V2
Bottom line: The certification definition is as I have said, the meaning on the flight deck is as I have said, and a proper first principles understanding of that part of certification allows no other definition.
I think he did provide a definition, at post #9:
V1 --- the speed at which the takeoff must be continued, if the stopping has not already been commenced.
Which he indicates is a definition arrived at by Boeing (a manufacturer who has derived it from the FAR's etc - even though he has discounted any other manufacturers interpretations of the derivation).
This is correct. From the FAR, the decision to stop must be made BEFORE V1, thus V1 is NOT a decision speed, so the first part of below is correct, however his interpretation that:
The second part of this is incorrect, as the FAR clearly states states that V1 is the speed achieved AT WHICH the brakes are applied, not the speed reached immediately after.
If Leadies main issue is with V1 being referred to as a "decision" speed, then he is correct, there is no decision at V1, you are committed. However, V1 has to be defined somehow, and I think the FAR is quite explicit, and even the quoted Boeing one is a little vague. If Boeing certificate to the FARs why not just use the FAR one? Surely that is the correct one?
There is no decision at V1, it is go.
The decision to stop, and the initial actions to stop must be before V1.
If Leadies main issue is with V1 being referred to as a "decision" speed, then he is correct, there is no decision at V1, you are committed. However, V1 has to be defined somehow, and I think the FAR is quite explicit, and even the quoted Boeing one is a little vague. If Boeing certificate to the FARs why not just use the FAR one? Surely that is the correct one?
I agree that the second bit is incorrect, if assessed against the FAR. It seems to me that the FAR definition anticipates initation action before or at V1. It seems to me that the Boeing definition quoted by Leaddie anticipates that as well. Perhaps Leaddie is misinterpreting the Boeing definition?
That said, I also agree that the Boeing definition is vague. What does "stopping has ... been commenced" mean? Does it mean deceleration has commenced? I don't think that is what the FAR definition anticipates. There's a difference between initiating action to stop and that action starting to take effect.
That's why it seems that you don't 'unmake' a decision to reject, even if you exceed V1 after initiating stopping action before or at V1.
That said, I also agree that the Boeing definition is vague. What does "stopping has ... been commenced" mean? Does it mean deceleration has commenced? I don't think that is what the FAR definition anticipates. There's a difference between initiating action to stop and that action starting to take effect.
That's why it seems that you don't 'unmake' a decision to reject, even if you exceed V1 after initiating stopping action before or at V1.
Moderator
Some thoughts (from a pilot with a reasonably extensive professional design engineering and certification background) –
There are two sets of rules in play -
(a) Certification (eg FAR 25, ANO 101.5/101.6 and antecedents, now all long gone to the rules graveyard somewhere ..)
(b) Operations (eg FAR 121, CAO 20.7.1B)
plus ayres and minor variations in other codes.
It would be nice if both sets of rules in each of the various jurisdictions were neatly aligned but that is not always the case .. engineers and pilots don’t always think the same way and confusion sometimes is the result. CASA has some certification experienced engineering/pilot folk in the operations regulatory arena so, perhaps, we might see things progressively improve.
We have the historical baggage associated with older local requirements (now defunct – the old 101 series of Orders, especially those with many dot subordinate identifiers in the callout). All but the very much older folk (probably Leaddie, due to the performance engineering folk with whom he came in contact in his early airline years and, perhaps, Stallie) in the PPRuNe sandpit will have no knowledge/recollection of these at all. These long preceded 101.5/101.6, themselves also gone to the archives and, I daresay, most here will not have any recall of their content either.
For many years, especially in respect of 101.5/101.6, these local requirements modified either the US or UK rules in various ways and caused the Industry all sorts of nuisances (until Ron Yates' Report pushed the rule makers to change things somewhat and those local rules were binned). Then, to confuse matters, 20.7.1B purported to talk operational implementation of the certification bases, occasionally introducing disjoints along the way. Add to that the penchant of pilots to produce 101 answers for most questions and the scene is set for OWTs.
It might be useful to keep the two sets of rules a little separate .. if you want to consider certification, then talk FAR 25 (or whichever set might apply in the circumstances). Ideally, the operational rules would look to flying the aeroplane in a manner compatible with the certification basis rather than confusing pilots’ minds in respect of (occasionally incorrect/incompatible) certification detail.
I see various posters quoting liberally from the FARs. Be VERY careful when you do this other than in a generic and, preferably, qualified way. The certification rules have varied GREATLY over the years, in keeping with technological capability BUT one generally doesn’t see retrospective application of new rules. That is to say, if you are looking at Aeroplane ABC, then you MUST check the TCDS to determine what version of the rules applied to its design and certification and then talk that version of the rules rather than the current set. In general, it is not valid to infer that a revised or new rule (not applicable to the particular frozen design standards defined for the original design) will apply, or be relevant to, that particular aeroplane. It follows that the rules applicable to one aeroplane may be quite different in detail to those applicable to another. This is quite relevant to a discussion on scheduled speeds where rules and interpretation has varied somewhat over the years.
Several posts query exceeding V1 with the reject commenced immediately prior to V1 .. once you start the reject, regardless of the speed, there necessarily will be a short period of (reducing) continued acceleration before things get sorted out (ie the brakes are actually doing their thing in earnest) and the speed starts to reduce very rapidly. In the case of the idealised sudden engine failure reject, engine rundown characteristics, timing and sequence of crew actions, etc., are very relevant to this observation. Once the levers are closed, boards up, and brakes on full song, deceleration will be very high in most cases (those who flew the 727 with the nosewheel brakes option will know what I mean) .. but it does take a finite time for this all to occur. The 2 second delay introduced at FAR 25 A/L 42 (and ANO 101.6 A/L 62 if I recall correctly ?) provided some much-needed, if small, fat for pilot comfort and rational reality
For a normal (dry runway) reject, reverse is held in reserve .. in any case, by the time significant reverse is achieved, the brakes have done the bulk of the deed and reverse has the main benefit of adding noise to all the other excitement. On the other hand, in the case of a slippery runway surface, reverse might become very important to the pilot’s wish list.
