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All aircraft have to undergo testing to determine how much runway they need in order to land and come to a stop without running out of runway, and how much runway they need in order to be able to safely reject a takeoff.

These tests are conducted:

  • With full braking on all wheels so equipped (although with the brake disks and pads worn down right to the metal)
  • With full use of airbrakes/spoilers (if so equipped)
  • Without using reverse thrust, even if the aircraft is so equipped, despite the fact that, for anything other than a small general-aviation aircraft, in real-world line operations, reverse thrust is essential for a successful landing or RTO unless conditions are damn near perfect.

Given that thrust reversers are indispensable for slowing any larger-than-small aircraft in less-than-optimal conditions (for instance, if the runway is wet or icy, or if you bounce the initial touchdown and lose the next chunk of runway, or if some of the aircraft’s tyres burst during takeoff, causing the brakes on those wheels to work poorly when you reject said takeoff, or if you're landing overweight, or if the speedbrakes can’t be extended because you’re out of fuel and the aircraft’s ram air turbine can’t power more than the basic flight controls, the navball, and the radio, or if you touch down long, or fast, or long and fast, or if you’re making a forced landing and have to take whatever reasonably-flat surface you get), why are aircraft certified without them? If it’s to make sure that the aircraft can safely land without reversers, why not also run additional certification tests where the reversers aren’t locked out, but, instead, the spoilers stay retracted, or some (or all) of the wheel brakes are nonfunctional?

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    $\begingroup$ "reverse thrust is essential for a successful landing or RTO unless conditions are damn near perfect". So how do you land when an engine is lost in flight? You use a longer runway? $\endgroup$
    – mins
    Jan 20, 2019 at 17:19
  • $\begingroup$ @mins: Well, presumably, yes. $\endgroup$
    – Vikki
    Jan 21, 2019 at 4:12
  • $\begingroup$ That 3rd bullet point is overstated, verging on nonsense. "Essential"? Hardly. Shortens stopping distance, yes. More so on slick runways. But not at all essential. $\endgroup$
    – Ralph J ♦
    Sep 19, 2020 at 15:00

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Would it be better to have numbers with thrust reversers and then forget to deploy them (or failed reversers) or to have numbers without reversers and use them on landing?

The first case will cause the airplane to exceed the published distance while the second case will cause the airplane to safely stop the aircraft before the published distance.

Simply put, a little extra conservatism on these airplanes.

Please use thrust reversers for the rejected takeoff and landing. If you know you will land long or bounce the landing, go around and try again. If you know spoilers are inoperative, get numbers without it. The same for contaminated runways, use appropriate numbers.

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    $\begingroup$ If the reason for your RTO is because of a lost engine, would you want to use reverse thrust with only one engine operative? I think not. $\endgroup$
    – Gerry
    Jan 20, 2019 at 0:24
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    $\begingroup$ Why not. Nose wheel steering should be sufficient. $\endgroup$
    – wbeard52
    Jan 20, 2019 at 0:39
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    $\begingroup$ @Gerry Reversers only provide about 30% of forward thrust. If asymmetrical forward thrust from an engine failure didn’t exceed your maneuvering ability, then reverse certainly won’t. $\endgroup$
    – TomMcW
    Jan 20, 2019 at 17:13
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    $\begingroup$ @wbeard52: Plus the rudder, at the higher speeds where reverse thrust is more effective (which, conveniently enough, also happen to be the speeds where the rudder is more effective). $\endgroup$
    – Vikki
    Jul 27, 2019 at 23:17

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