If you're doing 2048x TC, you are "living" over 30 minutes of game time per second of real life. An airplane can drop a bomb on you six times in that time from, or you could be shelled by a shore emplacement, rammed by a ship, or shot at by a ship. The game generally does an OK job of dropping out of TC in good order, but not always, especially if there is a "hiccup" in the system just then as it tries to spawn the world around your submarine. If you don't see a minefield around your area as cdrsubron7 suggested - but minefields can be in several mis files in SH4, then I would suspect an airplane next. It's there, it has released its bomb, and it's gone before you drop out of high TC. Death spiral...
