AD 2020-22-07 Was Prompted By An Accident And Multiple Reports Of A Cracked Main Gearbox (MGB) Support Case

The FAA is adopting a new airworthiness directive (AD) for all Bell Textron Inc. (Type Certificate previously held by Bell Helicopter Textron Inc.) Model 412, 412CF, and 412EP helicopters.

This AD requires revising the existing Rotorcraft Flight Manual (RFM) for your helicopter. This AD was prompted by an accident and multiple reports of a cracked main gearbox (MGB) support case. The FAA is issuing this AD to address the unsafe condition on these products. This AD is effective November 18, 2020.

Supplementary Information: The FAA is adopting a new AD for Bell Textron Inc. Model 412, 412CF, and 412EP helicopters. This AD was prompted by an accident on a Model 412EP helicopter and multiple reports of a cracked MGB support case. Initial investigations showed that excessive pylon pitch vibrations likely caused overload that resulted in these failures, and investigations are ongoing to determine the root cause of these vibrations. However, field experience and flight test data indicate that excessive degradation of the transmission mounts and friction dampers could cause the sudden increase in one-per-rev vertical vibration, and minimum collective and cyclic controls friction not meeting the maintenance manual specifications may also be a contributing factor.

This condition, if not addressed, could result in structural failure of the MGB support case and subsequent reduced control of the helicopter. To address this unsafe condition, this AD requires revising Section 2, Normal Procedures, under both “BEFORE TAKEOFF” and “IN-FLIGHT OPERATION(S)” of the existing RFM for your helicopter.

FMI: www.regulations.gov