BOEING 747-422United Airlines
Pacific Ocean, A1 · 2013-02-19·N174UA
What happened
NTSB summary, verbatimThe flight crew reported that the flight experienced unexpected light-to-moderate turbulence during cruise flight for about 3 hours. The seatbelt sign was illuminated, and the passengers and flight attendants had been seated. A flight attendant, who was on her rest break and was resting in the bunk room, reported that the turbulence had stopped for a while and that she thought she heard a "faint ding" indicating that the seatbelt sign had been turned off, so she went to the lavatory. However, the flight then encountered moderate turbulence, during which the flight attendant sustained a serious injury while walking from her bunk to the lavatory. The flight attendant reported that announcements made over the public address system could not be heard in the bunk room and that it was not always possible to hear when the seatbelt sign was turned on or off. It is likely that, if the flight attendant had a visual indication that the seatbelt sign was on, she would not have attempted to get up until safe movement was assured.
Photographs
1the aircraft, and what the investigators foundProbable cause
the Board's determinationThe flight’s encounter with moderate clear air turbulence while en route, which resulted in a serious injury to a flight attendant. Contributing to the accident was the lack of communication equipment in the rest compartment, which, if installed, could have alerted the cabin crewmembers that the seatbelt sign was on.
Occurrence sequence
1 stepsNTSB coding · CICTT taxonomy- 1 · Enroute-cruiseTurbulence encounterdefining event
Findings
2 causal · 0 contributing- CAUSEEnvironmental issues › Conditions/weather/phenomena › Turbulence › Clear air turbulence — Effect on equipment
- CAUSEAircraft › Aircraft systems › Communications system › Interphone — Not installed/available
Sequence of events
9 timed eventsfrom the FDR factual report · claude-sonnet-5- 0540 UTCDeparturep.1Flight departed Sydney (YSSY/SYD), Australia airport on an IFR flight plan
- 1500 UTCCruisep.1N174UA encountered turbulence during cruise flight over the Pacific Ocean while en route to SFO
- 14:16:00 UTCCruisep.3FDR data indicated vertical acceleration variations began, ranging between 1.3 g's and 0.65 g's; pressure altitude started at about 37,000 ft
- 14:24:00 UTCCruisep.3Pressure altitude increased to about 39,000 ft (approximately 8 minutes after 14:16:00 UTC)
- 16:41:40 UTCCruisep.3Pressure altitude, having remained at about 39,000 ft for approximately 2 hours and 18 minutes, began to decrease
- 16:41:40 to 17:13:30 UTCCruisep.3Over approximately 31 minutes and 50 seconds, pressure altitude decreased to a minimum of 37,575 ft, then increased to a maximum of approximately 41,000 ft before decreasing and settling at a pressure altitude of about 33,000 feet
- 17:13:30 UTCCruisep.3Vertical acceleration variations ended
- 18:31:07 UTCLandingp.3The aircraft landed
- 18:40:00 UTCPost-landingp.2End of FDR recording
NTSB analysis
from the final reportThe flight crew reported that the flight experienced unexpected light-to-moderate turbulence during cruise flight for about 3 hours. The seatbelt sign was illuminated, and the passengers and flight attendants had been seated. A flight attendant, who was on her rest break and was resting in the bunk room, reported that the turbulence had stopped for a while and that she thought she heard a "faint ding" indicating that the seatbelt sign had been turned off, so she went to the lavatory. However, the flight then encountered moderate turbulence, during which the flight attendant sustained a serious injury while walking from her bunk to the lavatory. The flight attendant reported that announcements made over the public address system could not be heard in the bunk room and that it was not always possible to hear when the seatbelt sign was turned on or off. It is likely that, if the flight attendant had a visual indication that the seatbelt sign was on, she would not have attempted to get up until safe movement was assured.