I can fly the campaign but free flight and single missions are not available. Please can someone tell me why.

because you don't have them unlocked?

Thanks for your response. Do I unlock them by flying the campaigns? How many do I have to fly to unlock them? Thanks again.

Each mission is only unlocked for free flight and single mission after you have beat the previous mission in campaign.

Smoke, Ldogg

If you are looking for a game where you can start playing any level, instead of just oh I dunno, the first one; try Mega Man.

Smoke, Ldogg