NTSB Identification: FTW97IA261.
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Scheduled 14 CFR AMERICAN AIRLINES
Incident occurred Thursday, July 10, 1997 in DICKINSON, ND
Probable Cause Approval Date: 12/31/1998
Aircraft: Boeing 757-223, registration: N660AM
Injuries: 22 Minor,133 Uninjured.
NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.
The airplane was in level cruise flight at FL370, flying in an area of widely scattered thunderstorm cells. The airborne weather radar was set to the 160 nm scale, and the tilt was approximately 1 to 2 degrees down. One cell was observed 20 nm to the left of the airplane towering above its altitude, a second cell was 40 nm to the right, and a third cell 'came up independently underneath' and in front of the airplane. The FASTEN SEATBELT sign was not illuminated, but earlier, the captain had delivered an address to the passengers advising them of the possibility of a bumpy ride ahead and to '...keep your seatbelts on while in your seats.' The flight encountered convection induced turbulence (CIT), which resulted in minor injuries to 20 passengers and 2 flight attendants. There were no injuries to the other 120 passengers and 5 crew members. Vertical acceleration was between +2.01 and -0.75 g's. American Airlines meteorologists prepared the flight plan and entered a turbulence index of '0' for that segment of flight (from Billings, Mt, to Dupree, SD), indicating smooth air on average for the segment. Convective activity had been forecast for the area.
The National Transportation Safety Board determines the probable cause(s) of this incident to be: an encounter with unforecast convection induced turbulence (CIT). Related factors were: the flight crew's improper evaluation of the weather, and an inaccurate preflight weather briefing by company weather personnel. Full narrative available
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