This acceleration is for any change in speed. It does not matter whether the object increases or decreases in speed – it remains an acceleration. If you know the acceleration for something, you can find the stopping distance using the following kinematic equation (here’s a derivation if you like).
In this expression v1 is the takeoff speed (20 mph in this calculation) and v2 would be the terminal speed – hopefully zero because it stops. So with a known gear, the braking distance (Δx) would be:
Now I just need to get a value for the acceleration of a stopping Boeing 747. Ah ha! It is not that easy. Of course, big planes always stop – this is normally called ‘landing’. However, the normal method during a landing does not work here. Usually, a large plane such as the Boeing 747 uses two things to slow down. Not only does it use the wheels, which brake, but it also has reverse thrusters. The reverse thrusters are essentially the power of the rear-facing engines (ie the “reverse” part). This rearward thrust, along with the brakes, slows the plane.
For this stunt Tenet, the 747 will only have brakes because it is not a fully functioning aircraft. So, what would the acceleration be if an aircraft didn’t use the reverse thrusters? Well, we’re in luck. Here’s this thing called a Failed Start Test (RTO). For this maneuver, an aircraft takes off and rises to increase speed. At that moment the pilot steps on the brake (no reverse thrusters) and comes to a stop. It’s a worst-case scenario test to make sure the aircraft’s brakes can handle extreme cases.