Hi Dave,
Comments interspaced below.
Regards,
WRB
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On Sep 25, 2009, at 15:33, [email protected] wrote:
All,
Mike Sigman, the previous owner, and I spoke last night while I was on
my way to DFW. He said he had looked at two Ercoupes, an original
415C with no mods and a 415 with bucket seats. The original airplane
had two holes on centerline in the shallow 'V" of the main spar cap
that the tab on the seat pan fastens to. Most other people I've
talked to have these two holes. I believe this is the factory
configuration. According to Mike, the 'coupe with bucket seats had
exactly the same pattern as my main spar cap-- four holes on the left
outboard, two holes on the left inboard, two holes in the center of
the "V", two holes in the right inboard, and four holes in the right
outboard. Our new theory is that my airplane once had bucket seats.
I suggest you take measurements and compare with the following
information from my email to the FAA of (/23/09):
"Per production drawing F53180 (Rev. B dated 6/10/60), the Forney F-1A
bucket seats are secured at the front by one left and right hook mounts
of similar construction.
Centerlines of these hooks are 4.437" outboard of the aircraft
centerline and then 10" further outboard on each side. Each such hook
is mounted to the main spar by four 8-32 fasteners. Installation
required a total of sixteen 11/65" (.171) holes to be drilled through
the spar cap. These are drilled in pairs, aligned fore and aft, at
eight locations. Per production drawing F53189 L/R (Rev. A dated
2/4/60) the fore-aft separation is .875". Per production drawing
F53190 L/R (Rev. A dated 2/4/60) the port-starboard separation is
1.468".
Holes drilled in the main spar for the forward attachment of bucket
seats installed in later production Forney, Alon and M10 (TCDS 787)
airframes may or may not be identical in number, size and location
between manufacturers. Please research and advise as to any
variations, considering this request my IR#17. The production change
to bucket seats received appropriate FAA review, was timely approved
almost fifty years ago, and has proven safe in extended service, and
has been approved as a retrofit in earlier airframes by approved 337.
Accordingly, there should be a strong presumption that any associated
reduction in spar strength resulting from the drilling or presence of
such holes is of no overall structural significance."
There is no record of this and no 337 or STC in the FAA file, so it
was probably just a logbook entry.
Probably. All mechanics and FSDOs do not necessarily agree as to when
a modification submitted by a manufacturer to the FAA and subsequently
approved as a production or model change is considered a "minor one"
for mere log book documentation or a "major one" requiring a 337.
We think a subsequent owner probably removed the buckets and went back
to the original seat. The A&P probably drilled 12 holes in the front
lip of the seat pan and installed 10-32 screws rather than leaving the
holes open to make the pan fit flush with the top of the spar cap.
Since re-installing the original seat would not require a 337, we are
looking to see if there is a logbook entry to confirm this.
If there were a log book entry documenting the original bucket seat
installation, then likely there would be one for going back to the
original configuration. There are mechanics that would look in the log
books and find no mention of the bucket seat installation that would
"restore the aircraft to its original configuration" (bench style
seats) and deem no log book notation necessary because the original
change had not "been made" officially.
Consider also the aircraft in the firld that may have, for one reason
or another, replaced the main spar. At any time since the mid fifties,
such main spar furnished would be from Forney, Alon or Mooney stock
with bucket seat holes there as "standard".
Here's the interesting thing-- there are probably a LOT of Ercoupes
that had bucket seats installed and had a 337 submitted. By
definition, that would mean these are FAA-approved modifications that
would have additional holes drilled into the main spar cap to mount
the seats. I urge 415 owner with extra holes in the main spar cap to
look for documentation and 337's to show that they may have had an
FAA-approved bucket seat installation.
Prof. Ed has been "beating the bushes" for some time on this list
trying to find even ONE such 337, insofar as I can tell without
conspicuous success.
That doesn't necessarily mean that the additional holes could not be a
structural integrity issue, but it would at least prove that the FAA
did not think they would create a problem at the time of approval.
When the FAA approved of production bucket seats in the Forney, Alon
and M10s, they essentially certified that such holes of such size,
number, size and configuration were NOT a "structural integrity issue".
The "burden of proof" that such holes now constitute a "structural
integrity issue" would clearly be on the FAA now or at any time in the
future.
Mike is going to try to get pictures of the Ercoupe with bucket seats
to corroborate this. Unfortunately, without documentation my holes
are probably unauthorized.
Regards,
Dave
Regards,
WRB
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