How long does it take on average before a pilot initiates an action in reaction to a co-pilot's callout? Are there any research data on this subject?

I'm asking this question in relation to the V1 speed, or more specifically to figure out whether it's a reasonable procedure to require pilots to continue takeoff (even) when an engine has failed one or two seconds prior to reaching the V1 speed, taking into account their reaction time.

  • $\begingroup$ Pilots (other than me) aren't superhero's, so it would be accurate to say that a typical reaction time is the same for any average human being. Usually the problem isn't reaction time though, it is how long it takes to recognize a problem and make the decision to abort. Sometimes you get to V1 and then recognize a problem when you can't rotate and the pilot attempted to fix it before calling for a rejection. $\endgroup$
    – Ron Beyer
    Sep 26, 2017 at 4:20

1 Answer 1


The best research on this is done with real crews & expensive simulators, and I think their results are exactly the proposition you're looking at, namely that the callout "V1" needs to be said something like a second or two before the actual latest-point-of-first-action to reject the takeoff.

The reason that we can't just say, how long does it take me to respond to the other pilot's callout routinely is, it's a different world between the routine stuff and the abort decision close to V1. As an example, if I'm flying an approach, I know when the callout 100 feet above minimums is coming. If I'm not badly tunnel-vision on some isolated part of my scan (very, very rare when you're at that point in an approach... not impossible but quite rare), I can see the altimeter unwinding toward the minimums bug, and so when the other pilot makes the callout, I'm ready to reply "going outside." And I know that a few moments after that, he's going to call out "minimums" and I have my next callout to make. No surprises, and if you measured how promptly I respond to his callouts, you'll probably get results showing that I'm pretty prompt.

Compare that with the one takeoff in thousands where things are getting weird close to V1, and I'm actually processing the "is this actually worth stopping for now that we're high speed" decision. I've never had to do that in the actual aircraft, but talking to guys who have, there is some very real time compression -- events happen fast. On a normal takeoff, I'm almost always aware of exactly when the "V1" callout is coming. But if it is "that dark & stormy night" and I'm trying to sort out the difference between fluxing indication, minor burp, or beginning of an engine failure, that will be the time when the "V1" call WILL catch me by surprise, and how quickly I react to it & remove my hand from the throttles may not correlate to how quickly I've taken it off during the last 999 takeoffs.

On a normal takeoff, my habit is a fairly spring-loaded motion where my hand comes up and away from the throttles immediately at the "V1" call, so that if we get the proverbial big bang, lotsa yaw, and the fire bell right after the callout, I'd be able to catch myself & not go reaching back toward the throttles to initiate an abort-after-V1. So on those days, you might could get away with pushing the callout closer in time to the latest-first-action-to-stop point. But not every day is going to be like that, so the Boeing procedures build in the greater level of reaction time.

Because taking the aircraft flying even when you had another second or two that you could have stopped it, is generally (looking at the historical track record of takeoffs rejected & takeoffs continued) less dangerous than stopping the aircraft a couple of seconds after you shouldn't have.


  • $\begingroup$ Thank you so much for your wonderful reply and link to the great study sources on V1! $\endgroup$ Sep 26, 2017 at 10:44
  • 2
    $\begingroup$ Note that in certification, there is a one second delay incorporated before V1 at which the engine failure (or other event) occurs which gives the pilot time to react. This is for a well-trained test pilot who is expecting it, and may not always be duplicated in real life. See this question for a little more background on the certification: aviation.stackexchange.com/questions/3564/… $\endgroup$
    – Lnafziger
    Oct 17, 2017 at 19:30

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