question re v1 and v rotate on take off.

mickdw

Question for anyone in the know.
On takeoff, co pilot calls v1 and v rotate - my understanding being the v1 is the point at which they are committed to taking the plane into the air and v rotate obviously for rotation.
Im just wondering because surely there must be instances of where there would be more than adequate length to stop left on runway right up to the point of rotation so as such it should be possible to cancel takeoff right up to rotation point. I'm sure there is more to it than that so can someone explain?

LeftBase

mickdw wrote: »

Question for anyone in the know.
On takeoff, co pilot calls v1 and v rotate - my understanding being the v1 is the point at which they are committed to taking the plane into the air and v rotate obviously for rotation.
Im just wondering because surely there must be instances of where there would be more than adequate length to stop left on runway right up to the point of rotation so as such it should be possible to cancel takeoff right up to rotation point. I'm sure there is more to it than that so can someone explain?

Depends on the size of the aircraft. A small cessna will have no v1 as it will accelerate to Vr well before it would run out of stopping distance. A large passenger jet however will use so much runway to get to Vr that it is rare to find a runway that is long enough for V1 to not be a factor. Also getting close to Vr and then hitting the brakes will damage or overheat the brake pads and reduce their life. V1 will also consider the effects on the aircraft of stopping at high speed. In a case where Vr is less than V1 then V1 is brought down to meet it...if the engine hasn't failed by Vr/V1...we go into the air!

basill

Nope v1 is v1 which is the point where it is decided if we are stopping or not. Irrespective of how much tarmac is in front of you. These days there can be any number of v1s depending on how you calculate the figures and given that we try and reduce engine wear wherever possible to keep costs down. But whichever one we have chosen then we stop or go based on that figure.

Also the copilot doesn't always call the v1. In most airlines roles are shared during the day. Whilst the captain has the legal responsibility for the aircraft and the copilot is his 2nd in command we also have roles such as pilot flying and pilot not flying or pilot monitoring depending on the airlines lingo. The leg or legs if a multiple sector day will be split taking into account any number of factors. So the copilot could be doing everything flying related from pushback to taxi, take off, flying the departure, cruise, landing and taxi in. In that scenario the captain as pilot not flying would be calling the v1. As to who actually stops the the aircraft in the case of a rejected takeoff depends on each individual airlines policies. Mostly it's the left seat - captain that makes the call and takes control but not everywhere.

mickdw

So if v1is set taking account of stuff like worries over overheating brakes etc, that would mean that an aircraft with a catastrophic failure could be taken into the air even where it could have been brought to a halt on the ground.

LeftBase

mickdw wrote: »

So if v1is set taking account of stuff like worries over overheating brakes etc, that would mean that an aircraft with a catastrophic failure could be taken into the air even where it could have been brought to a halt on the ground.

Once you get to Vr the nose goes up and you lift off. If the issue was noticed and assuming that Vr/V1 are the same speed then the aircraft would be taken into the air. Remember V1 is the speed that you will go at...the failure must be recognised before V1. If the failure was recognised before Vr/V1 in this case you would abort take off. However if the V speed was deemed by the performance data to be too high for the brakes and/or tires/engines then V1 would be lowered to a sufficiently low speed.

Remember that "Catastrophic" implies in most cases you are in big trouble no matter what you do.

Stovepipe

well, there was a famous case of a 748 that suffered a catastrophic failure of an engine on take-off, just at rotation.Technically,legally, the guy could have continued to fly, done a circuit and landed back on.Instead, the skipper elected to chop the power and land ahead, which was the right decision as the failed engine disintegrated and would have brought down the aircraft.He was lucky in that he had loads of room left to land.Look it up.

regards
Stovepipe

basill

And then there was the Kalitta 747 that decided to stop after V1 in Brussels a few years back with its forward motion being arrested by a train embankment. It closed the airport, broke the the aircraft in two totalling the airframe. Fortunately no passengers participated in this feat of airmanship as it was a cargo operation and by pure luck they all walked away. No doubt the party involved in the decision to stop is flying somewhere in outer sh*teville.

smurfjed

Also getting close to Vr and then hitting the brakes will damage or overheat the brake pads and reduce their life.

