Calling V1 early
 

According to an article I have "As a safety precaution, many departments actually call V1 five knots early to give the pilot's time to act before reaching the critical spot in the takeoff run"

What are the potential ramifications of doing this?

V1
 

We call it five knots early with my operator, idea being that by the time the pilot flying has heard and registered the call you will be through that speed.

Seems a good idea in helping to prevent an attempted reject above V1, and continuing with the take off.

We've just gone over this thoroughly in the sim a few days ago with my company. We make the V1 call slightly before V1, because the decision to go/stop must be made by V1. If you get the call at V1, it's too late.
We did a limiting takeoff in the sim, where the engine failed about two seconds before V1 but kept going and the plane took off just fine.
Five seconds sounds excessive to me, but as long as it's before that's a good thing.

I wonder...
 

Let us suppose that it is the Captain making the takeoff.
The First Officer makes the V1 call, and at the same time 'bang', there goes an engine.
The Captain continues as he should, but is he listening specifically for the First Officers V1 call, or does he primarily depend on what his airspeed indicator indicates?

In other words, is he depending on the call?

Personally, I do not.
At heavy weights, I have already determined (approaching V1) that I will more than likely continue, as I have absolutely NO intention of sliding off the end, following a high speed abort.

Several years ago departing FUK, at max weight, I asked the First Officer if he thought we could stop safely, with an abort just before V1.
His answer was...'not likely Captain, we surely would end up in the drink.'
He was more than likely correct.

18-Wheeler,

It should come as no surprise that "the engine failed about two seconds before V1 but kept going and the plane took off just fine", that's what the aircraft is certified to do!

Certification is based upon Vef (speed of engine failure) being 2 seconds before V1, the intent being to allow for suitable recognition time. (In earlier times it was 1 second, a little unrealistic). So, 18-Wheeler, what you have done is to exactly replicate the certification process, and obviously the test pilot also found it to be "just fine", which is why the aircraft gained it's certification.

Calling V1 5 seconds before actual is a disaster in the making. V1 is a two way speed, you Stop, or you Go. For the Stop case, call it as early as you like, and the Accelerate-Stop performance can only be improved, but for heaven's sake don't GO!. The continued Takeoff case assumes Engine out acceleration from V1 (Vef actually) to Vr, then to V2. The distance consumed in this manoeuvre is considerable, and some would want to make it longer, but you're limited already, so you crash. Does stilton's operator calculate the extra Takeoff distance required to accelerate that extra 5 knots with an engine inoperative? With all engines, 5 knots worth of acceleration would be over in the blink of an eye, but with an engine inoperative, perhaps another 1000 Metres or so.............

That's the Performance aspect, but has the control aspect been considered? V1 must not be less than Vmcg (to cover the continued Takeoff case), and, in many instances, V1 does indeed equal Vmcg. Now, someone wants to continue the Takeoff 5 knots below Vmcg, and directional control will be lost. At least the ensuing crash will be within the airport boundaries, making it easier for the fire engines and blood wagons to get to the wreckage.

GET REAL! Fly the aircraft the way it was certified, you're tinkering with very small safety margins. The manufacturer already assumed that it would take you 2 seconds to recognise the engine failure, it's built in to the figures. Don't try to re-invent the wheel.:*

Regards,

Old Smokey

Seem to be a lot of 'test pilots' with pax on board on 'Tech Log'.
In addition to flying for several outfits, I've had a command with two respected majors and they all called V1 AT V1. On the other hand, perhaps they and the manufacturers were totally wrong :E

I have read too many accident reports to be convinced there is no problem with an abort on a balanced field length from a engine failure close to V1 even if the crew performs perfectly in all respects.

The veracity of these accident reports over the years is further confirmed from what I observed on countless occasions during simulator training. Having watched experienced and inexperienced pilots occasionally stuff up an abort in the simulator due to factors such as not immediately being aware that an engine has indeed failed. Or that noise and a heavy vibration accompanied by a swerve might mean a tyre and not an engine has failed. Or an unusual engine instrument indication is brought to the pilot's notice at a critical time by the PNF in the take off run.

