December 30, 1997 – The National Transportation Safety Board is investigating an accident occurring over the Pacific Ocean on December 28 involving United Airlines flight 826, a Boeing 747-100 on route from Tokyo to Honolulu. The aircraft apparently encountered turbulence, resulting in one passenger fatality and scores of injuries.
The aircraft's digital flight data recorder (DFDR) arrived at NTSB headquarters at approximately midnight Monday, December 29. The DFDR records 17 flight characteristics, or "parameters." Safety Board engineers have been downloading the data since that time and report the following preliminary information.
About 1 hour and 31 minutes into the flight, while cruising at 31,000 feet (not 33,000 feet as initially reported to authorities), wings level at a heading of approximately 103 degrees, the aircraft sustained a 1.8G upward load, with a 0.1G lateral (sideways) load. This upward load would have the effect of pushing an occupant down into the seat. Simultaneously, a 15 knot wind shear increased the air speed of the plane from 335 knots to 350 knots.
Six seconds later, the aircraft sustained a -0.8G load. This would have the effect of pulling an occupant out of the seat, or against a seat belt if the occupant were restrained. The G forces were less than "0.0" for approximately one half of a second. During this period, the aircraft rolled to 17 degrees right wing down.
The data indicate that altitude excursions up or down during the incident were less than 100 feet.
Pilot control column position does not appear to have been a factor in either the positive or negative G excursions. The aircraft turned around about 23 minutes after the incident, landing in Tokyo about 2 ½ hours later.
The Board's investigation will continue, including a more detailed review of the DFDR; interviews with the flight crew, cabin crew and passengers; documentation of the damage to the aircraft; weather; and analysis of air traffic control communications. The Board does not expect to issue any updates on this accident for several weeks.
A final Safety Board report on the cause of this accident will be issued next year. Safety recommendations may be issued at any time.