The calculation of V1 doesnt care about the lifespan of the brakes, the V1 speed is compared to the brake energy speed, VMBE, this is the maximum speed where the brakes can absorb the energy involved in stopping, that doesnt mean that they wont go on fire (http://www.youtube.com/watch?v=f4LFErD-yls) and their fuse plugs will most certainly melt to allow the tires deflate rather than explode.

V1 used to be a decision speed, the critical engine was assumed to have failed 1 second prior to V1 (VEF), the crew reacted and the times required for the aircraft to transition to a stopping configuration were assessed, various increases were added to this depending on when the aircraft was certified. Now it is considered an action speed, so the "actions" to commence the stopping were commenced at V1 rather than the "decision".

There is a minimum V1 speed where it is assumed that that the aircraft can continue the takeoff after the engine failure, and maximum V1 speed where the aircraft can stop. There is also Balanced field where both the stop distance and go distance are the same, this is the usual speed calculated by most FMS computers.

To answer your original question, yes it is possible to reject the takeoff right up to VR, and you will see this on long runways when using a Maximum V1 policy.

Basill, the classic 747 was certified with good brakes and tires with no line up allowance., following a series of flight simulator tests, i would doubt that the aircraft will remain on the runway following a V1 abort at a takeoff weight limited by the runway length.

smurfjed

knucklehead6

Stovepipe wrote: »

well, there was a famous case of a 748 that suffered a catastrophic failure of an engine on take-off, just at rotation.Technically,legally, the guy could have continued to fly, done a circuit and landed back on.Instead, the skipper elected to chop the power and land ahead, which was the right decision as the failed engine disintegrated and would have brought down the aircraft.He was lucky in that he had loads of room left to land.Look it up.

regards
Stovepipe

any chance you could give us a hint??? Airline? Location?

smurfjed

@knucklehead6

http://aviation-safety.net/database/record.php?id=19980330-1

smurfjed

NewSigGuy

LeftBase wrote: »

Depends on the size of the aircraft. A small cessna will have no v1 as it will accelerate to Vr well before it would run out of stopping distance. A large passenger jet however will use so much runway to get to Vr that it is rare to find a runway that is long enough for V1 to not be a factor. Also getting close to Vr and then hitting the brakes will damage or overheat the brake pads and reduce their life. V1 will also consider the effects on the aircraft of stopping at high speed. In a case where Vr is less than V1 then V1 is brought down to meet it...if the engine hasn't failed by Vr/V1...we go into the air!

Single engine aircraft do not have a V1. It only applies to multi-engine aircraft, the assumption is that with the failure of the critical engine at this speed the aircraft can climb away at the required climb gradient, below the speed the aircraft will stop in the remaining runway available. The brakes are only a consideration from the point of their stopping ability, in fact in most large transport category aircraft a rejected Takeoff at MTOW will lead to burned out brakes and deflated tires, they are also designed to deflate rather then explode in these cases.

V1 is interesting because it normally sits in a range which is calculated from a number of speeds, including Vmcg(minimum control speed on the ground) and Vcef(Critical engine failure speed) Vmbe(maximum brake energy speed) etc.

The assumption is also that when One Engine fails the aircraft can climb away on the remaining engine(s), hence Twins are typically over powered(as they will loose at least 50% of the performance) whereas three and four engined aircraft will only loose 25-33% of the performance and therefore appear underpowered.

LeftBase

NewSigGuy wrote: »

Twins are typically over powered(as they will loose at least 50% of the performance) whereas three and four engined aircraft will only loose 25-33% of the performance and therefore appear underpowered.

Does this not bring up that question MEIR examiners always ask about how much performance we loose when we loose an engine? Example being cruising with both engines at 70% of full power.You have 30% performance to play with. If an engine fails you loose half that cruise power and all the excess power and now need full power on the remaining engine to stay level. At 100% performance now you are just about staying level. Typically a light twin will loose 80% of it's performance when an engine fails when you take into account the fact the failed engine is now giving only drag with no thrust at all(even if a prop is feathered).

NewSigGuy

LeftBase wrote: »

Does this not bring up that question MEIR examiners always ask about how much performance we loose when we loose an engine? Example being cruising with both engines at 70% of full power.You have 30% performance to play with. If an engine fails you loose half that cruise power and all the excess power and now need full power on the remaining engine to stay level. At 100% performance now you are just about staying level. Typically a light twin will loose 80% of it's performance when an engine fails when you take into account the fact the failed engine is now giving only drag with no thrust at all(even if a prop is feathered).

