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?