Flight History
On 17 October 2011, a Boeing 777-300, registered 9V-SYH, operated a scheduled passenger flight from Shanghai to Singapore. The Senior First Officer (SFO), undergoing command training, occupied the left seat as pilot flying. The Pilot-in-command (PIC), a Line Instructor Pilot, was in the right seat as pilot monitoring. A safety officer (First Officer) occupied the observer seat.
A pre-flight briefing based on significant meteorological information led the PIC to advise the cabin crew to expect turbulence one hour into the flight, lasting two hours. The aircraft was equipped with a Honeywell RDR 4B weather radar system.
About three hours into the flight, while cruising at 35,000 ft approximately 80 nm from waypoint KARAN, the SFO noticed a green weather cell on the navigation display. The cell was about 5 nm in diameter, and the aircraft's track would pass by its left edge. The SFO switched the radar tilt to manual and assessed the cell. At 60 nm from the cell, the PIC obtained ATC clearance to deviate 10 nm to the left, upwind of the cell.
At 40 nm, the SFO initiated a heading change of about 11° left (to approximately 210°) and began the deviation. Two and a half minutes later, the aircraft was turned back to a track parallel to the original, estimated 5–7 nm left of the original track (FDR data later showed a deviation of 4.5 nm).
Turbulence Encounter
The flight was smooth and weather clear; the crew did not switch on the seat belt sign or reduce speed to turbulence penetration speed. As the aircraft was abeam the weather cell, the SFO observed light radar returns (green, short fine lines) directly ahead. He turned on landing lights, saw very light cloud traces, and immediately turned 20° left to increase clearance. During a left bank of about 9°, the aircraft encountered severe turbulence lasting about eight seconds. The SFO switched on the seat belt sign and slowed from Mach 0.83 to 0.82. FDR data recorded vertical accelerations between 1.66 g and -0.27 g, and vertical speeds of +800 to -1,336 fpm. The aircraft lost about 100 ft altitude. After the turbulence, the flight was smooth again; the aircraft landed in Singapore without further incident.
Injuries
Twenty-one persons sustained injuries: 1 serious (rib fracture in a passenger) and 20 minor. Among these: 3 flight crew (minor), 5 cabin crew (minor), and 13 passengers (1 serious, 12 minor). None were fatal. A doctor on board assisted with four more serious injuries, which stabilised; the PIC did not declare a medical emergency. All injuries occurred in the economy class at the back of the aircraft. One injured passenger was seated without a fastened seat belt; another was exiting an aisle seat; the rest were not at their seats, most waiting for lavatories.
Crew Actions
The crew coordinated with cabin crew and arranged for medical assistance on arrival in Singapore. They did not inform ATC of the turbulence encounter.