Originally Posted by Geoffersincornwall
It is quite stunning for this non-technically qualified pilot to hear that the design of both the S92 and the 225 used single pathways for the activation of both main and back-up oil pumps that serve the single most important component in the drive train - the Main Transmission Gearbox. Tell me I have it wrong somebody - please. I cannot believe this is true - I must have misunderstood.
I initially thought the same thing, but I saw a picture today of the gearbox minus the housing, so all the gears were exposed and held in place to show how they all mesh. Looking at it the pump drive is simplicity and genius in a sense.
The pumps are driven by the one shaft that never stops when we are airborne, the main rotor shaft.
Each pump has its own gear on that shaft that it is driven by.
The standby pump is lower with a lower intake to draw the oil in reducing the amount of pipework necessary.
The end result is no one looking at that design prior to these two incidents would imagine the shaft(s) shearing and causing this problem. So credit to Aerospatiale when they designed the Superpuma system that the 225 inherited.
Si