Infiltrator is a classic helicopter action game designed and programmed by Chris Gray and published in 1986 by US Gold (in Europe) and Mindscape (everywhere else).
The aim is to fly a chopper (called the Gizmo DHX-3) to an enemy compound, then infiltrate the base on one of three separate missions. Each mission is split into two halves: a first-person flying game, then an isometric stealth/exploration game.