There is a pragmatic approach to the question of abort speed and there is the official company approach based upon the manufacturer's figures. Rightly or wrongly I have always quietly planned on continuing the take off from 15 knots below the published and bugged V1 - unless the event is catastrophic, in which case all bets are off. Others may vehemently disagree and I have no problem with that.

Forget the lower screen height - when the chips are down the deadly risk is the over-run from a botched abort at high speed nearing V1. My simulator observations of aborts gone wrong over the years have biased my thoughts toward the V1 minus 15 knots policy I prefer. Of course I would not insist other pilots do what I do. It is just a private conviction that I would act on. The chances of an abort going deadly wrong are a thousand times higher than hitting an obstacle in the first or second segment in IMC because of a low screen height coupled with a real net flight path climb out.

Sitting in down the back cattle class I would be terrified if late in the take off run I heard the engines suddenly cut a minute into the take off run and the sound of screaming tyres, brakes, and reverse thrust - knowing from memory the chances of a botched up abort were high. I would be less terrified if an engine failed near V1 and I realised the pilot was continuing the take off run.

As far as the V speed calls by the PNF, I suggest concentration on my own ASI reading - not the V speed calls by the PNF. Again in the simulator I have seen too many incorrect V speed calls by the PNF to act blindly on his call, rather than my own ASI backed up by the planned ground speed display. The PNF call is a back up only - not the action call. The V speed word (not command) "Rotate" can be a powerful incentive to pull back on the stick simply because of the word itself.

It is a not uncommon sight in the simulator for the PF to momentarily disbelieve his own ASI and instead be startled enough to rotate at the call of "Rotate".

Scary reading!

Any reference to that article or to which flight departments are using this?


In the (fortunately very rare) case of having an engine fail at V1 (recognized at V1) - I personally would prefer approaching the end of the runway DECCELERATING as opposed to trying to accelerate S/E (for a twin) from a speed 5-15kts below V1 (outside of all published data)! Btw. are you talking specifically about the B747, 4-engines or aircraft performance in general?)

And Centaurus - any thoughts on controllability/VMCG as mentioned before? Would you always use the -15kts or do you use other personal corrections - for crosswind etc. You mentioned "sitting back in cattle class" - knowing the guys up front could be inventing their own procedures for T/O is something I will try not to think about next time I'm in the back.


[Edit: Btw. are you talking specifically about the B747, 4-engines or aircraft performance in general?)]

I've got a lovely chart based on the 747, HVY weight, balanced field, dry, no reverse which shows that if you decide to abort at 1kt over V1 you will go off the end of the runway at 20kts and 4kts over V1, it's up to 60kts.

Now if you 'GO' at 20kts below V1 you will cross the end of the runway @ 15', 10kts below 20', 5kts below 25' and @V1 as you'd expect 35'.

So if you ask me the benifits of going early are obvious.
(1kt < V1 = 34' and 1kt > V1 = 20kts off the end).

I'll try and get a hold of a twin graph.

EDIT: Just to clarify a few things,
I'm certainly not saying call V1 early, or "GO" anywhere near VMCG or fly an unflyable A/C.
It just shows you don't have to be stop minded below V1. Come back and use the full length.

Aha...

...but what of wet or contaminated runways where the screen height is 15 ft, not 35??? :ouch:

And what about slippery runway conditions? Also isn't VMCG calculated with a fairly light crosswind.? I have heard 7 knots crosswind. Do you take this into consideration. What about when lightly loaded and a very long runway with a good headwind? Lot's of variables.

