7022
What if I told you that a derate power take-off actually increases your margins and reduces your V1? How do you feel about 3-engine take-offs and I don't mean on a tri-motor? Again, based on your plans when BFL is less than ASDR, do you calculate an accelerate-stop distance and a refusal speed, that is maximum speed on all-engine acceleration and stop and a maximum brake energy speed? An actual tire limit speed would also be a good idea, if you do these calcs. If not, how do you know your performance limits?
Now that ICAO Annex 6, as amended requiring SMS and an Operations Manual, have done a risk assessment on youre operating rules?
GF
PS: if you read my post, you would have noted it wasn't a Boeing product. But one that turns into a 28-tired, 24-braked art gum eraser when the anti-skid is functioning. Ever see an acre or two of anti-skid marks?
What if I told you that a derate power take-off actually increases your margins and reduces your V1? How do you feel about 3-engine take-offs and I don't mean on a tri-motor? Again, based on your plans when BFL is less than ASDR, do you calculate an accelerate-stop distance and a refusal speed, that is maximum speed on all-engine acceleration and stop and a maximum brake energy speed? An actual tire limit speed would also be a good idea, if you do these calcs. If not, how do you know your performance limits?
Now that ICAO Annex 6, as amended requiring SMS and an Operations Manual, have done a risk assessment on youre operating rules?
GF
PS: if you read my post, you would have noted it wasn't a Boeing product. But one that turns into a 28-tired, 24-braked art gum eraser when the anti-skid is functioning. Ever see an acre or two of anti-skid marks?
J_T
On the thread Brian referred to, a poster offered a LH "formula" that for every knot over V1 that the reject is initiated, the plane will overrun at 10 knots. That is, a 1 knot exceedence of V1 will result in a 10 knot overrun on a limiting runway. A mad scientist ran the numbers and thought that was correct in the 6-9 knot range, a greater multiple at slower speeds and a lower one at greater speeds. Works for me.
GF
On the thread Brian referred to, a poster offered a LH "formula" that for every knot over V1 that the reject is initiated, the plane will overrun at 10 knots. That is, a 1 knot exceedence of V1 will result in a 10 knot overrun on a limiting runway. A mad scientist ran the numbers and thought that was correct in the 6-9 knot range, a greater multiple at slower speeds and a lower one at greater speeds. Works for me.
GF
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That makes no sense...what's a 10 knot over run? That you over run at a speed of 10kts, when you get to the end of your balanced field?
What if you have 5000 feet of buffer? Which has been my premise........oh that's right you never do...because no matter what the runway length is...your derate it right into the over run.....
So yeah, I guess, if you decide to burn up 12000 feet in your balanced field numbers...passing the 6000 ft taxi way at 32 knots...sure I get it...at the very end...if you abort past V1...you will hit the weeds a little faster..
Sure I buy that...
What if you have 5000 feet of buffer? Which has been my premise........oh that's right you never do...because no matter what the runway length is...your derate it right into the over run.....
So yeah, I guess, if you decide to burn up 12000 feet in your balanced field numbers...passing the 6000 ft taxi way at 32 knots...sure I get it...at the very end...if you abort past V1...you will hit the weeds a little faster..
Sure I buy that...
Evidently, Newtonian mechanics wasn't your forte. 1/2mv squared is a pain, the higher you speed when beginning a stop translates into greater distance to stop or a set speed when going off the end, pretty elemental.
A 10 knot overrun occurs when, after rejecting above V1 by 1 knot, apply all the braking, spoilers deployed what speed you go into the grass on a field limited runway. If you are such an aviator, you should be aware of this si ple physics problem.
The BR700 series doesn't offer derated, but flex power is available on the FMS and used when indicated.
How are those answers coming?
GF
A 10 knot overrun occurs when, after rejecting above V1 by 1 knot, apply all the braking, spoilers deployed what speed you go into the grass on a field limited runway. If you are such an aviator, you should be aware of this si ple physics problem.
The BR700 series doesn't offer derated, but flex power is available on the FMS and used when indicated.
How are those answers coming?
GF
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You want to talk physics...ok..and let's use Brian's numbers....
Assuming I am on my 10,000 ft field...balanced field today is 5000 feet...135 standards...not 91...when I RTO 5 knots past V1, just prior to VR.. then passed my original balanced field point of 5000 feet...at 50 knots...I now have 5000 feet to stop my aircraft that is only doing 50 knots...which might be...what? 200 feet? Nah...let's I take it easy...and not even apply brakes and let the plane coast for 5000 feet, on it's own....
