Singapore B772 near Singapore on Aug 1st 2017, turbulence injures six people

Last Update: April 24, 2018 / 14:33:04 GMT/Zulu time

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Incident Facts

Date of incident
Aug 1, 2017

Classification
Report

Flight number
SQ-974

Aircraft Registration
9V-SQN

Aircraft Type
Boeing 777-200

ICAO Type Designator
B772

A Singapore Airlines Boeing 777-200, registration 9V-SQN performing flight SQ-974 from Singapore (Singapore) to Bangkok (Thailand) with 219 people on board, was climbing out of Singapore, the fasten seat belt signs had already been extinguished at 10,300 feet MSL, when the crew observed weather ahead on their weather radar screens, a significant buildup of CBs to their left and scattered CB's to their right. The crew illuminated the fasten seat belt signs again while climbing through about FL200 and requested to deviate to the right on a heading of 010 degrees, however ATC cleared only for a heading 350 degrees and instructed to stand by for turning further right. About 28 seconds after the seat belt signs were illuminated again, the aircraft encountered moderate to severe turbulence for about 3-5 seconds causing serious injuries to one passenger and two flight attendants and minor injuries to three other flight attendants. The aircraft continued to Bangkok where medical services were already awaiting the aircraft to take care of the injured.

Singapore's Transport Safety Investigation Bureau (TSIBS) released their final report concluding the probable causes of the accident were:

- The aircraft was flying through the edges of some scattered clouds and encountered turbulence, resulting in serious injuries to one passenger and two cabin crews and minor injuries to three other cabin crew members.

- The flight crew were aware of the weather build-up in their planned flight path and requested for deviation from the weather, but the Air Traffic Control (ATC) could only provide incremental heading change owing to the relative busy air traffic situation at that time.

- The flight crew switched on the fasten seatbelt sign when ATC could not give them clearance for heading change when the flight crew requested a second time, but all the cabin crew did not recall seeing the fasten seatbelt sign illuminated or hear the chime when the fasten seatbelt sign came on.

- The QAR data indicated that the fasten seatbelt sign was switched on about 28 seconds before turbulence encounter.

- The investigation could not establish the reason why the cabin crew did not notice when the fasten seatbelt sign was switched on.

The TSIBS reported the passenger received a broken right leg when he fell as result of the turbulence. Two flight attendants received hairline fractures in their heels, three other flight attendants received minor injuries. At the time of the turbulence the five injured cabin crew were providing food service to the passengers. The passenger was walking back to his seat from the lavatory when the turbulence occurred.

The TSIBS analysed:

Data from the QAR indicated that the fasten seatbelt sign was switched on before the onset of the turbulence. This was corroborated by the account of the passenger who was seriously injured as well as the flight crew’s account. Yet all the cabin crew members were quite certain that the fasten seatbelt sign was not turned on at the time of the turbulence encounter.

While it was possible for the fasten seatbelt sign and cabin interphone systems to malfunction, the probability was considered very low, considering that there was no report of any defect relating to the fasten seatbelt sign or cabin interphone systems before and after the occurrence.

It is difficult to understand, in the absence of any evidence to suggest a malfunction of the fasten seatbelt sign system, how the cabin crew had perceived that the fasten seatbelt sign was not turned on. It cannot be proven but one possibility was that the cabin crew members were too engrossed in their service to have noticed the sign and the suddenness of the turbulence encounter and painful injuries could have affected their recollection.

When to switch on the fasten seatbelt sign is a judgment to be made by the flight crew. In this occurrence, the sign was switched on some 28 seconds before the turbulence struck. The PF made a sensible decision to switch on the fasten seatbelt sign when he judged that the ATC clearance for a deviation to the right (which would enable the aircraft to clear the scattered CBs) was not forthcoming (see paragraph 1.1.9(b)). However, judging by the flight crew’s subsequent actions, viz. responding to the CIC regarding offer of drinks, trying to contact the CIC to warn the cabin crew of possible turbulence ahead, communicating with ATC regarding heading change, the flight crew probably did not expect that the turbulence could set in so soon. Had the flight crew judged that the turbulence encounter would be imminent, they could have made an urgent and direct broadcast to the cabin crew and passengers over the PA system.

Deviation from weather

The operator in this occurrence had a guidance in its training for flight crew on weather avoidance and turbulence management that flight crews should maintain clearance from a CB by 20NM laterally and 5,000 feet vertically to minimise risk of encountering severe turbulence.

It may not be always possible or practical to deviate 20NM laterally or 5,000 feet vertically from weather clouds. Flight crew may have to make informed decisions using weather radar to determine on how best to route the flight path around weather in order to minimise turbulence encounter. In instance when deviation distance cannot be adequately achieved, it would be prudent for the fasten seatbelt sign to be switched on early for passengers to be seated and cabin crew to be alerted.
Incident Facts

Date of incident
Aug 1, 2017

Classification
Report

Flight number
SQ-974

Aircraft Registration
9V-SQN

Aircraft Type
Boeing 777-200

ICAO Type Designator
B772

This article is published under license from Avherald.com. © of text by Avherald.com.
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