Hmmm...i'm affraid there is no way to make AI retract or lower gear. However, AI should automatically perform those actions or the chopper has a autoretracting gear (like the KA-50 has).
My first idea was to use the "action" command and there is indeed an action for lowering, respective retracting gear. But for sake's reason this works only for player controlled units and not for AI.
Sorry mate i can't give better news on this.
Where from Switzerland if i may ask?