Incident Overview
On December 28, 2008, at 0700 Pacific standard time, a Northwest Airlines Boeing 757-351 (registration N585NW) and a Delta Air Lines Boeing 737-832 (registration N397DA) collided during pushback operations at Seattle-Tacoma International Airport (SEA), Seattle, Washington. Both flights were domestic scheduled passenger services under Title 14 Code of Federal Regulations Part 121. Night visual meteorological conditions prevailed, and instrument flight rules flight plans were filed for both airplanes.
Aircraft and Occupants
The Boeing 757-351 carried two airline transport pilots, seven flight attendants, and 186 passengers. The Boeing 737-832 carried two airline transport pilots, four flight attendants, and 151 passengers. No injuries were reported on either aircraft. Both airplanes were substantially damaged.
Pushback Sequence
The Boeing 757-351, operating as Northwest Airlines Flight 620, was scheduled to depart for Minneapolis, Minnesota. The Boeing 737-832, operating as Delta Air Lines Flight 1288, was destined for Covington, Kentucky.
According to the captain and first officer of the Delta Boeing 737-832, after receiving clearance from ramp control to push back with the tail to the north, the ground crew conducted a normal pushback into the alleyway. The captain set the parking brake as the first officer was starting the number 2 engine when they felt the airplane shudder. The captain was then notified by the ground crew that their aircraft had been struck by the Northwest Boeing 757.
The ground crew for the Delta 737-832, consisting of an aircraft marshaller, two wing walkers, a tug driver, and an assistant, reported that after receiving clearance, they began pushback from gate Alpha 11 with the tail facing north. During the pushback, the tug operator noticed a Northwest airplane slowly pushing back from the S gates but did not pay attention to its ground crew, assuming it had stopped. As the ground crew disconnected the tow bar, they felt the 737-832 shake and saw the Northwest airplane immediately behind it.
The captain and first officer of the Northwest Boeing 757-351 stated that they were cleared to push back from gate Sierra 6 with the tail to the south. The captain cleared the tug operator to begin pushback and subsequently started the right engine. During the left engine start sequence, they felt what seemed to be the nose wheel sliding on the wet ramp. The tug driver positioned about 30 degrees left of the aircraft center and set the brakes. The ground crew disconnected the tow bar and returned to the gate. After completing their After Start checklist, the flight crew saw a status message concerning the left elevator, which the captain cleared using the Cockpit Operating Manual procedure. Shortly after, the ramp controller notified them of the collision. The captain shut down both engines, and the flight was towed back to gate Sierra 6.
Ground Crew Actions
The tug operator and wing walker for the Northwest 757-351 stated they received instructions to push back from Sierra 6 with the tail to the south. After pushback, the wing walker disconnected the tow bar and started returning to the gate. In a telephone interview, the wing walker reported he was positioned near the left wing, walking sideways during pushback, and at no time saw the other airplane.
Ramp Control Communication
The Port of Seattle ramp controller stated that the Northwest 757-351 crew initially requested pushback from Sierra 6, which she cleared with tail to the south. Immediately after, the Delta 737-832 crew requested pushback from gate Alpha 11, which she cleared with tail to the north. During a telephone interview, the controller noted she originally thought the Delta flight was requesting pushback from gate Alpha 14.
Video Evidence
Review of airport security surveillance footage facing gates Sierra 6 and Alpha 11 showed that the Delta 737-832 initially pushed back from gate Alpha 11 into the alley with its tail facing north as the Northwest 757-351 pushed back from gate Sierra 6 with its tail facing south. The video revealed that the Delta 737-832 appeared stationary for about 36 seconds before the movement of the Northwest 757-351 stopped.
Damage
Examination by an NTSB investigator revealed that the Boeing 737-832 sustained damage to its left elevator, and the Boeing 757-351 also sustained damage to its left elevator.
Communication Recordings
Recorded communications between the Port of Seattle Ramp Controller and both aircraft showed that at 0657:46, Northwest Airlines Flight 620 requested pushback clearance from "South 6." Four seconds later, the ramp controller cleared them with tail to the south. About seven seconds later, Delta Flight 1288 contacted ramp control requesting pushback from Alpha 11, followed by approval with tail to the north.
Company Procedures
Review of Northwest Airlines’ Ground Operations Manual (Revision 03-2008) stated that the marshal (tractor operator) is responsible for ensuring guidepersons are in proper position; the aircraft shall never be moved until guidepersons are in position and ready. Guidepersons are responsible for ensuring adequate clearance at wingtips, tail, and fuselage. The manual also specified that guidepersons must remain in full view of the marshal at all times and provide hand signals to the boarding bridge operator.
Delta Air Lines’ Ramp Procedures Manual (Chapter 6, Section 1.4) stated that ramp agents share responsibility for obstacle clearance during pushback. When the tug is disconnected, the aircraft is turned over to the dispatch agent, who remains responsible until the flight crew’s salute is acknowledged. If obstacle clearance remains in doubt, the captain should request wing walkers.