I guess I will be sitting there at mid field......looking at the bomb hole in my baggage department that just took out half my controls, and reduced the structural integrity of my empenage by 99%
Oh by I forgot, I am supposed to pull the plane off...sorry...my bad...
Assuming I am on my 10,000 ft field...balanced field today is 5000 feet...135 standards...not 91...when I RTO 5 knots past V1, just prior to VR.. then passed my original balanced field point of 5000 feet...at 50 knots...I now have 5000 feet to stop my aircraft that is only doing 50 knots...which might be...what? 200 feet? Nah...let's I take it easy...and not even apply brakes and let the plane coast for 5000 feet, on it's own....
I guess I will be sitting there at mid field......looking at the bomb hole in my baggage department that just took out half my controls, and reduced the structural integrity of my empenage by 99%
Oh by I forgot, I am supposed to pull the plane off...sorry...my bad...
The example is not a BFL 5000 feet and an ASDA of 10,000 feet, the example is BFL = ASDR, no overrun or stopway, just a cliff, down into a gorge. FAR 91 or FAR 135. no difference, the physics are the same.
How do you pass the end of BFL at 50 knots, at that point you should either be stopped (ZERO Knots) or at V2 at 35 feet, V2 better exceed 50 knots!
GF
How do you pass the end of BFL at 50 knots, at that point you should either be stopped (ZERO Knots) or at V2 at 35 feet, V2 better exceed 50 knots!
GF
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No one disputes that aborting past V1 might result in a stop past your calculated balance field length...although the argument could be made that my using TRs, better braking technique, soaking up manufacturer's fudge factor......vs the 200 hour pay to fly guy you have in your plane might result in my stopping at the end and you going into a lake of lava at the end....
But that said....if my balanced field equals the runway...a very rare condition that only lives in the world people who run derated/assumed thrust or people who routinely fly jets, heavy, in and out of short runways....
I have to tell you..that I would take my chances with a post V1 RTO if prior to rotation, if I saw some Tali-ban with an RPG a few taxi ways back, then heard an explosion in my tail......
Not an unrealistic scenario to consider, if your flying around Iraq and Afghanistan these days.....
But that said....if my balanced field equals the runway...a very rare condition that only lives in the world people who run derated/assumed thrust or people who routinely fly jets, heavy, in and out of short runways....
I have to tell you..that I would take my chances with a post V1 RTO if prior to rotation, if I saw some Tali-ban with an RPG a few taxi ways back, then heard an explosion in my tail......
Not an unrealistic scenario to consider, if your flying around Iraq and Afghanistan these days.....
No PTF pilots t my operation, it's not an airline, btw. Though I have taught a lot who have been paid to learn. You still have not understood derate power or flex power and their effects. Try this one-- why can you increase your TOGW by derating?
GF
GF
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That is, a 1 knot exceedence of V1 will result in a 10 knot overrun on a limiting runway
Hadn't seen that before but it is in the ball park I would expect to see - the concerns come down to the two items
(a) penalty lost distance associated with the overspeed itself
(b) gradient of the stopping part (and this is the reason that one MUST keep the anchors pushed into the floor until the aircraft lurches to a stop in the angry situation .. more than a few folk have perceived that all was well .. eased off the brakes .. and then danced into the weeds).
My view, on an ASD limiting runway is that I'd rather err on the side of continuing a couple of knots low rather than rejecting a few knots high on the historical stats.
Assuming I am on my 10,000 ft field...balanced field today is 5000 feet...
Of course your argument probably will be valid from the physics of the thing .. you have some fat to elect to reduce speed on reverse or distance and then use brakes if you were in a brake energy limit situation.
However, the Citation (as I recall you fly) is a low Vmcg, low V1 aircraft and not typical of the situation which most heavy drivers face. This is especially the case for the larger twin aisle machines. GF is talking C5A and that has the double whammy of being big iron with flea power motors.
The underlying arguments and concerns, however, are those of
(a) risk management/control (trying to stack the numbers in the pilot's favour on the day) in a rational and objective manner
(b) minimising the need for super rapid decision making with only a fraction of the story to hand at the time .. ie adhere to SOP unless the situation is pretty clear cut. Routinely winging these processes at the time has been shown to be a less than optimal approach over the years.
although the argument could be made that my using TRs
.. true but, other than in contaminated conditions, mainly a maker of noise and not much stopping value
better braking technique
.. that's a silly statement to make .. however, we would be interested in knowing what better technique you might propose compared to that used by the TP .. which will be THE best for the aircraft .. that's why the TP is employed for the purpose.
soaking up manufacturer's fudge factor
.. while there are fudge factors built into most performance data, ASD is pretty well hard data. We have, for instance, negotiated time delays (which usually are quite realistic) and the delay factor required by A/L 42 (which is not all that fat).
