FlarePath

What happened

NTSB summary, verbatim

The captain stated that the ride had been smooth at their cruise altitude of 36,000 feet, and the seatbelt sign was off. He further stated that there was some thunderstorm activity, and some towering cumulus in the area, and that the airplane’s radar indicated the presence of a cell about 30 miles south of the airplane’s position, with tops that reached about 28,000 to 30,000 feet. He said they encountered an area of higher clouds, but the radar still did not indicate any activity, and within a few seconds they felt an initial bump, followed by "moderate" turbulence. He said he then turned the seatbelt sign on, and a short while later he was notified that there were some injured passengers and flight attendants. The NTSB’s Recorder Laboratory, Washington DC, read out the DFDR, and the data indicated that at 13:27:22 FDR Recorded GMT, at a pressure altitude of 36,000 feet, the vertical acceleration changed from 0.9 g’s to 1.8 g’s to -0.5 g’s to 1.7 g’s and then back to 0.9 g’s all within 3 seconds, consistent with clear air turbulence. See the NTSB DFDR Factual Report. In addition the NTSB conducted a meteorological study, using data to include synoptic, upper air, and satellite data. See the NTSB Meteorological Factual Report.

Photographs

1the aircraft, and what the investigators found

The aircraft before the accident

Probable cause

the Board's determination

An inadvertent in-flight encounter with unforecasted clear air turbulence

Occurrence sequence

1 stepsNTSB coding · CICTT taxonomy

1 · Enroute-cruise
Turbulence encounter
defining event

Findings

1 causal · 0 contributing

CAUSE
Environmental issues › Conditions/weather/phenomena › Turbulence › Clear air turbulence — Not specified

Sequence of events

3 timed eventsfrom the FDR factual report · claude-fable-5-1 (in-session)

13:20:20-13:34:20 GMTcruisep.3
14-minute window plotted around the encounter
13:27:22 GMTcruisep.3
About 5 hours 21 minutes after takeoff at 36,000 ft pressure altitude, vertical acceleration changed from 0.9 g to 1.8 g to -0.5 g to 1.7 g and back to 0.9 g within 3 seconds
about 14:53 GMTlandingp.3
Aircraft landed at Guam approximately 1 hour 26 minutes after the encounter

NTSB analysis

from the final report

The captain stated that the ride had been smooth at their cruise altitude of 36,000 feet, and the seatbelt sign was off. He further stated that there was some thunderstorm activity, and some towering cumulus in the area, and that the airplane’s radar indicated the presence of a cell about 30 miles south of the airplane’s position, with tops that reached about 28,000 to 30,000 feet. He said they encountered an area of higher clouds, but the radar still did not indicate any activity, and within a few seconds they felt an initial bump, followed by "moderate" turbulence. He said he then turned the seatbelt sign on, and a short while later he was notified that there were some injured passengers and flight attendants. The NTSB’s Recorder Laboratory, Washington DC, read out the DFDR, and the data indicated that at 13:27:22 FDR Recorded GMT, at a pressure altitude of 36,000 feet, the vertical acceleration changed from 0.9 g’s to 1.8 g’s to -0.5 g’s to 1.7 g’s and then back to 0.9 g’s all within 3 seconds, consistent with clear air turbulence. See the NTSB DFDR Factual Report. In addition the NTSB conducted a meteorological study, using data to include synoptic, upper air, and satellite data. See the NTSB Meteorological Factual Report.

MCDONNELL DOUGLAS DC10Omni Air International