The current “how it is done” description lies within FAR AC 25-7 which can be found at https://www.faa.gov/documentLibrary/...2025-7C%20.pdf
Page 32 of this document indicates Section 25.107(a)(2) was revised to remove the reference to “takeoff decision speed” from the definition of V1. V1 is the speed by which the pilot has already made the decision to reject the takeoff and has initiated the first action to stop the airplane … this should be taken to be the likely current FAA thoughts on V1.
Keep in mind, when reading the FARs, that one always has to read the applicable ACs to get the behind-the-scenes FAA story on what they thought the rules should mean.
If things go significantly awry, for whatever oddball reason (eg, in keeping with some concerns expressed in this thread - no brakes) and the certification boundary condition expectations cannot be met in reasonable measure, the whole thing then is very much in the lap of the Gods. Leaddie’s post #29 is pertinent.
A similar oddball case is the low speed (Vmcg-limited) V1 critical fail reject in the presence of a significant adverse crosswind .. continuing, with the aircraft out of control directionally, is not a good option and a post-scheduled V1 reject might be the way to go (ie stop). Another example is the airborne Vmc case where the pilot fails to apply the necessary bank inputs … and over we go. A read of the Darwin Braz mishap is useful, and sobering, for this one.
However, whatever the situation, if you are well outside the postulated certification parameters, then the performance capabilities of the aircraft on a critical runway probably aren’t going to give you a nice outcome ... if the initial OEI reject decision is reversed on a critical runway, the runway head speed probably isn’t going be useful. Sometimes we just have to accept that the Gods are mischievous on occasion and we might not make it home. Certainly, the certification rules don’t give guarantees .. only probabilities.
Keep in mind that the basic certification idea is a single major failure to contend with. Sure, historical reality tells us that the real world doesn’t always mirror the certification idealisations as nicely as we might like to see, but the further we get away from the test conditions .. the further we get away from a potentially happy outcome. Refer Aerocats’ #34.
Note the 3 second margin that's built into the V1 certification data. Refresh my memory as to the story here ?
2 seconds after you initiated braking and retarded the thrust levers you realise the brakes are not working. You are now over V1 and the engines are spooling down. You will be WELL over V1. What to do ? All depends on a heap of things which defy analysis in an instant on the fly. Retracting the gear/ground looping might be an option if all else appears to be covered in blood. If you have another 10,000 ft or so ahead, you may be having a somewhat better day. In any case, I doubt that one would take anything like two seconds to recognise a significant brake failure ...
What does concern me is the apparent thinking that all this is black and white. That just ain’t the case. The certification standards presume certain conditions etc. and, to be sure, generally those presumptions work out reasonably well in practice as we don’t have aircraft falling about us day in day out.
However, one should not lose sight of the fact that the certification performance rule book presumes an idealised, prescribed world – it has to do that if there is to be any repeatability in testing - albeit with a bit of fat here and there to provide some protection for innocents abroad. Now, if the real world on the day varies significantly from that postulated .. don’t be surprised if you don’t see the aeroplane match the book. If the delta is significant and not your way, then don’t be surprised to see tears at the end of the day.
The present Industry thought about V1 (viz., in general the outcome is far more likely to be happy if the takeoff is continued from V1) endeavours to incorporate real world, historical, statistical reality while generating cockpit simplicity for SOP. IT DOES NOT GUARANTEE a happy outcome ALL the time .. but, certainly, most of the time things will end well.
If, on the day, the boundary conditions vary significantly from those presumed, and were not amenable to pretakeoff planning (I'm sure we all do think about the what-ifs and how we might handle them ?) the Commander gets to earn his/her pay in a very short time .. win (hero/heroine), lose (scapegoat), or draw (lives to fly another day, albeit with sweaty palms at the time).
The thread discussion, however, is invaluable, as it encourages thinking and provides an opportunity for newchum education.
It has been my observation that the majority of endorsement courses and recurrent training probably don’t give enough detail to the details and the limitations .. which is why some of us, with a foot in both camps, have approached pilot training from a quite different starting point. Those of you who are fortunate enough to have very experienced ops engineers (especially those with significant heavy aircraft operational experience) associated with your operation and training are, indeed, most fortunate. Do heed their technical counsel.
There are two sets of rules in play -
(a) Certification (eg FAR 25, ANO 101.5/101.6 and antecedents, now all long gone to the rules graveyard somewhere ..)
(b) Operations (eg FAR 121, CAO 20.7.1B)
plus ayres and minor variations in other codes.
It would be nice if both sets of rules in each of the various jurisdictions were neatly aligned but that is not always the case .. engineers and pilots don’t always think the same way and confusion sometimes is the result. CASA has some certification experienced engineering/pilot folk in the operations regulatory arena so, perhaps, we might see things progressively improve.
We have the historical baggage associated with older local requirements (now defunct – the old 101 series of Orders, especially those with many dot subordinate identifiers in the callout). All but the very much older folk (probably Leaddie, due to the performance engineering folk with whom he came in contact in his early airline years and, perhaps, Stallie) in the PPRuNe sandpit will have no knowledge/recollection of these at all. These long preceded 101.5/101.6, themselves also gone to the archives and, I daresay, most here will not have any recall of their content either.
For many years, especially in respect of 101.5/101.6, these local requirements modified either the US or UK rules in various ways and caused the Industry all sorts of nuisances (until Ron Yates' Report pushed the rule makers to change things somewhat and those local rules were binned). Then, to confuse matters, 20.7.1B purported to talk operational implementation of the certification bases, occasionally introducing disjoints along the way. Add to that the penchant of pilots to produce 101 answers for most questions and the scene is set for OWTs.
