Northwest Flight Crew In Japan Noted Airspeed Fluctuations

The NTSB has released a preliminary finding in an incident involving a Northwest Airlines Airbus A330 on a flight in Japan last month in which the onboard computers switched off the aircraft's autopilot possibly due in part to inconsistent airspeed indications.

The report reads:

NORTHWEST AIRLINES INC
Incident occurred Tuesday, June 23, 2009 in Kagoshima, Japan
Aircraft: AIRBUS A330-323, registration: N805NW
Injuries: 217 Uninjured.

This is preliminary information, subject to change, and may contain errors. Any errors in this report will be corrected when the final report has been completed.

On June 23, 2009, at 0303 UTC, an Airbus 330-323, U.S. registration N805NW, operated by Northwest Airlines as flight 8 from Hong Kong, China, to Tokyo, Japan, experienced an airspeed anomaly while in cruise flight at FL390 approximately 50 miles southwest of Kagoshima, Japan. The crew reported that they were in normal cruise at FL390 and in visual conditions with some convective weather displayed on radar about 25 miles north of track, with thin cirrus clouds ahead.

After entering the cirrus and moderate precipitation and turbulence, the crew observed, and FDR confirms, the autopilot and autothrust switch off, and the aircraft switched to Alternate Law. The master caution and warning messages were activated. The crew followed flight manual procedures and the autopilot and normal law returned in about one minute, however the event quickly repeated itself, lasting for about 2 minutes. The crew turned the airplane 60 degrees off course to exit the weather as soon as the anomalous indications were observed. The autopilot, autothrust and other controls returned to functioning, but the airplane remained in alternate law for the rest of the flight.

File Photo

The crew observed, and FDR confirms, large airspeed fluctuations, small altitude fluctuations, and an overspeed alert. The flight continued to Tokyo, Narita airport and landed with no damage or injuries to the 9 crew and 208 passengers on board.

The incident occurred in Japanese airspace, and the investigation was delegated to NTSB by the Japanese Transportation Safety Board, who assigned an Accredited Representative to the investigation.

FMI: www.ntsb.gov