Reason and overview of the Service Bulletin (cause of problem if known)
A pressure regulator is fitted into the Cavalon and Sport 2017 pneumatic control box that limits the pressure applied to the trim cylinder in the event of a trim system ‘runaway’. This enables lower pitch stick control force if the system fails to full pressure. This is a legacy item, installed for Rotorhead II. Aircraft fitted with Rotorhead III (see photos) have a shorter distance between the rotorhead pitch axis and trim cylinder attachment, such that a higher trim cylinder pressure results in the same hand force on the stick. Extra trim pressure has been shown to be beneficial in certain aircraft configurations This service bulletin instructs how to either increase the pressure of the pressure restrictor, or remove the restrictor and replace with a single piece of pneumatic hose.