It might be useful to keep the two sets of rules a little separate .. if you want to consider certification, then talk FAR 25 (or whichever set might apply in the circumstances). Ideally, the operational rules would look to flying the aeroplane in a manner compatible with the certification basis rather than confusing pilots’ minds in respect of (occasionally incorrect/incompatible) certification detail.
I see various posters quoting liberally from the FARs. Be VERY careful when you do this other than in a generic and, preferably, qualified way. The certification rules have varied GREATLY over the years, in keeping with technological capability BUT one generally doesn’t see retrospective application of new rules. That is to say, if you are looking at Aeroplane ABC, then you MUST check the TCDS to determine what version of the rules applied to its design and certification and then talk that version of the rules rather than the current set. In general, it is not valid to infer that a revised or new rule (not applicable to the particular frozen design standards defined for the original design) will apply, or be relevant to, that particular aeroplane. It follows that the rules applicable to one aeroplane may be quite different in detail to those applicable to another. This is quite relevant to a discussion on scheduled speeds where rules and interpretation has varied somewhat over the years.
Several posts query exceeding V1 with the reject commenced immediately prior to V1 .. once you start the reject, regardless of the speed, there necessarily will be a short period of (reducing) continued acceleration before things get sorted out (ie the brakes are actually doing their thing in earnest) and the speed starts to reduce very rapidly. In the case of the idealised sudden engine failure reject, engine rundown characteristics, timing and sequence of crew actions, etc., are very relevant to this observation. Once the levers are closed, boards up, and brakes on full song, deceleration will be very high in most cases (those who flew the 727 with the nosewheel brakes option will know what I mean) .. but it does take a finite time for this all to occur. The 2 second delay introduced at FAR 25 A/L 42 (and ANO 101.6 A/L 62 if I recall correctly ?) provided some much-needed, if small, fat for pilot comfort and rational reality
For a normal (dry runway) reject, reverse is held in reserve .. in any case, by the time significant reverse is achieved, the brakes have done the bulk of the deed and reverse has the main benefit of adding noise to all the other excitement. On the other hand, in the case of a slippery runway surface, reverse might become very important to the pilot’s wish list.
The current “how it is done” description lies within FAR AC 25-7 which can be found at https://www.faa.gov/documentLibrary/...2025-7C%20.pdf
Page 32 of this document indicates Section 25.107(a)(2) was revised to remove the reference to “takeoff decision speed” from the definition of V1. V1 is the speed by which the pilot has already made the decision to reject the takeoff and has initiated the first action to stop the airplane … this should be taken to be the likely current FAA thoughts on V1.
Keep in mind, when reading the FARs, that one always has to read the applicable ACs to get the behind-the-scenes FAA story on what they thought the rules should mean.
If things go significantly awry, for whatever oddball reason (eg, in keeping with some concerns expressed in this thread - no brakes) and the certification boundary condition expectations cannot be met in reasonable measure, the whole thing then is very much in the lap of the Gods. Leaddie’s post #29 is pertinent.
A similar oddball case is the low speed (Vmcg-limited) V1 critical fail reject in the presence of a significant adverse crosswind .. continuing, with the aircraft out of control directionally, is not a good option and a post-scheduled V1 reject might be the way to go (ie stop). Another example is the airborne Vmc case where the pilot fails to apply the necessary bank inputs … and over we go. A read of the Darwin Braz mishap is useful, and sobering, for this one.
However, whatever the situation, if you are well outside the postulated certification parameters, then the performance capabilities of the aircraft on a critical runway probably aren’t going to give you a nice outcome ... if the initial OEI reject decision is reversed on a critical runway, the runway head speed probably isn’t going be useful. Sometimes we just have to accept that the Gods are mischievous on occasion and we might not make it home. Certainly, the certification rules don’t give guarantees .. only probabilities.
Keep in mind that the basic certification idea is a single major failure to contend with. Sure, historical reality tells us that the real world doesn’t always mirror the certification idealisations as nicely as we might like to see, but the further we get away from the test conditions .. the further we get away from a potentially happy outcome. Refer Aerocats’ #34.
Note the 3 second margin that's built into the V1 certification data. Refresh my memory as to the story here ?
2 seconds after you initiated braking and retarded the thrust levers you realise the brakes are not working. You are now over V1 and the engines are spooling down. You will be WELL over V1. What to do ? All depends on a heap of things which defy analysis in an instant on the fly. Retracting the gear/ground looping might be an option if all else appears to be covered in blood. If you have another 10,000 ft or so ahead, you may be having a somewhat better day. In any case, I doubt that one would take anything like two seconds to recognise a significant brake failure ...
What does concern me is the apparent thinking that all this is black and white. That just ain’t the case. The certification standards presume certain conditions etc. and, to be sure, generally those presumptions work out reasonably well in practice as we don’t have aircraft falling about us day in day out.
However, one should not lose sight of the fact that the certification performance rule book presumes an idealised, prescribed world – it has to do that if there is to be any repeatability in testing - albeit with a bit of fat here and there to provide some protection for innocents abroad. Now, if the real world on the day varies significantly from that postulated .. don’t be surprised if you don’t see the aeroplane match the book. If the delta is significant and not your way, then don’t be surprised to see tears at the end of the day.
The present Industry thought about V1 (viz., in general the outcome is far more likely to be happy if the takeoff is continued from V1) endeavours to incorporate real world, historical, statistical reality while generating cockpit simplicity for SOP. IT DOES NOT GUARANTEE a happy outcome ALL the time .. but, certainly, most of the time things will end well.
If, on the day, the boundary conditions vary significantly from those presumed, and were not amenable to pretakeoff planning (I'm sure we all do think about the what-ifs and how we might handle them ?) the Commander gets to earn his/her pay in a very short time .. win (hero/heroine), lose (scapegoat), or draw (lives to fly another day, albeit with sweaty palms at the time).
