Helicopters get all their lift from the rotor. So, either there's a huge amount of air being blown around, making parachute deployment impossible, or the helico

Helicopters get all their lift from the rotor. So, either there's a huge amount of air being blown around, making parachute deployment impossible, or the helicopter has no lift and is free falling, which doesn't give enough time to deploy a parachute at the low altitudes helicopters generally operate at. Small fixed wing general aviation aircraft are often equipped with ballistic parachute systems, however. It's just what you envisioned - a parachute with rocket-assisted deployment.