Fatal crash Arizona

On 9/13/2016 9:26 AM, Dave Nadler wrote:
On Tuesday, September 13, 2016 at 10:34:20 AM UTC-4, BobW wrote:
As for the report's claimed missing pawl spring...I must be getting dense
in my old age, since I'm still puzzled by the intended function and line
of force of that implicated piece of (missing?) hardware. Back to the
hook design - what am I missing? Thanks!

Bob W.

If I understand correctly, the missing spring pushes the pawl in the
direction opposite of pulling the release knob. Otherwise, the pawl is not
secured in the "latched" position, except by a bit of friction with the
hook plate (from the spring that is present and any rope tension).

Do I understand correctly??


Quite possibly. I suppose such a spring fairly might be considered the
"suspenders" to the hook-retract-spring's "belt." It's not obvious from the
photos (Figure 1 shows it best), but installed-geometry, plus gravity, in the
pawl's as-installed position/angle work "against" the pawl remaining
detent-seated...i.e. the pawl pivoting by itself (no other physical contacts)
would tend to flop its "business end" *away* from the detent due to the longer
cable-attach arm's length compared to the detent-engagement arm's length
(unequal length teeter-totter).

Nonetheless, whether the absence of a compression spring between the pawl and
receptacle/pawl-spring-housing was a crucial element in this accident is
debatable; it would take very little force on the rope to rotate the cable
hook from the barely-engaged position (Figures 9) to the fully engaged
position (Figure 8). Once there, further testing definitely required to
determine whether the design would be more or less prone to back-releasing in
the absence of the pawl spring, in the presence of a rope bow...

That said - and since a number of these hooks have been installed into the
noses of German-built ships originally entering the USA with only a CG hook -
owners of ships with these hooks SHOULD (and easily can) VERIFY the
presence/absence of such a compression spring by checking to see if the pawl
is positively forced against the rotating piece of the cable hook throughout
its rotation range. Positive engagement = spring-present. (Note that the
spring itself is hidden in the hook's assembled state...and might easily
escape unnoticed in the event of the hook being disassembled for any reason.)

Bob W.