Airworthiness Directives; Bell Helicopter Textron Canada Model 407 Helicopters

This amendment adopts a new airworthiness directive (AD) for the specified Bell Helicopter Textron Canada (Bell) model helicopters that requires preflight checking and repetitively inspecting for a crack in certain tailbooms that have not been redesigned and replacing the tailboom if a crack is found; modifying and re-identifying certain tailbooms and installing an improved horizontal stabilizer assembly; and assigning a 5,000 hour time-in-service (TIS) life limit. This amendment is prompted by cracking discovered in other areas of certain tailbooms and introduction of a redesigned tailboom with a chemically milled skin, which does not require the current inspections. The actions specified by this AD are intended to prevent separation of the tailboom and subsequent loss of control of the helicopter.