12th Aug 2001, 19:52
Dear colleagues.

I am looking for an easy to use (and explain) document on the correct meaning and application of V1, with clear, concise diagrams etc.

This will be used for initial jet training with new pilots. I have accumulated plenty of info over the past 15 years or so, however I am yet to see something that stands out as definitive. I have acquired much of my knowledge from other pilots. This has been great, but I would like to try a different approach if possible.

I have "The mechanics of flight" by Kermode and "The Airline Training Pilot" by Smallwood and Fraser and a few other publications. If there are any good quality publications you think appropriate, I would sincerely appreciate your input.

Thank you in advance.

13th Aug 2001, 09:28
The first action to stop the aircraft must be initiated at V1, although included in the FAR 25 definition is a 2 second buffer of constant speed (not accelleration)after V1.

13th Aug 2001, 12:15
Thanks for those replies'

I have the JAR and FAA definitions of V1 but I find them inconclusive. Different operators appear to use varying criteria. For example, some colleagues flying the A320 say that at V1, they can make a decision to STOP OR GO. Where as some Boeing and BAe 146 drivers will tell you that at V1, you go flying, end of story! In other words, V1 is the DECISION TO GO speed.

I am aware of the buffers built into V1 determinaton (recognition and reaction time, average pilot ability etc), however I still find myself short on a good series of diagrams and explanations to use for new sprogs.

Anyway, thanks for the input to date.

13th Aug 2001, 15:43
The most definitive answer that I can give you is courtesy of the Federal Aviation Authority Takeoff Safety Guide.

V1 Speed Defined.

What is the proper operational meaning of the key parameter “V1 Speed” with regard to the Go/No Go criteria? This is not such an easy question since the term “V1 speed” has been redefined several times since commercial jet operations began more than 30 years ago and there is possible ambiguity in the interpretation of the words used to define V1.

Paragraph 25.107 of the FAA regulations defines the relationship of the takeoff speeds defined in the AFM, to various speeds defined in the certification testing of the airplane. Although the terms engine failure speed, decision speed, recognizes, and reacts are all within this “official definition”, for our purposes here, the most important statement within this “official” definition is that V1 is determined from “… the pilots application of the first retarding means during the accelerate stop test”

One common and misleading way to think of V1 is to say that “V1 is the decision speed”. This is misleading because V1 is not the point to begin making the operational Go/No Go decision. The decision must have been made by the time the airplane reaches V1 or the pilot will not have initiated the RTO procedure at V1. Therefore by definition the airplane will be travelling at a speed higher than V1 when stopping action is initiated, and if the airplane is at a Field Length Limit Weight, an overrun is virtually assured.

Another common held misconception: “V1 is the engine failure recognition speed”, suggesting that the decision to reject the takeoff following engine failure recognition may begin as late as V1. Again, the airplane will have accelerated to a speed greater than V1 before stopping is initiated.

The certified accelerate-stop distance calculation is based on an engine failure at least 1 second (see note 1) prior to V1. This standard time allowance has been established to allow the line pilot to recognize the engine failure and begin the subsequent sequence of stopping actions.

In an operational Field Length Limited context, the correct definition of V1 consists of two separate concepts:

First with respect to the “No Go” criteria, V1 is the maximum speed at which the rejected takeoff maneuver can be initiated and the airplane stopped within the remaining field length under the conditions and procedures defined in the FAR’s. It is the latest point in the takeoff roll where a stop can be initiated

Second, with respect to the “Go” criteria, V1 is also the earliest point from which an engine out takeoff can be continued and the airplane achieve a height of 35 feet at the end of the runway.

The Go/No Go decision must be made before reaching V1. A “No Go” decision after passing V1 will not leave sufficient runway remaining to stop if the takeoff weight is equal to the Field Length Limit Weight

When the airplane actual weight is less than the Field Length Limit Weight, it is possible to calculate the actual maximum speed from which the takeoff could be successfully rejected. However, few operators use such takeoff data presentations. It is therefore recommended that pilots consider V1 to be a limit speed: Do not attempt an RTO once the airplane has passed V1 unless the pilot has reason to believe that the airplane is unsafe or unable to fly.

