If it's a balanced field length I'd suggest it's rather unlikely to get get airborne in the distance remaining if, two seconds after applying brakes - which would also be somewhere in the reverser deploy process, and speed brakes activated - you then try to reverse those actions. You would be crashing off the end of the runway at high speed

V1 stop is a maximum effort manoeuvre. Two seconds of no braking + the time recognise and use the emergency braking is likely to result in rolling off the end of the runway - but at a significantly lower speed than crashing trying to get airborne.

Lead Balloon,
My "you are on your own" was intended to mean ---- there is no one answer, 'tis up to you.
However, I would be doing my best to stop, including making certain that the apparent lack of stopping was not caused by failure of spoilers to auto deploy, failure to properly close thrust levers/throttles (you might be amazed what is on some flight recorders/what I have observed in the sim.) or "relying" on auto-brakes.

Megan,
If you read the definition as a anything other than the the GO speed, if the rejected takeoff has not already been commenced, you ain't reading it right.

As to what is built into the derivation of V1, there have been all sorts of changes over the years, far too many to go into here, all to try and make a real world rejected takeoff more likely to succeed, without unacceptable payload penalties, but that doe NOT, in any way, change what the pilot in command is going to do, has to do, on the day it happens for real.

I would suggest I have quite a good handle on this particular issue, including membership a some "interesting" working groups, going right back to SFAR 422B, which is probably before many of you ( and FAR 25) were born.

As I said in my first post, there are still too many FCOMs/text books/training manuals etc., that vary from misleading to just plain wrong.

Tootle pip!!

I don't think I've suggested otherwise, have I? I posted, "V1 may not be less than VEF plus the speed gained with critical engine inoperative during the time interval between the instant at which the critical engine is failed, and the instant at which the pilot recognizes and reacts to the engine failure, as indicated by the pilot's initiation of the first action (e.g., applying brakes, reducing thrust, deploying speed brakes) to stop the airplane during accelerate-stop tests." Ergo, if you reach V1 and have not already initiated a reject (brakes, power, speed brakes) yes it's GO.

Though I did work with a guy who did a successful reject after V1 (RAAF Herc) after a bird strike at Darwin. Distance to run markers on the runway undoubtedly aided his decision making in the circumstance, he had doubt as to the damage sustained and if it was flyable.

Perhaps he had the Electra N5533 accident in mind.

Megan,
There is no direct correlation between the approach of many military arms and civil certification of takeoff performance.

The existence of and use of runway distance markers on military airfields --- of no relevance to civil operations ---- is evidence of that.

A common military alternative (I can't speak to RAAF practice) to the civil V1 approach is to have a maximum takeoff rejection speed, which, at light weights on long runways, can be at least rotate speed, and theoretically beyond. This usually included "takeoff monitoring", which means checking acceleration on the roll by timing passing runway distance markers.

You continue to re-quote various items that go into certifying V1, but the point I want to make, yet again, is what must happen in the flight deck, the niceties of what go into the establishment of V1 are not important to the pilot in command handling a critical engine failure.

KISS is the only thing that is important --- and getting it right!!

Tootle pip!!

The military approach.
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA319982

That's specific for the bus, I'd take it. For the airplane I fly, if you were single engine above V2 +10, the crossbars would pitch up to bring you back down to V2 + 10. All other speed scenarios are the same as the bus.

Ok, everybody, how about we get the thread back to where it started, and attempt to give the OP some suitable and sensible answers. The last few pages have contained overly dry and technical definitions which we can safely assume would not be suitable for his target audience.

The OP quite rightly assumed that, of all the places in the world, this was the one that should have given him exactly the answers he needed, in exactly the wording appropriate for the audience. We can do far better. I believe the following is more along the lines of what he was looking for:

V1:Vr:V2:

ozziekiwi,

Here are the explanations I obtained direct from Beechcraft and Bombardier when developing ground schools for the 1900D and DH8 (Classic and Q400). Couple years old now, but like weather, I don't think aircraft performance changes much:

Vcef is the highest speed at which the aircraft can be accelerated, experience a loss of the critical engine, and continue or stop in the computed minimum field length. Vcef must be demonstrated to be at or above Vmcg.

Because most pilots are not test pilots, most regulators require that 1 second of acceleration be added to Vcef. Vcef + 1 second = V1.

