The report should have read “Pilots’ “ rather than “Pilot’s”. “Pilot’s” is singular possessive, and means it was Captain’s cable that separated. In any case, there was only one pilot on board, the Commander. It was 1961, pre CRM, and the flight deck was NOT a democracy.
The cables are in tension at 70 pounds, as I read it.
I applaud your patience, Captain.
It is my belief that the control cable in discussion did NOT separate in flight from its insertion into the forward junction block of the slack absorber. During your read, remember the cable that survived intact was right where the mechanics left it.
Here’s why.
To remove the boost unit, it is necessary to slacken the cable control loop, which involves “unthreading” both cables from each slack absorber. Now that statement might be misleading, because the cable is not turning, it is stationary; it is the slack absorber that is being rotated. Rotate the slack absorber one way, (sixteen turns), the system slackens. Rotate the other way, the system tightens.
Why is the cable stationary? Because it is fixed at its other (forward) end to the Lockclad run ahead of it via a swaged connector. It is also fixed in place during tensioning by the lead mechanic’s helper. The cable will not rotate sufficient to loosen the one inch the mechanic needs to remove the boost unit. This one inch is only half of the total release, since as the slack absorber turns it “expels” each cable connector; the slack absorber has opposite threaded blocks at either end. So, two inches total.
The cable that remained attached had but one half inch of threads nested in the junction block, and CAB claim that was the position left by the mechanic when the system was loosened. There is no reason to assume the mechanic treated the other slack absorber differently.
This partially enclosed cable connector withstood all impact loads, as I believe its counterpart did. In any case, flight loads were insignificant compared to the enormous stresses of impact(s).
The safety wire is not installed to prevent the flexible cables from “retreating”. Safety wire, in this application, is utilized to keep the slack absorber from rotating. Conceptually, the cables keep the system constant, not the slack absorber.
The Spring in the barrel of the slack absorber? Once the cables are inserted to the prescribed depth, the spring is attached to either end of each flexible cable. It pulls them together, in tension greater than control forces, >70 pounds. Why? So the cable is not loaded to pull out, it is loaded to push in. Ninety nine percent of the time in flight, the cable wants to screw IN not OUT. Seventy pounds is not arbitrary.
I have some comments about the testing method used by Lockheed in its test of the control cabling resistance to failure in tension.
Lockheed mounted an exemplar cabling system and slowly added tension to failure point. The cable snapped. No mechanism for the slow addition of “tension to failure” exists in flight. A more accurate demonstration of failure would be shock loading, something that actually existed in this accident. There was no “slow increase in tension” post impact; none that I can find. In shock, the energy dissipation has a completely different behavior. My thought is that in shock, the brass block would fracture, and release the cable’s connector. This would explain the CAB’s finding re the cable impacting the aft wing spar hole with the connector intact.
My cynical side would claim Lockheed knew beforehand how the exemplar would fail. They were working to a theory, NOT experimentally building a foundation for study.
If this analysis is inaccurate, my bad, please correct. Also, if this is not the design Lockheed used, then it is mine, and it’s for sale.
Best,
Bill
(Your comment about inflight failure re cables is not what I addressed in my post. I was discussing the post impact evidence of failures, including, but not limited to, the control cables.....)