Singapore B773 near Hanoi on Oct 17th 2011, turbulence injures 21

Last Update: October 4, 2013 / 14:59:18 GMT/Zulu time

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Incident Facts

Date of incident
Oct 17, 2011

Classification
Accident

Cause
Turbulence

Airline
Singapore Airlines

Aircraft Registration
9V-SYH

Aircraft Type
Boeing 777-300

ICAO Type Designator
B773

Singapore's AIB released their final report into the accident without a formal conclusion.

The AIB reported that the captain, training captain, pilot in command and pilot monitoring, occupied the right hand seat while the senior first officer, on command training, occupied the left hand seat and was pilot flying. Another senior first officer was occupying the observer's seat as safety officer.

The crew detected a green dot on their weather radar, size about 5nm is diameter, their track would take them through the left edge of the cloud. About 60nm ahead of that dot the crew requested and were cleared to deviate 10nm to the left of their track and set course that took them about 4.5nm to the left of the edge. They remained visible with the stars and ground at all time and were able to see the silhouette of the cloud in night time conditions. Due to the smooth flight and visual conditions the pilot in command did not see a necessity to turn on the fasten seat belt signs.

About abeam of the cloud the crew received more light radar returns directly in front of the aircraft. The crew turned on the landing lights and spotted light traces of cloud. The crew immediately turned left another 20 degrees, however, in that turn the aircraft began to encounter turbulence that reached severe turbulence levels within the next 8 seconds. Although the fasten seat belt signs were turned on immediately upon noticing the first indications of turbulence, one passenger received a serious injury (rib fracture), 15 and 5 cabin crew passengers received minor injuries. During those 8 seconds the aircraft experienced vertical accelerations between -0.27 and +1.66G, the vertical speeds fluctuated between -1336 and +800 fpm.

A doctor on board took care of the injured and advised they would need medical attention after arrival in Singapore, the crew thus decided to continue the flight to destination.

The AIB reported all injuries occurred in the back of the aircraft, all of the injured were not wearing their seat belts, most of them waiting in the queue to use the lavatory, one in his seat without seat belt, one just standing up from the seat to permit another get into the next seat.

The aircraft was equipped with a weather datar system RDR4B that "requires a flight crewÃ¢â‚¬â„¢s skills to manipulate and experience to interpret the severity of the weather cell as compared with the fully automated RDR 4000 system which provides a more detailed picture of weather cell without any crew action." Two other company aircraft, trailing the accident aircraft but equipped with the fully automatic RDR 4000 systems scanning the entire sky on its own, received indication of a larger weather system consisting of about 3-4 cells totalling about 10-12nm in diameter, each cell of up to about 5nm, about 40nm out the system showed yellow and red.

The operator recommended to deviate at least 20nm from any thunderstorm cell, but did not provide guidance of cloud returns that did not paint yellow or red. The crew of the accident flight thus requested clearance to deviate about 10nm but turned parallel to the track about 4.5nm off the center line due to what appeared to be favourable conditions.