Originally Posted by
gulliBell
From what I understand, if the after start hydraulic servo checks had been done properly in the Copterline example then that aircraft should have been grounded.
gulliBell:
Your theory is naive. Helicopter servos doesn’t move much while the helicopter is in the ground or the helicopter is taxing. When the autopilot is engaged the Electric Line Actuators are giving some slight control commands to the servos. When the helicopter is lifted to the hover and during the flying phase 99.99 percent of the servo's movements, loads and stress will be actualized to the Servo Actuators. In the practice the work load, aerodynamical load, vibrations to the Servo Actuators will be generated during flight phase only.
Your theory doesn’t take into account that the most likely the plasma flakes or plasma particles are chipping (remove)from the head of the Servo Actuator’s Piston during flight phase and blocks the C3 return port or C3 ports during the flight phase.
It is very unlikely that the plasma will be removing from the piston head at time when the helicopter is in the ground run or taxing. In the ground the servo actuators don’t have any moves, loads, aerodynamical loads or vibration. This all loads are mostly generated by the M/R Blades as a function of airspeed / vibration. The Servo Actuators will take on all the aerodynamic loads that the main rotor generates during the main rotor generates the lift. This aerodynamic load is very huge especially for the forward Servo Actuator. The other Servo Actuators are having much less aerodynamic load than the forward Servo Actuator.
It is possible but improbably that the Servo Actuator’s piston plasma coating chipping will happen in the ground when the Servo Actuators are almost “frozen” phase.
The helicopter will be safe if this plasma chipping or plasma flakes separation from the Piston will happen in the ground phase. The common sense is saying that the risk for chipping or plasma separation from the Piston head and that the plasma flakes will obstruct Servo Actuator’s C3 return fluid ports. The partial blockage is enough to cause the Actuator Piston Jam. When the Piston is jammed, the Servo out put will not respond to control inputs. This will lead to the Loss of the affected channel. The loss of Servo Channel will possible cause the loss of the control of entire aircraft. The consequence may most likely to be a fatal.
The S76 system design is not capable to identify Actuator Piston Jam by SER.JAM CAUTION because in case the “jam” has been caused by the blockage of the C3 return port(s). The MCV is still capable to move but the return port(s) are block. The Servo Actuator is “jammed” but with out any caution to the helicopter caution and warning system. The SER.JAM CAUTION is activated if the MCV is mechanically jammed. The flight crew don’t have any indication that the Servo Actuator has failed. When the one of the tree Servo Actuators are frozen, fully extended or not working parallel with the other the Mixing Unit will finally to mix helicopter steering logic. This will lead to the situation where the helicopter is unflyable. The problem is very well investigated and analyzed already by the end of 70’s e.g. by H-53 helicopters accident investigations.
Looking forward to see Bristow Helicopter’s accident 12th of August, 2015 accident report why the S76C+ was spiraling and acting precisely like COPTERLINE 103 and what was the reason for the second accident when Bristow Helicopter S76 become unflyable 3rd of February, 2015.