This recommendation should prevail no matter what runway length appears to remain after V1

Note 1: the time interval between VEF and V1 is the longer of the flight test demonstrated time or 1 second.


Lear23 has pointed out that aircraft are certified to different criteria depending on when they were certified, while this is true, you are better off forgetting about it. If you have reached V1 you are going. Forget about trying to second guess the transition times that were used in certification.


Finally, your local Boeing rep should be able to get you a copy of this takeoff safety guide and the video that goes with it.

Mutt. :)

13th Aug 2001, 19:38
If I may echo Mutt's thoughts ...

Both Boeing and Airbus have quite useful videos relating to the V1 question. Each sings to the same basic words and music - in the accel-stop limited case if you aren't stopping by V1 then the decision is programmed - you go.

The real world risks of an overrun are manifest. Consider aircraft deterioration, crew surprise (regardless of training and mindset), runway debris contaminants, etc - the risk equation is very definitely skewed to a go decision as the aircraft approaches V1.

The question of the various rule changes is quite irrelevant. The Standards provide reference performance data which will be approximated in the real world to a greater or lesser degree.

13th Aug 2001, 21:03
In case you missed this on another thread, I'm pasting this here as food for thought:

posted 11 August 2001 02:46
I think many of us in the flying business have taken this "High speed aborts are Dangerous" to the extreme.
Sure, you can be at Max TOW for any given runway, but there are thousands of departures every day at weights WELL below that. The acceleration of most transport jets on takeoff roll are very similar. (Excluding the extreme density altitude and very heavy weight/high temperature takeoffs.)

Most jets get to 80 kts. only about 2000' into the takeoff roll, and about 110-120 at the 3000' point. Now, if I'm on a 10,000 foot runway, and I abort for any reason at 80 kts., I've got 8000 feet in which to get it stopped! From 115 kts, I've got 7000'. What's the problem?

No way I'm taking a fire warning or other questionable situation in the air (on purpose) when I've got all that runway left.

Sure, there are situations where you ARE right up against the MTOW. AT real heavy weights, your V1 might be 150 or so. We get paid to make plans in the event something out of the ordinary occurs.

When you research the accident reports involving high speed aborts/attempts, you will find that many of those happened AFTER V1, and many of those involved confusion in the cockpit, one guy pulling, the other pushing.

In my opinion, it's not the high speeds that are the factor, it's the lack of pre-planning for THIS takeoff.

Every takeoff is different. I urge you not to get into a simplistic mindset. Would your decisions be any different if the two runways were 6000' vs 12,000? Mine sure are.


13th Aug 2001, 23:31
Mutt, that was excellent thanks. J.T. and Quid, thank you also. Quid you have a very valid point when talking about long runways. My concern when teaching new pilots is that I do not want to confuse the troops by giving potentially ambiguous information.

Perhaps I need to change my thinking, but I would not like to see a flight crew get into a discussion on each and every take-off about the merit of continuing versus stopping when V1 has been called. The Captain may think it suitable to continue and the F/O may think he is wrong. Stalemate, followed by a possible breakdown of communication and lack of confidence. Now the situation has become potentially unsafe.

If we drill the troops that at V1 we go flying, I believe we are making our job a little easier. I think there are plenty of pilots who would tell you that on a 4000 metre runway, they may well stop after V1 if a major problem ocurred, but the company would not mandate such a procedure, nor would they support the pilot, if as a consequence of stopping, a disaster ensued.
Balanced field or not, I think continuing has to be the safer option in most cases.

There are just so many variables that my brain hurts when I try and think of all the possibilities! There are certainly some valide points on both sides of the argument.

Eli Vator
14th Aug 2001, 01:11
Some of the ideas and inuendo in quid's quote are frighteningly dangerous. The long/short runway example is potentially the most scary.

Imagine the scenario - This pilot is coming out with all the Most jets get to 80 kts. only about 2000' into the takeoff roll ..... etc. to a new F/O on his first line sector on type.
You can picture the mental turmoil now going through the co-pilot's mind.
Where has he/she (not quid) acquired his/her specific take-off performance data from ?
Did I miss something in ground school ?
Did the line training team sell me short ? How do I deal with this using good CRM and not look a complete pratt ?