Most disapppointing to see such a load of (dangerous) untruths / personal preferences / ideas posted here.
The calculated V1 is not necessarily the "Stop V1". it might be the "Go V1", or anywhere in between.... Anyone who chooses to "Go" even 1K below a "Go V1" is asking for trouble :confused: You are as likely to go off the end/side at very high speed / power as someone is to go off the end at low speed who RTOs 1K late from a "Stop V1" :{
Aircraft Performance is not an exact science, but based on years of experience, deaths and wrecked aeroplances. Aviation Authorities and Manufacturers have spent many hours deciding the best policy for calculating V1. If they meant it to be called 5K lower, then they would calculate it 5K lower.
Call V1 at V1. You are not storing up a decision to be actioned then - so the time factor is not really relevant. If you have not called "Stop" prior the call (or you seeing) V1, then there is no decision to be made...
IMHO :)

I agree with Centaurus; when I was on the DC-10 there was many a time when we were "going" 10 knots before V1 and were as sure as hell not going to try and stop "at V1".

Once you shut those throttles there are no options left. There are plenty if you keep going.

Reaction time allowances are built into V1 calculations. I suppoes, then, the question is whether you are as fast as the calculations assume...

The major ramification of an early V1 call is a higher probability of taking a broke airplane airborne. Since there are few rejected takeoffs within 5 knots of V1 anyhow, the specific probability of this happening to YOU on THIS flight is very low. However, it MAY make the difference in the case where the airborne weather is marginal, especially in the case where you will be forced to go to a distant takeoff alternate instead of simply turning around and landing.

Bottom line: Do what your SOP says to do, and discuss any contingencies or planned deviations in the takeoff briefing.

Interesting discussions all with valid points. Do I or don't I ?

Agree that if you follow the book you will be safest. However, training limitations coupled with min experience has shown that more accidents will be avoided by calling V1 early then by increasing risks due to reduction of obstacle clearance margins brought on by early V1.

The call therfore is a collective decision/recommendation considering the training and experience of the average crew.

Wow!:mad:

With all due respect, I don't know how you came to be Old Smokey, but I think your dissertation is a little off the mark. :confused:

I suggest you read some performance books, especially Boeing's Takeoff Safety Training Aid, IMMEDIATELY. :ok:

Empty Cruise
"...but what of wet or contaminated runways where the screen height is 15 ft, not 35??? "

Where in Gawd's name did you get that from?

Centaurus
Do I understand you to mean that you are reading and ASI approaching V1 rather than looking outside???

It is recommended by Boeing (and other manufacturers) that the V1 callout be made 3-5 knots prior to the actual V1 so that the spoken word is complete and registers by V1. That does not mean V1 Decisions are replaced by deciding to STOP before V1 unless, of course, circumstances dictate otherwise. It's obvious and confirmed by the variety of opinions on this topic that performance remains the least understood by pilots.

I dont quite agree with calling V1 earlier than calculated.
The reasons being, firstly i believe that manufacturer has done enough tests to determine the correct speeds and have put it in the Perf manals.
Secondly the whole idea about callling V1 earlier seems to be to avoid rejecting take off above V1 and there by causing an over run, if we keep in mind the following things it would help
1) Ef occurs before you have heard the call V1, you have the option to reject.
2)Ef occurs at the moment you hear the call V1, not much of a choice there but to go, because by the time you react to it you would have crossed V1.
3)Ef occurs after the call V1, by now your hands are already off the thrust levers so the decision has already been made.

V1 speed takes into account the reaction time, therefore by calling the speed early you are committing yourself to the takeoff earlier than you have to.

Willie Everlearn,

JAR-OPS 1, Subpart G - "Performance Class A". OPS 1 operators are allowed to reduce screen heights on wet & contaminated runways to 15 ft. - and include effect of reverse thrust in MOTM vs. TODA and MLM vs. LDA :eek:. See http://www.pprune.org/forums/showthread.php?t=201568 for more on how adviseable this is considered to be :rolleyes:

Only other 2 euro-cents worth - rolling into the approach lights at the other end of the runway @ 40 kts. is generally survivable (not talking FCA, FAE, FRO et al here). Not advocating one way or the other here, but if you cut it down to sheer survivability on the majority of airports most of us operate from, I feel there might be a point in this. Sure, aircraft gets damaged, but everybody walks. Can you ensure that if you go at V1 - 10kt? Given the knowledge of performance that I've seen many pilots in the industry demonstrate (not dissing anyone on this forum, so keep the flame-throwers in their holsters), I doubt that even 50% would be able to use the AFM charts to calculate independent "stop" and "go" V1s, much less in the time available in the flightdeck for preflight prep.

