Summary
We propose to adopt a new airworthiness directive (AD) for certain Bombardier, Inc. Model BD-700-1A10 airplanes. This proposed AD was prompted by a report that the manufacturer has determined that some completion centers used the heater/brake monitoring unit (HBMU) logic circuit to control the line voltage of the drain mast heaters. Since the drain mast heaters are connected in parallel with the number 2 pitot static (PS) probe heater circuit, a number 2 PS probe heater failure may not be detected by the fault monitoring capabilities of the HBMU. This proposed AD would require a modification of the air data probes and sensors. We are proposing this AD to detect and correct an unannunciated failure of two PS probe heaters, which could affect controllability of the airplane in icing conditions.