Action
Supplemental notice of proposed rulemaking (NPRM); reopening of comment period.
Summary
We are revising an earlier proposed airworthiness directive (AD) for certain Bombardier, Inc. Model DHC-8-400 series airplanes. That NPRM proposed replacing all three advance pneumatic detectors (APDs) with new detector assemblies. That NPRM was prompted by reports of ADPs 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 action revises that NPRM by adding airplanes to the applicability. We are proposing 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. Since these actions impose an additional burden over that proposed in the NPRM, we are reopening the comment period to allow the public the chance to comment on these proposed changes.