However, the next time you de-rate, you might want to consider taking 4-6 deg. C off the max allowable derate - and there's your margin! It's easy to do and does not require altering the SOPs. Oh, and it will hold in a court of law - going at V1 - 10 won't (imho).

Cheers, Empty

I am probably about to upset the theoriticians, mathematicians, Monday morning quarterbacks and promising hysterics among you.

Let me first of all tell you that I have been operating Perf A aircraft (mostly 4-engined) since 1962.

I have to tell you that some aircraft are great "stoppers" and others are great "goers".

For example, the DC-10 is a great "goer" and a lousy "stopper". Therefore, an engine failure 10 knots before V1 at St Maarten heading for JFK at MTOW with a tailwind (better solution than heading for the mountain) definitely makes the "going" option much more attractive.

On the other hand, the Short Belfast was a lousy "goer" but an absolutely brilliant "stopper". So an engine failure at MTOW at V1 at Gan would mean a fistful of meaningful reverse thrust and an early return to the bar with the brakes hardly warm!

Both aircraft conformed to Perf A but common sense dictated that they be treated entirely differently.

I always understood a couple of seconds thinking time were already built into V1 calculations, so any personal tampering with it takes you into territory that may be beyond your knowledge. By that I mean the call 'V1' is made, and you decide immediately Go/No Go. Then a few seconds are allowed for to get the thrust levers back to idle, select reverse and make sure autobrakes and speedbrakes deploy. Simple as that, tamper with it and you are at a lawyers mercy.

On a heavyweight takeoff from BOM, when I called V1, I was 'impressed' how close the end of the runway was. I reported that I did not think we could have stopped even with 4 in reverse. Some months later our Safety team sent me calculations to show that we could have stopped with a couple of hundred yards to spare- which I discounted as wrong. Sure enough, one of our 747s, with a reverser locked out already, lost another engine just below V1, with a brake unit locked out as well. They stopped OK and did not run off the end.

Personal tampering like that is dangerous. You could be obliged to take an unflyable aeroplane into the air. Can you imagine what the Courts would make of you?

Astonishing level of varied 'understanding'!
Please see http://www.ais.org.uk/aes/pubs/aip/pdf/aic/4P182.PDF
which is UK CAA AIC 141/1998 (Pink 182) - still current.
Then perhaps the mis-informed will stay quiet!

Rainboe

I am by no means an expert, but I believe you'll find that V1 calculations involve no additional increments. They are de facto performance calculations, under standard WAT conditions. Your statement, "I always understood a couple of seconds thinking time were already built into V1 calculations" refers, in fact, to the 'after V1' reaction buffers to bring the aeroplane to a stop.

It is my understanding that there was a one second, plus buffer, plus another second, plus buffer to get it stopped. This accounted for recognition AT V1, closing the thrust levers, apply max. braking and allow for spoilers up, plus an additional factor to stop. Under FAR 25 Amendment 42 an additional 2 seconds was added to the calculation of the Balanced Field calculation, which I suppose affects the initial V1 calculation.

Boeing has an excellent download called Takeoff Safety Traing Aid which explains everything in clear and uncertain terms.
Great discussion. :)

Empty Cruise

Thanks for the reference. I appreciate your trouble and truly must remember our friends who operate under the JARs. I stand better informed thanks to you. :)

cheers,
Willie :ok:

An important subject and one needing lots of airing in places such as this. May I summarise the basics as discussed so far ...

