NTSB Factual Report

On December 28, 2008, at 0700 Pacific standard time, a Boeing 757-351, N585NW, operated by Northwest Airlines collided with a Boeing 737-832, N397DA, operated by Delta Air Lines, Inc. during pushback operations at the Seattle-Tacoma International Airport (SEA), Seattle, Washington. Both flights were being operated under the provisions of Title 14 Code of Federal Regulations Part 121 in domestic scheduled passenger service. There were no injuries to the two airline transport pilots, seven flight attendants, and 186 passengers on board the Boeing 757-351, or to the two airline transport pilots, four flight attendants, and 151 passengers on board the Boeing 737-832. Both airplanes were substantially damaged. Night visual meteorological conditions prevailed and an instrument flight rules (IFR) flight plan was filed for both airplanes. The 757-351's intended destination was Minneapolis, Minnesota, and the Boeing 737-832's intended destination was Covington, Kentucky.

In written statements from the captain and first officer of the Boeing 737-832, it was reported that after receiving clearance from ramp control to pushback with the tail of the airplane to the north, the ground crew conducted a normal pushback into the alleyway. The captain stated he set the parking brake as the first officer was completing "the start flow" for the number 2 engine when they felt the airplane "shudder." The captain contacted the ground crew and was notified that their aircraft was struck by a Northwest Airlines' Boeing 757-351.

Written statements were obtained from the ground crew for the Boeing 737-832, which consisted of an aircraft marshaller, two wing walkers, a tug driver, and a tug driver assistant. The ground crew reported that after receiving clearance from the captain, they began to pushback the airplane from gate Alpha 11 with the tail facing to the north. The tug operator stated that during the pushback sequence with the Boeing 737-832 in the alleyway, she noticed a Northwest airplane slowly pushing back from the S gates. She added that she didn't pay attention to the Northwest ground crew, since it appeared like they had stopped at their gate. As the ground crew was disconnecting the tow bar, they noticed the Boeing 737-832 starting to shake. The tug operator and assistant immediately ran towards the rear of the Boeing 737-832 and observed a Northwest airplane immediately behind the Boeing 737-832's position.

The captain and first officer of the Boeing 757-351 reported that they were cleared to pushback from gate Sierra 6 with the tail to the south. The captain cleared the tug operator to begin the push back. As the pushback commenced, the captain and first officer were cleared to start the aircraft engines by the tug driver. After starting the right engine, the flight crew began the start sequence of the left engine when they felt "what appeared to be the nose wheel sliding slightly on the wet ramp." The captain observed the tug driver positioned about 30 degrees left of the center of the airplane and set the brakes per the tug driver's request. The ground crew proceeded to disconnect the tow bar and return to the gate. The flight crew stated that as they were completing their After Start checklist, they saw a status message concerning the left elevator. The captain was able to clear the message using "the com (Cockpit Operating Manual) procedure" and everything "appeared normal." Shortly after, the ramp controller notified the flight crew of the Boeing 757-351 that a collision had occurred. The captain shut down both engines and the flight was later towed back to gate Sierra 6.

In written statements, the tug operator and wing walker for the Boeing 757-351 stated that they received instructions from the captain to pushback from Sierra 6 with the tail of the airplane to the south. After completing the pushback process, the wing walker disconnected the tow bar and started to return to the gate. During a telephone interview, the wing walker for the Boeing 757-351 reported that he was positioned near the left wing and the driver was facing the forward part of the fuselage during the pushback process. He stated that during the pushback he was walking sideways and at no time did he "see the other airplane."

The Port of Seattle ramp controller reported in a written statement that the flight crew of the Boeing 757-351 initially requested permission to push back from Sierra 6. The controller instructed the crew of the Boeing 757-351 to pushback with the tail to the south. Immediately following, the flight crew of the Boeing 737-832 requested to the ramp controller to pushback from gate Alpha 11. The controller subsequently cleared the Boeing 737-832 to pushback from Alpha 11 with the tail to the north. During a telephone interview, the controller stated that she had originally thought that the Boeing 737-832 was requesting to be pushed back from gate Alpha 14.

Review of recorded footage from an airport security surveillance camera that was facing gates Sierra 6 and Alpha 11, revealed that the Boeing 737-832 initially pushed back from gate Alpha 11 into the alley with the tail facing to the north as the Boeing 757-351 pushed back from gate Sierra 6 with the tail facing to the south. The video revealed that the Boeing 737-832 appeared to be stationary for about 36 seconds before the movement of the Boeing 757-351 stopped.

Examination of both airplanes by an NTSB investigator revealed that the Boeing 737-832 sustained damage to the left elevator and the Boeing 757-351 sustained damage to the left elevator.

Communication recordings between the Port of Seattle Ramp Controller and both aircraft revealed that at 0657:46, Northwest Airlines Flight 620 requested pushback clearance from "South 6." Four seconds later, the ramp controller cleared Northwest Flight 620 to pushback with the tail to the south. About 7 seconds later, Delta flight 1288 contacted ramp control requesting pushback clearance from Alpha 11, followed by the ramp controller approving the pushback with the tail to the north.

Review of Northwest Airlines company procedure manuals revealed that within the Ground Operations Manual (GOM), Revision 03-2008, section A General Requirements, subpart 2 Marshal (Tractor Operator) states in part "...responsible for ensuring guideperson(s) are in proper position. The aircraft shall never be moved until the guideperson(s) is in position and ready. A minimum of one guideperson is required for all aircraft movement. It is the Marshal's responsibility to have an adequate number of guidepersons for safe movement of the aircraft." Subpart 3, titled "Guideperson(s) - responsible for," the manual states in part d, "The guideperson(s) is responsible for ensuring that the aircraft has adequate clearance at wingtips, tail, and fuselage for the intended movement. e. The guideperson(s) must always be in position where he/she remains in full view of the Marshal at all times. If visual contact is lost, the Marshal will signal the flight deck crew to stop the aircraft. f. The guideperson(s) must always be in position where he/she is clear of moving aircraft and/or the pushback vehicle. g. The guideperson shall provide handsignals to the boarding bridge operator to ensure safe movement from the aircraft prior to pushback and signal the marshal when boarding bridge has been safely parked outside the safety zone."

Review of the Delta Air, Lines Ramp Procedures Manual, chapter 6, section 1.4, Obstacle Clearance, states in part "...the ramp agents share the responsibility for obstacle clearance during pushback. When the tug is disconnected, the aircraft is then turned over to the dispatch agent who remains responsible until he returns the flight crew's salute. Once the salute has been acknowledged, no personnel, except the dispatch agent, are to walk in front of the aircraft. If obstacle clearance remains in doubt, the Captain should request wing walkers."

NTSB Probable Cause

The failure of the tug operator and wing walker of this airplane to maintain clearance with the other aircraft during the pushback process in dark night. Also causal was the ramp controller's misinterpretation of the other airplane's gate location and her improper clearance for both airplanes to simultaneously push back from nearly opposing gates.