SINGAPORE: Preliminary investigations into the severe turbulence on Singapore Airlines flight SQ321 have showed that "rapid" changes in gravitational force (G) and an altitude drop of around 54m likely caused injuries to passengers and crew who were not belted up.
1G is equivalent to the force of gravity on Earth’s surface.
SQ321 had been travelling from London to Singapore last Tuesday (May 21) when it encountered extreme turbulence. One passenger died and dozens were injured, resulting in an emergency diversion of the plane to Bangkok.
In a statement on Wednesday, the Ministry of Transport (MOT) said its Transport Safety Investigation Bureau (TSIB) had extracted the data stored in the flight data recorder and cockpit voice recorder of the plane.
A team comprising TSIB investigators and United States representatives - from the National Transportation Safety Board (NTSB), Federal Aviation Administration (FAA) and Boeing - then compiled a chronology of events based on preliminary analysis of the data.
This is what they found:
SQ321 departed London and the flight was normal prior to the turbulence event. At 7.49am UTC (3.49pm Singapore time) on May 21, the aircraft was passing over the south of Myanmar at 37,000 ft (11,300m) and “likely flying over an area of developing convective activity”, said MOT.
The G force, recorded as vertical accelerations, fluctuated between positive 0.44G and positive 1.57G for a period of about 19 seconds. “This would have caused the flight to begin to experience slight vibration,” said MOT.
Around the same time as the onset of the vibration, an “uncommanded" increase in aircraft altitude, reaching a peak of 37,362 ft, was recorded. In response to this, the autopilot pitched the aircraft downwards to descend back to the selected altitude of 37,000 ft.
In addition, the pilots observed an uncommanded increase in airspeed which they addressed by extending the speed brakes, said MOT.
Eleven seconds after the initial vibration, it was heard that a pilot called out that the fasten seat belt sign had been switched on.
These uncommanded increases in aircraft altitude and airspeed were most likely due to the aircraft being acted upon by an updraft, or the upward movement of air. During this period, autopilot was engaged.
The aircraft then experienced a rapid change in G, 19s after the initial vibrations, as recorded vertical acceleration decreased from positive 1.35G to negative 1.5G, within 0.6s.
“This likely resulted in the occupants who were not belted up to become airborne,” said MOT.
Just one second later, the vertical acceleration changed from negative 1.5G to positive 1.5G, within 4s. “This likely resulted in the occupants who were airborne to fall back down,” said MOT.
The rapid changes in G over the 4.6 sec duration resulted in an altitude drop of 178 ft, from 37,362 ft to 37,184 ft.
“This sequence of events likely caused the injuries to the crew and passengers,” said MOT.
In the midst of the sequence of rapid changes in G, recorded data “indicated that the pilots initiated control inputs to stabilise the aircraft, disengaging the autopilot in this process”.
The pilots manually controlled the aircraft for 21s and reengaged the autopilot at 07.50am UTC, just 44s after the initial vibrations.
The recorded vertical acceleration showed more gradual fluctuations over the next 24s, ranging from positive 0.9G to positive 1.1G, while the aircraft returned to 37,000 ft 18s after the pilots reengaged the autopilot.
After the pilots were informed by the cabin crew that there were injured passengers in the cabin, the decision was made to divert to Suvarnabhumi Airport in Bangkok, Thailand, said MOT.
“On the way to Bangkok, the pilots requested for medical services to meet the aircraft on arrival.”
Approximately 17 minutes after the turbulence event, at 8.06am UTC, the pilots initiated a normal, controlled descent from 37,000 ft and the aircraft reached 31,000 ft at 08.10am UTC.
“The data showed that the aircraft did not encounter further severe turbulence during this diversion”, said MOT, adding that the flight touched down in Suvarnabhumi Airport at 8.45am UTC.
Interviews with passengers painted a harrowing scene on SQ321 - one where those who were unbelted flew out of their seats and onto the ceiling of the plane, before slamming back down.
Others described the experience on the plane as akin to riding a roller coaster.
Many who went through the ordeal hit their body parts on the cabin interior such as armrests of overhead panels, with some people suffering cuts on their heads and bleeding ears from the incident.