Just which manufacturer's fudge factors might you have been thinking of ?
Hadn't seen that before but it is in the ball park I would expect to see - the concerns come down to the two items
(a) penalty lost distance associated with the overspeed itself
(b) gradient of the stopping part (and this is the reason that one MUST keep the anchors pushed into the floor until the aircraft lurches to a stop in the angry situation .. more than a few folk have perceived that all was well .. eased off the brakes .. and then danced into the weeds).
My view, on an ASD limiting runway is that I'd rather err on the side of continuing a couple of knots low rather than rejecting a few knots high on the historical stats.
Assuming I am on my 10,000 ft field...balanced field today is 5000 feet...
Of course your argument probably will be valid from the physics of the thing .. you have some fat to elect to reduce speed on reverse or distance and then use brakes if you were in a brake energy limit situation.
However, the Citation (as I recall you fly) is a low Vmcg, low V1 aircraft and not typical of the situation which most heavy drivers face. This is especially the case for the larger twin aisle machines. GF is talking C5A and that has the double whammy of being big iron with flea power motors.
The underlying arguments and concerns, however, are those of
(a) risk management/control (trying to stack the numbers in the pilot's favour on the day) in a rational and objective manner
(b) minimising the need for super rapid decision making with only a fraction of the story to hand at the time .. ie adhere to SOP unless the situation is pretty clear cut. Routinely winging these processes at the time has been shown to be a less than optimal approach over the years.
although the argument could be made that my using TRs
.. true but, other than in contaminated conditions, mainly a maker of noise and not much stopping value
better braking technique
.. that's a silly statement to make .. however, we would be interested in knowing what better technique you might propose compared to that used by the TP .. which will be THE best for the aircraft .. that's why the TP is employed for the purpose.
soaking up manufacturer's fudge factor
.. while there are fudge factors built into most performance data, ASD is pretty well hard data. We have, for instance, negotiated time delays (which usually are quite realistic) and the delay factor required by A/L 42 (which is not all that fat).
Just which manufacturer's fudge factors might you have been thinking of ?
RPG fire is not a daily occurrence, get real! Have a realistic scenario, or are there daily RPG attacks at your base? BTW, on Iraq, where there were RPG attacks, the reject criteria didnt change, just the spiral up procedure.
Why do you ignore questions that you should know, if you operate legally? Don't have answers or don't know wht you're doing? Or does baloney just reject the grinder?
GF
Why do you ignore questions that you should know, if you operate legally? Don't have answers or don't know wht you're doing? Or does baloney just reject the grinder?
GF
Moderator
As an aside, we need to keep in mind that some of our colleagues enjoy stirring the pot a little - I have no idea whether johns7022 fits that label or not.
However, the technique does engender vigorous discussion at times and has been used to great effect by some of our more interesting members .. 411A and Milt come to mind .. both are very experienced aviators.
In Milt's case that experience incorporates a long time TP background and one wouldn't be surprised to see his participation in this thread in due course. As another aside, I have no doubt that he will be a little teary-eyed at the withdrawal of the F111 from RAAF service this month, having introduced the Type into operation so many years ago.
However, the technique does engender vigorous discussion at times and has been used to great effect by some of our more interesting members .. 411A and Milt come to mind .. both are very experienced aviators.
In Milt's case that experience incorporates a long time TP background and one wouldn't be surprised to see his participation in this thread in due course. As another aside, I have no doubt that he will be a little teary-eyed at the withdrawal of the F111 from RAAF service this month, having introduced the Type into operation so many years ago.
Per Ardua ad Astraeus
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JT - you are well aware of my standing views on 'discussions' on a thread and the contribution to safety, I'm sure. All challenges to 'tradition' are always welcome as long as they are rational, and have indeed changed 'established' procedures in the past, as with the BA 737 fatal abort at Manchester some years ago.
You will, no doubt, have a shrewd idea of identity. IF we have a 'SSG' re-incarnation we are wasting our time here
May I draw to the attention of all, from another thread:
from that I believe there is quite a lot he/she does not comprehend.
You will, no doubt, have a shrewd idea of identity. IF we have a 'SSG' re-incarnation we are wasting our time here
May I draw to the attention of all, from another thread:
Originally Posted by johns7022
Here's my take on CRM,....from the perspective of a pilot flying a Citation Encore Single pilot...
Level 1- Captain is that a mountain up ahead?
