V1 Question

[south coast]

I understand the whole 'GO' theory about V1, but what are your opinions on this...

If on a turbo-prop, say medium category, (because I have never flown anything else to comment on) you have a cabin door or cargo door light come on at V1, and there is enough runway for you to abort your take off and safely stop, would you reject the take off, or continue?

[ifleeplanes]

I thought the whole point of V1 was that you didnt have enough runway to stop if beyond it. Continue at V1

[Mad (Flt) Scientist]

V1+n doesn't mean you don't have enough runway to stop; all you can say is that at V1-n, you do have enough runway to stop.

Similarly, V1-n doesn't mean that you can't continue the takeoff; but V1+n tells you that you can.

Only if you are on a truly balanced field - where the accel-go and accel-stop cases are balanced AND equal to the available surface(s) - is the V1 decision balanced on a knife-edge.

Procedurally it's much simpler, and safer, to have a single decision point. But in reality you have a "minimum V1" and a "maximum V1" for a given set of conditions. Above the minimum, a takeoff could be safely continued; below the maximum, you can safely stop. So if V1min<V<V1max, you can choose whether to stop or go.

The actual scheduled V1 will lie within the V1min-V1max range; if you know what your actual range of allowable V1 is, you can at least theoretically consider whether a given condition should lead to an abort or not....

[London Jets]

I always thought that V1 was the point of no return and V2 is when you rotate.

What is V1+n ?

L J

[Mad (Flt) Scientist]

V1 is indeed the decision speed, below which you will decide to abort and above which decide to continue. The important thing is that it's a decision criteria, not necessarily a limiting condition.

Vr is rotation speed. V2 is "takeoff safety speed".

By V1+n I was just being lazy - "V1 plus n knots" is what I meant. Apologies.

[Old Smokey]

south coast,

As Mad (Flt) Scientist has pointed out so well, you may have enough runway left for the "V1 of the day", and then again you may not, it depends upon whether you were Accelerate-Stop limited or not.

In the end, for the scenario that you describe, it comes down to a judgement call of whether or not the aircraft is capable of flight. If it is capable of flight, then GO! I've seen many newsreel footages of aircraft returning with doors / hatches wide open (e.g. a F28 with the forward airstairs fully down) for a fully controllable safe landing. If, on the other hand you assess that continued flight is impossible or very 'dicky' (e.g. a control jam), you now must assess the relative dangers of an overrun in a rejected takeoff, or a parlous in-flight problem.

Regards,

Old Smokey

[Jetdriver]

In fact V1 isn't a "decision speed" it is an accelerate stop distance speed. So if the initial steps to reject the takeoff have not been taken by V1 the aircraft may well overrun the available runway.

As V1 approaches the decision to reject the take off would only be taken for a serious performance related issue, such as an evident engine failure or a serious flying control malfunction. Other parameters might be included in the take off brief but it is very unlikely that a door or cargo hatch warning would elicit such a response. Far better to return to land and sort that issue out, than reject at high speed with all the likely consequences of such an action.

[charterdriver]

So if you elect to continue before V1 or abort after V1 and something goes awry, are you liable???

[safetypee]

The industry defines V1 as the ‘Decision Speed’ (JAR/FAR 25.107), although it assumes that the decision to stop has been taken.
V1 has to be higher than the Engine Failure Speed, Vef (a certification term), the difference between Vef and V1 includes a recognition and reaction time factor. Thus V1 is the speed at which the pilot has taken at the decision to stop and is ready to, and/or is commencing the first actions to stop the aircraft.

Note the statistics from the Propulsion System Malfunction & Inappropriate Crew Response (PSM+ICR) report for turbo fan aircraft (data from 1959-96). There were 30 events involving RTOs at or above V1, 16 resulted in accidents, 10 hull loss, of which 6 were fatal. Many good reasons for being ‘Go Minded’.

charterdriver, the industry strives to be blame free, thus if the crew ‘do the right thing’ in the circumstances they should not be liable. Many of the problems identified in the PSM+ICR report had their roots in training, experience, and human factors; crews should not be blamed for any errors resulting from these issues. Unfortunately in our current litigious society this makes flight safety training and safe operations that much more difficult.

[hercboy]

V1 and V2 are just speeds. it dosent mean that u have enough runway left to abort the take off, what happens if i got a runway thats 2000 ft and a nother runway thats 3000ft your V1 and V2 would be different.

