50 minutes to transfer is plenty of time. The only thing - on long haul flights the wind can make a difference. I've had flights to/from Europe that were an hour longer, others an hour shorter (not very often, but it does happen).

(I always go for long connections in AMS that also allow for a quick walk through Amsterdam. It's the only place I know where you can be in the center of the city within 45 minutes of landing.)