Direct flight? A direct flight?

Hello, everyone.
I've got a question about grammar of English, so if you don't mind, I'd like to ask you a favor and ask which one is correct answer.

Delta Airline has __ from New York to Sanfransisco.

I answered "direct flight", but someone said to me he looked up the dictionary and it said that flight is a noun, so a direct flight is right. But when I searched web sites, I found out both words were used – direct flight/ a direct flight.

I'm really confused which one is correct answer. Direct flight? A direct flight? Could you let me know the answer?

Thank you in advance.