The thread discussion, however, is invaluable, as it encourages thinking and provides an opportunity for newchum education.
It has been my observation that the majority of endorsement courses and recurrent training probably don’t give enough detail to the details and the limitations .. which is why some of us, with a foot in both camps, have approached pilot training from a quite different starting point. Those of you who are fortunate enough to have very experienced ops engineers (especially those with significant heavy aircraft operational experience) associated with your operation and training are, indeed, most fortunate. Do heed their technical counsel.
Note the 3 second margin that's built into the V1 certification data. Refresh my memory as to the story here ?
I may have misinterpreted what is said, but there's 3 seconds of something built into the number.
Moderator
Didn't have time to look at the video first time through .. boy, but that's an old training video .. I can recall it being introduced, guessing now, around the early 80s ? As I recall, Boeing led an Industry study group on rejects and the video was one of the outcomes. Nonetheless, it's pretty good gen. Memory is a bit ragged on this .. if the video is the one referred to in the link at the bottom of this post, it will have been developed somewhat later. However, I seem to recall having seen it during recurrent training sessions in the 80s at AN - perhaps that might have been later in NZ - doesn't really matter.
Ref the three seconds .. all OK, the long-established one second time sequence to reconfigure expeditiously for the reject (which had been the basis for most certifications for many years prior to A/L 42 - watch guys in the sim and be startled at how many take somewhat longer to achieve the reconfiguration to throttles closed, boards up, and max braking .. and that's with them primed for action .. ) plus the A/L 42 two second pad at V1 to provide a bit of a pad for things such as crew startle response and so forth ie acknowledgement that one second really didn't cut the mustard. If my recollections are correct, the original 707 certification program introduced the one second timing ?
I would hesitate to call it a margin. At best it's a bit of fat to acknowledge that the typical reject crew is going to be hard pressed to get the thing stopping in under three seconds ...
Main thing for all to keep in mind, that time pad disappears VERY rapidly and a tardy PF can find him/herself eating up stopping distance with considerable ease before the reconfiguration is completed ...
Another useful reference is https://flightsafety.org/files/RERR/...gSafetyAid.pdf
Ref the three seconds .. all OK, the long-established one second time sequence to reconfigure expeditiously for the reject (which had been the basis for most certifications for many years prior to A/L 42 - watch guys in the sim and be startled at how many take somewhat longer to achieve the reconfiguration to throttles closed, boards up, and max braking .. and that's with them primed for action .. ) plus the A/L 42 two second pad at V1 to provide a bit of a pad for things such as crew startle response and so forth ie acknowledgement that one second really didn't cut the mustard. If my recollections are correct, the original 707 certification program introduced the one second timing ?
I would hesitate to call it a margin. At best it's a bit of fat to acknowledge that the typical reject crew is going to be hard pressed to get the thing stopping in under three seconds ...
Main thing for all to keep in mind, that time pad disappears VERY rapidly and a tardy PF can find him/herself eating up stopping distance with considerable ease before the reconfiguration is completed ...
Another useful reference is https://flightsafety.org/files/RERR/...gSafetyAid.pdf
Is 'a bit of fat' an esoteric engineering unit of measurement, JT? Sounds to me like a colloquialism for 'margin'...
Whatever it is, it's built into the number.
Given that I'm 'on my own' because the scenario I brought up is outside the certification parameters, my decision to unmake the rejection decision on discovery that my brakes have failed will depend on the spool up time for the good engine/s that have been spooling down for only a few seconds, noting that I'm over V1...
Whatever it is, it's built into the number.
Given that I'm 'on my own' because the scenario I brought up is outside the certification parameters, my decision to unmake the rejection decision on discovery that my brakes have failed will depend on the spool up time for the good engine/s that have been spooling down for only a few seconds, noting that I'm over V1...
Moderator
High tech engineering term .. all part of the in-house jargon.
.. but, as you wish, good sir .. I think our thoughts are in formation.
As to no brakes .. rather you than me ... unless one were looking off the end at Edwards ...
.. but, as you wish, good sir .. I think our thoughts are in formation.
As to no brakes .. rather you than me ... unless one were looking off the end at Edwards ...
It appears that Lead Sled is largely arguing that the stopping must have been commenced prior to V1.
The main problem with this is that without further definition, "before V1" is meaningless.
How much before V1?
I assume that if I suffer an engine failure and take stopping action AT V1 (i.e., V1 - 0 seconds) then I'm not complying with Lead Sled's interpretation. However if I take action at V1 - 1 second then I am. Presumably I'm also complying if I take action at V1 - 0.0000000000000000001 seconds. The latter is of no practical difference to being "at V1" so the phrase "before V1" is meaningless and has no distinction from "at V1" without further definition, e.g., by V1 - 1 second.
The decision to stop, and the initial actions to stop must be before V1.
How much before V1?
I assume that if I suffer an engine failure and take stopping action AT V1 (i.e., V1 - 0 seconds) then I'm not complying with Lead Sled's interpretation. However if I take action at V1 - 1 second then I am. Presumably I'm also complying if I take action at V1 - 0.0000000000000000001 seconds. The latter is of no practical difference to being "at V1" so the phrase "before V1" is meaningless and has no distinction from "at V1" without further definition, e.g., by V1 - 1 second.
Another thought: Although V1 is not a decision speed, from a practical point of view it should be a decision speed*. The monkeys up the front have just two things to do, make a decision and then action the decision. Assuming they have a healthy sense of self preservation, the actioning of the decision will be as soon as possible after the decision has been made. The monkeys don't necessarily know how long it will take between making the decision and actioning it though, and they therefore don't have the information required to know whether or not they will be taking action by V1. Far better for V1 to be the fastest speed a stop decision can be made, allowing for some standard reaction times. That way all the monkey needs to know is that if they are not at V1, they can decide to stop.
