Narrative:

We were repositioning beechjet empty. We were cleared to 39000 ft shortly after departure. Both departure and arrival airfields were VMC. After level off at 39000 ft; we noticed some higher clouds ahead. We requested and were cleared to 41000 ft to fly over this weather. As we continued; there was scattered visible moisture at cruise altitude. We decided to use engine anti-ice and it remained on for the remainder of the flight. As we proceeded; there was a large thunderstorm to the southwest of our route of flight. We followed its echo on our radar; and determined to keep 150NM or more separation from the storm. Approximately 1 hour into the flight; we entered IMC conditions at 41000 ft; the clouds were from the downwind outflow from the storm to our southwest. Winds at altitude were from the southwest at 60-70 KTS. At some point; we noted the sat to be approx -60C. In the cloud; we encountered nothing more than light chop; similar to what we had experienced before entering IMC. We continued to monitor the storm cell on radar and requested 15 degrees left of course to maintain our distance from the cell. We were in IMC approximately 15 minutes; when center cleared us to 24000 ft at pilot discretion and expect to cross an intersection at 11;000 ft. With the expected crossing loaded in the FMS; it generated a 3000 FPM decent rate to stay on profile. We began our let down to 24000 ft. After only a few minutes into the descent; a flashing boxed IAS appeared on the airspeed tape of my pfd. I alerted the first officer to this and noticed his pfd had the same indication. The airspeed indication began to decay on both P and cp tapes. The airspeed on the peanut airspeed indicator was decaying too. I recognized this as possible pitot tube icing. I disengaged the autopilot and told the first officer to find the loss of airspeed indication emergency procedure. Complying with the procedure; we began flying by the aoa gauge. The altitude tape was still working on both sides; as were the vsis. The peanut altimeter was also still functioning. We felt there was little risk of going too slow and possibly a risk of going too fast; so we reduced thrust to below 70%. We contacted center and told them about our problem; then declared an emergency. Both airspeed tapes continued to decay to zero; as did the peanut airspeed indicator. Both airspeed and altitude tapes then vanished from the pfd display. They were replaced by 2 red flashing boxes that contained letters I cannot remember at this time (possibly air data computer and FD?). During the entire sequence; there was never any annunciator panel illumination (particularly anything pitot related). Pitot heat had been on the entire flight per SOP and checklist. We broke out into the clear at approximately 24000 ft. We were cleared down to 11000 ft by that time and given a vector further left of flight plan course. We confirmed our altitude reading with ATC. Shortly thereafter; say 22000 ft; on our continued descent; all pfd indications rapidly re-appeared; on both pfds; including both the airspeed and altitude tapes. All warning flags also disappeared. We undeclared our emergency with ATC. We continued for a normal arrival; approach; and landing into ZZZ. On taxi in; we noticed the FMS indicated only a 20 minute flight. We suppose; that since the airspeed indicators dropped to zero; the FMS recognized it as a landing and reset all leg parameters. We contacted maintenance with the problem. They instructed us to write up a check of the pitot tube heaters. The pitot tube heaters were checked by manual feel the next morning; the fault signed off; and the aircraft was returned to service. We have had no subsequent failures. We checked the FMS maintenance failure page and found 2 events that may be related to our encounter: air data computer xa:56Z failure code #350 and #351; air data computer xa:57Z failure code #350 and #351. Those are the facts; as we remember them. The following is our interpretation of what happened. We believe both pilotand copilot pitot systems iced up due to a unique combination of high moisture and very cold ambient temperatures. We don't believe the pitot heating system failed; it just couldn't keep up with the icing demand we encountered. Once we left the high moisture/temperature environment and descended to warmer ambient temperatures; the system de-iced and began to function normally again. I remember this dual ice up IAS failure being discussed at recurrent training. They spoke of a pitot heater modification being available for the beechjet. I don't know if an ad was ever issued or what aircraft were modified. It appears our experience is remarkably similar to the airbus incident in the south atlantic. We would suggest some aoa scenarios be incorporated into our simulator training.

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Original NASA ASRS Text

Title: A BE400 in IMC at FL410 lost both PFD and standby airspeed indications. Using AOA the aircraft was descended below FL220 where airspeed indications returned. Pitot heater anti-ice capability was suspected by the flight crew.

