Remember that iPhone that caught fire on an Aussie plane? The Australian Transport Safety Bureau has now identified the problem: a misplaced screw that punctured the battery casing.
Here's the full ASTB explanation:
The technical examinations found that a small metal screw had been misplaced in the battery bay of the mobile telephone; the screw puncturing the battery casing and causing an internal short circuit leading to heating and thermal runaway. It was probable that the screw had been misplaced during an earlier repair carried out on the telephone. That repair had not been conducted by an authorised service provider.
In other words: the screw was in the wrong place because the screen had been replaced, a scenario that's not exactly uncommon with iPhones. So if you do have a repaired iPhone, make sure you carry it with you and don't check it in hand luggage. Flying has enough hassles without emergency landings because of a burning handset in the hold.