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There are plenty of stories of large aircraft accidentally, or emergently, landing at airports that don't meet the plane's runway length requirements. The only solution to getting them out that I've read is stripping them to the point that some authority deems them light enough for takeoff on the short runway.

What I haven't read of are the use of any measures to increase the thrust available for the takeoff run. The first idea that came to mind was the use of RATO. Is this possible with civilian aircraft? Is it done? If not, why not?

(My second thought was to temporarily install water injection. But then I figured that by the time a system like that could be tested and approved the plane could have been disassembled for overland shipping.)

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    $\begingroup$ You'd be surprised how short of a runway you would need for a large airliner if it is unloaded and has minimum fuel. Usually if it can land there without damage, it can take-off again too. $\endgroup$ – Ron Beyer Feb 17 at 23:58
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    $\begingroup$ When I was a teen, a 727 with an emergency of some sort landed at Moscow-Pullman airport -- a strip normally serving GA and 12-18 passenger turboprop regionals, nothing larger. They had to bring in another pilot with short-field experience, but they got it out with enough fuel to get to Lewiston, ID or Spokane, WA, don't recall which... $\endgroup$ – Zeiss Ikon Feb 18 at 12:11
  • $\begingroup$ The first thing that comes to my mind is crashing airframes left and right while failing to rescue hostages in the late 80s. $\endgroup$ – Mazura Feb 19 at 3:37
  • $\begingroup$ This video shows an empty 737 taking-off in just 2300ft. As Ron Beyer said, "Usually if it can land there without damage, it can take-off again too." $\endgroup$ – Fiddlesticks Mar 10 at 0:57
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The DH Comet was equipped with RATO.

The Fairchild SA226 had a RATO bottle in the tail to improve single engine performance. As I recall, removing the spades on the main landing gear eliminated enough drag to render the RATO unnecessary.

Boeing built twelve "727-200/JATO" variants for use by Mexicana Airlines. Mexicana 727-200 with RATO activated during takeoff

The rocket installation was intended for emergency use only when flying out of a hot and high airport at maximum gross weight. Without the JATO, the aircraft would have to be payload restricted to account for the need to reach a safe altitude in the event of an engine loss after committing to takeoff. By having the JATO provision, Mexicana could operate its 727-200s at full payload. In the event of a loss of engine at past V1, the JATO unit would fire and allow the heavily-laden jet to reach a safe altitude and get aerodynamically cleaned up.

This old video shows a demonstration of that scenario with one of those special 727-200s:

The JATO provision was eventually made obsolete by later developments in the JT8D engine that featured "APR" automatic power reserve. It sensed a power decrease from one of the engines failing on takeoff and automatically boosted the power to the remaining two engines by a significant margin.

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The same reason you give for water injection would apply to RATO. The airframes are not structurally reinforced, nor are there any mounting points or wiring and switches needed for igniting them. It would be a major endeavor to test and certify such a system for the rare occasions when someone might want to have that option.

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  • $\begingroup$ Would not water injection bring engine to power output same as it is during low temperature (high altitude) operation? $\endgroup$ – user482745 Feb 18 at 13:42
  • $\begingroup$ I don't know very much about water injection. I answered in the context of the major modification and certification required. You seemed to discount water injection for that reason, and I just wanted to point out that installing RATO on an airframe not designed for this capability would require as much or more engineering effort. $\endgroup$ – Michael Hall Feb 18 at 16:33
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The difficulty of engineering a RATO is only half the reason, the rest is that reducing weight is really effective.

Typically the empty weight of an airliner is about half the max take off weight. That means that it can accelerate twice as fast, only requiring half the distance to reach the same speed. Also, a lighter plane can take off at lower speeds (although not half, as lift depends on speed squared). Put the two together, and wait for the coldest part of the day when the air is densest and it could manage with about a third of the normal runway.

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    $\begingroup$ @llama Would you and the three people that upvoted your comment please get out a pencil and piece of paper and do the math. V=a * t. If V is constant and a is doubled, t is halved. x = 1/2 a t^2. Therefor new x = 2 * 1/4 old x. That's half the distance to get to the same speed. At the same distance and a doubled, t is .71 old t. v= 2 * .71 = 1.42. That part was correct. $\endgroup$ – Phil Sweet Feb 18 at 21:59
  • $\begingroup$ Lift depends on speed squared, so at half the weight the aircraft needs 1/√2 the speed, but it can accelerate to 1/√2 in ½ the distance. So you have quarter the distance before even waiting for favourable weather. $\endgroup$ – Jan Hudec Feb 22 at 21:34
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RATO capability must be designed into the airframe to a certain extent, you need either built-in structural reinforcement and thermal protection or the ability to retro-fit it later. Built-in capability adds weight that airplanes would be lugging around, retro-fit capability costs money to design in, test, certify, maintain and train pilots to use it. All this would add up to significant extra costs for what is best described as a very infrequent edge case. It's cheaper to very occasionally break up an airframe.

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