Mutt's post speaks volumes. Bear in mind that in "most" cases when considering a dry, non-field length limited departure from long runways at "lighter" weights, Vr will equal V1 - end of arguement. :)

Also consider if you were to use Professor Pat Pending's V1 calculation method and successfully reject the take-off above V1 without an overun. You then decide to evacuate the aircraft and some pax. incur minor/major injuries. Their jolly smart Lawyers subsequently discover that you used a non-established and non-approved method to reject following a false warning. The least you will expect to hear is the Chief Pilot saying "what a very strange way to resign !!!"

Perhaps extreme, but still worth thinking about to keep it in context ?

14th Aug 2001, 01:35
One can always, without too much trouble, find an example to prove or disprove a point.

What we should be considering is the roll of the die and putting our future in the overall best guess low risk outcome.

The Boeing and Airbus videos put it so succinctly - by continuing the takeoff in the near V1 situation

(a) the risk of overrun is avoided
(b) one then has the whole runway on which to land .. with prearranged F-troop attendance, cabin preparation, etc.

The practical problem is that, while the engineers amongst us may be able to do some sums and such, .. the average line pilot is not well placed to decide just how far he/she can push his/her luck .. and, as I frequently suggest, in support of the previous post ... the subsequent inquiry often becomes very tedious..... and very, very lonely......

14th Aug 2001, 02:00
We were given a flight safety booklet, with many examples of rejected T/O's above V1 resulting in overuns. It is very interesting to note that in EVERY case, had they continued they could have safely become airborne.

re: Quids Post, we give a very specific brief saying, "once thrust is set we will ONLY abort for an engine fire, failure, or something affecting the safety of the aircraft (to fly)".

If in your own mind you are not sure whether to stick with this, then you are very much leaving yourself open to a abort leading to an accident. Most aborts above V1 were due to sensory inputs eg) loud bangs (tyres etc).
You must be in a mind set to resist the temptation to stop for this alone. If tyre(s) have burst then you MAY NOT stop in time even if you abandon BELOW V1, as you do not have full braking capacity (assumed for the calculations).

You are almost always better continuing, sorting the problem out, returning for a full length landing with fire trucks etc. eg) follow your brief.

I don't know about you, but I tend to call V1 about 5 kts BELOW V1, as any problem which occurs above V1-5 CANNOT be assessed and a stop be ACTIONED by V1 (I fly an aircraft with rapid acceleration) . This is especially true if V1 coincides with Vr - if you call "VeeWun,Rotate" at V1/Vr then by the time you've said that and the other guys reacted you're about 10kts past Vr - this starts to impact on your climb and obstacle clearance performance. Don't forget that it is ME who is calling any potential failures, so obviously I will only call V1 at V1-5 IF a major failure has not already occured. I believe this is a practice that is approved in several flight safety quarters.

14th Aug 2001, 02:39
Quid, my friend, we are not talking about DC-8's, on newer aircraft we can reduce the takeoff thrust by 45%, thereby making even a light aircraft runway limited. (This is another discussion which J_T and I have had in the past)

But in general, it is better NOT TO MESS with V1, because you do NOT KNOW what people like me have done to ensure your takeoff weight!

Mutt :)

[ 15 August 2001: Message edited by: mutt ]

14th Aug 2001, 05:43
Dont' get me wrong, guys. I'm not in any way advocating throwing V1 out the window.

What I AM saying, however, is recognize that every takeoff is different than any other. Many carriers have the "Optional V1" procedure that, when an unbalanced situation exists, allows the PIC some latitude in selecting a V1 that is best suited to THIS takeoff. OK so far?

Now, if there is a microburst threat, most companies also have an "increased Vr" procedure that also addresses the excess runway to give a higher Vr and V2 speed. OK again?

Also, many cariers used an improved climb procedure that moves the V1 (and other V speeds) way up there. Still OK?

So the concept of adjusting V speeds for various reasons to fit the situation is not heresy!

Now, who here can say with certainty that in a split second after hearing/feeling a loud BANG, or shudder, etc., that the aircraft will indeed fly (and fly safely enough to be controlled)?

