Action
Final rule.
Summary
We are adopting a new airworthiness directive (AD) for certain Bombardier Inc. Model DHC-8-400 series airplanes. This AD was prompted by reports that the automatic de-icing mode became unavailable due to a failure of the timer and monitor unit (TMU). This AD requires replacing the TMU. We are issuing this AD to prevent loss of the automatic de- icing mode and consequent increased workload for the flightcrew, which, depending on additional failures, could lead to loss of control of the airplane.