Document:

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                                                                    EXHIBIT 10.5

                                 AMENDMENT NO. 4
                         Decommissioning Trust Agreement
                                 (PVNGS Unit 3)

         This Amendment No. 4 dated as of December 19, 2003, to the
Decommissioning Trust Agreement (PVNGS Unit 3), dated as of July 1, 1991, as
amended by Amendment No. 1 thereto dated as of December 1, 1994, Amendment No. 2
thereto dated as of December 16, 1996, and Amendment No. 3 thereto dated as of
March 18, 2002 (the "Decommissioning Trust Agreement", terms used herein as
therein defined), is entered into between Arizona Public Service Company ("APS")
and Mellon Bank, N.A., as Decommissioning Trustee ("Decommissioning Trustee").

                                R E C I T A L S:

         WHEREAS, the parties hereto wish to amend the Decommissioning Trust
Agreement.

         NOW, THEREFORE, in consideration of the premises and of other good and
valuable consideration, receipt and sufficiency of which are hereby
acknowledged, the parties hereto agree as follows:

         SECTION 1. Amendment.

                  (a)      A new Section 29 will be added at the end of the
                           Decommissioning Trust Agreement and will read in full
                           as follows:

                           Section 29. Notice Regarding Disbursements or
                           Payments. Notwithstanding anything to the contrary in
                           this Agreement, except for (i) payments of ordinary
                           administrative costs (including taxes) and other
                           incidental expenses of the Funds (including legal,
                           accounting, actuarial, and trustee expenses) in
                           connection with the operation of the Funds, (ii)
                           withdrawals being made under 10 CFR 50.82(a)(8), and
                           (iii) transfers between the Funds in accordance with
                           the provisions of this Agreement, no disbursement or
                           payment may be made from the Funds until written
                           notice of the intention to make a disbursement or
                           payment has been given to the Director, Office of
                           Nuclear Reactor Regulation, or the Director, Office
                           of Nuclear Material Safety and Safeguards, as
                           applicable, at least 30 working days before the date
                           of the intended disbursement or payment. The
                           disbursement or payment from the Funds, if it is
                           otherwise in compliance with the terms and conditions
                           of this Agreement, may be made following the
                           30-working day notice period if no written notice of
                           objection from the Director, Office of Nuclear
                           Reactor Regulation, or the Director, Office of
                           Nuclear Material Safety and Safeguards, as
                           applicable, is received by the Decommissioning
                           Trustee or APS within the notice period. The required
                           notice may be made by the Decommissioning Trustee or
                           on the Decommissioning Trustee's behalf. No such
                           notice is required for withdrawals being made
                           pursuant to 10 CFR 50.82(a)(8)(ii), including
                           withdrawals made during the operating life of Unit 3
                           to be used

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                           for decommissioning planning. In addition, no such
                           notice is required to be made to the NRC after
                           decommissioning has begun and withdrawals are being
                           made under 10 CFR 50.82(a)(8). This Section 29 is
                           intended to qualify each and every provision of this
                           Agreement allowing distributions from the Funds,
                           including but not limited to Section 10 hereof, and
                           in the event of any conflict between any such
                           provision and this Section 29, the provisions of this
                           Section 29 shall control.

         SECTION 2. Miscellaneous

                  (a)      Full Force and Effect.

         Except as expressly provided herein, the Decommissioning Trust
Agreement shall remain unchanged and in full force and effect. Each reference in
the Decommissioning Trust Agreement and in any exhibit or schedule thereto to
"this Agreement," "hereto," "hereof" and terms of similar import shall be deemed
to refer to the Decommissioning Trust Agreement as amended hereby.

                  (b)      Counterparts/Representations.

         The Amendment No. 4 may be executed in any number of counterparts, all
of which taken together shall constitute one and the same instrument, and any of
the parties hereto may execute this Amendment No. 4 by signing any such
counterpart. Each party represents and warrants to the other that it has full
authority to enter into this Amendment upon the terms and conditions hereof and
that the individual executing this Amendment on its behalf has the requisite
authority to bind that Party.