*I'm not saying the current V1 should be treated as a decision speed, I'm saying that V1 should be redefined and recalculated to be a decision speed.
*I'm not saying the current V1 should be treated as a decision speed, I'm saying that V1 should be redefined and recalculated to be a decision speed.
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At V1 and above, decision/s still need tobe made to continue or "try" abort.
* a critical engine (uncontained) failure at V1 - One must ask oneself. Will Ireach the required height above the takeoff surface within the takeoff distance? Or has this failure given me a lot more drag than I got in the SIM last week? A727 the other day may well have been better aborting above V1 than soldier on.
* Just hit V1 and God Dam it a 747 just pulled onto the my runway, right before my expected rotate point. Excuse me old chap, I am now at V1 would you mind moving off my runway? -------------Do you copy?
*V1 - Dear thrust reverser please retract, I am committed to take off and am getting dizzzy.
I think John has said it well - read the book but it isn't a bible, too many variables. But at V1 and above the "better option" is often, but not always to continue with the take off. The option is always there to abort at any speed above V1, but it will have levels of pain/hurt attached in many cases.
So V1 is where the preferred decision changes - below the preference is to stop, above preference is to continue with take-off.
Either way pick the one that will cause least fatalities, better still none.
Aerocat, what is the error of the ASI? so even V1 has a tolerance of acceptance.
the scale errors at the major graduations of the scale must not exceed ± 4 knots up to the maximum speed of the aircraft.
* a critical engine (uncontained) failure at V1 - One must ask oneself. Will Ireach the required height above the takeoff surface within the takeoff distance? Or has this failure given me a lot more drag than I got in the SIM last week? A727 the other day may well have been better aborting above V1 than soldier on.
* Just hit V1 and God Dam it a 747 just pulled onto the my runway, right before my expected rotate point. Excuse me old chap, I am now at V1 would you mind moving off my runway? -------------Do you copy?
*V1 - Dear thrust reverser please retract, I am committed to take off and am getting dizzzy.
I think John has said it well - read the book but it isn't a bible, too many variables. But at V1 and above the "better option" is often, but not always to continue with the take off. The option is always there to abort at any speed above V1, but it will have levels of pain/hurt attached in many cases.
So V1 is where the preferred decision changes - below the preference is to stop, above preference is to continue with take-off.
Either way pick the one that will cause least fatalities, better still none.
Aerocat, what is the error of the ASI? so even V1 has a tolerance of acceptance.
the scale errors at the major graduations of the scale must not exceed ± 4 knots up to the maximum speed of the aircraft.
Last edited by Band a Lot; 1st Jan 2017 at 10:39.
Moderator
Another thought or two, if I may ..
It appears that Lead Sled is largely arguing that the stopping must have been commenced prior to V1.
Recommended practice from both the current Design Standard (via AC interpretation) and the older Industry video are similar in that, if one hasn't commenced the first action (ie levers closing/closed or size 12s on the pedals - ideally simultaneously) then one is probably better off keeping on going ... Leaddie, as a younger chap, was drilled in this philosophy. Further, within the higher pre-V1 range, typically taken as above 80KIAS, one only rejects for major problems.
That doesn't mean one discounts thinking .. there are foreseeable situations where it is sensible to reject from higher speeds and take a lesser hurt than going. Far too many variables to be other than vague.
The main problem with this is that without further definition, "before V1" is meaningless.
The situation doesn't lend itself to precise definition. The recommended practice is as above .. if you haven't already commenced the stopping sequence by V1, then it is generally better to keep going.
from a practical point of view it should be a decision speed
Which is what it was under previous versions of the Standards. We really are getting into splitting hairs. The main concern is to have a routine procedure which will cover most events .. with the Commander paid appropriately to call a different shot should unusual circumstances dictate.
The history of overruns led to adoption of the present philosophy. That you, or others, may disagree, is fine.
At V1 and above, decision/s still need to be made to continue or "try" abort.
Of course, the occasional situation may call for such a non-SOP decision. The problem is that the line pilot generally has little, if any, basis for making the decision on rational, technical grounds.
a critical engine (uncontained) failure at V1
Commander's call. Generally can only be on the basis of a gut feel.
a 747 just pulled onto the my runway
Little likelihood of stopping in most situations. Between a rock and a hard place, I suggest.
Dear thrust reverser please retract
For most installations, pulling the buckets is commitment to stopping for just the concern you express.
but it will have levels of pain/hurt attached in many cases
Which is why most of us would like information on the ASD-limiting speed, regardless of other considerations .. so that a pre-takeoff consideration of what the level of hurt might be .. might be made.
what is the error of the ASI
Too much precision just gives the crew a headache. Reasonable accuracy and best efforts probably is a more useful goal.
It appears that Lead Sled is largely arguing that the stopping must have been commenced prior to V1.
Recommended practice from both the current Design Standard (via AC interpretation) and the older Industry video are similar in that, if one hasn't commenced the first action (ie levers closing/closed or size 12s on the pedals - ideally simultaneously) then one is probably better off keeping on going ... Leaddie, as a younger chap, was drilled in this philosophy. Further, within the higher pre-V1 range, typically taken as above 80KIAS, one only rejects for major problems.
That doesn't mean one discounts thinking .. there are foreseeable situations where it is sensible to reject from higher speeds and take a lesser hurt than going. Far too many variables to be other than vague.
The main problem with this is that without further definition, "before V1" is meaningless.
The situation doesn't lend itself to precise definition. The recommended practice is as above .. if you haven't already commenced the stopping sequence by V1, then it is generally better to keep going.
from a practical point of view it should be a decision speed
Which is what it was under previous versions of the Standards. We really are getting into splitting hairs. The main concern is to have a routine procedure which will cover most events .. with the Commander paid appropriately to call a different shot should unusual circumstances dictate.
