That's a brilliant piece of similar-triangles analysis, but it begs a couple of questions.
It assumes an airplane directly approaching the telescope at a distance of 1.6km. Otherwise, those "huge headlights" wouldn't be pointing at you, and the plane would be through your visual field in a small fraction of a second. How often will this happen?
It assumes a telescope directly pointing at the approaching airplane. How often will you be observing something low enough to the horizon to make this possible, never mind in the precise direction from which the airplane is approaching?
Please, though, go ahead and provide some references to vision hazards associated with pointing large telescopes at anything other than the Sun or a laser emitter. I haven't come across any in the past, I didn't turn up any with a couple of quick Google searches, and I don't think you'll find any professional or advanced amateur astronomers who agree with you.