when to use "a" with que vas

In the conversations on travel there is the phrase: Que vas a hacer?
When I speak to my Spanish friends they say that they do not use the "a". Instead they leave out the "a" and say Que vas hacer?
In other parts of the conversation on travel the phrase Que vas a tomar el sol ? is used and the "a" is spoken.My Spanish friends agree that in such a situation the "a" is used and pronounced.
Can someone explain this
Thanks

I was looking for information about something else when I came upon two sources that confirmed that what I said in my previous message about "¿Qué vas a hacer?" is correct. One source was a website for learning Spanish. One of the sentences that the instructor provided was "Vas a hacer la tarea esta noche" (You're going to do the homework tonight). The other confirmation comes from one of the grammar books I like best: ¡Búscalo! A Quick Reference Guide to Spanish Grammar and Usage. On p. 101 of the paperback version, the authors say clearly "When a form of ir is followed by an infinitive, "a" is required before the infinitive." The first example they give to illustrate this is ¿Qué vas a hacer?

So it seems to me pretty clear that your Spanish friends are either poorly educated (i.e., they don't know how to write correctly in Spanish) or simply weren't thinking clearly.