Action
Notice of proposed rulemaking (NPRM).
Summary
We propose to supersede an existing revised airworthiness directive (AD) for all Bell Model 204B and certain serial-numbered Model 205A-1 helicopters with a certain tail rotor pitch control chain (chain) installed. The existing AD requires visually inspecting the chain to detect a crack in the link segments and, for affected Model 205A-1 helicopters, replacing the tail rotor chain and cable control system with a push-pull control system. Since we issued that AD, we have determined the need to apply the requirements to a newly-produced, similarly-designed chain with a different part number. Also, for the Model 204B, data shows the need to reduce the inspection interval of the chain and revise its inspection procedures because the rapid growth of a crack can lead to premature chain failure and to install a tail rotor cable and chain damper kit (damper kit) to reduce the oscillatory loading. We have also determined that installing a push-pull control system should apply to Model 205A-1 helicopters with certain serial numbers, regardless of the chain part number installed. These proposed actions are intended to prevent failure of the chain, loss of tail rotor blade pitch control, and subsequent loss of control of the helicopter.