If you have an emergency and are in need of a helicopter ambulance, dial 9-1-1.
Below is a directory and list of EMS helicopter(emergency chopper) groups all over the United States:
Helicopter Air Ambulances - A directory of EMS Helicopter groups in the U.S.A.
The Helicopter Air Ambulance VS. Fixed Wing
For short range transport of patients, helicopters are used for emergencies most of the time. Helicopter air ambulances tend to be more expensive than fixed wing(private airplane) air ambulance transport.
For longer range transports, airplane air ambulances are used more often. For long and medium range emergencies, airplanes are used to transport patients. Yet transports on airplanes are usually non-emergency.