In
response
to
these
comments,
we
refer
to
Sections
231(
a)(
2)(
B)
and
(
b)
of
the
CAA.
Section
231(
b)
requires
that
any
emission
standards
"
take
effect
after
such
period
as
the
Administrator
finds
necessary
(
after
consultation
with
the
Secretary
of
Transportation)
to
permit
the
development
and
application
of
the
requisite
technology,
giving
appropriate
consideration
to
the
cost
of
compliance
during
such
period."
The
language
in
Section
231(
b)
is
forward
looking
and
on
its
face
assumes
that
the
requisite
technology
to
meet
emission
standards
might
not
currently
be
in
widespread
production.
Section
231(
b)
thus
allows
EPA
to
establish
aircraft
engine
emission
standards
at
a
level
that
is
currently
not
achieved
in
practice
by
all
aircraft
engines
(
i.
e.,
the
standards
would
force
some
technological
improvements),
provided
there
is
sufficient
lead
time
before
such
standards
become
effective,
and
the
agency
gives
appropriate
consideration
to
the
cost
of
compliance
within
such
period.
We
recognize
that
there
are
limitations
on
our
authority
to
establish
new
emissions
standards
relating
to
implications
on
noise
and
safety.
Section
231(
a)(
2)(
B)
provides
that
the
Administrator
shall
consult
with
the
Administrator
of
the
FAA
on
standards,
and
"
shall
not
change
the
aircraft
engine
emission
standards
if
such
change
would
significantly
increase
noise
and
adversely
affect
safety."
Therefore,
if
it
is
demonstrated
that
aircraft
engines
meeting
the
changed
standards,
when
installed
on
airframes,
would
significantly
increase
noise
and
adversely
affect
safety,
EPA
is
prohibited
from
promulgating
such
standards.
