Sec. 231. (a)(1) Within 90 days after the date of enactment  of
the  Clean  Air  Amendments  of  1970,  the  Administrator  shall
commence a study and investigation of emissions of air pollutants
from aircraft in order to determine- 
       (A) the extent  to which such emissions affect air quality
     in air quality control regions throughout the United States,
     and
       (B)  the technological  feasibility  of  controlling  such
     emissions.
  (2) The Administrator shall, from  time to time, issue proposed
emission  standards  applicable  to   the  emission  of  any  air
pollutant  from any class or classes of aircraft engines which in
his judgment causes,  or contributes to, air pollution  which may
reasonably be anticipated to endanger public health or welfare.
  (3) The  Administrator shall hold public  hearings with respect
to  such proposed standards.  Such hearings shall,  to the extent
practicable,  be held  in air quality  control regions  which are
most  seriously affected  by aircraft  emissions. Within  90 days
after the issuance  of such proposed regulations,  he shall issue
such regulation with such  modifications as he deems appropriate.
Such regulations may be revised from time to time.
  (b)  Any  regulation prescribed  under  this  section (and  any
revision  thereof) shall  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 within such period.
  (c) Any regulations  in effect  under this section  on date  of
enactment  of the Clean Air Act Amendments of 1977 or proposed or
promulgated thereafter,  or amendments  thereto, with respect  to
aircraft shall not  apply if disapproved by the  President, after
notice  and opportunity  for public  hearing, on  the basis  of a
finding by the Secretary of  Transportation that any such regula-
tion would create a  hazard to aircraft safety. Any  such finding
shall include  a reasonably specific statement of  the basis upon
which the finding was made.
[42 U.S.C. 7571]