         IN WITNESS WHEREOF, the parties hereto have caused this Amendment No. 4
to the Decommissioning Trust Agreement to be duly executed as of the day and
year first above written.

                                        ARIZONA PUBLIC SERVICE COMPANY

                                        By: Barbara M. Gomez
                                           -------------------------------------
                                        Title: Treasurer
                                              ----------------------------------
                                        MELLON BANK, N.A. as Decommissioning
                                        Trustee

                                        By: Carlos Pacheco
                                           -------------------------------------
                                        Title: Vice President
                                              ----------------------------------

                                        2

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STATE OF ARIZONA                    )
                                    ) ss:
County of Maricopa                  )

         The foregoing instrument was acknowledged before me this 12th day of
December, 2003, by Barbara M. Gomez, the Treasurer of ARIZONA PUBLIC SERVICE
COMPANY, an Arizona corporation, on behalf of said corporation.

                                        Debra L. Blondin
                                        ----------------------------------------

                                        Notary Public

My commission expires:

June 7, 2004
--------------------------

COMMONWEALTH OF PENNSYLVANIA                              )
                                                          ) ss:
County of Allegheny                                       )

         The foregoing instrument was acknowledged before me this 19th day of
December, 2003, by Carlos Pacheco, a Vice President of Mellon Bank, N.A. a
national banking association having trust powers, as Decommissioning Trustee, on
behalf of said national banking association.

                                        Julie Ann Mosco
                                        ----------------------------------------

                                        Notary Public

My commission expires:

October 13, 2007
----------------------------

                                        3<PAGE>

                                  Exhibit 10.6a

                               FOURTH AMENDMENT TO
                      THE PINNACLE WEST CAPITAL CORPORATION
                         ARIZONA PUBLIC SERVICE COMPANY
                               SUNCOR DEVELOPMENT
                        AND EL DORADO INVESTMENT COMPANY
                           DEFERRED COMPENSATION PLAN

         Effective January 1, 1992, Pinnacle West Capital Corporation (the
"Company"), Arizona Public Service Company, SunCor Development Company and El
Dorado Investment Company adopted the Pinnacle West Capital Corporation, Arizona
Public Service Company, SunCor Development Company and El Dorado Investment
Company Deferred Compensation Plan (the "Plan"). The Plan was thereafter amended
several times. The Plan was amended and restated in its entirety on December 1,
1995 and amended several times thereafter. The Plan was most recently amended on
October 22, 2002 to increase the threshold for automatic cashout for terminated
or retired Participants under certain circumstances and revise crediting of
interest for certain Participants.

         By this instrument, the Plan is being amended to revise its claim
procedures.

         1.                This Amendment shall amend only those Sections set
forth herein and those Sections not amended hereby shall remain in full force
and effect.

         2.                Section 1.1.7 is hereby amended in its entirety to
read as follows:

                  1.17 "Disability" shall mean (i) in the case of a Participant
         who is an employee of an Employer, a period of disability during which
         a participant qualifies for benefits under the Participant's Employer's
         long-term disability plan, or (ii) in the case of a Participant who is
         a Director, a period of disability during which the Participant would
         have qualified for benefits under such a plan, as determined in the
         sole discretion of the Committee, had the Participant been an employee
         of the Employer.

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         3.                Section 8.1(b) is hereby amended in its entirety to
read as follows:

                           (b)      Waiver of Deferral; Credit for Plan Year of
                                    Disability. A Participant who is determined
                                    to be suffering from a Disability shall be
                                    excused from fulfilling that portion of the
                                    Annual Deferral commitment that would
                                    otherwise have been withheld fro a
                                    Participant's Bas Annual Salary, Year-End
                                    Bonus and/or Directors Fees for the Plan
                                    Year during which the Participant first
                                    suffers a Disability. In addition, the
                                    Participant's Account Balance shall be
                                    credited with that portion of the Annual
                                    Deferral commitment that is excused in
                                    accordance with the preceding sentence,
                                    unless the Disability ceases in the Plan
                                    Year that it commences, in which case, the
                                    crediting shall apply only for the period of
                                    Disability.

