one. Unless you are modifying or attaching something to
a primary structure, you are not having an appreciable
effect on the structural strength of the aircraft.
There are similar definitions in 8110.46 for performance, powerplant operation, flight characteristics, or
“other qualities affecting airworthiness.” Read these definitions carefully in your evaluation of whether an alteration is major or minor.
Part 43 Guidelines
Part 43 Appendix A of the FARs specifically defines major
alterations to airframes, powerplants, propeller, and appliances. These regulations also shed some light on how the
FAA wants us to determine major versus minor alterations. Fortunately, both 8110.46 and Part 43 Appendix A
continue the same theme; major alterations are changes
to the foundations of the aircraft certification. If you
are changing how a system works, the basic structural
integrity, or the certified operational characteristics of the
aircraft, you are making a major alteration.
For example, let’s consider an alteration to the aircraft’s
electrical system. Is adding a new circuit to the existing
power bus a major alteration? Not
unless it exceeds the basic capacity
of the system. It’s the system design
that we’re concerned with. Adding
a backup alternator or a new electrical bus are both examples of major
Part 43 Appendix A asks: “Does
the proposed alteration change the
basic design of the fuel, oil, cooling,
heating, cabin pressurization, electrical, hydraulic, deicing, or exhaust
systems?” If it does, it’s a major alteration.
Because of this type of confusion,
Aircraft Electronics Association has
been working closely with the Small
Airplane Directorate to better clarify
the intent of the regulations concerning electrical system alterations.
They have had numerous discussions
with FAA leadership concerning what
constitutes a major change to the
electrical system of the aircraft. All
parties agree that major changes are
those that would affect the basic
certification of the aircraft by the
manufacturer. These include changes
in power generation, distribution,
and regulation. Expect to see new
guidance materials from the FAA on
this matter soon.
Jeff Simon is the president of Approach
Aviation, a provider of educational
products, tools, and supplies for aircraft
owners. To learn more about aircraft
ownership and maintenance, visit www.
ApproachAviation.com or call 877-