Is a passport needed to travel in an airplane within the united states?

No, you don't need a passport to travel within the US by plane.

Tick

You will need a official government ID that has a photo.

So you will need a state ID, a drivers license, or a passport

You do not need a passport. Passport is only need when going out of the Country.

Monica: Just to be clear - all the above responses assume that you are a US citizen and have some other form of goverment-issued photo ID, such as a driver's license. But if you are visiting the US, for example on a tourist visa from a foreign country, then you will indeed need to have your passport with you to fly within the US.