Tue, Aug 09, 2011
New Advisory Circular AC 20-24C The Result Of 11-Month
Process
The FAA has responded to a rapid increase in the pace of
development of alternative fuels for aircraft with an updated
version of a 25-year-old advisory circular, AC 20-24B. The new AC
20-24C took almost a year to finalize including the public comment
period. It is dated July 29, 2011, but is just now showing up in
electronic document databases.
The new AC specifically accepts military, ASTM and other
industry-consensus standards as acceptable for defining fuels and
oils for turbine engines, as well as piston engines made by TCM and
Lycoming, and makes clear that other standards are acceptable to
the FAA provided they adequately define performance, and how it is
to be measured.
The complexity of the topic is underlined by many of the public
comments, which mischaracterized the circular as a regulation, or
misinterpreted it as a requirement to use ASTM's process.
The new guidance allows definitions of new fuels based on
performance criteria without regard to the feedstocks used to
create them. This may lower the barriers to introductions of
drop-in fuels made from biomass for both turbines and piston
engines. It also provides a system for commonality in
specifications for developing type certificates and STCs for fuels
which may not work in legacy engines fleet-wide.
While traditional fossil-based oils used for engine lubrication
are considered a lower priority for phase-out, for both economic
and environmental reasons, the new AC 20-24C also covers their
specifications.
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