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In a multi-engine airplane, if an engine failure occurs at the exact moment that a decision needs to be made to reject or continue the takeoff, and there is plenty of runway available to do either, which one is statistically safer?

A more technical way to ask the same question would be: When there is sufficient runway available, is it better to artificially increase $V_1$ (via an assumed temperature takeoff or similar approved procedure) in order to stay on the runway longer in case an abort is required, or would it be better to leave $V_1$ at the lower speed and take any problems into the air?

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    $\begingroup$ I don't know about the statistics (I don't think there are that many for that scenario), but you know the saying: in case of doubt: I'd much rather be on the ground wishing I was in the air then being in the air wishing I was on the ground. $\endgroup$ – Philippe Leybaert Jan 22 '14 at 22:07
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    $\begingroup$ You specifically assumed that there's plenty of runway available. If it's plenty, an abort shouldn't go bad in a spectacular way I guess. (please forgive my oversimplification of the issue, I'm not an expert) $\endgroup$ – Philippe Leybaert Jan 22 '14 at 22:19
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    $\begingroup$ If such a situation arises in the real world, you don't have time to post to StackExchange and wait for an answer. In truth, the decision has to be made before you enter the runway, then the only thing to do is execute the plan. If you called V1, you continue the takeoff. If you have not called it, you abort TO. The safest course comes in acting decisively. $\endgroup$ – abelenky Jan 22 '14 at 22:50
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    $\begingroup$ @abelenky Absolutely! My question centers on the different philosophies used to determe V1 though. $\endgroup$ – Lnafziger Jan 22 '14 at 23:06
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    $\begingroup$ What is waiting for you at the end of the runway? Is it a nice green pasture or a 3000' drop straight into the ocean? $\endgroup$ – Radu094 Feb 19 '14 at 20:07
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In my experience, admittedly dated (retired 1999) whether it's 'better' or not didn't enter into the consideration. A reduced-power assumed-temperature was always used (unless there was something that prohibited it) because of the cost factor, and the power reduction used was always such that there was the proper amount of runway but not 'plenty' of runway. There was a maximum amount of reduction above which you could not legally go, but that was rarely used in my experience.

All that said, it's the captain's airplane. While I was a 747 f.o., I occasionally saw captains use less than the power reduction called for. More often, but still not a lot, I saw captains simply call for a max power takeoff rather fussing with adjusting the reduced power. Max power takeoffs were always entered into the aircraft maintenance log because it was required to do one every so often. I forget the exact requirement..

When I was a captain, I almost always observed the recommended reduced power. Twice doing this it became a closer thing than I would have liked. The first time was on the reef runway at Honolulu. We were over 800,000 lbs, it was my leg, and we lifted off at the very end. I rotated a couple of knots or so early because the end seemed to be getting very close. I thought a lot about that takeoff and discussed it with a number of people. My view, and I think the consensus view was: beware of high-humidity reduced power takeoffs. Humid air is less dense than dry air, but the performance charts (at least the ones we used) didn't take that into account.

A year or so later at Dhahran, Saudi Arabia, we were bringing a full load of troops back from Desert Storm. Reduced power was called for, the humidity was very high, and it was the f.o.s leg. A little over half way down the runway I didn't like how it was looking, and called for max power. Discussing it later with the f.o. and the f.e., we had all come to the same conclusion at about the same time. I had simply been the first to verbalize.

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The best answer I can provide is it depends.

For an emergency involving flight controls, trim runaways, pitch trim fail, full hydraulic failure, or a windshear indication, if the remaining runway was what I knew I could land and rollout on, I would abort the takeoff.

For all other emergencies including engine failure and/or fire, I would takeoff.

That is how I briefed my FO when I was a captain and similar to how my captains briefed me when I was an FO. The most common verbiage other captains used was "I'll abort after $V_1$ for failure to fly", and I consider the specific scenarios I mention to meet that criteria for the EMB-145.

