This acceleration is for any change in velocity. It does not matter if the object increases or decreases – it is still an acceleration. If you know the acceleration for something, you can find the stopping distance using the following kinematic equation (here is a distraction if you like it).
In this expression, v1 is the initial velocity (20 mph in this calculation) and v2 the final velocity would be – hopefully zero as it would stop. Thus, with a known acceleration, the stopping distance (Δx) would be:
Now I just have to get a value for accelerating a stopping Boeing 747. Ah ha! It is not so easy. Of course, large planes stop all the time – this is usually called ‘landing’. However, the normal method during landing may not work here. Usually a large aircraft like the Boeing 747 uses two things to slow down. Not only does it use the wheels that have brakes, but it also has reverse carriers. The rear thrusters are essentially the power of the rear-facing engines (hence the ‘rearward’ part). This reverse thrust, coupled with the brakes, slows down the aircraft.
For this stunt in Tenet, the 747 will only have brakes because it is not a fully operational aircraft. So, what would the acceleration be if an airplane did not use the reverse gear? Well, we’m lucky. It is this thing that is called a rejected ascent test (RTO). For this maneuver, a plane starts and gets up to pick up the speed. At that point, the pilot lowers the brake (no reverse gear) and stops. This is a worst case scenario test to make sure that the brakes of the aircraft can handle extreme cases.