Yes all valid for a light twin..
But they are not certified to JAR 25 as per transport category aircraft and therefore do not have to be able to carry out a departure after the loss of a critical engine, they do not have a V1 speed etc.. they are certified to totally different specs (CAR 3 IIRC) and there minimum requirement is to maintain level flight at a set altitude with the loss of the critical engine, under FAR they have a blue line speed which is similar to V2, that is the OEI(one engine inoperative) safety speed, but they would not have to demonstrate a climb at a specified gradient at that speed in the OEI situation. And yes in a JAR 25 Twin aircraft the loss of one engine is a loss of performance of more then 50% due to drag etc, hence they have a larger excess of power relative to three and four engined aircraft.

LeftBase

NewSigGuy wrote: »

Yes all valid for a light twin..
But they are not certified to JAR 25 as per transport category aircraft and therefore do not have to be able to carry out a departure after the loss of a critical engine, they do not have a V1 speed etc.. they are certified to totally different specs (CAR 3 IIRC) and there minimum requirement is to maintain level flight at a set altitude with the loss of the critical engine, under FAR they have a blue line speed which is similar to V2, that is the OEI(one engine inoperative) safety speed, but they would not have to demonstrate a climb at a specified gradient at that speed in the OEI situation. And yes in a JAR 25 Twin aircraft the loss of one engine is a loss of performance of more then 50% due to drag etc, hence they have a larger excess of power relative to three and four engined aircraft.

That would depend largely on the length or runway they are departing off. Light Twin performance data gives an ASD graph and an AGD graph and it is up to the pilot to know if has the length of runway to stop or go. My point comes more from the pilot point of view(making the correct decision to save your life) and not the certification.

I agree with and do not dispute your points on Transport Category aircraft however when I did my MEIR in a light twin we did have a V1 speed above which it was a very slow cheek clenching climb or a face full of shrubbery. That may have been just to put the concept in my mind for later commercial ops on Transport Aircraft but it did apply in reality.

mickdw

This is all quite interesting but I guess my main point is that surely one would think that V1 would in all cases be the absolute limit point, after which the aircraft can no longer be stopped. It appears from this thread that there are many more issues considered in deciding V1.
If for example, the aircraft suffers a failure that will mean a certain crash if taken into the air, it would be rather unfortunate to take it into the air if an emergency stop was possible irrespective of damage to brakes etc.
I don't know enough on this topic to go into any detail on this but it doesn't appear to be a perfect system / procedure.

smurfjed

emergency stop was possible irrespective of damage to brakes etc.

In an Emergency Stop we expect the brakes and tires to be destroyed, we do not give a hoot about their lifespan, Leftbase gave you a bum steer on this.

The only concern regarding brakes is that they can provide a retarding force whilst absorbing the energy of the emergency stop, this is calculated prior to takeoff and is called VMBE, remembering that the brakes were designed for the aircraft, so its very unusual for them to be a limiting factor on modern aircraft.

smurfjed

smurfjed

I can find lots of events following high speed RTO's or in the case of the TWA L1011, rejecting after rotation, but the HS-748 is the only occasion that i know where continued flight would have meant certain death.

http://www.airdisaster.com/reports/ntsb/AAR93-04.pdf

On July 30, 1992, at 1741 eastern daylight time, Trans World Airlines
scheduled passenger flight 843, an L-1011, N11002, experienced an aborted takeoff
shortiy after liftoff fmm John F. Kennedy International Airport, Jamaica, New Yo&,
en route to San Francisco International Airport, California. The airplane came to
rest, upright and cn fire, on grass-covered soil, about 290feet to the left of the
depamre end of runway 13R. There were no fatalities among the 280 passengers
on board the aipkme, but there were 10 reported injuries that occurred during
egress.

http://www.ntsb.gov/doclib/reports/2010/AAR1002.pdf

The National Transportation Safety Board determines that the probable cause of this accident was the operator’s inadequate maintenance of the airplane’s tires, which resulted in multiple tire failures during takeoff roll due to severe underinflation, and the captain’s execution of a rejected takeoff (RTO) after V1, which was inconsistent with her training and standard operating procedures.

smurfjed

however when I did my MEIR in a light twin we did have a V1 speed above which it was a very slow cheek clenching climb or a face full of shrubbery

Did you ever try an engine failure at the fictitious V1??

smurfjed

NewSigGuy

LeftBase wrote: »

That would depend largely on the length or runway they are departing off. Light Twin performance data gives an ASD graph and an AGD graph and it is up to the pilot to know if has the length of runway to stop or go. My point comes more from the pilot point of view(making the correct decision to save your life) and not the certification.