The history of overruns led to adoption of the present philosophy. That you, or others, may disagree, is fine.
At V1 and above, decision/s still need to be made to continue or "try" abort.
Of course, the occasional situation may call for such a non-SOP decision. The problem is that the line pilot generally has little, if any, basis for making the decision on rational, technical grounds.
a critical engine (uncontained) failure at V1
Commander's call. Generally can only be on the basis of a gut feel.
a 747 just pulled onto the my runway
Little likelihood of stopping in most situations. Between a rock and a hard place, I suggest.
Dear thrust reverser please retract
For most installations, pulling the buckets is commitment to stopping for just the concern you express.
but it will have levels of pain/hurt attached in many cases
Which is why most of us would like information on the ASD-limiting speed, regardless of other considerations .. so that a pre-takeoff consideration of what the level of hurt might be .. might be made.
what is the error of the ASI
Too much precision just gives the crew a headache. Reasonable accuracy and best efforts probably is a more useful goal.
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My reverser comment was the recent one side self engaged - if that happened at V1 we aint going!
We have an allowable 4 knots on the gauge but zero on V1, not even a conditions variant.
Now what would the call be on this famous crash be if they had Tail Cam? it happened in the "fat Zone".
At 14 h 42 min 31 s, the PF commenced takeoff. At 14 h 42 min 54.6 s, the PNF called.
one hundred knots, then V1 nine seconds later.
A few seconds after that, tyre No 2 (right front) on the left main landing gear was
destroyed after having run over a piece of metal lost by an aircraft that had taken off five
minutes before. The destruction of the tyre in all probability resulted in large pieces of
rubber being thrown against the underside of the left wing and the rupture of a part of
tank 5. A severe fire broke out under the left wing and around the same time engines 1
and 2 suffered a loss of thrust, severe for engine 2, slight for engine 1.
We have an allowable 4 knots on the gauge but zero on V1, not even a conditions variant.
Now what would the call be on this famous crash be if they had Tail Cam? it happened in the "fat Zone".
At 14 h 42 min 31 s, the PF commenced takeoff. At 14 h 42 min 54.6 s, the PNF called.
one hundred knots, then V1 nine seconds later.
A few seconds after that, tyre No 2 (right front) on the left main landing gear was
destroyed after having run over a piece of metal lost by an aircraft that had taken off five
minutes before. The destruction of the tyre in all probability resulted in large pieces of
rubber being thrown against the underside of the left wing and the rupture of a part of
tank 5. A severe fire broke out under the left wing and around the same time engines 1
and 2 suffered a loss of thrust, severe for engine 2, slight for engine 1.
The history of overruns led to adoption of the present philosophy.
My 'take' on the introduction to the video, and your comment above, JT, is that the main safety issue was take offs that should have been continued rather than rejected, not vice versa. Yet when I give a scenario in which stopping action is initiated prior to or at V1, but the action fails, and the aircraft is now over V1, no one can bring themselves to say: Maybe the safer option is balls to the wall on the good engine/s and continue.
Let me change my scenario. Trundling down the runway the critical engine fails at V1. It is therefore not possible to intiate stopping action before or at V1. On my understanding of the collective expert wisdom, the decision must be to continue the take off - that decision having been made prior to or coincident with the critical engine failure at V1.
The only difference between the above and my original scenario is that the thrust levers were retarded at or before V1 in my original scenario.
Can I suggest that during the three seconds from the point at which the thrust levers were retarded until the thrust levers were advanced (amateur pilot Lead Balloon having realised the brakes were not working):
(1) the aircraft has exceeded V1
(2) the aircraft hasn't decelerated much, and is nearly as far down the runway as it would have been if the thrust levers for the good engine/s had not been retarded, and
(3) the good engine/s would not have spooled down that much and will spool back up to take off thrust 'quite quickly'.
However, I concede that number (3) is the critical variable. And this is where one of the points you (JT) made earlier becomes very important: Against which standard is the aircraft (and its engines) certified?
I can understand why spool up times would weigh heavily on the minds of the crews of e.g a B707. But 'modern big jet engines' are a little more responsive than P&W JT-3Ds - I posted the current FAR standard earlier.
For example, my understanding is that a version of the B777 will roll at 30kts with both engines at idle, unless the crew rides the brakes to keep the taxi speed down. My understanding is also that a B777 will take off and fly on one engine with the OAT 50c. Lessons learnt on B707s and early B747s may not be directly transferable to aircraft fitted with engines certified to the contemporary standard.
(And can I note how impressed I am with BaL's google skills?
)
What was the first aircraft in Australia to have V1 & V2 speeds, the DC-4, Electra?
Didn't DCA want the TAA Twin Otters to have calculated V1 and V2 speeds, or they wouldn't let them go on the register?
Didn't DCA want the TAA Twin Otters to have calculated V1 and V2 speeds, or they wouldn't let them go on the register?
What was the first aircraft in Australia to have V1 & V2 speeds, the DC-4, Electra?
Anybody remember the Caribou Ansett bought for PNG --- DCA insisted on applying "modern" takeoff performance criteria, which made the airplane useless for the intended purpose in the highlands, but the DC-3/C-47 soldiered on for years after the Caribou was sold, as DCA only applied the old Developmental Air Services rules to the Dak.
Typical of bureaucratic application of arbitrary criteria. The problem with commons sense is that it is so uncommon.
John T,
Many thanks for your contribution, so many of the posters not only have no idea of the developments of the standards since the original SFAR 422B, but are totally resistant to any modification of their chosen misinterpretation, and I just shake my head at the cut and paste brigade --- they found "it" printed somewhere, so "it", or more accurately, their interpretation of "it" must be correct.
Never let the facts stand in the way.
All,
The point I have been trying to make, all along, is that, despite changes over the years, including the details of how an actual number is derived, the cockpit meaning of V1 should be very clear, and KISS must prevail.
