Tornando a leggere su
http://www.avherald.com/h?article=41bb9740&opt=0 questa segnalazione relativa a Northwest A333 over East China Sea on Jun 23rd 2009, unreliable airspeed trovo alcune rilevanti analogie proprio con quanto comunicato da BEA nell'ultimo rapporto.
............. 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.........
In particolare ........ 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. ..........
In pratica perdita delle velocita' su tutti e tre gli indicatori e indicazione di 60 KIAS che guarda caso e' simile al reportb BEA dove leggiamo .....Les param่tres enregistr้s montrent une chute brutale d’environ 275 kt vers 60 kt de la vitesse affich้e du c๔t้ gauche, puis quelques instants plus tard de la vitesse affich้esur l’instrument de secours (ISIS). ..........
ed inoltre disconessione autopilota ...e la attivazione di una serie di allarmi nel volo Northwest A333 ..... autopilot and autothrottle disconnected, the fly by wire changed to alternate law, master warning and master caution illuminated, a number of aural alerts sounded.......(non viene specificato comunque quello di stallo)
La differenza piu rilevante che penso sia quella che ha permesso al volo A333 Nordwest di non avere problemi piu' gravi mi pare invece ........... The pilot concluded his report saying, that they had good conditions like daylight, a relatively small area of rain and light turbulence only......... ossia ,,,,,, like daylight, a relatively small area of rain and light turbulence only........ tutte condizioni purtroppo assenti nel caso dell A330 Air France.
Edgar
