Defender,
Your refering to what is called 'LAMS' Land to Air mechs. I know there were a few used in the novels, but it was a old, lost star league technology. I want to say it was on the Smoke Jaguar homeworld? I will double check, you have my interest running.
But like Criminal said, that was like robotech. The LAMS faced a number of technical difficulties with changing over and so forth. Also when a system was taking out it forced you to either stay in the mech mod or aero mod. I also think the LAMS sacrificed armor and weapon systems as well..