(a) performance can be approached theoretically, in which case the numbers are all good fun and can be run to whatever accuracy is considered pleasing to the eye. Alternatively, one can look at the real world and note that the distribution curve shows up a degree of variability in achieved performance when compared to calculated. He who blindly puts all faith in charts beyond a reasonable scatter accuracy lives with the potential for excitement .. ie a little bit for mum and the kids in usually a good idea.

(b) the discussion so far shows clearly the variability in knowledge within the Industry on matters technical.

(c) the line pilot generally will not know whether the go or stop case is limiting or closer to being limiting for the particular takeoff on the day in question. Consider quizzing your ops engineering folk for runways which you might consider to be more exciting than others.

(d) Vmcg is a real limit and can make for exciting times if abused. Consider that the transition from easy directional control to loss of control may manifest itself in the space of several knots and the rate of onset of control problems is fast as the failure speed decreases.

Keep in mind that real world Vmcg (as opposed to the certification animal) is very crosswind dependent (typically 0.5 kt/kt for twins increasing to something in excess of 1 kt/kt for 4-engined beasties). This is made more interesting when one considers that the certification value usually is based on zero wind (7 kts under the old British standards). The certification value is there more for line in the sand purposes but, if you happen to be near or at the limit on the day, that doesn't help you much.

Taking an arbitrary decision to reduce the go decision to a speed significantly below V1 may be hazardous, especially for low weight, low altitude, low OAT takeoffs. Keep in mind that our simulator experience is a two-edged sword and that the great majority of simulator failure training exercises are done under non-limiting handling conditions .. this can create an unjustified comfort zone .. this is especially the case for aircraft where Vmcg is not usually a critical takeoff limitation.

(e) history suggests that more people have trouble with high speed aborts than they do with high speed continued takeoffs.

(f) current thinking (and this has been the case for quite some years) is that if you haven't initiated the stop BY V1 (ie the first abort action has been executed - normally brakes full on) then you keep going (unless there is a real perception that the aircraft will not fly). Particularly with older certifications initiating the stop after "deciding" at V1 (if the ASDA is, in fact, limiting) might be a bit worrying. Keep in mind that, in the real world, the bit of the runway on which you are hoping to stop is the bit on which umpteen thousands of tyres have left a thick film of rubber over the past however many months/years since it was all cleaned off .....

(g) the pilot who doesn't monitor his own instruments during the takeoff is asking for a surprise sooner or later.

(h) there is some fat in accel-stop scheduling (which varies with certification basis) but not a great deal (amendment 42 sought to redress this problem to some extent).

(i) the calculations should be made for the ambient conditions, not standard day. An earlier poster's reference to WAT conditions left me a little confused .. perhaps he might add some additional commentary ?

(j) being able to justify one's actions at the investigation is an important part of the plan. If you think you won't be able to, then maybe you ought not to be about to do whatever it is you are contemplating ... ?

Forget all this just "GO" Russian :}
http://www.!!!!!!!!!!!!!!/open.file/995911/L/

Willie, what part of <<"By that I mean the call 'V1' is made, and you decide immediately Go/No Go. Then a few seconds are allowed for to get the thrust levers back to idle, select reverse and make sure autobrakes and speedbrakes deploy. Simple as that, tamper with it and you are at a lawyers mercy.'>> do you not understand? You have repeated what I said above!

Willie Everlearn,

I suggest you check out FAA AC91-6B regarding contaminated runways using a 15ft screen height and reverser thrust.


Rainboe, the FAA certified the B747-400 using the constant velocity transition method for the accelerate stop. Basically, Vef is 1 second prior to V1, then they use the demonstrated brake, spoiler , reverse time FOLLOWED by 2 Seconds at a constant velocity before the aircraft is assumed to be decelerating.....

This method applied to the 737-300/400/500. B757-200, B767-200/300 and B747-400. The following are the various methods used by Boeing:

Willie Everlearn, you just explained how the B707,B727,B737-100/200, B747-100/200/300 were certified.

