Just curious as to how a Airline decide what aircraft to fly on a particular route.For instance how do they decide to Fly a smaller boeing 757 vs a Bigger more comfy 767 or 777 aircraft on long flights to europe?

I am presuming they await intructions from the flight deck. What if the flight deck crew are incapacitated on impact.

Do the flight attendants make the decision to evacuate? How do they know when to act if they hear nothing from the flight deck crew? Can they over ride orders from the flight deck or can they simply do what they feel is right at any given time in the interests of safety?
IAN M: I have never heard or seen such a ridiculous and naive answer on Yahoo Answers in the entire time I have had the pleasure of contributing here.

Thank goodness you don’t write safety manuals

LOL
Flight Deck is the cockpit.

If you don’t know what a flight deck is I am unsure you should even be attempting to answer the question