Accident Overview
On February 23, 2012, at approximately 1430 central standard time, a Southwest Airlines Boeing 737-7H4 (registration N915WN) encountered moderate turbulence while in cruise flight between Chicago, Illinois, and Los Angeles, California. The turbulence lasted 2 to 3 seconds. At the time, the aircraft was at Flight Level 360 and in visual meteorological conditions on an Instrument Flight Rules flight plan. The flight had departed Chicago Midway Airport about 55 minutes prior to the encounter.
Flight Details
The flight was a scheduled domestic passenger operation under 14 Code of Federal Regulations Part 121, en route to Los Angeles International Airport. The crew reported that the airplane had been in smooth air for approximately 30 minutes before the turbulence, with no turbulence reports from Air Route Traffic Control Center or other aircrews in the area. The passenger seatbelt sign remained on from an earlier period of light chop.
Crew Statements
According to both flight crew members, the airplane reacted in a manner consistent with flying through the wake of another preceding or crossing airplane. During the encounter, the aircraft experienced a momentary altitude deviation and a left roll of less than 10 degrees, both of which were corrected by the autopilot with a slight overshoot past wings level. After the turbulence and autopilot correction, the airplane returned to straight and level flight in smooth air. The captain then announced over the public address system for flight attendants to take their seats immediately.
Injuries and Aftermath
The captain and first officer, both airline transport pilots, were not injured. None of the 135 passengers were injured. One of the three flight attendants received minor injuries, and another flight attendant sustained a serious injury to her right hand. During the turbulence, that flight attendant was thrown back against the aft galley door, where her hand hit the recyclable can door, causing immediate pain. After the flight landed in Los Angeles, she sought treatment at an Urgent Care facility, where X-rays revealed a closed fracture of the carpal bone in her right hand. The aircraft was not damaged.