Mutt
Mutt

Wait until you see what the Airbus does !

Longer runways, always goes for incresed V2 which drags V1 up with it. the number of times we look at remaining runway at V1 and go - Naaaah, that wouldn't have worked !

Don't always but blind faith in the V speeds either - we had a certain desert destination where luck features a lot - back in 2001, our perf people omitted the aerodrome elevation of over 2,000' in the perf calcs for a whole season !

They were interesting departures :eek:

I have found this thread to be quite educational. Thank you all. I think J.T.'s summary brought many of the good points made into a unified, or at least more easily recognizable statement on the importance of understanding takeoff performance data to a somewhat more advanced level than is provided by typical type training. As illustrated by mutt's point about the differences in certification methodology used in the certification of older vs newer aircraft, It seems that it would be useful to learn what assumptions were made in the performance data for each specific type we fly. It's nice to know what margins are and are not built in. Since this is outside the normal curriculum of a standard type training course, I'll consider it to be an advanced learning assignment which may come in handy someday on a limiting runway. Once again, thanks.

Best regards,

Westhawk

Hey there, some of you might be surprised, but modern airplanes do have automatic call function, ergo V1 call is made automatically by nice synthetic voice. All you have to do is decide. I personally will stick to most common Airbus philosophy: up to 100 kt Stop minded, above GO minded, unless severe damage, fire (all mentioned in the airbus manual). I agree that a stop decision near V1 is more critical, as its been proven by statistic, but if its necessary to stop, then do it.
Cheers.:ok:

There is no argument in my mind that the book figures are valid and correct.
While I respect the book V1 and I know that fudge factors and decision times have been built into those V speeds, the experience of observing many botched aborts in simulator prof checks and when training for type ratings has convinced me there is a theoretical world and a real world when it comes to lightning fast decision making with an event close to V1. And we all know you have to be real quick and perfect on a balanced field length abort. Few pilots are both.

Certainly V1 must be correctly bugged using the book figure. And V1 is called when it arrives but once I pass beyond 15 knots below V1 and heading fast towards the bugged V1, I can afford to relax a little as I know the danger of a botched abort is less because I ain't stopping for no man - unless it is a catastrophic event where continuing is not on. Of course commonsense prevails when it comes to Vmcg. Its called playing the statistics, I suppose.

Our company flys classic 747's. However, we use a bit of wisdom from the -400 in our thinking. Above 80 knots, the front C&W panel is blanked out. Boeing thinks that anything on that panel is not worth rejecting for over 80 knots. So, we keep this in our thinking while in the sim and try to use it on the line.
So, that leaves an engine failure or a fire to think about, or something really obscure.
At V-1, our hands come off the throttles, feet off the brakes.

Boeing says that the v-1 decision can be made at v-1 and that allows for the few seconds it takes to make a decision.
Well, our policy is , at V1, hands come off the throttles, were going. Our OPS system has made things very scary. it basically turns every runway into a balanced field, except for when your really light.
Don't make up your own rules, that will get you into trouble!

I'm just a line pilot, and I like to learn from other folks misfortunes.

It would seem that first one has to define how V1 was computed. I have seen numerous methods to calculate V1 including min V1s.

Second, a high speed RTO is always a problem. It is probably the most dangerous thing that faces a pilot and is seldom done correctly. Studies have shown in most cases the pilot fails to use maximum braking rendering the numbers invalid. Unless you can shove a phonebook under your butt when you are standing on the brakes, you are probably not getting max braking. This of course discounts using autobrakes.

Even with autobrakes, many times an aviator will disconnect the brakes when s/he feels the situation is under control and unfortunately this is when they are entering the latter portion of the runway where once again you are getting into the rubber build-ups.

