Maintenance and Modifications
Safety Alert Addresses Bell 206/407 Transmission
There have been two accidents involving Bell 206s where a malfunction of the main transmission freewheel system led to a failure of the main rotor mast.

Following up on an earlier, Airworthiness Directive Transport Canada has issued a Civil Aviation Safety Alert (CASA) to address transmission issues with Bell 206, 206L and 407 helicopters. The purpose of this CASA is to inform operators of “the vulnerability of the main transmission freewheel lubrication system to contamination, to emphasize how critical it is to ensure a conforming filter is installed and to follow the manufacturer's recommended procedures for aircraft storage and reactivation.”