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Let us say fire or smoke is detected during a takeoff roll when the speed is so high that the pilots can not make a full stop using the remaining runway. What is the best option: using full brake to stop even if that will cause a runway excursion or continue the takeoff and re-land?

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    $\begingroup$ Voting to close as there is no way to give a definite answer to this, as it obviously depends on many different variables $\endgroup$ Nov 9 '20 at 7:28
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Before starting the takeoff, the pilots will have calculated at least 3 V speeds: V1, VR and V2. The important one for your question is V1, the takeoff decision speed. This is the critical speed that determines whether or not to reject the takeoff in case of a critical failure or other problems.

During the takeoff, there are 3 phases relevant for the decision of rejecting:

  1. Until reaching 80 knots: At these relatively low speeds, you would reject the takeoff for any reason. Any caution message appearing or any failure you notice results in rejecting the takeoff.
  2. Between 80 knots and V1: At these speeds, you would only reject for critical failures, like e.g. an engine failure or a fire warning.
  3. At or after V1: At these speeds, you should never reject the takeoff unless the captain determines that the aircraft is unable to fly.

The details may depend on the exact aircraft, but here is the official list of reasons for rejecting for the Boeing 737 NG:

Prior to 80 knots, the takeoff should be rejected for any of the following:

  • activation of the master caution system
  • system failure(s)
  • unusual noise or vibration
  • tire failure
  • abnormally slow acceleration
  • takeoff configuration warning
  • fire or fire warning
  • engine failure
  • predictive windshear warning
  • if a side window opens
  • if the airplane is unsafe or unable to fly.

Above 80 knots and prior to V1, the takeoff should be rejected for any of the following:

  • fire or fire warning
  • engine failure
  • predictive windshear warning
  • if the airplane is unsafe or unable to fly.

(Boeing 737 NG QRH MAN 1.2 - Maneuvers - Non-Normal Maneuvers, emphasis mine)

As you can see, a fire or fire warning is serious enough that you want to reject up to V1. At or after V1, you should not reject for a fire warning. Rejecting a takeoff after V1 usually results in an accident, even if there is enough runway available, because the brakes may not be capable of stopping the aircraft any more:

Rejecting the takeoff after V1 is not recommended unless the captain judges the airplane incapable of flight. Even if excess runway remains after V1, there is no assurance that the brakes have the capacity to stop the airplane before the end of the runway.

(Boeing 737 NG FCTM 3.23 - Takeoff and Initial Climb)

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    $\begingroup$ @jcaron No, V1 usually comes from balanced field length, which must not be larger than available runway, but it could be much shorter. That way you have a lot of runway left, but possibly too much kinetic energy for the brakes to absorb and you might still overrun after melting your brakes. $\endgroup$
    – Bianfable
    Nov 9 '20 at 14:29
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    $\begingroup$ Or to put it bluntly: if something happens after V1 that means the aircraft is unable to fly, you are screwed. You are neither able to take off nor able to stop before the end of the runway. Whatever you do, bad things are going to happen. $\endgroup$ Nov 9 '20 at 15:48
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    $\begingroup$ @JörgWMittag: V1 is calculated assuming engine failure. If the thrust reversers are still working, you might have more wiggle room. $\endgroup$
    – Joshua
    Nov 9 '20 at 17:20
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    $\begingroup$ @Mark Many fires proved to be really deadly really fast. And not just Concorde AF 4590. $\endgroup$
    – Vladimir F
    Nov 9 '20 at 22:34
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    $\begingroup$ @VvV My apologies, I automatically assumed you were talking about a transport category aircraft. For single engine (or light twin) aircraft, the situation is a bit different. There is no V1 speed, so you cannot know if it still safe to reject. I would say the decision depends on the exact situation. For an engine fire in a single engine I would always reject regardless of speed. It is unlikely that the aircraft will be able to fly safely with the engine on fire, so it's better to crash at low speed after trying to stop than crashing at high speed after trying to fly. $\endgroup$
    – Bianfable
    Nov 11 '20 at 7:32

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