Airplanes have been known to float for so long that they became a menace to navigation and had to be sunk by gunfire.
10 seconds sound clip from the The High and the Mighty (1954) movie soundboard.
You can hear this line at 01:15:19 in the DVD version of the movie.
Quote context
[...]
- Some of which can land on water.
- And surface vessels will be directed toward us.
- Casualties come from panic. So you must not hurry.
- They've been known to sink in a few minutes, too.
- This is an inflatable life raft.
- It's really a wonderful gadget. It's got everything in it but T-bone steaks.
- It will hold all of you very comfortably.
- Mr. Wheeler, our second officer, will be in charge.
[...]