I've been following this thread and it looks like we've moved to a new/old topic, i.e.,
trim chains/definition of "freely suspended/definition of "
overhead lifting". And lots of inconsistencies.
The following is IMHO from 49 years and 7 months of professional rigging. I know that some agree and some disagree. FWIW, I have seen and, officially and unofficially, investigated a significant number of "incidents" and "accidents". I have never seen a
trim chain fail, regardless of the chain size or grade. As part of my regular work, I do facility
safety inspections. Rigging is of course the major component of those inspections. I have found chains,
wire rope and other components with well over 50 years in use.
Trim chains, as a group, are by far the least affected by long and hard use. I regret now that I didn't foresee this conversation and document those observations until now.
My major observation is not unique or new.
Trim chain, even the smallest size of G30 proof coil, is far stronger than the
wire rope used in the
system. Example: 1/4", 7x19
GAC has a
breaking strength of 7,000# and a
WLL of 875#. 1/4" G30
proof coil chain has a
WLL of 1,300# and a
breaking strength of 5,200#. As
trim chain is, when properly used, rigged in a "
basket" configuration, the load capabilities are doubled. What that means is that the load ratings, both
breaking strength and
WLL, of even the lowly 1/4" chain is over a ton greater than the aircraft cable that supports it.
My second observation is that the suspension
point terminations, i.e. the
wire rope thimble eye and the first link of the chain, show zero evidence of wear due to friction. This supports the definition of "freely suspended" as a single
point with no restrictions to twisting or swaying.
My major
point here is I wish that, as an industry, we could make a standard that is recognized, to define, specifically, what a
trim chain is and must be. To define what "
overhead lifting" is.
If we define grade 80 chain as the only acceptable chain, we will all eliminate
trim chains. All riggers will go to
batten clamps and turn buckles. If we create a code that specs STC or Alpha chain, fine. Over kill IMHO but we're all on the same
page and playing field. If a Standard were to be drafted and approved, it would have to include a paragraph on how to deal with existing installations and what "must" be upgraded and what "shall" be upgraded.