Summary
We propose to adopt a new airworthiness directive (AD) for certain Bombardier, Inc. Model DHC-8-102, -103, and -106 airplanes, Model DHC-8-200 series airplanes, and Model DHC-8-300 series airplanes. This proposed AD was prompted by several occurrences of loss of airspeed data on both pilot and co-pilot air speed indicators due to the accumulation of ice on the pitot probes. An investigation revealed that the accumulation of ice was due to inoperative pitot probe heaters. This proposed AD would require replacing the existing circuit breakers in both the left and right side of the pitot heater system with circuit breakers that have higher trip points. We are proposing this AD to prevent circuit breakers from tripping and cutting power supply to the pitot probe heater, which could cause loss of airspeed data and result in the flightcrew not being able to control the airspeed of the airplane.