"aren't they supposed to be able to land on one? "
Yeah but not take off. Those 747s are very heavy on takeoff on route to Singapore. Full of fuel, people and luggage. They wind them up and they take most of the runway to take off - I've been on that one many times.
Don't know if they could take off with 2 - probably not so to get up with 3 probably panicked the captain a bit if he called in a Mayday ??????
