Mike Richardson‘s Combat Lynx is a very effective helicopter combat sim, first released for the Sinclair ZX Spectrum by Durell Software in 1984.
It features a kind of pseudo 3D landscape over which your centralised chopper must fly; picking up troops and supplies; fending off enemy attacks; and keeping local bases operational. Depending on the skill level, between three and six bases will be created, and the main aim of the game is to protect them.
Combat Lynx is relatively simple, although there is still an excellent game in there if you are willing to learn how to play it properly. The game was way ahead of its time back in 1984.