Loss of tail rotor effectiveness (LTE) or unanticipated yaw in helicopters SIB 2010-12

Loss of Tail rotor Effectiveness (LTE) has been determined to be a contributing factor in a number of accidents of various models of helicopters. Recently several helicopter reported accidents or incidents emphasize the phenomenon of loss of yaw control.
LTE or unanticipated yaw results from lack of yaw margin encountered in certain flight conditions is not related to a failure or malfunction. LTE is a critical, low-speed aerodynamic flight condition that could affect all single main rotor helicopters equipped with a tail anti-torque device. The
uncommanded yaw occurs to the right in helicopters with a counter clockwise rotating main rotor and to the left in helicopters with a clockwise rotating main rotor.

SIB Attached