Photos of the plane’s interior following the incident showed broken overhead panels, oxygen masks can be seen dangling from the ceiling, and food strewn all over the floor.
Continue reading...
1G is equivalent to the force of gravity on Earth’s surface.
SQ321 had been travelling from London to Singapore last Tuesday (May 21) when it encountered extreme turbulence. One passenger died and dozens were injured, resulting in an emergency diversion of the plane to Bangkok.
In a statement on Wednesday, the Ministry of Transport (MOT) said its Transport Safety Investigation Bureau (TSIB) had extracted the data stored in the flight data recorder and cockpit voice recorder of the plane.
A team comprising TSIB investigators and United States representatives - from the National Transportation Safety Board (NTSB), Federal Aviation Administration (FAA) and Boeing - then compiled a chronology of events based on preliminary analysis of the data.
This is what they found:
SQ321 departed London and the flight was normal prior to the turbulence event. At 7.49am UTC (3.49pm Singapore time) on May 21, the aircraft was passing over the south of Myanmar at 37,000 ft (11,300m) and “likely flying over an area of developing convective activity”, said MOT.
The G force, recorded as vertical accelerations, fluctuated between positive 0.44G and positive 1.57G for a period of about 19 seconds. “This would have caused the flight to begin to experience slight vibration,” said MOT.
Around the same time as the onset of the vibration, an “uncommanded" increase in aircraft altitude, reaching a peak of 37,362 ft, was recorded. In response to this, the autopilot pitched the aircraft downwards to descend back to the selected altitude of 37,000 ft.
In addition, the pilots observed an uncommanded increase in airspeed which they addressed by extending the speed brakes, said MOT.
Eleven seconds after the initial vibration, it was heard that a pilot called out that the fasten seat belt sign had been switched on.
These uncommanded increases in aircraft altitude and airspeed were most likely due to the aircraft being acted upon by an updraft, or the upward movement of air. During this period, autopilot was engaged.
The aircraft then experienced a rapid change in G, 19s after the initial vibrations, as recorded vertical acceleration decreased from positive 1.35G to negative 1.5G, within 0.6s.
“This likely resulted in the occupants who were not belted up to become airborne,” said MOT.
Just one second later, the vertical acceleration changed from negative 1.5G to positive 1.5G, within 4s. “This likely resulted in the occupants who were airborne to fall back down,” said MOT.
The rapid changes in G over the 4.6 sec duration resulted in an altitude drop of 178 ft, from 37,362 ft to 37,184 ft.
“This sequence of events likely caused the injuries to the crew and passengers,” said MOT.
In the midst of the sequence of rapid changes in G, recorded data “indicated that the pilots initiated control inputs to stabilise the aircraft, disengaging the autopilot in this process”.
The pilots manually controlled the aircraft for 21s and reengaged the autopilot at 07.50am UTC, just 44s after the initial vibrations.
The recorded vertical acceleration showed more gradual fluctuations over the next 24s, ranging from positive 0.9G to positive 1.1G, while the aircraft returned to 37,000 ft 18s after the pilots reengaged the autopilot.
After the pilots were informed by the cabin crew that there were injured passengers in the cabin, the decision was made to divert to Suvarnabhumi Airport in Bangkok, Thailand, said MOT.
“On the way to Bangkok, the pilots requested for medical services to meet the aircraft on arrival.”
Approximately 17 minutes after the turbulence event, at 8.06am UTC, the pilots initiated a normal, controlled descent from 37,000 ft and the aircraft reached 31,000 ft at 08.10am UTC.
“The data showed that the aircraft did not encounter further severe turbulence during this diversion”, said MOT, adding that the flight touched down in Suvarnabhumi Airport at 8.45am UTC.
Interviews with passengers painted a harrowing scene on SQ321 - one where those who were unbelted flew out of their seats and onto the ceiling of the plane, before slamming back down.
Others described the experience on the plane as akin to riding a roller coaster.
Many who went through the ordeal hit their body parts on the cabin interior such as armrests of overhead panels, with some people suffering cuts on their heads and bleeding ears from the incident.
Photos of the plane’s interior following the incident showed broken overhead panels, oxygen masks can be seen dangling from the ceiling, and food strewn all over the floor.
Continue reading...