What's V1?

[Shaggy Sheep Driver]

I understand this is speed, on take off, above which the aircraft is committed to fly (if possible) despite any failure occurring. You take the failure into the air.

I always assumed this speed was calculated taking available runway length into account, and if you try to stop after V1 you are in serious danger of over-running the runway and going off the end. Hence the need to fly with a failure after V1.

However, I was talking to a couple of retired Big Aeroplane driver mates the other day and they told me this was not the case! V1 is calculated for weight and other factors, but runway length isn't one of them. As one of these guys said "if you were taking off from Bonneville Salt Flats the calculated V1 would be the same as from any airfield. I'd probably stop after V1 if there was no doubt about available length to stop in, but it would get me a fail on a sim check".

What's the point of V1, then?

[Whopity]

You can read more in this article (http://flightsafety.org/asw/jul-aug11/asw_jul-aug11_p23-24.pdf?dl=1) which defines V1 as:

V1 means 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

[AirborneAgain]

The required runway length for take-off depends on both the distance required to stop the aircraft in case of an aborted take-off and the distance required to reach a safe height over the runway end in case of continued take-off after engine failure.

A low v1 speed means that the stopping distance in case of engine failure will be short, but the continued take-off distance will be long as the aircraft must accelerate longer with one engine out. A high v1 means the opposite. The v1 speed where the stopping and continuing take-off distances are equal is the optimum v1 and will give the shortest required runway length (the "balanced field" length). Clearly both v1 and the required runway length will depend on factors such as aircraft mass, weather and runway conditions...

Thus the important thing for the pilot is to ensure that the actual runway length is at least as long as the required runway length. There is no need to change v1 depending on actual runway length.

That is not to say that you couldn't change v1 if the runway is longer than the minimum required but there is usually no reason to and I don't think pilots generally have the performance data to do such calculations.

[Shaggy Sheep Driver]

But if you were taking off from the Salt Flats with a 'runway' many, many miles long, you could ignore V1 and stop any time up to just after Rotate Speed?

And even then, in the event of, say, a serious engine fire you might consider chopping the power and landing straight ahead rather than continuing flight?

[AirborneAgain]

But if you were taking off from the Salt Flats with a 'runway' many, many miles long, you could ignore V1 and stop any time up to just after Rotate Speed?
Not necessarily. There is a lot of kinetic energy in an aircraft at Vr. The wheel brakes must be able to absorb this energy without overheating or catching fire. Thus there is a maximal possible v1. Of course, this assumes maximum braking so if you are braking carefully you could stop from higher speeds. But then you would be in unknown territory as regards stopping distance. (Wheel/brake fires are not unheard of in emergencies...)

And even then, in the event of, say, a serious engine fire you might consider chopping the power and landing straight ahead rather than continuing flight?
Sure, but again this is all very hypothetical. A transport category aircraft is moving really fast and runway will disappear behind it quickly. Since you have no figures, you would need very very large margins to do this safely.

It is not like the spamcans we PPL types usually fly where you could safely make several take-offs/immediate full stop landings in sequence on a 3000 m runway.

[AirborneAgain]

Vmbe being the speed I implicitely referred to here:

There is a lot of kinetic energy in an aircraft at Vr. The wheel brakes must be able to absorb this energy without overheating or catching fire. Thus there is a maximal possible v1.

[foxmoth]

V1 is calculated for weight and other factors, but runway length isn't one of them. As one of these guys said "if you were taking off from Bonneville Salt Flats the calculated V1 would be the same as from any airfield.

Whilst they are correct in one way, what will be the case on some airfields is that the runway length would restrict the TAKE OFF MASS, this take off mass would then dictate the V1, so you might have the same V1 at Bonneville as a shorter runway, but only up to a more limited Max TO on the shorter runway. Also, on a longer runway you can have a range of V1 whereas if the TO mass is restricted by runway length there will only be the one V1.

[AirborneAgain]

And of course don't forget changes in V1 due to second segment obstacle clearance requirements.
I guess that would be calculated by the operator rather than the pilot? Or using assumed lower take-off performance?

[Shaggy Sheep Driver]

Yeah but... At the Salt Flats you have effectively an infinitely long runway. No need to use the brakes at all!

[keith williams]

If we discount Vmbe for our "infinite runway case", V1 must not exceed the tyre speed limit.

[Shaggy Sheep Driver]

Of course; I use The Salt Flats example merely to make a point, as it is effectively not runway-length limited.

