Incident Overview
On February 27, 2011, at 2239 Pacific standard time, a Boeing 757-232, registration N684DA, operated by Delta Air Lines as Flight 1557, encountered turbulence while descending approximately 80 miles southeast of Seattle-Tacoma International Airport, SeaTac, Washington. The flight was on a scheduled domestic service under 14 Code of Federal Regulations Part 121, having departed Salt Lake City, Utah, at 2154 mountain standard time en route to Seattle-Tacoma on an Instrument Flight Rules flight plan. Visual meteorological conditions prevailed at the destination, but light rain and surface winds gusting over 20 knots had been moving through the area.
Sequence of Events
About 45 minutes before arrival, the Seattle Center controller informed the crew of a Pilot Report (PIREP) indicating expected light to moderate chop between Flight Level 200 and 16,000 feet. In response, the Captain advised the flight attendants of a bumpy descent and that the initial and final chimes would be given earlier than the standard 20 and 10 minutes prior to landing. The descent began from Flight Level 350, with the Captain (non-flying pilot) turning on the seatbelt sign and announcing cabin preparation. As the aircraft descended through Flight Level 260, the Captain gave the final two-bell chime, instructing the flight attendants to finish securing the cabin and take their seats. At Flight Level 250, the First Officer (flying pilot) reduced speed to turbulent air penetration speed. About one minute later, while passing through a cloud layer at Flight Level 240—4,000 feet above the PIREP-defined turbulence layer—the aircraft suddenly encountered moderate turbulence lasting approximately 30 seconds.
Injuries and Aftermath
At the time of the encounter, three flight attendants and one passenger were not seated. Two flight attendants and the standing passenger were thrown to the floor by the abrupt motion. One flight attendant, who was completing a public address announcement near the aft galley, sustained fractures to the second, third, and fourth metatarsal bones in her right foot. The passenger reported a sore ankle. The aircraft was not damaged. The remaining 183 passengers, three flight attendants, and two pilots were uninjured. After landing, the passenger was evaluated by paramedics at the airport and released, while the flight attendant was hospitalized for treatment and subsequently released.