Summary
We propose to adopt a new airworthiness directive (AD) for certain Model 400A, and 400T airplanes. This proposed AD would require a detailed inspection for proper sealant of the left and right pylon firewall structures, and corrective actions if necessary. This proposed AD results from reports of missing sealant on the left and right pylon firewall structures. We are proposing this AD to detect and correct missing sealant on the left and right pylon firewall structures, which, in the event of an engine fire, could result in flames penetrating the seams in the firewall between the engine and the aft fuselage, and a subsequent uncontrolled fire in the aft fuselage.