You picked the wrong example. Helmets will do very little to reduce fatalities from air travel simply because the mechanics of how those fatalities occure.

Wearing a helmet while driving a car, however, has a pretty good chance of reduxing injuries and fatalities (probably even better than wearing a helmet when riding a bike on a seperated bike path.)

I don't think this is really a question of people analyzing the trade-offs. This how to do with how the risks and the activity are percieved, people are generally really at accurately assessing such risks.