Hartmut suggests these possibilities for holes found in the center section
spar:
> We should give reasonable advice on how this
> amendment will look like.
>
> 1. First , no extra holes , no further action
> 2. Extra holes, documented - verify that it follows
> an approved pattern
> 3. Extra holes, not documented - certify if it follows
> the approved number and pattern
> 4. Extra holes not following an approved pattern
> or number. Replace spar cap or add stiffener
> provided by Univair ( has to be developed)
At the least, I would suggest a second remedy to option 4: Provide an
engineering analysis by a DER or other qualified individual showing the
extra holes do not degrade the spar strength beyond required limits.
For example, the designer's letter:
http://edburkhead.com/Ercoupe/fred_weick_reply_on_holes.htm
And, indeed, before an AD is issued or amended, the FAA should show that
spar holes degrade the strength beyond acceptable limits. So far, we have
only a single instance in which a spar failed, very possibly due to extreme
loads due to aileron flutter and/or a sudden high-g pull-up, possibly at
higher than normal airspeed. I question that this instance justifies
grounding aircraft due to the spar holes.
As always, aircraft which have controls that don't meet the specifications
in ERCO Service Department Memorandums 56 and 57 are unairworthy.
Ed
