Incident Overview
On December 24, 2008, at about 0700 Pacific Standard Time, a Boeing 737-890 transport category airplane, registration N516AS, was involved in an incident during deicing operations at Seattle-Tacoma International Airport (SEA), Seattle, Washington. The airplane was parked on the ramp with engines shut down when smoke filled the cabin area. The aircraft was not damaged. Operated by Alaska Airlines as flight 528 under Title 14 Code of Federal Regulations Part 121, the flight was scheduled for passenger service to Burbank, California. There were no injuries among the two airline transport pilots, four flight attendants, and 135 passengers. Visual meteorological conditions prevailed, and an instrument flight rules flight plan was filed.
Sequence of Events
Alaska Airlines personnel reported that flight 528 began to push back from gate N14 with the auxiliary power unit (APU) running. As the pushback sequence was completed, deicing crews in both deicing vehicles began applying deicing fluid before the flight crew had configured the airplane for deicing. Shortly after, flight and cabin crews noticed fumes in the cabin and cockpit. The flight crew instructed the deice crew to discontinue operations and performed the smoke removal checklist. They then started both engines and taxied back to gate N14, where passengers and crew exited via the jet way.
Crew and Deicing Crew Reports
Captain's Report
The captain stated that the initial pushback was less than one airplane length due to a deicing vehicle behind. He requested the primary deicing vehicle (at the front) to have the rear vehicle moved. After that, the tug operator continued pushback, and the captain saw a gray cloud in the cockpit. He transmitted "don't spray 528" and opened his cockpit window to ventilate, but closed it due to snow and water. Another spray hit the front of the aircraft, and the first officer got fluid in his window. The captain transmitted a second time, "stop deice 528," and told the tug driver they were returning to the gate. He noted that the ground deicing crew never directed the flight crew to prepare for deicing, nor did he clear them to start.
Tug Driver's Report
The tug driver initially pushed back to clear the jet way and verified with the captain. After a conversation with the deicing crew, the captain instructed a further pushback. The tug driver pushed back a second time and stopped about 30 seconds later. She reported being sprayed with deicing fluid from the front truck.
Primary Deicing Truck Driver's Report
The driver contacted the flight crew, asking if they were ready to push back and deice. He was informed to "push deep" due to a snow bank. After the push, they waited about two minutes because the tug driver was not leaving. As the tug driver started to exit, the driver reported fluid types, freeze points, and concentrations to the flight crew, adding he would call start time when they reached the left wing root. He noted considerable radio chatter on three radios. The bucket operator started clearing snow "after we received no objections." Shortly after, the driver received a call from the crew asking if they were configured for deicing, and noticed the other deice truck already deicing the right wing area.
Primary Deicing Bucket Operator's Report
While positioned on the left side, the bucket operator saw a snow mound too large to drive through and requested the flight crew push back another 10 feet. After positioning, the deicing truck driver told him to begin deicing. He sprayed the radome with the airplane windows closed until the driver told him to stop immediately.
Secondary Deicing Truck Driver's Report
The driver, positioned outboard of the right wing, watched the pushback and stop. He moved in to deice the right stabilizer but observed the airplane push back again, so he repositioned. After the second pushback, he moved into position. He was instructed by the primary truck not to deice until instructed. He observed the primary truck begin deicing the left side but never received a message to start again.
Secondary Deicing Bucket Operator's Report
Positioned at the right stabilizer, the bucket operator began clearing the horizontal stabilizer and then deiced the fuselage from the tail to the right trailing edge of the wing. He noticed the primary truck was not deicing yet. He proceeded to the right wing tip, with no radio communication from the primary truck. He stopped immediately when the primary truck finally contacted his truck.
Company Procedures
Alaska Airlines' Cold Weather/Deicing Procedures Manual emphasizes that proper communication between Ground Deicing Crew and Flight Crew is essential. Poor communications may result in fumes in the cabin. The Flight Operations Manual states that aircraft deicing may occur after pushback, and the aircraft shall be positioned for access to critical surfaces. The flight crew shall prepare the aircraft when directed by the Ground Deice Crew. Prior to fluid application, the Ground Deicing Crewmember shall confirm with the Flight Crew that the aircraft is configured for deicing. The manual also specifies that the primary deicing vehicle starts the final application and establishes holdover time; additional vehicles shall not start until the primary vehicle has started.
The Alaska Airlines 737-400/NG deicing card lists pre-deicing steps, including setting APU and Engine BLEED Air Switches to OFF. According to the flight crew, these switches were in the ON position when deicing fluid was sprayed, allowing fluid to enter the air supply lines and the cabin and cockpit.