Most critical aircraft part?

[Ayahuasca]

Had a passenger joyride recently in an 86 year biplane, powered by the same type of engine that took Lindbergh across the Atlantic.

Whilst hopefully few of the critical parts were actually themselves 86 years old, it did lead me to ponder on what single part, if it were to fail, would be most disastrous (pilot's heart excepted).

I opted for the nut that fixes the elevator cable to the elevator.

Any other thoughts?

[Ayahuasca]

Simpo Two said:

You could argue that the only bit that really needs to work is the parachute!

Didn't get one of those!