At or near V1, the airplane is accelerating at about 5-7kts per second and in an earlier report (PSM+ICR) it discussed how many simulator events were created not from actual data but what was supposed to be. In talking to a few aviators who had blown tires or blown engines, they said the same thing, "It was nothing like the sim!" Having landing with a disconnected nosewheel pin (727 many years ago) when we landed the airplane shook like a wet dog and I had no idea of what was going on. Had this happened on takeoff, I imagine I would have had great concern about whether or not it would fly.

The V1 -kt call has worked at my old house (now retired) and I would imagine that more than V1 or V1-5kts the best plan would be to know what you are going to do as you near V1, execute it flawlessly and then lift a glass to expert airmanship.

Wileydog3 raises another critical factor in this discussion and that is that the braking technique on a rejected take-off has to be accomplished perfectly.

I did my DC-10 conversion at DFW and our very, very wise instructor used to set up an exercise on a short runway at Waco. Provided that FULL braking was applied at V1 it was JUST possible to stop the aeroplane before going off the end.

In order to achieve FULL braking it is necessary to have the rudder pedals right back so that it is possible to get your full body weight on to the brakes.

If you are the sort of chap that likes to have your rudders adjusted forward then you are for sure going to cock it up for your ankle muscles simply cannot get FULL brake pressure on in time if at all.

Think on that before you next go flying.

From UKCAA-AIC 151/1993 :-
V1 must be respected as the latest speed by which a decision to stop must have been taken to assure a stopping capability within the distance available on a limiting runway.
It is not the speed called at which the PF decides to reject the take-off and use the appropriate procedure. In other words when V1 is called (human or automatic voice) the decision must be to GO.
The JAR accelerate-stop definition differs from the FAR definition in that the JAR includes the stopway in the calculation, whereas the FAR determines that the aircraft will stop on the runway itself.
In JAR's a 1.5 to 2 second "thinking time" is included in the V1 calculation.
If V1 is called early (beware the lawyers if is is found to be a factor in an accident!) then it is not guaranteed that the a/c will achieve lift-off before the end of the runway, following a power-plant failure nor achieve the 35' screen height (15' if wet or contminated conditions).
V1 and its' definition has been argued since long ago and will be argued for a long time yet. The 'sense' in the GO decision, when above Vmcg but below V1 may be obvious but ill-advised. Stick to SOP's and if you don't, be prepared with a good defence!!

Centaurus, how do you apply this in the real world? Do you always brief the FO about your plan? If not, it would certainly add to the confusion if the FO is PF and an engine fails 15kts before V1!

How? Is it never a factor in the type you are operating, or do you account for that when you plan each T/O?

I think we all understand your concerns, but I still think you are on very thin ice.

Time for the next summary ... and the thread is developing very nicely, I believe.

(a) the detail of the certification basis for V1 has evolved over the years and can be studied via the reg changes and the flight test guide for those who are interested (FAR25). That is, V1 for a B707 means something a bit different to what applies for the latest offering from the OEMs.

(b) early aircraft are PARTICULARLY accel-stop critical on limiting runways. Effectively, there is near nil room for the pilot to think about what he is doing at the time .. lest he desire a near guaranteed overrun.

(c) amendment 42 addressed a gaping deficiency but is not the comfort zone which some might suppose. Consider two (2) seconds at, say, 150 kt .. equivalent to around 150 metres (if I have my conversions lined up correctly). That's still around 500 ft (in real numbers) but not very far in real runway eaten up at V1 terms .... so one needs to be very focussed.

(d) "V1 is the speed where the first actions to abort the T/O should be initiated" ... NO. He who follows this point of view sets himself up for needless excitement. As a general rule, if it isn't already stopping by V1, then it's going .. especially for the earlier aircraft.

(e) it is a lemma that the calculations are only as good as the quality of the information fed into the sums.

(f) it would be nice if pilots knew all the ins and outs of the basis for performance calculations. Unfortunately that is unlikely ever to be the case. Some of us, either due to interest or employment, end up with a bit more knowledge than most pilots. Mutt, for instance, is an experienced operations engineer rated on most (and possibly all) of the aircraft for which he crunches the numbers. Centaurus, while having a piloting background, possesses a knowledge base on this subject far greater than the great majority of pilots. I would suggest that, in respect of his reference to "V1 - 15", he is probably suggesting that he starts to become GO-minded at that delta.

