Forgive my lack of understanding, I thought I'd just buy a simulator and mess with it. I really don't know much of anything in terms of MSFS2020 or simming really at all.

I realize that airliners can taxi backwards. So, I'm wondering. At its top speed, how fast can a 747 taxi backwards, if it tried to do so?

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    $\begingroup$ Related: aviation.stackexchange.com/q/13350/36893 $\endgroup$ – CatchAsCatchCan Jan 3 at 14:18
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    $\begingroup$ Are you referring to powerback (going backwards using reverse thrust) or pushback (pushed by a tug)? $\endgroup$ – Bianfable Jan 3 at 15:50
  • $\begingroup$ Have you tried it on the Simulator? Let us know the results. $\endgroup$ – gwally Jan 4 at 17:59

From a pure theoretical standpoint, the speed limit would be whatever rolling speed can be achieved with max reverse thrust. If you deployed max reverse on a landing, and left the max reverse on until you stopped, then released the brakes and left it on as you started to roll backward, you would accelerate backwards, and if you were able to maintain steering control (unlikely) and the engines were able to operate with the turbulent reverse inlet conditions without stall/surge, you'd accelerate until there was no longer any surplus reverse thrust.

You'd eventually be careening along backwards along the runway at, maybe 30kt, 50kt, 80kt... who knows? You could probably estimate some number based on available thrust and rolling friction/air resistance, but safe to say it's never been tried, or even thought of. Don't even think of touching the brakes once rolling backward with any velocity.

From a practical standpoint, some operators may allow backing up under reverse thrust in specific circumstances, keeping in mind that you can't see where you're going so people need to be outside to clear the area behind, debris is being stirred up and ingested into the engines (ramp areas are a rich source of luggage zipper tags), and there's the problem of stopping without tipping over onto the tail when braking (the airplane's loaded C of G is not that far ahead of main gear, so it won't take much braking force for inertia to lever it over; safer to use forward thrust to stop than brakes).

So you may see power-back operations in the right circumstances, but the maximum speed in such cases won't generally be faster than a walking, (or maybe jogging) pace.

  • $\begingroup$ "Don't even think of touching the brakes once rolling backward with any velocity." Intrigued, why not? $\endgroup$ – Party Ark Jan 3 at 20:55
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    $\begingroup$ The plane would tip over and hit it's tail on the ground. The center of gravity of planes is just a bit forward (pls note the scientific accuracy here :) of the main landing gear. So even very light braking might end up in a tailstrike. $\endgroup$ – Jpe61 Jan 3 at 22:15
  • $\begingroup$ Added a bit to para 2 to make it clearer. The other problem is the brakes on a transport a/c are tough to modulate and feel a bit like the air brakes on a transport truck; there's no hydraulic resistance feedback like with car brakes or even light aircraft brakes, you push against springs and the amount of braking is how far you push, with the feedback just being the resistance of springs. $\endgroup$ – John K Jan 3 at 23:25
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    $\begingroup$ "You'd eventually be careening along backwards along the runway at, maybe 30kt, 50kt, 80kt... who knows?" - that is the essence of the question, isn't it? I don't see an answer here at the moment. $\endgroup$ – Mike Brockington Jan 4 at 13:56
  • $\begingroup$ If you think someone is going to provide a hard and fast number, like 62 kts, you'll need to visit another planet because you aren't going to find that number here. The answer is, theoretically, indefinite, and in practical terms, a few kts. We could just close the question as unanswerable, but better to provide some context at least no? $\endgroup$ – John K Jan 4 at 15:19

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