HISTORY OF FLIGHT On May 31, 2005, at approximately 1938 Central Daylight Time (CDT), a flight attendant on board United Express flight 5533, operated by Air Wisconsin, a Bombardier CL600-2B19, N417AW, was ejected from the airplane's service door and sustained serious injury following the boarding of the airplane at Chicago O'Hare International Airport (ORD), Chicago, Illinois. The scheduled passenger flight was being operated under the provisions of Title 14 CFR Part 121 on an instrument flight plan and was en route to Allentown, Pennsylvania. The flight attendant sustained serious injuries; there were no injuries to the 2 flight crewmembers or 24 passengers. The airplane was parked at gate F6B and an external air conditioning cart was providing cooled air to the cabin when the accident occurred. The captain briefed the flight attendant, before boarding the airplane and again in the cockpit, that there was an air conditioning cart hooked up to the airplane to cool the cabin and that she must keep one door open. The flight attendant stated that after the passengers had boarded the airplane, she approached the cockpit and the captain asked her to shut the service door and the main cabin door, however, none of the other doors were open and the airplane began to pressurize. After shutting the doors she turned toward the galley and the captain asked her if she closed the service door. She responded, "Yes! Do you want it open?" and the captain stated, "GET THE DOOR OPEN." She bent down, held the service door assist handle with her left hand, and opened the door with her right hand. As she lifted the handle upward, the door exploded open and she was blown out of the airplane and onto the ground. The flight attendant sustained a fractured left shoulder. TRAINING and PROCEDURES Air Wisconsin flight crewmembers receive training regarding the operation and warnings associated with the use of the external air conditioning cart. The CL-65 flight recurrent training material and Flight Crew Manual warn: At least one door to the cabin must remain open when using an outside source such as an air conditioning cart. The ramp operators also receive training that the air conditioning cart can pressurize the cabin and to keep the passenger entry door or cargo door open to prevent pressurization of the cabin. Air Wisconsin flight attendants do not receive training regarding the operation of the air conditioning cart and its ability to pressurize the cabin unless one door remains open. AIR CONDITIONING CART AND AIRPLANE SYSTEM INFORMATION The air conditioning cart is diesel powered and uses an on/off switch to control the 1,500 cubic feet per minute of conditioned air (cooled or heated) to the cabin. The cart has no means of regulating the amount of pressurized conditioned air that it feeds to the cabin. Bombardier places two placards on the CL-65 airplane relating to the dangers of opening a door when an air conditioning cart is being used. The placard on the overhead console in the cockpit and a placard on the external fuselage skin above the ground air conditioning system port read: "Warning" when the low pressure air ground connection is used the main cabin door or avionics bay door must be open. This narrative was modified on April 23, 2007.