On December 24, 2008, about 0700 Pacific Standard Time, a Boeing 737-890 transport category airplane, N516AS, was not damaged when smoke filled the cabin area during deicing operations at the Seattle-Tacoma International Airport (SEA), Seattle, Washington. When the incident occurred the airplane was parked on the ramp with its engines shutdown. The airplane was registered to and operated by Alaska Airlines as Alaska Airlines flight 528 under the provisions of Title 14 Code of Federal Regulations Part 121 scheduled passenger service. There were no injuries to the two airline transport pilots, four flight attendants, and 135 passengers. Visual meteorological conditions prevailed and an instrument flight rules flight plan was filed. The flight's intended destination was Burbank, California.

In a written statement, Alaska Airlines company personnel reported that flight 528 began to push back from gate N14 with the auxiliary power unit (APU) running. As the push back sequence was completed, deicing crews in both deicing vehicles began applying deicing fluid to the airplane prior to the flight crew configuring the airplane for deicing. Shortly after, the flight and cabin crews noticed fumes within the cabin and cockpit area. The flight crew instructed the deice crew to discontinue deicing operations. The flight crew performed the smoke removal checklist as the deicing operation stopped. The flight crew started both engines and taxied back to gate N14 where the passengers and flight crew exited the airplane via the jet way.

The captain reported that initially the flight was pushed back from gate N14 less than one airplane length due to a deicing vehicle directly behind the airplane. The captain requested to the primary deicing vehicle, which was located at the front of the airplane, to have the rear deicing vehicle moved. After the deicing vehicle was moved, the tug operator continued to push back the airplane and the captain noticed a gray cloud within the cockpit. The captain transmitted "don't spray 528" as the first officer and he opened both cockpit windows to ventilate the cockpit. Due to snow and water coming inside, the captain closed his window and noticed another "shot of spray hit the front of the aircraft" and the first officer was "getting fluid in his window." The captain transmitted a second time, "stop deice 528," and notified the tug driver they were going back to the gate. The captain stated that at no time did the ground deicing crew direct the flight crew to prepare the aircraft for deicing. He added that he did not clear the ground deicing crew to start their deicing operations.

The tug driver of the push back tug reported that she initially pushed the airplane back to clear the jet way and verified with the captain if it was ok. Following a conversation with the deicing crew, the captain informed the tug driver to push back the airplane further. The tug operator pushed the airplane back a second time and stopped about 30 seconds later. The tug driver stated that "once I pushed the aircraft back a second time and stopped, I was sprayed with deicing fluid from the front truck."

The driver of the primary deicing truck reported that that he contacted the flight crew and asked if they were ready to push back and deice. The driver stated that the ground crew was informed to "push deep" due to a snow bank near the airplane. The driver further stated that as the tug driver "finished the push," they waited for about two minutes "because the tug driver was not leaving the tug." As the tug driver started to exit the tug, the driver reported to the flight crew fluid types, freeze points, and concentrations. He also informed the flight crew that he would "call in our start time when we got to the left wing root." The driver added that there was a lot of "radio chatter" on all three radios he was monitoring and that the bucket operator on his truck started clearing the snow "after we received no objections." Shortly after, the driver reported that he "got a call from the crew asking did we call configured for deice" and noticed the other deice truck positioned near the rear of the airplane "was already deicing the right side wing area."

The bucket operator of the primary deicing truck reported that while positioned on the left side of the airplane, he noticed a snow mound that was too large to drive through. He requested that the driver ask the flight crew to push back another 10 feet. The bucket operator stated that as the airplane was positioned, the deicing truck driver "told me to begin deicing." He further stated that "the windows [of the airplane] were closed and I sprayed the radome" as he heard the driver of the deice truck telling him to stop immediately.

The driver of the secondary deicing truck reported that he was positioned outboard of the right wing as he watched the airplane push back and come to a stop. The driver moved the truck "in to begin deicing the right stab[ilizer]" when he observed the airplane start to push back again. The driver repositioned the truck to clear the airplane’s right wing. Once the airplane pushed back a second time, the driver moved the deicing truck into position. The driver stated that he was instructed by the primary deicing truck not to deice until instructed. He added that he observed the primary truck begin "deicing the left side" of the airplane. The driver added that he "never received a message from truck 12 [the primary deicing truck] to start again."

The bucket operator of the secondary deicing truck reported that while positioned at the right stabilizer of the airplane, the primary truck was positioned to the left of the nose of the airplane. The bucket operator began the "clear process on the horizontal." After completing the "clear process" of the horizontal stabilizer, the bucket operator began to deice the fuselage from the tail to the right trailing edge of the wing. The bucket operator stated "at this point, I noticed truck 12 [the primary deicing truck] was not deicing yet. Truck 10 [the secondary deicing truck] proceeded to r/h [right hand] tip. All while no radio communication had been taking place from truck 12 to truck 10." As the bucket operator began deicing at the right wing tip, "truck 12 finally made contact with truck 10" and he immediately stopped deicing.

Alaska Airlines’ Cold Weather/Deicing Procedures Manual, section 12, page 4, paragraph A, sub part 1 states "proper communication between the Ground Deicing Crew and the Flight Crew is essential to the safety of the Ground Deicing Crew, the Flight Crew and passengers. Poor communications may result in injury to the Ground Deicing Crew, fumes in the cabin and the aircraft leaving the deicing facility before deicing is complete."

Alaska Airline's Flight Operations Manual, page 14, section "Configuration for Deice/Anti-Ice” states in part "aircraft deicing may occur at the gate or after pushback and normally prior to engine start. Aircraft shall be positioned in such a way that Ground Deicing Crews have access to all critical surfaces. Flight Crew shall prepare aircraft for deice/anti-ice, when directed by Ground Deice Crew, in accordance with aircraft specific Flight Handbook." The manual further states on page 15, section "Deice/Anti-ice Procedure" in part "prior to fluid application, the Ground Deicing Crewmember shall confirm with Flight Crew that the aircraft is configured for deicing."

The manual further states on page 16, section "Simultaneous Use of Multiple Deicing Units", in part "the primary deice/anti-ice vehicle is the vehicle starting the final application of fluid on the left inboard wing area. This vehicle shall establish the start of the holdover time. Additional vehicles shall not start deice/anti-ice operations until after the primary vehicle has started."

The Alaska Airline's 737-400/NG deicing card, section "GATE DEICING" states in part:

1. APU……………………………………………...ON
2. Flaps……………………………………………..UP
3. Stabilizer Trim…………………………………..FULL APL NOSE DOWN
4. Air Conditioning…………………………………PACKS OFF
5. APU and Engine BLEED Air Switches……….OFF
6. WING Lights…………………………………….ON"

According to the flight crew, they had the APU and Engine BLEED Air Switches in the ON position when deicing fluid was sprayed on the airplane. This allowed the fluid to be introduced into the air supply lines leading to the cabin and cockpit.

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