EMB ERJ 135 ER/LR
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe; Deviation - Altitude Excursion From Assigned Altitude
Aircraft Equipment Problem Dissipated; Flight Crew Overcame Equipment Problem; General Maintenance Action
Aircraft; Weather
While in instrument conditions at FL370; I noticed my airspeed slowly bleeding off. As I mentioned this to the First Officer; we received IAS on my Primary Flight Display. When 'SPS speeds advanced' was annunciated; along with ALT on my Primary Flight Display; I manually disengaged the autopilot and asked the First Officer to request an immediate descent to vacate RVSM and find a warmer temperature; since I assumed that the pitot-static line for the Air Data Computer had frozen. Due to center frequency congestion; we were unable to make our request known before losing approximately 400 feet. Once communication was established; however; there was no issue or further delay in accommodating our descent. During the initial descent phase; the First Officer's Air Data Computer information was referenced and; when deemed correct; we utilized cross-side data via my reversionary panel; referencing the AOM procedure. Once a warmer altitude was reached (within just a few thousand feet - approximately FL340); the system returned to normal operation and the flight continued normally. Since the aircraft so quickly returned to a normal configuration; no emergency was declared. Freezing water (approximately 1 teaspoon) was discovered in the pitot static line during the subsequent maintenance inspection.
The pilots of an Embraer 135 identified an airspeed anomaly followed by crew alerting messages; they suspected a frozen pitot-static line to the Air Data Computer. After descending a few thousand feet the system returned to normal. Later; Maintenance personnel confirmed that frozen water was found in the pitot-static line.