Wake turbulence during the cruise phase of a flight is suspected as the cause of an incident which resulted in injuries to passengers during a US Airways Boeing 737-300 flight between Philadelphia, Pennsylvania, and Las Vegas, Nevada, on 7 August.
The captain reported the aircraft as acting "-like something was trying to roll it on its back". The 737, climbing through 29,000ft (7,400m) for 31,000ft was diverted to Pittsburgh. Evidence assembled from radar tapes suggests that the cause was wake turbulence from a McDonnell Douglas DC-10 about 17km (9nm) ahead, which had climbed through the same airspace.
Wake turbulence in the cruise is not uncommon, but usually causes no more than a slight vibration. In this case, the event - countered by the pilot who tripped out the autopilot and took manual control - lasted about 14s. It began with slight yaw and rolling motions and became violent. The captain feared that the problem might be uncommanded rudder input, but reported that the rudder was not displaced.
In the September 1994 crash of a US Airways 737-400 approaching Pittsburgh, the pilots faced a major upset during descent and failed to regain control. The cause is unknown. Wake turbulence is believed to be unlikely, but uncommanded rudder input is not ruled out.
Source: Flight International
