Narrative:

Level at FL330 with engine and wing anti-ice on; flying in IMC conditions; light continuous turbulence; above and to the west of convective weather sat -39 both standby airspeed indicators became erratic and unreliable. The primary airspeed indicators appeared stable and normal. I guarded the autopilot disconnect switch and prepared to disconnect. Pitch was verified and I disconnected the autothrottles and set about 85% N1. We seemed to be bleeding speed and I increased N1 to about 87% (heavy aircraft) while I tried to determine if the primary indicators were working. With pitch at recommended and N1 slightly above recommended for level flight; primary airspeed indication continued to decrease. Autopilot disconnected as expected at approximately vls minus a bit and I took over hand flying and began a descent at 2 degrees nose down and idle thrust. During transition to descent I felt a momentary stall buffet onset so I was unsure if primary airspeed indicators were reliable. I then descended using unreliable airspeed procedure. We advised ATC the nature of our emergency and requested divert to VMC conditions and airport. Descending through approximately FL250 all airspeed indications appeared to be normal again but being unsure I continued to hand fly using manual throttles and pitch. During maneuvers for the visual approach and through 180 degrees of turns I compared IAS; TAS; GS and wind vector to determine if IAS seemed correct which they did. Vref was 140 with winds 15 gusting 20 and landing weight of about 306;000 lbs on 10;000 ft. Runway and I chose to fly the approach at 145 KIAS. Pitch attitude and aircraft response was normal and ATC made ground speed call-outs on final which were all consistent with expected air speeds. After clearing the runway we requested arff to inspect the nose of the aircraft and pitot probes for damage; there was none visible so we taxied to the gateway and shutdown. We did advise company thru ACARS on descent about the divert and received an amendment from dispatch.

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Original NASA ASRS Text

Title: A300 Crew experiences unreliable airspeed indications at FL330 while flying in the vicinity of convective weather. ATC is advised and a divert to a VMC airport is requested using pitch and power to maintain a safe airspeed. Passing FL250 all airspeed indications returned to normal.

Narrative: Level at FL330 with engine and wing anti-ice on; flying in IMC conditions; light continuous turbulence; above and to the west of convective weather SAT -39 both standby airspeed indicators became erratic and unreliable. The primary airspeed indicators appeared stable and normal. I guarded the autopilot disconnect switch and prepared to disconnect. Pitch was verified and I disconnected the autothrottles and set about 85% N1. We seemed to be bleeding speed and I increased N1 to about 87% (heavy aircraft) while I tried to determine if the primary indicators were working. With pitch at recommended and N1 slightly above recommended for level flight; primary airspeed indication continued to decrease. Autopilot disconnected as expected at approximately Vls minus a bit and I took over hand flying and began a descent at 2 degrees nose down and idle thrust. During transition to descent I felt a momentary stall buffet onset so I was unsure if primary airspeed indicators were reliable. I then descended using unreliable airspeed procedure. We advised ATC the nature of our emergency and requested divert to VMC conditions and airport. Descending through approximately FL250 all airspeed indications appeared to be normal again but being unsure I continued to hand fly using manual throttles and pitch. During maneuvers for the visual approach and through 180 degrees of turns I compared IAS; TAS; GS and wind vector to determine if IAS seemed correct which they did. Vref was 140 with winds 15 gusting 20 and landing weight of about 306;000 lbs on 10;000 ft. runway and I chose to fly the approach at 145 KIAS. Pitch attitude and aircraft response was normal and ATC made ground speed call-outs on final which were all consistent with expected air speeds. After clearing the runway we requested ARFF to inspect the nose of the aircraft and pitot probes for damage; there was none visible so we taxied to the gateway and shutdown. We did advise company thru ACARS on descent about the divert and received an amendment from Dispatch.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.