A Gyrocopter is a kind of flying machine that can be piloted by one of your henchmen. Gyrocopters can carry more coal than henchmen, they move faster, and they can be used to build structures on cliffs and plateaus that aren't accessible by walking. This is a good way to erect defenses and protect important structures like the Research Clinic and Genetic Amplifier that don't need to be accessible from land.
The gyrocopter can also be used to airlift your units, but the gyrocopter henchman cannot build or repair structures or mine coal while airlifting a unit. In IC 1.0 and 1.1, only one unit may be lifted, although it was possible for more in later versions of the game.
The Gyrocopter can be built from a Landing Pad; only one Landing Pad can be built at a time, and likewise only one Gyrocopter. Note that you must command a normal henchman to man the Gyrocopter after it has been built; it doesn't come with a pilot. Once in the gyrocopter, the henchman will not get out until landed again. If damaged, the Gyrocopter can be repaired by commanding it to return to the Landing Pad.