AD FAA-2012-1003

We are adopting a new airworthiness directive (AD) for certain Bombardier, Inc. Model DHC-8-400 series airplanes. This AD was prompted by reports of advance pneumatic detectors (APDs) for engine fire/ overheat detector assemblies failing to reset after activation due to permanent deformation of the detector switch diaphragm after being exposed to high temperatures. This AD requires replacing all three APDs with new detector assemblies. We are issuing this AD to prevent a continued engine fire indication in the cockpit after the actual fire has been extinguished, which is misleading and might influence the pilot to conduct a potentially hazardous "off-airport" landing.