I agree with and do not dispute your points on Transport Category aircraft however when I did my MEIR in a light twin we did have a V1 speed above which it was a very slow cheek clenching climb or a face full of shrubbery. That may have been just to put the concept in my mind for later commercial ops on Transport Aircraft but it did apply in reality.

So in a light Twin you decide a decision speed but it is different, because in the case of an engine failure above your decision speed you may not be able to climb away, in the case of a JAR 25 aircraft you will cross the the fence at the far and at least 35ft above the threshold height for a dry runway and 15ft for a wet runway..

To answer the original question, V1 is decided from a range, most operators performance dept will use a speed at the lower end of the range in order to be go minded. In reality in modern aircraft it is safer to take the problem into the air and return, rather, then try and stop. I cannot think of any failures where it would be safer to stop and run off the end at high speed instead of getting airborne, performance calculations cannot take into account every possible situation and the possibility of some are so remote that they are disregarded from a performance stand point.
So in essence V1 is the decision speed above which the safer course of action is to get airborne. From an operators Legal and training point of view this is the case.

Stovepipe

Hi all,
the 748 accident happened in the UK, possibly Stansted and was an aircraft of Emerald Airways (?)and a football team was on board. I can't do the linky thing so you'll have to find it yourselves........when the late Gordon Baxter, who wrote for "Flying" in the US was doing his ME rating, he took off in an early Piper Apache and the FAA examiner "failed" an engine. Baxter cleaned it up, got to 30 feet or so and it wouldn't go any higher in the Texan heat. When the examiner realised that it wouldn't climb and any attempt to turn lost height, he asked Baxter what he was going to do now. Baxter said "I'm gonna stay on this heading until we burn off fuel or hit a two-storey house!". When the FAA man stopped laughing, he gave Bax a pass.

regards
Stovepipe

NewSigGuy

Stovepipe wrote: »

Hi all,
the 748 accident happened in the UK, possibly Stansted and was an aircraft of Emerald Airways (?)and a football team was on board. I can't do the linky thing so you'll have to find it yourselves........when the late Gordon Baxter, who wrote for "Flying" in the US was doing his ME rating, he took off in an early Piper Apache and the FAA examiner "failed" an engine. Baxter cleaned it up, got to 30 feet or so and it wouldn't go any higher in the Texan heat. When the examiner realised that it wouldn't climb and any attempt to turn lost height, he asked Baxter what he was going to do now. Baxter said "I'm gonna stay on this heading until we burn off fuel or hit a two-storey house!". When the FAA man stopped laughing, he gave Bax a pass.

regards
Stovepipe

My view of light twins is that the "second engine gets you to the scene of the accident"..

peter1892

The HS748 incident was indeed at Stansted, the aircraft was carrying the Leeds United team of the time (1998).

The captain wrote an interesting article in an issue of 'Pilot' a couple of years later detailing the event (can't find a link, sorry), but what I do remember about it was his description of using the full length of the runway rather than taking off from an intersection and how that gave them enough room to land again once the engine failure occurred.

LeftBase

smurfjed wrote: »

Did you ever try an engine failure at the fictitious V1??

smurfjed

Once yes.....I was warned beforehand though...although I suppose you should always expect the worst

smurfjed

Once yes..

V1 stop ? Or just after V1 go? What type of aircraft?

smurfjed

Growler!!!

Are you confusing V1 speed with blue line speed? Was v1 taken from the flight manual performance tables?
If you lose an engine on a piston twin how do you accelerate to Blue line speed?

smurfjed

Was v1 taken from the flight manual performance tables?

If it was, then it was a first as under FAR23 an engine failure is not considered during the takeoff to 50 feet.

smurfjed

Just saw this on TV, so found YouTube copy.....