Summary
We propose to adopt a new airworthiness directive (AD) for Bell Helicopter Textron Canada (BHTC) Model 407 helicopters with certain tailboom assemblies installed. This proposed AD would require, at specified intervals, inspecting the tailboom assembly for a crack, loose rivet, or other damage. This proposed AD is prompted by a stress analysis of the tailboom skin that revealed high-stress-concentration areas are susceptible to skin cracking. This condition, if not detected, could result in a crack in the tailboom assembly, failure of the tailboom, and subsequent loss of control of the helicopter.