V1, therefore, is both the maximum speed at which the pilot must take the first action to stop the aircraft within the accelerate-stop distance (ASDR) and is also the minimum speed, following a failure of the critical engine at Vcef, at which the pilot may continue the take-off to achieve a height of 35' AGL by the end of the Take-Off Distance Required (TODR).

Vr is the speed at which rotation begins. Although some books define it as when the nose wheel leaves the ground, it is not. It is the speed at which rotation may begin. Performance data for first segment climb begins not at Vr but at a speed known as Vlof - Lift Off Speed.

Vr must be demonstrated during flight testing be be not less than 5% above Vmca, to result in at least the minimum Vlof demonstrated during flight testing, and must permit acceleration to V2 prior to reaching 35' above the runway. Furthermore, manufacturers must demonstrate that Vr will not result in an increase in TODR if rotation is begun 5 knots lower than published Vr during one-engine acceleration or 10 knots lower than established Vr during all-engine acceleration.

Vlof, on the other hand, must be at least 5% above the one-engine inoperative minimum unstick speed (Vmu-oei) and 10% above the all-engine operative minimum unstick speed (Vmu-aeo). The minimum unstick speed is literally the minimum speed at which the aircraft will first become airborne - those cool pics of tails being dragged down a runway and the aircraft becoming airborne at stupid low speeds.

V2, while defined as the "take-off safety speed" is actually a factor of the stall speed, specifically it is:
- 1.2 x Vs for two and three engine aircraft.
- 1.15 x Vs for four engine aircraft.

So while V2 is does ensure the aircraft can be controlled, it is more closely linked to achieving a speed as close to the maximum lift/drag coefficient to enable maximum first segment climb performance, thus ensuring close-in obstacle clearance.

Let me explain why V2 is not specifically linked to aircraft control - All "V" speeds must be demonstrated to be at or above Vmcg/Vmca (where applicable). Where they are shown to be below Vmcg or Vmca, the applicable speed is arbitrarily raised to the next highest speed (normally). So while all V-speeds do ensure the aircraft can be controlled, only Vmcg/Vmca specifically deal with it. All the others deal with other performance factors.

Hope this helps to generate some technical discussion!

Fdg135. Not quibbling with your words but your average Jo(e) will probably skip reading a definition paragraph that long. Technical accuracy is not the agenda here. I'm guessing that if the non pilot reader remembers that v1 is a stop / go speed, vr is a pull the nose up speed and V2 is an after takeoff speed then the author's job is done.

Compressor stall,
Put another way, you are saying we should perpetuate misinformation for the sake of ????

Why not? It is just as easy to get it right (technically accurate) as to get it wrong. Or are you dedicated to that new phenomena, "truthiness", which is something that sound like it could right (like a CFMEU robophone campaign) but isn't.

+TRSA,
Once again, homegrown interpretations, and the "1 second" you mention is both wrong and nothing to do with "test pilots" ---- when the "technically accurate" definition is simple and straightforward ----- but doesn't fit the per-conceived prejudices/ learned errors that ------ as is so clear in this thread, abound, despite years of trying to get the correct definition across.

Tootle pip!!

I am with compressor stall, a person in the industry will have a good idea of the definitions (as we can see they vary!) the general public with some interest need only a basic definition - direct them to any FAA, Boeing or other definition web page but keep it simple.

V1 - the maximum speed during a take-off event that a take-off should be aborted, in the event of a malfunction or unforseen event. To continue a take-off after this speed would bring the aircraft to a stop beyond the end of the runway.

Vr - is the speed pitch input is given to become airborne.

V2 - the minimum target speed for controlled flight during a take-off event.

** Who at a speed 5 knots above V1 and then hitting a flock of birds that completely and instantly removes all vision on all windows except co-pilot side window will continue on to Vr and V2 speeds if there is 5 km clearing after runway finishes?

Me, I will apply brakes even after rotation(Vr) if 5km of flat cleared dirt lays in front of me.

Leadsled. Good science and technical communicators know how to tailor information to their audience, otherwise the audience will zone out through lack of interest or technical ability to comprehend.

