"The flight starts in the morning."
Translation:Η πτήση ξεκινά το πρωί.
To add to troll's comment, even if the verb worked in this case, it would be followed by "το", not "στο".
Nice one, many thanks to you both for explaining. I think I'd originally learnt both words as meaning 'start', but now you've explained it that way I can see the 'κινώ' in there and it's perfectly obvious.
I'm guessing: for the same reason that "in this morning" or "at last night" are incorrect in English :)
(Even though we say "in the morning" or "at night"... but not "in morning" or "at the night"... why? It just is!)