That point is that as runway length plays no part in calculating V1, then pilots surely have some leeway as whether they do indeed 'always take a post-V1 failure into the air'. I had, prior to my chat with my ex-BA mates, assumed that VI took runway length into account and therefore trying to stop after V1 would probably lead to an over-run accident.

Wasn't there a 748 some years ago that suffered a catastrophic engine explosion with massive fire after V1 and the pilot elected to stop straight ahead? Everyone walked away. It would have been unlikely the aeroplane and pax would have made it round even a very tight visual circuit had he flown.

[ETOPS]

and the pilot elected to stop straight ahead?

Yes - and he was a member of our illustrious aero club and I might :rolleyes: have had a hand in teaching him..........:oh:

[wiggy]

I always assumed this speed was calculated taking available runway length into account, and if you try to stop after V1 you are in serious danger of over-running the runway and going off the end. Hence the need to fly with a failure after V1.

However, I was talking to a couple of retired Big Aeroplane driver mates the other day and they told me this was not the case! V1 is calculated for weight and other factors, but runway length isn't one of them.

SSD

I somewhat doubt they meant that and I wonder if there's been a misunderstanding.

On one airline I know of on the line the V1 (amongst other things) is calculated by entering weight and other factors, as you put it, into either a computer program or by reference to a (thick) book which contains a page for every single runway on the network. If you're using the computer you enter the runway identifier and entry point, not the length into the "computer", if using the book you use the page appropriate to runway and entry point. In neither case do you as the pilot, actually enter the numeric runway length in feet or metres, since the "computer"/book has that inormation so it is a value most assuredly involved in determining the value of V1.

I suspect that is what your Big Aeroplane pilots were driving at ( at least I hope that was what they meant, otherwise :\ )

[Shaggy Sheep Driver]

SSD

I somewhat doubt they meant that and I wonder if there's been a misunderstanding.

On one airline I know of on the line the V1 (amongst other things) is calculated by entering weight and other factors, as you put it, into either a computer program or by reference to a (thick) book which contains a page for every single runway on the network. If you're using the computer you enter the runway identifier and entry point, not the length into the "computer", if using the book you use the page appropriate to runway and entry point. In neither case do you as the pilot, actually enter the numeric runway length in feet or metres, since the "computer"/book has that inormation so it is a value most assuredly involved in determining the value of V1.

I suspect that is what your Big Aeroplane pilots were driving at ( at least I hope that was what they meant, otherwise )

No, our conversation was quite specific and 'runway length not a factor in V1' was the whole basis of our discussion. In fact it was one of these ex-BA captain chaps who came up with the Salt Flats scenario to illustrate that V1 can be meaningless in some circumstances (i.e. you may be OK to stop when really at any point after V1 you should fly. There's a judgement to be made if it happens).

[foxmoth]

Quote:
SSD
That point is that as runway length plays no part in calculating V1
Well it does, because if V1 occurs after TORA ? that is one reason why V1 is a variable.


No, runway length restricts MTOW and the TOW then determines V1. V1 cannot occur after TORA for that reason.:ugh:

[Shaggy Sheep Driver]

TORA I guess is Take Off Run Available. So how can anything 'occur after TORA'? :confused:

[TheiC]

It's worth remembering that,most of the time, there is a range (sometimes a very wide range) of possible values for V1, because the first moment at which continuing becomes possible occurs before the last moment at which stopping is an option. The manufacturer and/or operator chooses a value to be used operationally.

[john_tullamarine]

as runway length plays no part in calculating V1

Not quite the case and very misleading without some caveats.

As with most performance limit calculations, the pilot/operator has to ensure that a number of considerations is addressed with the result that one will become the limiting case for the particular set of circumstances - normally we are concerned with determining the maximum weight for the takeoff. Indeed, change the situation a bit and the limiting case may/will change.

In respect of runway length

(a) if the runway is longish compared to the particular aeroplane's needs, it may not become the limiting consideration for figuring a suitable V1. However, it will still be addressed as part of the process to determine the limiting factor as that process usually is addressed as sausage machine calculation.

(b) if the runway is shortish compared to the particular aeroplane's needs, runway length may, quite definitely, become a significant input into the determination of an appropriate V1.

[mad_jock]

It can be meaningless in the situation that your V1 is the same as your Vr ie the runway left is more than your breaking distance required from Vr speed.

Light TP's which are pref A often have V1/Vr being exactly the same speed. And basically if the runway is longer than 2000m they don't even bother giving you performance tables. You just go straight into your climb performance.

