N720AX
MCDONNELL DOUGLAS DC10
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.
On May 19, 2008, about 1340 UTC, a McDonnell Douglas DC-10-30, N720AX, operated by Omni Air International, as a Title 14 CFR Part 121 supplemental, non-scheduled international passenger flight, reportedly experienced moderate turbulence, over the Pacific Ocean, while in cruise flight at FL360, about 450 nautical miles east of the Territory of Guam, United States of America. The airplane subsequently landed in Guam, uneventfully. Visual meteorological conditions prevailed, and an instrument flight rules flight plan was filed. Of the 150 passengers and 12 crewmembers on board, two passengers and two flight attendants received minor injuries, and one flight attendant received serious injuries. The flight originated at Honolulu International Airport, Honolulu, Hawaii, the same day, about 0745 UTC. According to Omni Air International’s Director of Safety, the accident captain stated in his irregularity report that at approximately 1330z while at 36,000 feet, they encountered moderate turbulence. He said that the ride had been smooth for the whole flight and that the seatbelt sign had been off. There was some thunderstorm activity in the area, and 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. The pilot said that they saw some towering cumulus clouds in the area, but that the ride still continued to be smooth. The lead flight attendant was on the flight deck, and they encountered an area of higher clouds, but the radar did not indicate any activity. The Captain said that within a few seconds they felt an initial bump, followed by moderate turbulence. The seatbelt sign was then turned on, and the lead flight attendant sat in the observer’s seat. According to the Captain the turbulence lasted only a few seconds, after which the lead flight attendant left the flight deck. A few minutes later the lead flight attendant communicated with the flight deck and informed the Captain of the injured passengers and flight attendants. The lead flight attendant stated that about 1330Z they encountered "bad turbulence", which lasted about 30 seconds. She further stated that she was in the cockpit at the time, and as soon as the turbulence was gone she left the cockpit to check on everyone, at which time another flight attendant informed her that two flight attendants were "down." She then communicated with the flight deck and relayed the information to the captain. Another flight attendant stated that the flight encountered two turbulence events while the cabin crew was making preparations for the second meal service. She said that the turbulence in the first event was slight but the second event was "drastic." She said that the second turbulence event caused her to hit the ceiling and then her entire body descended and slammed to the floor. The accident airplane’s flight data recorder (FDR) was sent to the NTSB’s Recorder Laboratory, Washington DC, for readout, and was found to contain 14 minutes of data pertaining to the accident flight. 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. The data showed that the airplane’s autopilot had been engaged, and that there was lateral acceleration during the drop in altitude, without corresponding flight or engine control input, consistent with severe clear air turbulence. See the NTSB FDR 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.
An inadvertent in-flight encounter with unforecasted clear air turbulence
Source: NTSB Aviation Accident Database
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