In the The Sims 2 base game, it only appears as a carpool for certain top-level jobs (General, Mayor, etc.), but with The Sims 2: Apartment Life installed, a Sim can buy a helicopter as a private vehicle.
Parked on a helipad, the helicopter mostly works the same way as a car. Sims can also WooHoo in the helicopter.
The expanded Sims 3 has yet to include helicopters.
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