V1 is NOT a decision speed.
Tootle pip!!
PS: "small" changes are not trivial, the Australian unique rules John T mentioned, that were swept away in mid-1998, by the only so far successful regulatory reform of CASA rules (CASR Parts 21-35) saved Qantas a fortune --- because payloads at limiting range out of mid-length runways increased by 50% or more for the B767. In particular, we were no longer required to comply with the Australian unique requirement, in calculating performance, to allow for a 2 second ALL ENGINE acceleration beyond V1, then transition stopping and finally full stopping.
Unsurprisingly, this Australian unique requirement , had it been applied universally since the dawn of the jet age, would not have changed the outcome of even one single flight, but Hey!!, you can't be "too safe", can you??
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"Let me change my scenario. Trundling down the runway the critical engine fails at V1. It is therefore not possible to intiate stopping action before or at V1. On my understanding of the collective expert wisdom, the decision must be to continue the take off"
I agree with that 100%. But if any other event has/is happening because of or independent flow the engine failure - the definition of V1 is out the window and you are on your own, untested territory.
V1 is a certification process with a perfectly serviceable aircraft with 1 failed engine and no other defect.
The affixation of MUST take-off at V1 or above with an engine failure, an engine surge, blown tyre and airframe damage is not justified under the definition/s of V1.
The concord captain had this affixation (V1 must go) but was fully aware they had more wrong than just one engine failure. None of us were there to see what the crew had to deal with during that take-off roll, but if he was not adamant he must take-off he may have elected to abort. If he did abort, all on board may well have still died in a probable fiery crash some distance from the end of the runway.
There is a chance some may have survived, notably the four in the hotel far from the runway.
I agree with that 100%. But if any other event has/is happening because of or independent flow the engine failure - the definition of V1 is out the window and you are on your own, untested territory.
V1 is a certification process with a perfectly serviceable aircraft with 1 failed engine and no other defect.
The affixation of MUST take-off at V1 or above with an engine failure, an engine surge, blown tyre and airframe damage is not justified under the definition/s of V1.
The concord captain had this affixation (V1 must go) but was fully aware they had more wrong than just one engine failure. None of us were there to see what the crew had to deal with during that take-off roll, but if he was not adamant he must take-off he may have elected to abort. If he did abort, all on board may well have still died in a probable fiery crash some distance from the end of the runway.
There is a chance some may have survived, notably the four in the hotel far from the runway.
Moderator
We have an allowable 4 knots on the gauge but zero on V1, not even a conditions variant.
I have it in mind that the Standard for I/F ASI is 5 knots but won't bother to dig that out to confirm/correct just now .. certainly, there is (and must be) a tolerance.
The usual calibration will result in a lesser error .. normally, the operational application is to apply the design tolerance as a "between gauges" figure. Like many things, we can split hairs all day .. in current practice, V1 should be called marginally early so that the call is completed by the observed V1 reading. A small error will be accommodated by certification tolerances and I certainly wouldn't be losing too much sleep over this particular concern.
Now what would the call be on this famous crash be if they had Tail Cam? it happened in the "fat Zone".
As most would be aware, there were various tales about this and that with the mishap aircraft.
However, the takeoff mishap, very clearly, was way outside the certification expectations and parameters. Evidently the Commander flew the failures exceptionally well but far too many things were against him and the outcome was predictable and is well known.
Some days it doesn't pay to get out of bed .. problem is, we don't have a crystal ball to identify the days in question.
Again, the Design Standards DON'T give you any guarantees .. only reasonable probabilities based largely on historical data. Unless the situation is well and truly outside the gameplan, there is a good chance of a successful outcome, given a competent (and, where necessary, innovative) crew.
For the small percentage of folks who find themselves up that well known creek without a paddle .. life's risks sometimes catch up with us and exact a dreadful toll.
Yet when I give a scenario in which stopping action is initiated prior to or at V1, but the action fails,
I, for one, have no problem with your scenario.
However, it is well outside conventional certification expectations. Unless there be significant spare runway (hence my Edwards reference) the likely outcome is not going to be nice regardless of however the Commander might play the cards on the day. As to what is the best call .. as so often, it depends. Nothing wrong with having the discussion, though.
the decision must be to continue the take off
That will be the normal SOP. However, as a wise checkie once emphasised to me at the debrief ... "Young John, keep in mind that the manual has an admonition on the front page in invisible ink .. 'To be read with a modicum of commonsense'".
We necessarily need to keep the routine balanced against the extraordinary. SOP intentions probably will provide an acceptable outcome on the great bulk of occasions .. so we stick routinely with SOP. On those occasions when the Commander is called upon to earn his/her salary, SOPs just may not cut the mustard and the Commander may have to be a bit innovative.
Lessons learnt on B707s and early B747s may not be directly transferable to aircraft fitted with engines certified to the contemporary standard.
That may be a fair comment. However, the underlying problem is that the sorts of scenario you postulate generally have not been tested and, hence, the crew on the day probably doesn't have much to go on other than gut feel. So long as that is understood, then the folks in the sharp end just make the best play they can out of a bad hand.
What was the first aircraft in Australia to have V1 & V2 speeds, the DC-4, Electra?
Both predate my Industry involvement slightly (although I did fly and loved the Goose in the late 70s). We would need someone a bit older who was involved in the early to mid 50s (good heavens, I still had to discover girls at that stage of my life ..) to recall the precise sequence.
Prior to the PAMC changes to performance - which were around this time (as I recall the F27 was probably the first to run the recertification gauntlet) aircraft performance was scheduled to older standards.
