[Top] [All Lists]

Re: [TowerTalk] Crankup Tower Cable Issues

Subject: Re: [TowerTalk] Crankup Tower Cable Issues
From: "" <>
Date: Fri, 30 Apr 2010 11:08:21 -0700
List-post: <">>

I thought this was a good read: wire rope failure forensics.
Nice photos for a lot of failure modes. From a guy whose career is analyzing 
wire rope 

Some nice stuff about lightning issues, pictures of heat melting etc

But in terms of failure modes and inspection, I liked this comment:
 "visual rope inspection = 20% evidence + 80% hope"

(he was talking about internal wire breaks, and how the outer wires only 
represent about 40% 
of the metallic cross section, in most ropes)

Also: how can you tell if a replaced cable needed to be replaced? You would 
have to test it 
to failure...and that's along all parts of the cable?

I've replaced rusty cables, that are clearly brittle, and strands broke when I 
bent the 
cable sharply. And I agree with the author above, that it's difficult to 
inspect a cable 
under load.

It would be interesting to test cables from towers that have failed. i.e. was 
the rest of 
the cable perfectly good, and only one exact spot weak? If so, then the risk is 
the one weak spot?

For people thinking stainless steel cable is better, here's an interesting page 
to read

an interesting story from there:
Flight Control cable failures have occurred even though the cable was inspected 
according to 
the book. An Aileron control cable failure on a Boeing 737-3TO on takeoff at 
September 27, 1997 just six weeks after the cable was inspected for wear. The 
consisted of checking for visible wear (external wire wear). However, the NTSB 
found that 
the internal wires were 90% worn. A Boeing 737-100, Flight 169 lost aileron 
control when the 
aircraft cable broke. The NTSB found that existing inspection methods could not 
detect the 
breakage of 98 of the 133 strands in the cable!  The broken strands were not 
detected using 
the prescribed method of drawing a cloth rag over the cable.  Only until 
tension was 
released from the cable were the broken strands detectable. Thus the need to 
release cable 
tension to better detect broken strands.



TowerTalk mailing list

<Prev in Thread] Current Thread [Next in Thread>
  • Re: [TowerTalk] Crankup Tower Cable Issues, <=