Top West, you ask a serious question.
Root cause?
The sequence of events:
The seat pan handle was operated - no one knows how or why. Speculation that the safety pin was not properly engaged and a strap had been passed through the yellow and black loop as young Cunningham moved about to settle into his seat and conduct his checks.
The seat fired.
The parachute failed to deploy. The cause being a bolt had been overtightened by an RAF technician. The bolt was quite critical. It should have not pinched the legs of the shackle together allowing it to swivel. The bolt was tightened such to show at least one and a half threads protruding from the nut. It had been tightened so tight to achieve this that it had cut a thread into the bolt. Poor design in that it was critical and should perhaps have been made fool proof. (A shoulder bolt or spacer tube to ensure the arms of the shackle were not pinched together.)
A simple check to ensure the shackle rotated about the bolt should probably have been wise. As this was essential to parachute deployment.
MB knew of the issue and had told other operators but apparently could find no evidence of having told their most “intelligent” customer.
Avoidable ? Yes. By design, by having appropriate training in place, by having appropriate documentation in place for maintenance, perhaps explaining the consequences of overtightening the bolt and knowledge of operation of the parachute deployment mechanism.
Oh and there being a Safety Case in place. The safety case would support the reasoned argument that the system posed no hazards to those involved in the maintenance or operation of the equipment. It would normally begin that the Designer is competent to design that type of equipment. It has been independently tested to ensure it meets the requirements specification. It has been maintained by competent people in line with a set of documented procedures. All to sub components are manufactured and sourced appropriately. Any hazards and incidents that come to light during use are properly investigated and addressed with lessons learned being promulgated.
So if it was known that overtightenng the bolt would prevent the parachute deploying that fact would be made known to the operators.