What happened
On December 24, 2008, at approximately 0700 PST, an Alaska Airlines Boeing 737-890, registration N516AS, was involved in an incident at Seattle-Tacoma International Airport (SEA) during deicing operations. The aircraft was parked on the ramp with engines shutdown and was preparing for a scheduled flight to Burbank, California.
During the pushback sequence from gate N14, two deicing vehicles began applying fluid to the aircraft. Shortly after the application began, the flight and cabin crews noticed fumes within the cockpit and cabin area. The captain reported that the aircraft was being pushed back to clear a deicing vehicle positioned behind the plane. As the pushback continued, the captain observed a gray cloud in the cockpit and requested that the deicing crew stop. The crew opened cockpit windows to ventilable the area, but noted that spray from the deicing process was entering the windows.
The flight crew instructed the deicing crew to cease operations and performed the smoke removal checklist. The engines were subsequently started, and the aircraft taxied back to gate N14, where all 135 passengers and the six crew members exited the aircraft without injury.
The investigation
The investigation examined the actions of the ground deicing crew and the configuration of the aircraft. The captain stated he had not cleared the ground crew to begin deicing operations. The primary deicing truck driver reported that after a period of radio chatter, the bucket operator began clearing snow and deicing after receiving no objections from the flight crew.
Mechanically, it was determined that the aircraft's APU and engine bleed air switches were in the ON position during the fluid application. This configuration allowed the deicing fluid to be introduced into the air supply lines that lead to the cabin and cockpit.