I'll also explicitly say that I consider the aborts I listed to be safer than to takeoff:

  • flight controls - for obvious reasons
  • trim runaways - an out of trim transport category airplane can be a beast to fly
  • pitch trim fail - in the EMB-145 a re-trim from "8 up" to "6 up" has to happen at pretty slow airspeeds after takeoff or the aerodynamic forces on the stab will overcome the trim motor.
  • full hydraulic failure - we did it in the sim and it is a two person job to manhandle the controls, not particularly fun.
  • windshear indication - low and slow and performance decreasing windshear means you'll probably be back on the ground anyway.

I would consider aborting, given a long enough runway, to be safer than taking off for these scenarios.

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    $\begingroup$ Well, my question is specifically about calculating a higher V1 (which we know is safe to abort at). While this is a good brief/procedure, it doesn't answer the question that I'm asking. :) $\endgroup$ – Lnafziger Jan 23 '14 at 2:16
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    $\begingroup$ Ah, I way be guilty of mainly reading the title of skimming the question. The primary implication of increasing V1 and aborting is going to be brake performance and in particular, break overheating and fire. So I don't know that I would arbitrarily adjust it. $\endgroup$ – casey Jan 23 '14 at 2:24
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    $\begingroup$ Well, I'm not suggesting arbitrarily adjusting it (which is why I said to use an assumed temp or similar approved procedure). :-) $\endgroup$ – Lnafziger Jan 23 '14 at 2:26
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    $\begingroup$ Yes, I see that now. We always did reduced thrust takeoffs when able, so we were already at the highest published V1 for weight and configuration. $\endgroup$ – casey Jan 23 '14 at 2:34
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    $\begingroup$ As an example of a successful abort after V1 for failure to fly, see this AvHerald link where a Chautauqua E135 aborted at Vr after their elevators came undone when trying to take off from JFK. $\endgroup$ – UnrecognizedFallingObject Apr 1 '15 at 1:43
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Well, since you are asking about 'statistically' :

I have a Boeing presentation entitled 'V1 and the Go / No Go Decision' from 2002

In there it presents the case of Rejected TakeOffs and Overruns out of an estimated 76,000 RTOs studied between 1958 and 1990 about 74 ended in Overruns. 56% of them were initiated after V1 (most of them >120kts), and also 56% of them were avoidable completely by continuing the takeoff.

This puts your statistical chances of a mishap about 0.1% in case of RTO before V1 and about 56% after. If you think you have a better chance in the air, take the flight.

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  • $\begingroup$ I would expect aborting after V1 (especially > 120kts) to be more dangerous! :) I'd love to see a speed (relative to V1) -vs- accident rate graph. That would provide some insight on the issue, but runway distance remaining would also be a factor. $\endgroup$ – Lnafziger Feb 20 '14 at 2:07
  • $\begingroup$ I'd guess the reason for the abort is also a factor. If 56% of the post V1 aborts were due to trouble that ended up inhibiting braking... $\endgroup$ – jwenting Feb 20 '14 at 8:04
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    $\begingroup$ While things can certainly go wrong on the ground, there are more things that can go wronger faster and worser in the air. $\endgroup$ – Bob Jarvis - Reinstate Monica Oct 28 '14 at 0:10
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In light airplanes, if you have runway remaining, landing is the preferred choice even once you've taken off. It's not a "ground reject or continue" choice. It's a 3 stage process.

  1. Can I reject safely on the ground?
  2. After that point, Can I now land safely in the remaining distance (or even have a survivable runoff, which you may choose if you know your particular airplane can't climb on remaining engines)
  3. After that, I'm committed to lost engine procedures and attempting to fly (in some configurations, sustained flight is not possible and you're actually committing to an off airport landing)
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    $\begingroup$ It helps if you have a retractable gear: you can use the retraction of the gear as the switch between the two, much like V1 does for big a/c $\endgroup$ – Radu094 Feb 20 '14 at 13:22
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    $\begingroup$ I'd clarify that to say that "gear up" is your switch between option 2 and 3. The switch between option 1 and 2 is leaving the ground. $\endgroup$ – Brian Knoblauch Mar 24 '14 at 18:05

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