Having a thorough technical understanding and grasp of the minutiae is fantastic, but one doesn't need to tell anyone that to get simple points across. In fact repeatedly doing so sometimes leads some to wonder the psychological motivations for such repeated pontification.
Notice professors who have weekly radio slots are good communicators as they can generalise highly technical concepts in bite sized chunks. They are not out to spread misinformation, they are selling a concept with deliberate simplifications. If I am explaining gravity to my younger kids, technical accuracy is NOT my agenda. The agenda it is their understanding and being able to understand it again the next day. So I talk Newtonian, not general relativity. Is this truthiness (whatever the #%^€ that is) or perpetuating misinformation?

LeadSled,

What else I agree there are more simple definitions out here, let me reiterate that those are not my definitions but those direct from aircraft manufacturers.

Perhaps I should rephrase that the data is adjusted for "normal pilot reaction time" which is defined by these manufacturers/regulators to be "1 second." Other manufacturers may be different and these ones may even have changed their definition, both of which I alluded to at the beginning of my post.

Also, I fear that in reducing a definition to its lowest level for the sake of the lowest common denominator is assuming a reader doesn't want to know the intricacies and does them a disservice.

I am a firm believer that there are two types of aviation books - technical and stories, and never should the two mix or dilute one another.

No "they" don't vary, what varies is the degree of misunderstanding, misinterpretation, and so forth.

I have lived through (quite literally) the whole development of performance standards certification from SFAR 422B on, and it is a pity that efforts over the years to eliminate flawed understandings has been obviously so unsuccessful.

Part of the history: In the '70s and early '80s, there were a series of rejected takeoff accidents, some with seriously fatal consequences to passengers, crew, and in several very sad cases, people on the ground.

Among other things, this resulted in a major study by the ATA, which also included a number of non-US airlines, of which Qantas was one.

The study was to find out what pilots really knew about aircraft performance, what they had learned, where and how they had learned, been examined etc.

A core finding was a fundamental misunderstanding of V1, its derivation, and what it means in the flight deck.

As we see here, in this thread, there is wide deviance from the actual definitions. Some of you have talked about manufacturer information, used to derive manual information. What you really mean is somebody employed by a manufacturer, with an imperfect knowledge of the subject, has passed along, in good faith, a flawed explanation, which has been "interpreted" by the airline person, and something has wound up on a manual, and treated as gospel by probably generations of crews. But it was wrong.

There were several good examples of that in Qantas manuals back in the 60s, it was only when a pilot who had professional qualifications and experience in aircraft certification, arrived on the scene, the errors were corrected.

Specifically, in one case, the "Qantas" explanation of "geometry limited" on takeoff was completely wrong. There were other, they all had one thing in common, the information was not derived from source, but were misconceptions built on misunderstandings by pilots whose executive positions did not qualify them as performance engineers.

In the early days of the B707-338C in Qantas, the instructions for trimming were quite wrong. That one I remember very very well.

And, up to and including the B767 program, sometimes even the performance engineers get it wrong.

At about the same time, in parallel, but not directly related, an AFAP tec. team was looking at the whole issue, including military approaches, because at the time there was much interest in performance monitoring and "wet runway" operations ---- is the aircraft really accelerating "by the book", but that is a whole other subject.

Back to V1, the disturbing outcomes of the flawed knowledge clearly illustrated why a mindset on the flightdeck contributed to disastrous rejected takeoffs.

A major retraining program, originally designed by Delta, was taken up by all members of ATA, and most members of IATA, and was carried out through briefings and changes to simulator renewal or cyclic training programs, and I well remember the Qantas program, and the resistance of quite a few pilots (and not necessarily the older pilots) to having their fondly held misconceptions about V1 disturbed.

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.

Tootle pip!!

PS 1: A Boeing have always been happy to admit, their aeroplanes go better than they stop.
PS 2: Most pilots are most paranoid about runway length, and accelerate/stop distances, but the record show that a very significant number of rejected takeoffs result in loss of directional control, and leaving the side of the runway.
PS 3: There were some quite fundamental errors in the RR book "The Jet Engine", I don't know if they have been corrected in later editions. D.P Davies, in "Handling the Big Jets", even misinterprets his own ARB certification requirements, and largely ignores (except where he criticizes) the US certification of the B707. In my opinion (having flown both extensively) the ARB modifications to a B707 for a British C.of A were dangerous.

Ok we need to disagree 3 pages with many examples most meaning the same in less words.

I call that varied, but the longest cut and past explanation is probably the most accurate description - but I can not be sure I only read about half of it. Surprisingly not finishing reading it didn't kill me.

