The difference I see is that pulling the lever for the trolley directly guarantees the killing of the one person and is the only possible alternative outcome, whereas the pilot scenario the alternative outcomes are variable until which point the pilot loses control.
With the plane, it is not as simple as the plane crashing towards an unavoidable skyscraper and the only other option is to point the plane directly at a nearby subdivision, or farmers house. If the pilot can guide the plane elsewhere, then he would logically avoid everything until he could no longer guide the plane.
The outcome is continually variable and dependent on the pilot’s continual sequences of choices until the point when he cannot make any other choices.
I cannot envision the pilot scenario being able to be constrained enough to where the choice was equivalent to that in the trolley scenario. If the pilot can steer the plane, then he has the choice to steer (or attempt to steer) it away from killing people. He may fail, but he can still try.
In the trolley, you have only two potential trajectories: the current trajectory into the four, or acting to alter the trajectory to kill the one.
I guess another way to say it is the plane is being steered with variable and unpredictable potential outcomes, where the trolley is not being steered; it is more a selection of an alternate, but exact outcome.
Another analogous scenario that I just remembered was mentioned earlier in the thread was the two locked chambers, one with four people and the other with one person.
A poison gas canister is is falling down a pipe towards the four and is guaranteed to kill them while the one person in the other chamber remains unharmed, but you are given an option to pull a lever that will divert the canister towards the chamber with only one person, guaranteeing their death instead of the four.
This scenario swaps the trolley for a gas canister, the rails for the pipe, and the people tied to the tracks for the people locked in the chambers.