Issues with A330 speed sensors are drawing more scrutiny, with the U.S. National Transportation Safety Board saying it is now closely looking at two instances where in-flight problems were reported in the past two months.
Airspeed information on the aircraft type has been much in focus since the crash of Air France Flight 447. Some of the final messages transmitted by the onboard Acars message system indicated a problem with air speed information.
The NTSB says it is looking at a May 21 TAM Airlines flight (JJ8091) and a Northwest Airlines June 23 incident. The TAM A330 was flying between Miami and Sao Paulo, while the Northwest flight was between Hong Kong and Tokyo.
Here’s an unconfirmed write up of the Northwest flight that’s been making the rounds on various internet message boards:
Yesterday while coming up from Hong Kong to Tokyo, a 1700nm 4hr. flight, we experienced the same problems Air France had while flying thru bad weather. I have a link to the failures that occurred on AF 447. My list is almost the same.
The problem I suspect is the pitot tubes ice over and you loose your airspeed indication along with the auto pilot, auto throttles and rudder limit protection. The rudder limit protection keeps you from over stressing the rudder at high speed.
Tuesday 23, 2009 10am enroute HKG to NRT. Entering Nara Japan airspace.
FL390 mostly clear with occasional isolated areas of rain, clouds tops about FL410.
Outside air temperature was -50C TAT -21C (your not supposed to get liquid water at these temps). We did.
As we were following other aircraft along our route. We approached a large area of rain below us. Tilting the weather radar down we could see the heavy rain below, displayed in red. At our altitude the radar indicated green or light precipitation, most likely ice crystals we thought.
Entering the cloud tops we experienced just light to moderate turbulence. (The winds were around 30kts at altitude.) After about 15 sec. we encountered moderate rain. We thought it odd to have rain streaming up the windshield at this altitude and the sound of the plane getting pelted like an aluminum garage door. It got very warm and humid in the cockpit all of a sudden.
Five seconds later the Captains, First Officers, and standby airspeed indicators rolled back to 60kts. The auto pilot and auto throttles disengaged. The Master Warning and Master Caution flashed, and the sounds of chirps and clicks letting us know these things were happening.
Jerry Staab, the Capt. hand flew the plane on the shortest vector out of the rain. The airspeed indicators briefly came back but failed again. The failure lasted for THREE minutes. We flew the recommended 83%N1 power setting. When the airspeed indicators came back. we were within 5 knots of our desired speed. Everything returned to normal except for the computer logic controlling the plane. (We were in alternate law for the rest of the flight.)
We had good conditions for the failure; daylight, we were rested, relatively small area, and light turbulence. I think it could have been much worse. Jerry did a great job fly and staying cool. We did our procedures called dispatch and maintenance on the SAT COM and landed in Narita. That's it.
In the TAM case, the NTSB says “initial reports indicate that the flight crew noted an abrupt drop in indicated outside air temperature, followed by the loss of the Air Data Reference System and disconnections of the autopilot and autothrust, along with the loss of speed and altitude information. The flight crew used backup instruments and primary data was restored in about 5 minutes. The flight landed at Sao Paulo with no further incident and there were no injuries and damage.”
The failure sequence the NTSB outlines is not unlike the series of events suggested by the AF 447 Acars messages.
The NTBS says data recorder information, Acars messages, crew statements and weather information are being collected by investigators for further assessment.