Level 2- Captain I think that is a mountain up ahead
Level 3- Captain I think we are headed into that mountain
Level 4- Captain we will hit that mountain in 5 minutes
Level 5- Captain if you don't change course, I am calling dispatch
Level 6- Captain, dispatch says you need to avoid the mountain
Level 7- Captain, the chief pilot says you need to avoid the mountain
Level 8 - Captain, the stewardess's and passengers took a vote and think you should avoid the mountain
Level 8 - Captain, I am considering taking the controls
Level 9- Captain, I am really, really considering taking the controls
Level 10- I don't mean to hurt your feelings but I am taking the controls
Level 11- Now that I have the controls, but only have 200 hours can you confirm I am on on the right heading and will not hit anything?
Level 1- Captain is that a mountain up ahead?
Level 2- Captain I think that is a mountain up ahead
Level 3- Captain I think we are headed into that mountain
Level 4- Captain we will hit that mountain in 5 minutes
Level 5- Captain if you don't change course, I am calling dispatch
Level 6- Captain, dispatch says you need to avoid the mountain
Level 7- Captain, the chief pilot says you need to avoid the mountain
Level 8 - Captain, the stewardess's and passengers took a vote and think you should avoid the mountain
Level 8 - Captain, I am considering taking the controls
Level 9- Captain, I am really, really considering taking the controls
Level 10- I don't mean to hurt your feelings but I am taking the controls
Level 11- Now that I have the controls, but only have 200 hours can you confirm I am on on the right heading and will not hit anything?
But, for better or worse, not shy about expressing opinions on that which he does not comprehend..........
GF
J_T. The "formula" on overrun speed is on about page 12 or 13 of the thread Brian Abraham linked to on the last page, this thread.
GF
J_T. The "formula" on overrun speed is on about page 12 or 13 of the thread Brian Abraham linked to on the last page, this thread.
Moderator
You will, no doubt, have a shrewd idea of identity.
Actually, no. We can elicit some information from the system but it is rather generic in nature. End result is that I have no idea who johns7022 might be. However, there are some stylistic similarities so he/she may well be someone else from the past ...
IF we have a 'SSG' re-incarnation we are wasting our time here
I'd take a contrary view. It has always been apparent that the best way to test one's own knowledge is to assess one's ability to express that knowledge. Thus, stimulating discussion (whomever might be the driving source) has the useful value of testing the participating readership's knowledge comfort. Folk such as SSG, and others, might be a tad irritating in some respects but that doesn't, of itself, reduce their value to the discussion.
page 12 or 13
Thanks, GF .. I'll have a looksee at the link.
Those that are taught to pour the tea, don't always know how to make it.
Good point. Knowing the makings may not be a necessary prerequisite to doing the pouring entirely satisfactorily. However, there may be some sideline issues for which the former may assist the execution of the latter.
I am reminded of a final year fluid mechanics exam question from many decades ago ... which considered the case of the PNR tea lady .. daily she would ascend the spiral iron staircase in that august building .. the question assigned one's pondering to whether she ought to stir the tea
(a) before she started up the stairs ?
(b) after she arrived at the last landing ?
(c) or, indeed, was it necessary to stir the tea at all ?
.. an interesting chap, that lecturer.
The answer, needless to say, involved a few pages of manuscript containing the usual run of the mill engineering undergraduate mathematical jiggery-pokery ...
Actually, no. We can elicit some information from the system but it is rather generic in nature. End result is that I have no idea who johns7022 might be. However, there are some stylistic similarities so he/she may well be someone else from the past ...
IF we have a 'SSG' re-incarnation we are wasting our time here
I'd take a contrary view. It has always been apparent that the best way to test one's own knowledge is to assess one's ability to express that knowledge. Thus, stimulating discussion (whomever might be the driving source) has the useful value of testing the participating readership's knowledge comfort. Folk such as SSG, and others, might be a tad irritating in some respects but that doesn't, of itself, reduce their value to the discussion.
page 12 or 13
Thanks, GF .. I'll have a looksee at the link.
Those that are taught to pour the tea, don't always know how to make it.
Good point. Knowing the makings may not be a necessary prerequisite to doing the pouring entirely satisfactorily. However, there may be some sideline issues for which the former may assist the execution of the latter.
I am reminded of a final year fluid mechanics exam question from many decades ago ... which considered the case of the PNR tea lady .. daily she would ascend the spiral iron staircase in that august building .. the question assigned one's pondering to whether she ought to stir the tea
(a) before she started up the stairs ?
(b) after she arrived at the last landing ?