(g) for the accel-stop manoeuvre, the brakes MUST be full deflection (assuming the Type has anti-skid) until the aircraft HAS stopped ... one needs to be VERY careful about releasing any pressure until the aircraft has actually stopped. Human estimation of speed under significant acceleration is not good.

(h) the point about AEO/OEI is very important. Other than for some later aircraft, all the accel-stop data is predicated solely on a fuel cut failure at the scheduled speed .. which history tells us is not the usual case facing our hapless pilot during the real world event.

(i) query ? FAR 25.109 appears not to support the contention that "the JAR accelerate-stop definition differs from the FAR definition in that the JAR includes the stopway in the calculation, whereas the FAR determines that the aircraft will stop on the runway itself". Perhaps the poster might give us some further guidance as to the origin of his assertion ?

(j) for those who might seek to develop their own techniques, it needs to be kept firmly in mind that the CVR/DFDR history on most modern aircraft may just bring you unstuck at the enquiry ....

Ref (i) I have now had a chance to search for the AIC referred to and cannot find a link to it. Can the poster provide one, please ?

A couple of notes from the peanut gallery:

In the mighty C-5, the engineers spent probably 20 minutes computing every detaicl on every take-off including Vmcg (corrected for xwind, just about 1 kt/kt), refusal speed and distance, and (of all things) take-off ground run. I cannot explain the reason for the last one other than it was surprisingly close to critical field length with zero height at DER. But, for a pilot that read and understood the data, no excuse for not having a full idea of what was going to happen when. So underpowered was the plane, we frequently made WAT-limited take-offs, esp in the Gulf.

I thought it was all interesting but rather pedantic....until I saw the data confirmed by a functional test or two. Limiting take-off at Sig to the east, just a couple of knots prior to V1, we were struck by a flock of birds, the A/C elected to stop. And stop we did, the end of the runway was not visible from the jump seat between the seats. Another time, landing on RCR 5 braking poor, the computed landing distance was 5000 feet on a 7000 foot runway. Standing on the brakes and I mean standing, we came to halt at the 2000 feet remaining marker. Guys, when the data says it will do it, it will, if you do your part.

On other thing, I always instructed new pilots that if they needed max anti-skid braking, they best plan on STANDING on the brakes like they did for a full power standing take-off. We did those too. Saved the guy at Sigonella.

Thanks J_T for the excellent thread guidance.

GF

Eh, no it doesnt!!!!! The FAR's permit you to use Stopway and Clearway, but they omit a line-up distance, so they almost guarantee that you will NOT stop on the runway itself!
Dont get fixated on a single V1 speed, "generally" there is a V1min and V1max, for most modern aircraft its possible to provide the crews with all 3 V1 values, the crew can therefore decide which V1 speed is suitable for his/her aircraft on a specific runway!!
Mutt

... and (of all things) take-off ground run .... I have no idea of the C5's certification basis but this is similar to the civil TORR parameter (except that, for civil certification it includes a portion of the takeoff rotation air distance - usually 50 percent). The purpose is to give some comfort that, for an unbalanced takeoff, the bird will actually be off the ground before it is in the weeds at the far end ...

Early V1
 

FAA has changed the definition of V1 in Far part 1 to read as follows:

1) V1 means the maximum speed in the take off at which the pilot must take the first action(eg apply brakes, reduce thrust,deploy speed brakes) to stop the airplane within the accelerate stop distance;and,

2)V1 also means the MINIMUM speed in the take off, following a failure of a critical engine at which the pilot can the take off and achieve the required height above the takeoff surface within the takeoff distance.

Point number 2 in the definition makes it clear that, following an engine failure if a decision to continue is made prior to V1 the required height above take off surface will be compromised.