Who gets to the airport 3 hours before a flight?! I'd aim for 2 at most depending on the airport
It depends where you live but if you are more than an hour from Heathrow and you've got a Transatlantic flight timing to arrive 2 hours before is fairly foolish, you only need an accident on the way or a cancelled train or whatever and your non-refundable ticket goes in the dustbin (and they'll automatically cancel the return leg too if you no show the outbound!)
2 hour is, I agree, plenty of time, but you have to have some leeway incase your scheduled 2 hours before arrival turns into an unscheduled 40 minutes before arrival and the woman at the desk says 'Bag drop closed, goodbye'