(c) or, indeed, was it necessary to stir the tea at all ?
.. an interesting chap, that lecturer.
The answer, needless to say, involved a few pages of manuscript containing the usual run of the mill engineering undergraduate mathematical jiggery-pokery ...
J_T
It was on page 13, here's MfS' quote
That was in response to Clandestino in post #251, about half way down the page. Drove me near round the bend finding it!
GF
It was on page 13, here's MfS' quote
Did some quick maths with some simplistic assumptions about accels and decels and that "rule of ten" is pretty good. It actually looks like it UNDERESTIMATES the runway exit speed for small values - it looks about right for 5-6 knots, for reasonable V1 values. For one or two knots, the multiple is more like 20, though. And for ten or more knots delay the factor drops to 7 or lower.
If I use the 40/70 break points for hazards, then any delay of more than, say, 4 knots is hazardous, and anything over 9 or 10 knots is catastrophic. And, as OORW astutely notes, that's assuming a relatively "friendly" overrun area...
Assuming a (lowish) takeoff T/W of, say, 0.25'g', that's an accel of about 5knots/sec. A light weight could see that nearly double. So those speed increases equate to about a second of delay.
If I use the 40/70 break points for hazards, then any delay of more than, say, 4 knots is hazardous, and anything over 9 or 10 knots is catastrophic. And, as OORW astutely notes, that's assuming a relatively "friendly" overrun area...
Assuming a (lowish) takeoff T/W of, say, 0.25'g', that's an accel of about 5knots/sec. A light weight could see that nearly double. So those speed increases equate to about a second of delay.
GF
Erm.... 10 kt overrun for each 1 kt above V1 in runway limited cases isn't actually a formula, it's more like rule of thumb. My apologies if I made it look like one. Mad (flt) scientist has pointed out correctly that actual relation is not linear yet the curve is close enough to 10 in 1 line for everyday use.
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Johns7022,
I'm curious. Do you bother calling V1 when you trundle off down the runway? If you do, why?
Also, is your view on post V1 rejects the same for contaminated runways?
When it goes bang and you look out of the window do you consider the weight of your aircraft, temperature, wind, distance to go, acceleration and runway slope in the split second before you decide to stop or go?
What was that bang? Do you consider the possibility of a tyre burst and a reduction in breaking efficiency?
What do you do on short strips where you might have a balanced field? Do you now use V1? What's V1, I aint used that for ages?!
I assume that you have flawless stereoscopic, binocular vision. Maybe Joe Bloggs hasn't so he can't rely on just his eyesight to accurately judge how much runway is left. What do you do if you have a bit of eye tension? That affects you depth perception and ability to judge distances.
Can you easily and quickly judge how much is left when you're taking off into sun with a bit of mist or haze? How about low vis, 300 meters or so? How much runway left now?
How about night? Again, depth perception is changed.
Depth or distance perception is based on previous visions of an object or scene. If you have knowledge of the size of an object from previous experience, then your brain can gauge the distance based on the size of the object on the retina. However, if you haven't seen the object previously then it is much harder for you to judge distance to it. The object, for you, would be the end of the runway. Now say the runway is narrower than your usual one, it would then appear longer and unless you'd seen that previously you are very likely to misjudge the distance to go to the end.
I'm curious. Do you bother calling V1 when you trundle off down the runway? If you do, why?
Also, is your view on post V1 rejects the same for contaminated runways?
When it goes bang and you look out of the window do you consider the weight of your aircraft, temperature, wind, distance to go, acceleration and runway slope in the split second before you decide to stop or go?
What was that bang? Do you consider the possibility of a tyre burst and a reduction in breaking efficiency?
What do you do on short strips where you might have a balanced field? Do you now use V1? What's V1, I aint used that for ages?!
I assume that you have flawless stereoscopic, binocular vision. Maybe Joe Bloggs hasn't so he can't rely on just his eyesight to accurately judge how much runway is left. What do you do if you have a bit of eye tension? That affects you depth perception and ability to judge distances.
Can you easily and quickly judge how much is left when you're taking off into sun with a bit of mist or haze? How about low vis, 300 meters or so? How much runway left now?
How about night? Again, depth perception is changed.
Depth or distance perception is based on previous visions of an object or scene. If you have knowledge of the size of an object from previous experience, then your brain can gauge the distance based on the size of the object on the retina. However, if you haven't seen the object previously then it is much harder for you to judge distance to it. The object, for you, would be the end of the runway. Now say the runway is narrower than your usual one, it would then appear longer and unless you'd seen that previously you are very likely to misjudge the distance to go to the end.