SEA99IA032

History of flight

On January 20, 1999, approximately 1230 hours Universal Coordinated Time (UCT), a Boeing 747-238B, N14024, registered to/operated by Continental Airlines, Inc., and being flown by a crew of three airline transport pilots, encountered clear air turbulence (CAT) while at flight level (FL) 330 in cruise near 33 degrees North latitude and 133 degrees west longitude, approximately 900 nautical miles east of Tokyo, Japan (refer to CHART I). The aircraft sustained only minor interior damage. The three flight crewmembers were uninjured, as were eleven of the fifteen flight attendants and 326 of the 336 passengers (four flight attendants and ten passengers sustained minor injuries). Visual meteorological dark night conditions existed at the time, and an IFR flight plan was in effect. The flight, being operated as Continental flight 910, a regularly scheduled passenger/cargo run from Tokyo, Japan, to Honolulu, Hawaii, USA, had departed Tokyo's Narita International airport at 1121 UCT. The aircraft was met by personnel from the Federal Aviation Administration's Honolulu Flight Standards District Office and members of the crew were interviewed.

The operator reported that "At 1121 UCT on January 20, 1999, Continental Airlines Flight 910 departed Tokyo/Narita (NRT), Japan, enroute [sic] for Honolulu (HNL), Hawaii. At approximately 1230 UCT while in cruise at FL330 and in the vicinity of 33 degrees North latitude and 155 degrees East longitude (900 nautical miles east of Tokyo), the flight encountered severe clear air turbulence lasting about 10 minutes. Altitude excursions ranged from plus 500 feet to minus 1000 feet. Although turbulence had been forecasted, no other aircraft had reported encountering any along the route of flight. The night was clear and nothing was displayed on the onboard radar. The Captain had turned on the seat belt sign about 5-8 seconds prior to the encounter after observing a sudden fluctuation in the OAT [outside air temperature] (-37F) as the aircraft entered an area of wave activity. Air Traffic Control was contacted to secure a block altitude of FL310 to FL330 which was subsequently approved. The decision to continue to destination was predicated on it took time to get information from the cabin on the status of the injured and that there would have been a time delay in getting a clearance back through the flow of departing flights. The return also would have been back through an area of known turbulence. Several Japanese nurses on board attended the injured and reported none appeared serious. Most of the injuries occurred in the back of the aircraft. The injuries consisted of bumps, bruises and minor lacerations. Coordination for medical assistance was done through Med Link and company dispatch. A total of 14 were taken to two medical facilities and all were treated and released." (Refer to attached NTSB Form 6120.1/2).

Meteorological information

The National Weather Service (NWS) High Level Significant Weather Prognostic chart of the Northwest Pacific area near the time of the event indicated a cold front extending over the area with a forecast of isolated embedded cumulonimbus clouds. The chart also indicated two jet streams traversing the area, one at 34,000 feet at 160 knots and the other to the south at 39,000 feet at 180 knots. The jet streams generally diverged in the area of the event.

Additionally, a satellite image (GMS-5) taken at 1230 UCT on the date of the event indicated a band of high level clouds in the immediate area of the event. The clouds were aligned in a "band" formation oriented northwest to southeast, and perpendicular to the wind flow pattern. This pattern was similar to previous CAT encounters with transverse wave cloud patterns (refer to attached Group Chairman Meteorological Review).

Flight and cockpit voice recorders

The aircraft's cockpit voice recorder (CVR), which remained powered for more than its 30 minute rewrite cycle following the event, was not examined.

Data from the aircraft's flight data recorder was examined at the Safety Board's Office of Research and Engineering, Vehicle Recorders Lab. The tape was found to be broken within the unit. Additionally, no useful data could be retrieved from the tape that could be associated with the event flight.