EMB ERJ 145 ER/LR
Flight Crew Air Transport Pilot (ATP)
Distraction; Training / Qualification; Troubleshooting; Workload
Aircraft Equipment Problem Less Severe; Inflight Event / Encounter Other / Unknown
Aircraft Equipment Problem Dissipated; Flight Crew FLC complied w / Automation / Advisory; Flight Crew Took Evasive Action
Aircraft; Weather
During initial descent we noticed both primary airspeed tapes read erroneous. We complied with the Aircraft Operations Manual (AOM) 1 Unreliable Airspeed procedure. It appeared to have unfroze around FL290. We continued to treat the indications as unreliable and landed in our filed destination. My belief is moisture was present in the PITOT lines beyond the protected areas. There was decent amount of frost present on the inside of the widows/windscreens; except where it is heated. After landing; there was water draining from the drain just aft of the nose gear. No airframe ice was encountered during the flight.Continue to retrofit our fleet with the modification. Continue to provide proper training to flight crews. I have experienced this exact scenario during a simulator training Line Oriented Flight Training (LOFT). It was easier to detect the malfunction having seen it before.
The report stated he did not believe the aircraft was not picking up ice based on the lack of accumulation on the wiper blade and neither ice detector 1 nor 2 were alerting but the aircraft had been intermittently IMC with an outside air temperature of -55°C. One odd circumstance was that frost was accumulating on the inside of the forward windshields. The reporter was not aware of the aircraft sitting in precipitation for an extended period and maintenance too was puzzled why the air conditioning system did not remove all moisture.
Both EMB-145 airspeed indications became unreliable during the descent initiation from FL360 so the Unreliable Airspeed procedure was accomplished. Airspeed indication returned to normal around FL290 and frozen moisture in the pitot system plumbing beyond the pitot tubes is suspected.