Narrative: We were repositioning Beechjet empty. We were cleared to 39000 FT shortly after departure. Both departure and arrival airfields were VMC. After level off at 39000 FT; we noticed some higher clouds ahead. We requested and were cleared to 41000 FT to fly over this weather. As we continued; there was scattered visible moisture at cruise altitude. We decided to use engine anti-ice and it remained on for the remainder of the flight. As we proceeded; there was a large thunderstorm to the SW of our route of flight. We followed its echo on our radar; and determined to keep 150NM or more separation from the storm. Approximately 1 hour into the flight; we entered IMC conditions at 41000 FT; the clouds were from the downwind outflow from the storm to our SW. Winds at altitude were from the SW at 60-70 KTS. At some point; we noted the SAT to be approx -60C. In the cloud; we encountered nothing more than light chop; similar to what we had experienced before entering IMC. We continued to monitor the storm cell on radar and requested 15 degrees left of course to maintain our distance from the cell. We were in IMC approximately 15 minutes; when Center cleared us to 24000 FT at pilot discretion and expect to cross an intersection at 11;000 FT. With the expected crossing loaded in the FMS; it generated a 3000 FPM decent rate to stay on profile. We began our let down to 24000 FT. After only a few minutes into the descent; a flashing boxed IAS appeared on the airspeed tape of my PFD. I alerted the First Officer to this and noticed his PFD had the same indication. The airspeed indication began to decay on both P and CP tapes. The airspeed on the peanut airspeed indicator was decaying too. I recognized this as possible pitot tube icing. I disengaged the autopilot and told the First Officer to find the Loss of Airspeed Indication EMER procedure. Complying with the procedure; we began flying by the AOA gauge. The altitude tape was still working on both sides; as were the VSIs. The peanut altimeter was also still functioning. We felt there was little risk of going too slow and possibly a risk of going too fast; so we reduced thrust to below 70%. We contacted Center and told them about our problem; then declared an emergency. Both airspeed tapes continued to decay to zero; as did the peanut airspeed indicator. Both airspeed and altitude tapes then vanished from the PFD display. They were replaced by 2 red flashing boxes that contained letters I cannot remember at this time (possibly ADC and FD?). During the entire sequence; there was never any annunciator panel illumination (particularly anything pitot related). Pitot heat had been on the entire flight per SOP and Checklist. We broke out into the clear at approximately 24000 FT. We were cleared down to 11000 FT by that time and given a vector further left of flight plan course. We confirmed our altitude reading with ATC. Shortly thereafter; say 22000 FT; on our continued descent; all PFD indications rapidly re-appeared; on both PFDs; including both the airspeed and altitude tapes. All warning flags also disappeared. We undeclared our emergency with ATC. We continued for a normal arrival; approach; and landing into ZZZ. On taxi in; we noticed the FMS indicated only a 20 minute flight. We suppose; that since the airspeed indicators dropped to zero; the FMS recognized it as a landing and reset all leg parameters. We contacted maintenance with the problem. They instructed us to write up a check of the pitot tube heaters. The pitot tube heaters were checked by manual feel the next morning; the fault signed off; and the aircraft was returned to service. We have had no subsequent failures. We checked the FMS maintenance failure page and found 2 events that may be related to our encounter: ADC XA:56Z Failure code #350 and #351; ADC XA:57Z Failure code #350 and #351. Those are the facts; as we remember them. The following is our interpretation of what happened. We believe both pilotand copilot pitot systems iced up due to a unique combination of high moisture and very cold ambient temperatures. We don't believe the pitot heating system failed; it just couldn't keep up with the icing demand we encountered. Once we left the high moisture/temperature environment and descended to warmer ambient temperatures; the system de-iced and began to function normally again. I remember this dual ice up IAS failure being discussed at recurrent training. They spoke of a pitot heater modification being available for the Beechjet. I don't know if an AD was ever issued or what aircraft were modified. It appears our experience is remarkably similar to the Airbus incident in the South Atlantic. We would suggest some AOA scenarios be incorporated into our simulator training.

Data retrieved from NASA's ASRS site as of April 2012 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.