The best book to get your hands on is Aircraft Performance Theory for Pilots by Swatton.

http://www.amazon.co.uk/Aircraft-Performance-Theory-Pilots-Swatton/dp/0632055693/ref=sr_1_3?s=books&ie=UTF8&qid=1384721706&sr=1-3

Or he has a second addition out but its a bit pricey at 40 quid new.

You need to go through what all the different distances are and what they all mean. As well as what the different speeds relate to.

[Shaggy Sheep Driver]

Many thanks. At a tenner inc. postage I ordered a copy 'in 1st class condition' from Amazon.

As a SEP pilot it'll only be of academic interest, but so is this thread I started!

[mad_jock]

Mate you will be surprised what you will learn and make use of.

[foxmoth]

In respect of runway length

(a) if the runway is longish compared to the particular aeroplane's needs, it may not become the limiting consideration for figuring a suitable V1. However, it will still be addressed as part of the process to determine the limiting factor as that process usually is addressed as sausage machine calculation.

(b) if the runway is shortish compared to the particular aeroplane's needs, runway length may, quite definitely, become a significant input into the determination of an appropriate V1.

If the runway is short then it restricts MTOW -put simplistically the V1 is then the max speed that the aircraft can stop in the remaining length. If under MTOW restricted by RW length then you can have a range of V1. If runway length is such that MTOW is not limited by runway length then it becomes largely irrelevant as far as V speeds go.

[keith williams]

TORA I guess is Take Off Run Available. So how can anything 'occur after TORA'?


Taken at face value that question is rather worrying. It suggests that you have not heard of the terms STOPWAY or ASDA. If that is the case, you really will benefit from reading peter Swatton's book.

Assuming that you have a stopway available (and the take-off has been properly planned), there will be enough space to bring the aircraft to a halt after the end of the TORA.

[john_tullamarine]

put simplistically the V1 is then the max speed that the aircraft can stop in the remaining length

You might be putting the cart before the horse. The statement is fine if one is looking for max V1 and there are no other limits to prevent that being high enough to make the statement true. However that is not the only driver for V1 ..

If runway length is such that MTOW is not limited by runway length then it becomes largely irrelevant as far as V speeds go

.. providing that one still goes through the box ticking exercise to make sure that all the limitations are addressed ...

there will be enough space to bring the aircraft to a halt after the end of the TORA.

It may be the the earlier poster has a flawed understanding of TORA ? .. which includes a proportion of air distance after liftoff (either 1/3 or 1/2 the airborne distance to screen according to the particular rules which might be relevant).

[TheiC]

I fear TORA and TODA have been confused. I won't say who has confused them... TORA is for taking off, not for rejecting and stopping. That's ASDA's job.

Again, it strikes me that the minutes and hours spent in debate here might better be spent in careful study of the relevant requirements etc...

Swatton's book is looking like a good one for the Christmas stocking!

[john_tullamarine]

I fear TORA and TODA have been confused ... ASDA's job

Perhaps .. however, all three conspire to generate the selected V1 ...

[AirborneAgain]

The distinction between TORA and TODA is rather important also for single-engine ops...

[john_tullamarine]

You are, of course, quite correct from a logical position .. however, while TORR may be scheduled for light aircraft (eg FAR 23.59) it doesn't appear to be common practice.

[Shaggy Sheep Driver]

Taken at face value that question is rather worrying. It suggests that you have not heard of the terms STOPWAY or ASDA. If that is the case, you really will benefit from reading peter Swatton's book.


No, I think it suggests the statement that led to it was poorly worded. ;)

It should perhaps have said 'beyond TORA' rather than 'after TORA', the latter implying TORA is a speed rather than a distance. That's what got me confused (easy in this territory, which is not home country to a SEP pilot). :)

As said, Swatton's book on order. :ok:

[mad_jock]

If the new edition of Swatton was 10 quid I would be fighting to get the company to buy a personal copy for every pilot.

And if there was a fleet electronic option for it for the EFB I would get it for every aircraft. Better than reading the newspaper in the cruise.

[M-ONGO]

What's V1

Happiness out of Cairo.

[Flap40]

A couple of real world examples for you.

For my day job I fly a 45T 100 seat twin for an international airline. We have a laptop on the flightdeck to calculate takeoff and landing performance at our destinations and alternates. We enter the weather (wind/QNH/Temp), Weight and runway and it calculates the speeds, flap setting and engine derate.

