V1 or V1 minus 5kt callout?

[start sequence 312]

Does any airline use V1 minus 5kt speed to callout V1 instead of calculated V1?

[Wino]

That would be dangerous.
V1 is a combination of things including accelerate stop (including a 2 second reaction time as I recall) and accelerate GO (continue flying and meet climb profile)

If you call v1 early you will stop, but you might not GO if you had an engine problem or something else that degraded your acceleration/climb performance after v1. Or you could inadvertently reduce your V1 below vmcg which is quite possible to do at low weights with wing mounted engines leading to a departure from the runway or even a vmca roll into the ground immediately after liftoff as the DC-8 did in tulsa about 6 years back.

People that arbitrarily do things like that don't always know what they are doing and may not have the performance to carry out said plan.

Now you could change your data to include accelerate go from the 5 knots slower and such is done in performance problems like clutter but as you see it involves a big weight hit.

Cheers
Wino

[411A]

312,

SriLankan used the term "minus 5" instead of a V1 call (to be called at V1 minus 5), on the TriStar aircraft. As all of their training was predicated on Air Canada procedures, would expect that it originated there.

So far as i'm concerned, not a bad idea. Recall one day departing from FUK rny34, max weight flaps 22 (short runway) the F/O (PF)mentioned that if we aborted at V1, we would be in the bay...and he was right!

I would always prefer "accelerate-go" rather than "accelerate-stop". FAR to many accidents have occured with a high energy stop.

[wonderbusdriver]

Calculations are based on the RTO being initiated at (!!) V1 not 1 knot later...

We say "Go!" at V1-3kias, figuring that the aircraft will be at V1 until the other guy has "processed" the info.
We used to say "V1".

This is standard in DLH, LHCargo, Condor.

[Captain Airclues]

If you are taking-off on a dry runway and you are concerned about the overrun then just use the 'wet' V1 which is usually several knots slower. Thus you have more chance of stopping on the paved surface in the case of a rejected take-off, while still having adequate performance in the case of a continued take-off.

Airclues

[Localiser Green]

wonderbusdriver,

Actually Wino is right here. Under JAR-OPS the V1 calculation allows a 2 second "thinking time" after V1 is reached before any means of retardation is applied.

The official JAR-OPS statement (relating to the calculation of V1) is:

"the sum of the distances to:

a) accelerate the aircraft to v1

b) after reaching v1, continue the acceleration for 2 seconds with all engines operating

c) at the end of the acceleration in (b) above, decelerate the aircraft to a stop, assuming no means of retardation is applied until the end of (b).

shall not exceed the accelerate-stop distance available"

Wino also correctly suggests that, in an engine failure scenario on a limiting runway, if you decide to "GO" far enough below V1, you might not make it off the ground at all.

[411A]

Capt'n Airclues is right on target.
Have reduced the dry runway V1 to "wet conditions" many times...it only results in a lower screen height. Better that sliding off the end with...big time trouble.

[Captain Airclues]

The screen heights to which 411A refers are 35ft for a 'dry' V1 and 15ft for a 'wet' V1. Therefore continuing from below the 'wet' V1 could become very noisy.

Airclues

[Fat Boy Sim]

You are quite correct about the acceleration after V1, but it is only used in the calculation for V1. As a matter of interest I am led to believe that one of the reasons the Airbus A321 has better performance than the 320, is because in that calculation the 321 is only considered to continue the acceleration at the single engine rate. not at the two engined rate for the 320.

However, both JAR and the FAA have redefined V1 as follows;

'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 aircraft within the accelerate- stop distance.' source: Flight Safety Digest, October 1998.

Which means that the decision to stop must be made before V1 to enable the first action action to be taken at V1.

Next time you are in the sim try it out. If the sim replicates your aircraft exactly (especially the engines)and it has an exact airfield model. Set up for still air, 15c, 1013hp and dry runway. find a weight from the charts and enter into the sim model.Do the drill so as the thrust levers start to close at V1 and you should stop with about 150 metres to spare if reverse is used. (reverse not included in calc for dry runway). Then do the same thing without reverse and bingo! you will find that the cockpit will be hanging over the end of the runway. If you do the same thing, but this time decide at V1 you will scoot off the end of the runway at around 50kts.

I now it's a computer game, but you will get the jist of it.

[john_tullamarine]

Be aware that the 2 second pad is a post FAR25 A/L 42 (if my memory serves me correctly) thing and that many older aircraft may not consider it in their flight manuals.

[doubleu-anker]

One problem to concider with reducing the V1 to "any great extent."

If you decide to go at the reduced V1 are you going to accelerate and be airbourne in the R/W distance remaining in the case of an engine failure?

I would rather run off the end of a R/W with idle power and low speed than be off the end at high speed and full power.

[PifPaf]

That would be dangerous.
V1 is a combination of things including accelerate stop (including a 2 second reaction time as I recall) and accelerate GO (continue flying and meet climb profile)

If you call v1 early you will stop, but you might not GO if you had an engine problem or something else that degraded your acceleration/climb performance after v1. Or you could inadvertently reduce your V1 below vmcg which is quite possible to do at low weights with wing mounted engines leading to a departure from the runway or even a vmca roll into the ground immediately after liftoff as the DC-8 did in tulsa about 6 years back.

People that arbitrarily do things like that don't always know what they are doing and may not have the performance to carry out said plan.

Now you could change your data to include accelerate go from the 5 knots slower and such is done in performance problems like clutter but as you see it involves a big weight hit.

Cheers
Wino

That would be dangerous.

Hi Wino and other friends!
Please let me differ a little bit from your opinion.
From the beggining of your message, I understood that you've said V1 computes a delay (2sec, for instance). I think this is not true.
From FAR definitions, we see that V1 is the speed at which the first braking action must be started. An that's why many companies use to make the callout a few moments earlier (5 kts, for many).
The FAR includes another consideration to calculate takeoff performance: the concept of VEF (Engine failure Speed); i.e, the speed at which the engine failure occurs. This means that, from the FAR yet, V1 considers acceleration from VEF to V1 with one engine failed!

From an airline manual: "The most important concept, common to all rejected takeoffs, is that V1 is the brakes on speed, not the decision speed. The decision to abort must be made, and the abort initiated, at or before V1, to ensure the likelihood of stopping on the remaining runway."

I've researched many policies regarding this issue, and I could send you documents from VARIG, United Airlines, Brazilian Air Force, Airbus and airlines which use V1-5Kt callout.

I'd like to hear your - and other members - comments!

Best regards,

PifPaf