[charterdriver]

You would surely already have gone into the ASDA graphs / tables in which case there would have to be enough runway to stop at V1???

[safetypee]

charterdriver, if your question “there would have to be enough runway to stop at V1???” relates to my comment on the PSM+ICR report that some aircraft did not stop from an RTO initiated at V1, then you may conclude that either the calculation of V1 was incorrect, the safety margins involved with V1 are marginal, and/or the crew employed an ‘inappropriate response’ i.e. did not follow the required procedures. Unless we can determine the reasons for the first or last alternatives, you cannot apportion blame; the industry has to seek the reasons why the crew behaved as they did – CRM, Human Factors?
Thus just because a pilot has decided to stop doesn’t necessarily mean that the aircraft will stop in the distance remaining; that requires additional and correct action. So in practical terms when defining V speeds, there is a need to explain all of the associated activities and assumptions.

[ifleeplanes]

By definition there will be at least enough runway to stop if the decision to stop has been made by V1. After V1 there may be but the chance are there isnt.

You dont have time to decide therefore V1 is a go case. Dont even think about it!

[Piltdown Man]

Fortunately, most aircraft are equipped with an alerting system that ignores minor failures when in excess of 80kts or so (the ones that get through are typically engine fire, failure or AFCAS - or whatever your aircraft calls it). Therefore, most of us stop for any alert below V1. Above V1, you stop at your own peril as we are now in uncharted territory - therefore this is only done "in extremis" such as control failure.

Liability doesn't enter into this - just do as you have been programmed (some might even call it training!). Trying to work out in split seconds whether you have enough runway to stop at a speed in excess of V1 will only end in tears.

Going back to the original question, if this happened at a low speed, yes I would stop, because I would get a warning and at a high speed I wouldn't, because there would be no warning. I don't let runway lengths change decisions, only the speeds if allowed by the performance tables.

Clear as mud?

[jarops]

It's confusing to say; Decision Speed. V1 is nothing like that. You can make the decision to stop anywhere between the start of takeoff run and V1. But, how about this; V1 is the maximum speed where the pilot must make the first action to stop the airplane on the remaining runway. :O

[hoggsnortrupert]

V1: That speed at which the pilot can with the critical engine inoperative, An average pilot using normal control inputs can keep control of the A/C,and can decide to safely continue the take off, or safely stop the take off.

Where all this gets jumbled is when we assign V1 a speed, and in some cases where you are limited due to weight and temperature, available runway etc etc, you may need to alter things accordingly.

Ref I think from Pan's Ops 1.

There are some abnomalies with this in the sense of cross wind, VS's critical engine, and the amount of usable rudder you have in a significant cross wind.

In some cases the critical engine will be assessed due to wind direction and strength.

Remember it does indeed help quite significantly if one keeps all there potential debris "on the centerline". :ok:

[Flyer 719]

Does the length of the runway affect V1 descision?

for example, if you had a BAe146 taking off from London City (rwy 28 - 4948ft) and it takes off in plenty of space where (on an average flight) would the V1 point be?

With that in mind, would there be a V1 point on the same scenario if the aircraft was taking off from Heathrow (rwy 27R - 12,802ft) a runway more than double the distance so one would assume plenty of stopping distance?

I hope I have not made it sound too confusing.

719

[Mad (Flt) Scientist]

On a longer runway you can clearly stop from a higher speed; therefore you could schedule a higher V1 on a longer runway and still respect the stopping distance limitation.

The normal practice would be to select a different V1 to account for changing limits, not to allow yourself more leeway in 'going against' the V1 stop/go criteria in those circumstances.

[Old Smokey]

Flyer 719,
Does the length of the runway affect V1 descision?
Up to a point, YES, and after that point, NO.

Any Takeoff is limited to the least of Accelerate-Stop Limit, Brake Energy limit, Takeoff Distance Limit, WAT Limit, and Obstacle Clearance Limit. With all else being equal, Takeoff on a very short runway will be Accelerate-Stop limited (and/or Accelerate-Go limited if using a balanced field technique). The V1 in this case obviously is governed by Accelerate-Stop, whilst WAT and Obstacle limits are not a problem.

