Summary
We propose to adopt a new airworthiness directive (AD) for certain Bombardier Model DHC-8-400 series airplanes. This proposed AD was prompted by a report of several cracks found on the forward passenger airstair door step assembly. This proposed AD would require an inspection to determine the serial number of the airstair step assembly, and if necessary, an electronic tap test, re-identification of the airstair step assembly, and replacement of the airstair step assembly. We are proposing this AD to detect and correct cracks in the forward passenger airstair door step assembly, which could propagate and result in the structural failure of the steps and impede the evacuation of passengers in the event of an emergency egress situation.