NTSB Identification: ANC01IA022.
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Scheduled 14 CFR UNITED AIRLINES INC.
Incident occurred Tuesday, December 12, 2000 in PORT HEIDEN, AK
Probable Cause Approval Date: 11/01/2001
Aircraft: Boeing 747-422, registration: N119UA
Injuries: 4 Minor,386 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.
A Boeing B-747 airplane departed San Francisco for Hong Kong. Prior to departure, no significant meteorological notices or forecasts for turbulence were issued for the area of the Alaska Peninsula, over which the flight would progress. The airplane was initially in radio and data link communications with Oakland ARTCC, then ARINC, and finally with Anchorage ARTCC. A PIREP at 1432 for moderate turbulence, and an Urgent PIREP at 1600 of severe turbulence, were recorded in the area of incident by Anchorage ARTCC. As the flight entered the Alaska ARTCC area, a delay in establishing communications with the airplane also delayed the transmission of the urgent PIREP concerning turbulence in the area of the flight. The crew noticed rolling clouds ahead of the airplane and advised the cabin flight attendants to be seated. At 1620, while in cruise flight at 31,000 feet, the airplane encountered moderate to severe turbulence. About 5 seconds after the notification to sit down, three cabin attendants were thrown to the floor of the airplane. The captain diverted the flight to Anchorage. Upon arrival at Anchorage, a belly mounted fuselage panel enclosing an air conditioning unit, was missing. Airplanes conducting oceanic flights are equipped with ACARS, over which flight crews can receive ATC clearances and weather data utilizing controller/pilot data link communications (CPDLC). The Anchorage ARTCC was not utilizing CPDLC because their software is not user friendly, requires substantial controller input for free text messaging, and is not as fast as voice communications. Hazardous inflight weather advisories are reviewed by each center weather coordinator, in conjunction with the National Weather Service for dissemination to pilots. The FAA does not a direct mechanism to alert air crews of significant weather in one sector, occurring in another sector, nor does the FAA have a mechanism to coordinate CPDLC data from an ARTCC sector to ARINC. A SIGMET for occasional turbulence was issued by the National Weather Service at 1619.
The National Transportation Safety Board determines the probable cause(s) of this incident to be: An encounter with severe turbulence while in cruise flight. Factors in the incident were a delay in notification of the turbulence, and the lack of controller/pilot data link communications in the Anchorage ARTCC area. Full narrative available
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