Does anyone know this movie where Farah Fawcett sings about a plane high jack the line she is something like Homeless are many in world?

You are likely thinking of the movie "The Cannonball Run" (1981).

In the film, Farah Fawcett plays the character J.J. She has a scene where she sings a song with the lyrics "There are millions of homeless people in the world!" while on a hijacked plane.

The scene is a comedic moment and not a serious portrayal of homelessness.

Let me know if this is the movie you were thinking of!