Calling V1 five knots early?

[SteveC]

Saw this idea mentioned again in the Sad Realisation thread and it got me wondering about the validity of calling V1 early. Specifically five knots early, I believe is what someone said they do at their airline. If V1 is based on a balanced field length, isn't committing to a takeoff earlier than calculated potentially as dangerous (or more) than deciding to abort late?

 

[PhilosopherPilot]

Saw this idea mentioned again in the Sad Realisation thread and it got me wondering about the validity of calling V1 early. Specifically five knots early, I believe is what someone said they do at their airline. If V1 is based on a balanced field length, isn't committing to a takeoff earlier than calculated potentially as dangerous (or more) than deciding to abort late?

That's our procedure. The theory goes that it's better to commit to going early than to reject late. And also that it takes a second or two to actually make the decision, so the 5 prior call means that you make the decision pretty much just prior to V1.

 

[Hacker15e]

that it takes a second or two to actually make the decision

Does your company's V1 calculation not include time to decide/react as part of it?

 

[Bumblebee]

but the idea of V1 is that it takes the delay into consideration. When it's V1 it's V1.

 

[jynxyjoe]

Saw this idea mentioned again in the Sad Realisation thread and it got me wondering about the validity of calling V1 early. Specifically five knots early, I believe is what someone said they do at their airline. If V1 is based on a balanced field length, isn't committing to a takeoff earlier than calculated potentially as dangerous (or more) than deciding to abort late?

The idea was pushed more than 13 years ago and most companies went "bleh". I like it

but the idea of V1 is that it takes the delay into consideration. When it's V1 it's V1.

Well the argument for it was that a pilot has the ability to hear all of V1, at the completion of the call "V1" you're committed. For some of us it is a little more intuitive.

 

[Bumblebee]

but at V1 there is no reaction necessary except to respond to the issue that happens at or after. Abort would need to be called before and that delay could go through the normal v1 call.

I don't get it.

It's like setting your watch 5 minutes fast...a false sense of security.

 

[dasleben]

The first action must be made to reject the takeoff by V1, not any later. The call 5 knots prior is there to give the PIC (or PF, however it's done at that company) a moment to make a final decision. Once you're at V1, it's too late to initiate.

 

[Hacker15e]

The first action must be made to reject the takeoff by V1, not any later.

Where is this defined?

 

[PhilosopherPilot]

Does your company's V1 calculation not include time to decide/react as part of it?

Well, the certification requirements include a one potato two potato.

I dunno. I just teach the procedure they tell me to.

 

[Kingairer]

My company actually changed on this during the merger. Its a valid discussion. As it stands now it specifically states to call V1 at V1.

 

[dasleben]

Where is this defined?

https://www.faa.gov/other_visit/avi...e_operators/training/media/takeoff_safety.pdf

Page 2.10. Also has a really good discussion included.

 

[PhilosopherPilot]

The first action must be made to reject the takeoff by V1, not any later. The call 5 knots prior is there to give the PIC (or PF, however it's done at that company) a moment to make a final decision. Once you're at V1, it's too late to initiate.

I stand corrected, per your FAA post.

 

[Kingairer]

Do you talk with a southern accent or yankee one? We must think of everything folks!

 

[dustoff17]

I'm Part 91 so my company pretty much lets us establish procedures (within reason, of course). We do the early call out as well; my reasoning is as follows:
V1 is based on demonstration to the FFA (Yes, I do this on purpose) based on the current conditions and aircraft configuration. It is demonstrated by a test pilot that KNOWS the emergency situation that is about to present itself. I, on the other hand don't know if something is going to happen so my reaction time will add to the distance used. V1 does NOT include reaction time other than that demonstrated by the test pilot during certification.
I guess there's no right or wrong on this, I just like the extra "what the hell just happened?" time AND distance.

 

[dasleben]

I stand corrected, per your FAA post.

No worries, I was just about to post that there's a delay included between Vef and V1, but the first action to initiate the RTO must be made at/prior to V1 (brakes on, thrust idle, etc.).

 

[Hacker15e]

Well, the certification requirements include a one potato two potato.

https://www.faa.gov/other_visit/avi...e_operators/training/media/takeoff_safety.pdf

Page 2.10. Also has a really good discussion included.

Interesting.

In the military jets I've flown, the Refusal Speed/Max Abort Speed included the "one potato, two potato" to make the decision and begin taking the action in the computation. Thus, it was still valid to abort if something happened *at* the computed speed, and accounted for the continued acceleration during that time.

From the linked FAA Training Aid:

One common and misleading way to think of
V1 is to say “V1 is the decision speed.” This is
misleading because V1 is not the point to begin
making the operational Go/No Go decision. The
decision must have been made by the time the
airplane reaches V1 or the pilot will not have
initiated the RTO procedure at V1. Therefore,
by definition, the airplane will be traveling at
a speed higher than V1 when stopping action
is initiated, and if the airplane is at a Field
Length Limit Weight, an overrun is virtually
assured.
Another commonly held misconception: “V1 is
the engine failure recognition speed”, suggests
that the decision to reject the takeoff following
engine failure recognition may begin as late as
V1. Again, the airplane will have accelerated to
a speed higher than VI before stopping action
is initiated.
The certified accelerate-stop distance calculation
is based on an engine failure at least one second
prior to V1. This standard time allowance
has been established to allow the line pilot
to recognize an engine failure and begin the
subsequent sequence of stopping actions.

 

[BobDDuck]

f V1 is based on a balanced field length

Often times it's not. The only time our takeoff data is balanced is if it comes out of the book. If we get an Aero data uplink from ACARS it may not be balanced.

 

[jtrain609]

Both my employers called V1 at V1.

It seems a little academic, at a point, being that nobody is even going to call it EXACTLY at where V1 is. It's a pretty close approximation even if you're within 5 knots.

 

[EIR]

That is how it was taught at my last company. The theory was, by the time you call "V1" you would be at it.

 

[jynxyjoe]

That is how it was taught at my last company. The theory was, by the time you call "V1" you would be at it.

We had this discussion in class more than a decade ago. The thought (which was obviously trashed except by a few companies) was to call out V1 early (back when it was still decision speed not action speed) so you could make a decision.

The reality is, if you were asleep and woke up at V1 and had to decide to go or stop it's (mathematically speaking) always better to go and deal statistically with that 0.01% where something was deathly wrong with the airplane.