Gents,
My example is of the double nut variety, something I presume was part of the tensioning shackles on the Electra.
A turnbuckle is a different animal than a shackle. In your example you show a turnbuckle with only safety wire preventing rotation of the barrel, (not the cables). So the wire is not technically a “fail safe”. It is the primary (and only) part that prevents disaster, if the barrel rotates.
I would ask if it has been your experience that threaded ends of control cables routinely wander out, or in, disrupting tension, and potentially causing separation? Mine is that if the barrel of any cable system is fixed, stranded Stainless cable can not rotate about its own axis. If both ends are attached, the cable is rigid in respect to torsion (twisting). To rotate a cable end with its opposite end still attached is not possible, certainly not for the purpose of removal.
I think the implication in the final report of 706 is that the co-pilot’s aileron command cable separated. The implication being that a safety wire’s absence prior to flight allowed the cable to rotate, unthread, and separate, causing the disaster. If safety wire was the sole retainer, that might be possible. If a true “safety wire” (fail safe) system, then it cannot have “caused” the crash. It can only be said that “it failed to prevent” the crash.
Semantic? Certainly. My assumption is that the tensioner was double nutted, a design sufficient to secure the cable. A safety wire may have been a part of the design, but my doubt is that the safety wire was the sole retainer of the cable. Hence, “fail safe”.
In any case, I believe the report mentions that none of the specific parts could be recovered, making proof impossible.
A similar cause of loss of aileron Control would be the “jammed” boost unit power arm, or seized piston. The unit was found, and showed evidence of seizure of piston or jamming of power arm. The conclusion was the seizure was caused by fire damage. What steps were taken to determine the aileron boost unit was not seized prior to launching, or final right turn?
To arrive at a probable cause involves not only supporting the theory, but eliminating all other possibilities?
Questions:
What angle of right aileron deflection was discovered on the power arm? Was it three degrees?
After unseizing and replacing the piston, the boost unit was serviceable. So the cylinder was not damaged by fire? Just the piston?
The pilot’s Control cables were found to have continuity, but lacked a safety wire. The co-pilot’s controls were not found, but they certainly must have been missing the safety wire? Why? Because there was no safety wire on the pilot’s set?