Chapter 66 for the Sikorsky S76 is the Powertrain, main gear box, intermediate and tail gear box , tail rotor drive shafts, rotor brake system, electrical system for the gear boxes ( chip detectors, pressure , temp, warning sensors on the main gear box).
From what I understand the authorities want an enhanced inspection of the flight controls and drivetrain.
Reading between the lines they are not sure what happened and want the aircraft critical systems inspected until they figure it out.