Now, progressively increase the runway length, Accelerate-Stop limit increases, whilst Obstacle limited weight decreases due to increased gradient required because of a shorter distance to the obstacle. Continue this runway lengthening process process up to the point where Accelerate-Stop limit equals the Obstacle limit, and the takeoff weight has been optimised. Up to this point, any rejected takeoff must be accomplished prior to V1. Any further increase in runway length is a bonus, if we used it, Accelerate-Stop limit will certainly increase, but the Obstacle limit will decrease, so, we don't use any more runway in our calculations than that necessary for Accelerate-Stop (or Balanced Field).

Thus, if we have 'excess' runway available, the aircraft could be stopped from a speed above V1, but such action is EXTREMELY inadvisable, except in a DIRE emergency.

Engine failures, tyre failures, doors opening etc. are not dire emergencies, and the mathematics of the situation allied with statistics, strongly advocate GO as the only option. If, on the other hand, the aircraft is judged as INCAPABLE OF FLIGHT, as would occur with a complete control jam, or control failure, then a STOP from a speed above V1 may be the only option, accepting that an over-run at 40 to 50 knots is infinitely preferrable to an uncontrolled ground impact from in-flight.

I speak from experience, it HAS happened to me. Fortunately, on the day, the aircraft required 2000 M of runway, but had 3500 M available. The aircraft was later proven to be incapable of controlled flight, if I had managed to somehow get it airborne, I would not be here now to make this assault on your senses.

Fly Safe, think outside the box,

Old Smokey

[safetypee]

Flyer 719, earlier in this thread Jetdriver noted that V1 is not a distance but a speed. Thus in your example at LCY, apart for the 146/RJ having a choice of 3 (some aircraft 4) configurations for take off, all with different speeds, the V1 speed can still be adjusted for wet / dry runway surfaces for all other unchanged conditions.

In non-limiting operations in the 146/RJ, (V1=Vr) we were taught to use a 10 kt split V1 … Vr; this reminded us that there are differences between wet and dry operations. On the other hand in the 146 the bugs had to be a split as they could not be overlaid on the same value, this also sequenced the crew calls of V1, and Rotate.

Most 146/RJ operations were ‘turboprop’ like; thus relating to the original question, the 146/RJ SOP was to abort for ‘anything’ up to 80 kts and after which only engine failure or fire. The RJ incorporated MWS inhibits using this logic, thus above 80kts the crew will only here the fire bell. ‘Anything’ was generally defined as double system failure or any aspect of similar consequence; a dual system failure after 80 kts is still safe for flight.

In recent years industry RTO training focussed on the problems of ‘what if the aircraft could not fly’? This stemmed in part, from several well published aborts beyond V1 where the crew perceived an engine failure as a bomb; note no such bomb events have been recorded and the probability of such an event occurring at or about V1 should be dismissed as extremely remote. The other aspect was the concern of control, but as has been seen in many accidents the problems appear to be due to something other than a control block. If the aircraft rotates it should fly (sooner or later); if it does not rotate then it is most unlikely to fly. Safety is ensured from correctly executed pre flight checks and good maintenance to ensure the serviceability of the split controls design certification criteria; if so then a control jam at or about V1 is another very remote event that crews should not burden them selves with. My advice to south coast is to concentrate on the simple aspects of an engine/system failure – the Go / No Go boundaries and follow well practiced procedures for continued take off.

[Rwy in Sight]

I don't want to hijack the thread but what happens if the significant problem (fire, engine explosion, ...... fill the blank) that requires a stop decision appears at a Knot or two before V1 and by the time it appears and it is time to react, the speed is above V1. Do you stop?

In other words is V1 a speed of abort a) when the problem appears b) the speed at which the rejection may start or c) or both.

If it is 2 complicated please either ignore it or make it clearer and answer it.

Thanks anyway

Rwy in Sight

[Old Smokey]

Rwy in Sight,

In the scenario that you describe you go. You speak of 1 or 2 knots before V1, yet the current certification rules allow for Vef 2 seconds before V1, such that recognition of the problem and initiation of the rejected takeoff are executed by no later than V1. Without knowing the acceleration characteristics of your aircraft, I would think that 1 or 2 knots was well within that 2 seconds.