If we assume a departure from Heathrow (ie long runway) there will be a considerable split between V1 and rotate, probably 15 - 20kts. If we then tell the computer that 1500m of the runway is closed at the far end the Vr, V2 and Vfs speeds will stay the same but the V1 will move much closer to the Vr.

As others have alluded to above there are effectively two V1 speeds which can be better explained by calling them V1go and V1stop. V1go is the lower of the two and is the lowest speed tat which the aircraft can still accelerate to Vr within the available runway after the failure of an engine. V1stop is the highest speed from which the aircraft can still be brought to a stop within the remaining runway.

History has proved in air transport that attempting to stop from high speed (usually considered to be above 80kts) is frequently more dangerous than taking the problem into the air hence performance programs erring toward the lowest possible V1. There is a very good article at http://flightsafety.org/ap/ap_sep90.pdf

The 748 at Stansted is not an example of stopping after v1 however as in this case they were already past Vr and airbourne when they decided to land. The report is at Air Accidents Investigation: 3/2001 G-OJEM (http://www.aaib.gov.uk/publications/formal_reports/3_2001_g_ojem.cfm)

[Lightning Mate]

As said, Swatton's book on order.

Good for you. I'm having lunch with him on Friday and I'll let him know.

I'm his illustrator and did all the performance diagrams for him (as well as the CAA CAPs).

[mad_jock]

LM can you ask him if there is any plans to have a company ebook type thing for electronic flight bags.

or just ebook full stop.

[Lightning Mate]

I know his publisher and as far as I know they only do normal scientific books.

[mad_jock]

Its a shame because most pilots now carry some form of ebook or tablet.

And the electronic flight bags all accept PDF or ebooks.

Lumping a book around isn't really practical or required these days. I certainly would have it on my kindle if it was available.

As its aimed at pilots it would be good to cater to how we as line pilots now operate.

[Lightning Mate]

That's not a decision for Peter - it's up to the publisher.

Bear in mind that it's primarily written for students of the ATPL syllabus.

I can 'phone him if you wish - he's only a few miles away.

[mad_jock]

not required a phone call, just put it into the mix.

Think they are missing sales because of it and to be honest it may be designed for that market but its price and content actually makes it more realistic for the line pilot reference market.

BTW I haven't seen the second addition but if you did the diagrams etc for the first, well done clear and to the point. :ok:

[Lightning Mate]

Yes - I did all the diagrams for the second edition as well.

We both used to teach this stuff.

[mad_jock]

Well I recommend all our FO's to get a copy and to be honest some of the Captains could be doing with reading it as well.

[Lightning Mate]

Try drawing all the graphs on a computer !!

When I did CAPs 696, 697, and 698 many answers to CAA questions had to be revised because the new graphs were accurate compared with the old ones. I still have all of them stored on my machine.

Those in Peters' book are accurate, but you would have to be a pilot to be able to draw them.

[mad_jock]

you did a good job :ok:

[Lightning Mate]

Cheers.

The CAA paid me for the CAPs, but I did Peters' books for no charge since he's a friend and ex-colleague.

[TheiC]

I know his publisher and as far as I know they only do normal scientific books.

I thought that Wiley did the Dummies guides etc - and a bit of googling shows they do. They're all available in e-versions.

...then from the front matter of Swatton's book: 'Wiley also publishes its books in a variety of electronic formats'.

Maybe there's hope? An e-version would be a great help, as others have pointed out.

Let's hope LM will report back with a positive spin after his lunch date.

[Barcli]

Wasnt Pete Swatton at PPSC years ago ?

[Lightning Mate]

Yes - we both were.

For anyone interested, Peters' performance book is not available in electronic format.

[ewillner]

I'm the publisher, and just to prove that we listen to you guys I'm setting up the eBook for this which should go live in the next couple of weeks! Kindle, iBooks etc.

Meantime, google 'aircraft v1 swatton' and the first link thrown up takes you to the relevant pages for the clearest explanation you'll find this side of a flying school.

[Jwscud]

Brilliant - thanks.

[mad_jock]

Thanks very much, can you post when it goes live please.

[Lightning Mate]

If ewillner doesn't come back, I'll probably be able to do that for you since I am in almost daily contact with Peter Swatton.

We just have to be careful that such posts do not constitute advertising.

[mad_jock]

Well that's true but then again its us that are asking for it.

I certainly don't have any contact or financial gain to be had out of him making it an ebook just glad that they have listened and are making it available so I can buy it.

If you two have a glass or two using the profits from my purchase that's fine by me. As I would more than likely buy you that anyway if I were to meet you.