
                                 Exhibit 10.15a

                             FIRST AMENDMENT TO THE
                                  TRUST FOR THE
                       PINNACLE WEST CAPITAL CORPORATION,
                       ARIZONA PUBLIC SERVICE COMPANY AND
                           SUNCOR DEVELOPMENT COMPANY
                           DEFERRED COMPENSATION PLANS


     Effective August 1, 1996, Pinnacle West Capital Corporation (the "Company")
established the Trust for the Pinnacle West Capital Corporation,  Arizona Public
Service Company and Suncor Development Company Deferred  Compensation Plans (the
"Trust"),  with Wells Fargo Bank of Arizona,  N.A.,  acting as Trustee,  for the
purpose of holding the assets of certain plans and  arrangements  established by
the Company and its affiliates.

     By this  instrument,  the Company intends to amend the Trust to clarify the
definition of "Change of Control."

     1. This Amendment shall amend only those sections of the Trust as set forth
herein and those  sections  not  expressly  amended  hereby shall remain in full
force and effect.

     2. Sections 13(d) of the Trust is hereby amended to read as follows:

     (d) "Change of Control"  shall have the same meaning as "Change in Control"
in the Pinnacle West Capital Corporation, Arizona Public Service Company, SunCor
Development Company and El Dorado Investment Company Deferred Compensation Plan,
as the same may be amended from time to time.

     3. This Amendment shall be effective as of January 1, 2000.

     IN WITNESS  WHEREOF,  the Company and Trustee have caused this Amendment to
be executed by their duly authorized officers this 7 day of December, 1999.
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                                         PINNACE WEST CAPITAL CORPORATION

                                         By Armando Flores
                                            ------------------------------------
                                         Its Vice President
                                            ------------------------------------



                                        WELLS FARGO BANK OF ARIZONA, N.A.

                                        By Vanessa Fulton
                                           -------------------------------------
                                        Its Assistant Vice President
                                           -------------------------------------

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