Mutt, in the situation I'm talking about, you have already given me the data to know that at 350,000 that my aircraft will stop/go at V1 of (let's say) 150 KIAS. If the data is correct, it will certainly stop/go at 150 if I'm 100,000 lighter than that, right? Now if my balanced field V1 is 120 in that situation, and my (much heavier) V1 is 150, there is some room for leeway.

Now, I'm not talking about a situation where you de-rate all the way down to make yourself runway limited. Then, of course, stick with the numbers. I'm only allowed a 10% thrust reduction, and even with max reduction, I've got LOTS of extra runway in many cases.

All my takeoff briefs talk about "We're right up against the MTOW on this slippery runway, so I'm only going to abort near V1 for the most critcal of reasons", or "We're 90,000 under the runway limit, so an abort right up to V1 should present no major problems," etc.

The V1 data presented to many of us flying older equipment makes NO adjustments of any kind for icy or wet situations. The same MTOW is used. That makes the data suspect for real world use. Should I not recognize this and talk it over with my crew beforehand? Or would some suggest I just use the published V1 no matter what?

15th Aug 2001, 11:42
Mutt just out of interest on which A/C are you permitted to use a 45% thrust reduction ?.

Best rgds

15th Aug 2001, 12:38

Take any aircraft with fixed Derates (TO-1/ TO-2) and apply the legal maximum assumed temperature reduction of 25% and you will get down to around a 45% thrust reduction.

For specific aircraft, B744 and B772.

Mutt :)

15th Aug 2001, 17:39
OK I see what you mean, legal max 25% thrust reduction on TO-2 which would equate to a reduction of about 45% on the eng's full rated thrust. Must be honest we don't use derates. (yet !)

Best rgds

18th Aug 2001, 05:38
It's a neat subject that will result in hours of discussion. Many areas are not well understood.
The FMC/QRH V1 speed is determined by the performance engineers (at least at Boeing) using an arbitrary V1/Vr. If the takeoff were to be calculated from the AFM you would see that for every takeoff there are two V1 figures, one for continuing and one for stopping. If you are doing the calculation the long way you would then select the figure that suits you for that particular takeoff. In other words, you select the V1/Vr. (Not that airlines would be happy allowing their pilots to use their judgement in such matters. Keep it simple for simple people.) Whenever you have excess runway the split can be very large, but in practical terms the highest V1 is equal to Vr and the lowest would be about 80%.
For a four engine airplane the engine failure case is not limiting. The limiting condition is for all engines, since the factor applied to the all engine takeoff is a reduction of 15%, while the engine failure case is not factored. A twin is not so lucky.
When reducing the V1 for a Wet runway, it is more correct to apply the speed correction to the Maximum V1 (the speed applicable to a takeoff at maximum takeoff weight for the runway length and conditions). Thus the actual V1 may not be reduced at all.
And if the Wet V1 is used, a continuing takeoff will result in a reduction of screen height (height at end of TOD) to as low as 10 feet. Now another question: if the screen height reduction is allowed on a wet runway, is it also allowed on a dry runway?

18th Aug 2001, 08:15

V1 Description - 1940's missile powered by pulsejet.

Application - London and surrounding areas.

19th Aug 2001, 15:48
Boofhead is correct in talking about V1go and V1stop. However, our performance tables (B737) seem to take some of what you are saying into account. The WET V1 correction, for instance, is LESS for a full length runway than for an intersection figure (2 kts full length, 5kts for an intersection 1100m into the runway).

The other intersting development is that it is possible to have a performance database on a laptop computer. This allows a higher RTOW due to being able to work out precise figures for the actual conditions of the aircraft on the day (the tables are generalised and have added anomolies in them). For instance, some performance pages say to REDUCE your RTOW for a HIGHER pressure above standard, which obviously doesn't make sense, but it is necessary because of the way the table is constructed.

I tend to calculate the performance for the intersection furthest into the runway, so on a very long runway like PARIS we know we can take any intersection up to 'Y8' etc. without having to recalculate the figures and so cause a delay, and we don't have to rush them under pressure. This obviously results in a more 'go minded' situation if we take the full length in the end.

19th Aug 2001, 19:37
There is some more interesting reading on the subject at the Flight Safety Foundation website: http://www.flightsafety.org/fsd/fsd_oct98.pdf

[ 21 August 2001: Message edited by: N.N.C ]