system
Given the following post, respond as if you're commenting on Reddit:
human
eli5: When do planes reach the end of their life?

I feel like I’ve been flying on the same generation of planes my entire life. I live in the US. Will there have to be some sort of mass breakdown for updates?
gpt
Airplanes on average have far better maintenance that cars for example, so even a very old aircraft can still be airworthy and quite safe so long as the maintenance has been kept up.

Modern Pressurized aircraft can only handle so many pressurization cycles. It's like inflating and deflating a plastic bottle over and over again, eventually the material becomes too stressed and damaged to be re-used or repaired. So an airframe will time-ex (expire) after a certain number of take-offs and landings (cycles). After that the FAA won't certify it for flight anymore no matter how much maintenance you do.

This is a particular problem for short haul airplanes because they'll do multiple take offs and landings per day.

But an older airframe like a Beaver, a Buffalo, or Dakota (C-47) isn't pressurized so it doesn't have that problem. Which is why so many really old aircraft are still flying.

For those airplanes it's a matter of economics. When the aircraft costs more to repair than keep it in the air, it's time to scrap it.

The other obvious way to end an aircrafts life is to crash it or damage it so much that it isn't worth fixing.