In hindsight, I regret my narration just 2 posts ago where I spoke of a reject which I was forced to carry out above V1 when the aircraft was absolutely unflyable. The story was absolutely true, and the aircraft was proven to be absolutely unflyable with a multiple control jam occuring during the takeoff roll. My regret arises from the fact that the chances were so far out of left field, literally one in millions, that it was a "one off" that would probably occur once every couple of decades, and may have added some weight to those who believe that an RTO above V1 may be acceptable in less than DIRE circumstances. A TOTALLY unflyable aircraft is the only justification for RTO > V1. My incident was some decades ago before multi-channel control redundancy became a reality. These days, the same problem would only justify a GO decision.

Regards,

Old Smokey

[Flyer 719]

Many thanks for your replies, it has given me plenty to digest and has cleared up some of the confusion I had.

I was using the 146 as an example as I knew that using a 747 taking off from LCY would not work but I guess the answer to my thread wouldn't change whatever aircraft it was.

719

[AirRabbit]

Hi Folks -- I hope you don't mind my jumping in here -- and please excuse the length of the post, but its necessary to get all the relative information straight....

Vmcg. (Minimum control speed on the ground): The minimum speed at which an aircraft is defined to be “controllable” (lateral excursion less than 30 feet) with aerodynamic controls only after an engine failure on the ground.

Vef – (Engine failure speed): the speed that the critical engine is assumed to fail. It may not be less than Vmcg.

V1 (often referred to as “Decision Speed”): Must not be less than Vef plus the speed gained between when the engine failed and the pilot recognized the failure. This means that this speed is the minimum speed at which an engine failure may occur and the pilot may continue the takeoff. At the same time, V1 speed must not be greater than the speed at which a rejected takeoff can be initiated and stop the airplane within the calculated accelerate-stop distance.

Vmu (Minimum unstick speed): Minimum airspeed at which airplane can safely lift off ground and continue take-off. Because of the way this speed is determined, lift-off is not possible prior to reaching this speed.

Vr (Rotation speed): Must be greater than V1 and greater than 1.05 Vmca and may not be less than the speed that would allow reaching V2 before reaching a height of 35 feet above the takeoff surface. This speed is selected so that the rotation begins at Vr and provides that Vlo occurs at a speed greater than VMU The rotation is continued at approximately 3 degrees per second until reaching the desired pitch attitude.

Vlo (Lift-off speed): Must be greater than 1.1 Vmu with all engines, or 1.05 Vmu with engine out.

Vmca (Minimum control speed in the air): Minimum airspeed at which, when the critical engine is made inoperative, it is still possible to maintain control of the airplane and maintain straight flight. [The rudder is used to compensate for the yaw moment caused by thrust asymmetry. There is a minimum speed at which full rudder will be necessary, in order to fly a constant heading with level wings. To reduce sideslip, this speed can be reduced even more, if the aircraft is banked on the live engine’s side. The lower the speed, the greater the necessary bank angle. The speed that corresponds to a 5-degree bank angle is defined as Vmca.]

V2min (Minimum fake-off safety speed): Must be greater than 1.1 Vmca and 1.2 Vs, the stalling speed in the take-off configuration.

V2 (Take-off safety speed): May not be less than V2min and may not be less than Vr plus the speed gained before reaching a height of 35 feet above the takeoff surface. [If one engine is lost before reaching V2, then the initial climb is flown at V2. If thrust is lost at a speed between V2 and V2+10, then the current speed is maintained, to ensure the most efficient climb speed. It is not necessary to increase pitch, in order to reduce the speed to V2, when a higher speed has already been reached.]

I think when you read through these definitions, you can see that V1 speed is selectable and may represent several different factors, depending on the airplane and the runway. For example, a very light airplane on a very long runway might combine to allow you to have a relatively low Vef – where you could experience an engine failure (as long as this speed is not less than Vmcg) and have enough runway to continue to accelerate with the remaining engine(s) and make a safe takeoff. At the same time, you might be able to accelerate to a relatively high Vef – where you could experience an engine failure, and have enough runway to bring the airplane to a safe stop within the confines of that runway. Here you would have two “selections” of V1, with different points along the runway and different values for the term. As the gross weight of the airplane increases, the first case V1 grows higher. As the runway length lessens, the second case V1 grows smaller. Eventually getting to the highly interesting "balanced field" runway, where the V1 speeds for the two cases should be the same.

AirRabbit