My guess is that the DC4 wouldn't have been reworked - although I did some engineering work on the Air Express ex-QF DC4s at Essendon, I just can't recall what the cockpit procedures were. However, the turboprops certainly were redone. So the Electra and F27 (flew both) had the normal schedules. I just gave Centaurus a call (he flew Viscounts for 34SQN) and he confirms they had the normal schedules. As to which may have been the first in country, that would require some homework in the archives. Likewise for the Twin Otter question.
we were no longer required to comply with the Australian unique requirement
Actually, that wasn't a local requirement. The Australian change reflected the FAR25 design change as discussed in earlier posts.
V1 is a certification process with a perfectly serviceable aircraft with 1 failed engine and no other defect.
Not exactly the case and has varied through the years but close enough for the purposes of this discussion.
The affixation of MUST take-off at V1 or above ..
Not exactly the Industry viewpoint .. suggest a review of the video cited earlier which is still reasonably valid vice the rulebook.
but if he was not adamant he must take-off he may have elected to abort.
At the time, the crew could not have known the full story - although they certainly would have known that they had a nasty situation on their hands. I suggest that it is most unlikely that a disciplined crew would reject for the situation faced. In hindsight, knowing the details which came to light during the investigation ... perhaps ... but that's information not available to those in the front seat at the time.
Again, I can only urge folks not to read things as being hard and fast black and white. It is all based on reasonable probabilities and what might be a reasonably reliable (not necessarily the best) way to achieve an acceptable outcome on the day when only part of the story's details are to hand.
I have it in mind that the Standard for I/F ASI is 5 knots but won't bother to dig that out to confirm/correct just now .. certainly, there is (and must be) a tolerance.
The usual calibration will result in a lesser error .. normally, the operational application is to apply the design tolerance as a "between gauges" figure. Like many things, we can split hairs all day .. in current practice, V1 should be called marginally early so that the call is completed by the observed V1 reading. A small error will be accommodated by certification tolerances and I certainly wouldn't be losing too much sleep over this particular concern.
Now what would the call be on this famous crash be if they had Tail Cam? it happened in the "fat Zone".
As most would be aware, there were various tales about this and that with the mishap aircraft.
However, the takeoff mishap, very clearly, was way outside the certification expectations and parameters. Evidently the Commander flew the failures exceptionally well but far too many things were against him and the outcome was predictable and is well known.
Some days it doesn't pay to get out of bed .. problem is, we don't have a crystal ball to identify the days in question.
Again, the Design Standards DON'T give you any guarantees .. only reasonable probabilities based largely on historical data. Unless the situation is well and truly outside the gameplan, there is a good chance of a successful outcome, given a competent (and, where necessary, innovative) crew.
For the small percentage of folks who find themselves up that well known creek without a paddle .. life's risks sometimes catch up with us and exact a dreadful toll.
Yet when I give a scenario in which stopping action is initiated prior to or at V1, but the action fails,
I, for one, have no problem with your scenario.
However, it is well outside conventional certification expectations. Unless there be significant spare runway (hence my Edwards reference) the likely outcome is not going to be nice regardless of however the Commander might play the cards on the day. As to what is the best call .. as so often, it depends. Nothing wrong with having the discussion, though.
the decision must be to continue the take off
That will be the normal SOP. However, as a wise checkie once emphasised to me at the debrief ... "Young John, keep in mind that the manual has an admonition on the front page in invisible ink .. 'To be read with a modicum of commonsense'".
We necessarily need to keep the routine balanced against the extraordinary. SOP intentions probably will provide an acceptable outcome on the great bulk of occasions .. so we stick routinely with SOP. On those occasions when the Commander is called upon to earn his/her salary, SOPs just may not cut the mustard and the Commander may have to be a bit innovative.
Lessons learnt on B707s and early B747s may not be directly transferable to aircraft fitted with engines certified to the contemporary standard.
That may be a fair comment. However, the underlying problem is that the sorts of scenario you postulate generally have not been tested and, hence, the crew on the day probably doesn't have much to go on other than gut feel. So long as that is understood, then the folks in the sharp end just make the best play they can out of a bad hand.
What was the first aircraft in Australia to have V1 & V2 speeds, the DC-4, Electra?
Both predate my Industry involvement slightly (although I did fly and loved the Goose in the late 70s). We would need someone a bit older who was involved in the early to mid 50s (good heavens, I still had to discover girls at that stage of my life ..) to recall the precise sequence.
Prior to the PAMC changes to performance - which were around this time (as I recall the F27 was probably the first to run the recertification gauntlet) aircraft performance was scheduled to older standards.
My guess is that the DC4 wouldn't have been reworked - although I did some engineering work on the Air Express ex-QF DC4s at Essendon, I just can't recall what the cockpit procedures were. However, the turboprops certainly were redone. So the Electra and F27 (flew both) had the normal schedules. I just gave Centaurus a call (he flew Viscounts for 34SQN) and he confirms they had the normal schedules. As to which may have been the first in country, that would require some homework in the archives. Likewise for the Twin Otter question.
we were no longer required to comply with the Australian unique requirement
Actually, that wasn't a local requirement. The Australian change reflected the FAR25 design change as discussed in earlier posts.
V1 is a certification process with a perfectly serviceable aircraft with 1 failed engine and no other defect.
Not exactly the case and has varied through the years but close enough for the purposes of this discussion.
The affixation of MUST take-off at V1 or above ..
Not exactly the Industry viewpoint .. suggest a review of the video cited earlier which is still reasonably valid vice the rulebook.
but if he was not adamant he must take-off he may have elected to abort.
At the time, the crew could not have known the full story - although they certainly would have known that they had a nasty situation on their hands. I suggest that it is most unlikely that a disciplined crew would reject for the situation faced. In hindsight, knowing the details which came to light during the investigation ... perhaps ... but that's information not available to those in the front seat at the time.
Again, I can only urge folks not to read things as being hard and fast black and white. It is all based on reasonable probabilities and what might be a reasonably reliable (not necessarily the best) way to achieve an acceptable outcome on the day when only part of the story's details are to hand.