Summary
We propose to revise an existing airworthiness directive (AD) for the Agusta Model AB139 and AW139 helicopters. The existing AD currently requires inspecting the fuselage frame to detect fatigue cracks which could lead to structural failure and subsequent loss of control of the helicopter. Since we issued that AD, Agusta has developed a frame reinforcement modification which supports extending the interval for inspecting the fuselage frame for a fatigue crack. This proposed AD would require inspecting the fuselage frame for a crack, but would reduce the applicability from the existing AD to exclude helicopters modified by the optional frame reinforcement modification. The proposed actions are intended to detect a fatigue crack that could result in failure of the fuselage frame and subsequent loss of control of the helicopter.