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| Date: | Monday 9 May 2011 |
| Time: | 04:06 LT |
| Type: |  Airbus A319-131 |
| Owner/operator: | United Airlines |
| Registration: | N801UA |
| MSN: | 686 |
| Year of manufacture: | 1997 |
| Total airframe hrs: | 47316 hours |
| Engine model: | IAE V2522-A5 |
| Fatalities: | Fatalities: 0 / Occupants: 125 |
| Aircraft damage: | None |
| Category: | Accident |
| Location: | Chillicothe, Missouri -
 United States of America
|
| Phase: | En route |
| Nature: | DSP |
| Departure airport: | Phoenix-Sky Harbor International Airport, AZ (PHX/KPHX) |
| Chicago-O'Hare International Airport, IL (ORD/KORD) | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
No adverse weather was forecast for the route. The seatbelt sign was turned off at FL320. The airplane leveled off at a final cruise altitude of 37,000' and the ride was smooth up until the turbulence encounter. Both the captain's and first officer's weather radar was in use before and during the turbulence event, and there was no adverse weather along the route visible on radar. The flight crew received no weather updates from Air Traffic Control, no pilot reports (PIREPS), and there was no traffic along the same route in front of this flight.
Evaluation of the winds using FDR data revealed that the aircraft sustained strong and adverse wind fluctuations on all three axes during the turbulence encounter, which included an upwards vertical wind gradient was about 80 knots in a 10 second timeframe. Recorded ground weather radar information revealed that the flight was probably passing over or through the extreme top of a rapidly developing area of convective weather at the time of the turbulence encounter. Although ground based radar reflectivity data indicated that the precipitation rate within this rapidly developing cell at the time was light to moderate, detection of the cell would likely have required active adjustment of the aircraft's weather radar system. However, the flight crew was not actively manipulating the aircraft radar at the time of the event given the lack of severe weather indications.
Probable Cause: An inadvertent encounter with unforecast convective turbulence.
Accident investigation:
 |
|
Sources:
NTSB DCA11FA053
Location
Revision history:
| Date/time | Contributor | Updates |
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