Also for number 4. If extra holes that don't follow a standard pattern, if they were approved by a field approved 337 there should be no required action.
Kevin1 --- In [email protected], "Ed Burkhead" <e...@...> wrote: > > > > > > 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 >
