A Northwest Airlines Airbus A330-300, registration N805NW performing flight NW-8 from Hong Kong (China) to Tokyo Narita (Japan), was enroute overhead the East China Sea, when the crew noticed a sharp drop of the indicated outside temperature followed by the loss of the air data reference system, disconnection of autopilot and autothrust system along with the loss of speed and altitude information. The flight crew used the stand by systems and was able to restore the primary data. The airplane landed safely in Tokyo Narita.
The NTSB is investigating, the flight data recorders have been retrieved, the aircraft condition monitoring system messages, crew statements and weather information are being collected by NTSB investigators.
The NTSB reported, that a very similiar incident happened on May 19th to a TAM Airbus A330-200, see Incident: TAM A332 enroute on May 21st 2009, unreliable airspeed and altimeter.
An e-mail is circulating in the Internet presumably from the copilot of the flight describing the event. The authenticity of the e-mail could not be entirely verified, there are indications suggesting, that the e-mail is authentic, and there are some indications to the contrary. The e-mail began to circulate before the NTSB issued their press release.
The e-mail reported, that the airplane was enroute at FL390 just entering Japanese airspace in daylight. The sky was mostly clear with occasional isolated areas of rain, cloud tops up to FL410. Outside Air Temperature (OAT) was -50 degrees Centigrade, Total Air Temperature (TAT - oncoming air gets heated due to compressibility effects of the air) was -21 degrees Centigrade, way too cold for liquid water at that altitude. The weather radar showed heavy precipitation below the aircraft, at the airplane's level the weather radar showed light precipitation, ice crystals, the crew thought. Entering the tops of the clouds the airplane encountered light turbulence at winds of about 30 knots. About 15 seconds later the crew saw moderate rain on the windshield. 5 seconds later all three airspeed indicators, captain's side, first officer's side and the standby instruments, rolled back to 60 KIAS, autopilot and autothrottle disconnected, the fly by wire changed to alternate law, master warning and master caution illuminated, a number of aural alerts sounded. The captain flew manually out of the rain on the shortest possible way. The airspeed indicators returned briefly, but were lost again. The captain flew at recommended thrust setting of 83% N1 (and maintaining the recommended pitch angle [editor's note]). When the airplane left the area of rain, everything returned to normal except for the fly by wire, which remained in alternate law for the remainder of the flight. The airplane was within 5 knots of its target speed, when the airspeed indications returned. The encounter lasted for about 3 minutes. The pilot concluded his report saying, that they had good conditions like daylight, a relatively small area of rain and light turbulence only.
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