If this OP is going to write his 40 odd years in the airliner industry in such detail, the pre-flight will take 20 pages.

What's the difference between a pre-flight and a Daily? In case the reader needs to know if its possible to do one and not the other or both need to be done we should define them.

Band a Lot,
I trust those who need to know, actually do! In a court/AAT, the difference is not trivial --- as people I know have found out to their great cost.

Indeed, the difference is a favorite of CASA counsel setting out to prove a defendant or witness is incompetent, and any other testimony should be considered in light of an incompetent answer to the above question.

As to the rest of the thread, I guess we will just have to accept that years of attempted education has failed, that fact just bounces off devout beliefs (obviously not limited to aviation) and there will undoubtedly continue to be avoidable accidents, as a result.

Tootle pip!!

Getting back to "they do not vary" and I know wiki can be wrong. I don't think their statement is. "V1 is defined differently in different jurisdictions:"


V1 definitions[edit]

V1 is the critical engine failure recognition speed or takeoff decision speed. It is the speed above which the takeoff will continue even if an engine fails or another problem occurs, such as a blown tire.[9] The speed will vary among aircraft types and varies according to factors such as aircraft weight, runway length, wing flap setting, engine thrust used and runway surface contamination, thus it must be determined by the pilot before takeoff. Aborting a takeoff after V1 is strongly discouraged because the aircraft will by definition not be able to stop before the end of the runway, thus suffering a "runway overrun".[33]


V1 is defined differently in different jurisdictions:

• The US Federal Aviation Administration defines it as: "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."[7]
• 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."[8]
  
  
  Given that a simple definition would be fine (with a disclaimer). And correctly a difference between pre flight and daily would do the reader no harm.

Band a lot,
The above is quite simply wrong, a very dangerous "definition", as the accident record so clearly shows, and inconsistent with the further definitions you have posted.
You have even chosen to ignore the history I posted, as it does not correspond with your learned errors.
I am quite simply wasting my time with any further attempts to correct your misconceptions, I just hope you are not, and never likely to be, the Captain of a HICAP RPT aircraft, or any aircraft where a V1 is likely to be critical to the risk management of flight operations.
Tootle pip!!

Oh Leady,


I think it was you that made the blunt statement along the lines, there is NO different interpretations and or definitions of these terms.

So I simply cut and pasted others in my last post (no me but from Wikipedia).

So you appear wrong - yes it appears FAA has a definition of V1, Transport Canada have a different definition, a Flight manual might have a different one and who ever wrote that other definition in Wikipedia has their definition (rightly or wrongly - they maybe from Canada with a older flight manual and thus it is correct).

Band a Lot " a person in the industry will have a good idea of the definitions (as we can see they vary!).

LeadSled "No "they" don't vary, what varies is the degree of misunderstanding, misinterpretation, and so forth."

Simple question asked simple.

Do FAA and Transport Canada have the same definition for V1?

or

Does the definition of V1 vary between FAA and Transport Canada?

Ever heard sayings

More than one way to skin a cat,

When in Rome do as the Romans do?

* The first is very true if you ask a few cat skinners, most have their own way (I don't like cats so more dead the better)

* The second is often a legal requirement, $999.99 says you don't chew gum in Singapore!


So in a big plane with "too" pilots and too islels (wide body) in Canada, you as Captain will argue to the death of all - "your definition" is the only one and that is final- I am Captain and I am right. seems like a captain of a RJ in a recent - oh you play soccer?

""I just hope you are not, and never likely to be, the Captain of a HICAP RPT aircraft, or any aircraft where a V1 is likely to be critical to the risk management of flight operations.""

Mutual, but sadly I expect not. Mate check many words on many different things on many dictionaries or regulators sites.

Things vary, only a fool till death will not accept that and die killing all with a Lead balloon!!

Enjoy your NY.

P.S I work in Aviation with tools, I often find a good aviation Tool.

TOOL tal PIP.

But you have given us no definitions. You have just pooh-poohed everyone else's, and made the assertion that only your interpretation is correct.

I think he did provide a definition, at post #9:

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?

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.

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.

It's mentioned in the video linked at post #17.

I may have misinterpreted what is said, but there's 3 seconds of something built into the number.

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

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...

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 ...

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.

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.

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.

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.

This is why I find the responses to my scenario so interesting.

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? :ok:)

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?

Folks,
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??

"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.

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.