         4.                Section 8.2 is hereby amended in its entirety to read
as follows:

         8.2               Disability Benefit. A Participant suffering a
                           Disability shall, for the benefit purposes under this
                           Plan, continue to be considered to be employed and
                           shall be eligible for the benefits provided for in
                           Articles 4, 5, 6 or 7 in accordance with the
                           provisions of those Articles. Notwithstanding the
                           above, the Committee shall have the right, in its
                           sole and absolute discretion and for purposes of this
                           Plan only, to terminate a Participant's employment or
                           service as a Director at any time after such
                           participant is determined to be suffering from a
                           disability. In determining the Participant's Account
                           Balance for purposes of the Disability Benefit
                           described in the previous sentence, the Preferred
                           Rate shall be used in lieu of the rates in Section
                           7.1

         5.                ARTICLE 14 is hereby amended in its entirety to read
as follows:

                                   ARTICLE 14

                                Claims Procedures

                  14.1     Claims. Any Participant, Beneficiary or any
                  authorized representative acting on behalf of the Participant
                  or Beneficiary ("Claimant") claiming benefits, eligibility,
                  participation or any other right or interest under this Plan
                  may file a written claim setting forth the basis of the claim
                  with the Employee Benefits Department. A written notice of the
                  Employee Benefits Department's disposition of any such claim
                  shall be furnished to the Claimant within a reasonable time
                  (not to exceed ninety (90) days) after the claim is received
                  by the Employee Benefits Department. Notwithstanding the
                  foregoing, the Employee Benefits Department may have
                  additional time (not to exceed ninety (90) days) to decide the
                  claim if special circumstances exist, provided that it advises
                  the Claimant, in writing and prior to the end of the initial
                  ninety (90) day period, of the special circumstances giving
                  rise to the

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                  need for additional time and the date on which it expects to
                  decide the claim. If the claim is denied, in whole or in part,
                  the notice of disposition shall include the specific reason
                  for the denial, identify the specific provisions of the Plan
                  upon which the denial is based, describe any additional
                  material or information necessary to perfect the claim,
                  explain why that material or information is necessary and
                  describe the Plan's review procedures, including the
                  timeframes thereunder for a Claimant to file a request for
                  review and for the Committee to decide the claim. The notice
                  shall also include a statement advising the claimant of his or
                  her right to bring a civil action under Section 502(a) of the
                  Employee Retirement Income Security Act of 1974, as amended,
                  if his or her claim is denied, in whole or in part, upon
                  review.

                           Within sixty (60) days after receiving the written
                  notice of the Employee Benefits Department's disposition of
                  the claim, the Claimant may request, in writing, review by the
                  Committee of the Employee Benefits Department's decision
                  regarding his or her claim. Upon written request, the Claimant
                  shall be entitled to a review meeting with the Committee to
                  present reasons why the claim should be allowed. The Claimant
                  may submit a written statement in support of his or her claim,
                  together with such comments, information and material relating
                  to the claim, as he or she deems necessary or appropriate. The
                  Claimant shall be provided, upon request and free of charge,
                  reasonable access to, and copies of, all documents, records
                  and other information which are relevant to the Claimant's
                  claim and its review. If the Claimant does not request review
                  within sixty (60) days after receiving written notice of the
                  Employee Benefits Department's disposition of the claim, the
                  Claimant shall be deemed to have accepted the Employee
                  Benefits Department's written disposition.

                           The Committee shall make its decision on review and
                  provide written notice thereof to the Claimant within a
                  reasonable time (not to exceed sixty (60) days) after the
                  claim is received by the Committee. Notwithstanding the
                  foregoing, the Committee may have additional time (not to
                  exceed sixty (60) days) to decide the claim if special
                  circumstances exist provided that it advises the Claimant, in
                  writing, prior to the end of the initial sixty (60) day
                  period, of the special circumstances giving rise to the need
                  for additional time and the date on which it expects to decide
                  the claim. In no event shall the Committee have more than one
                  hundred twenty (120) days following its receipt of the
                  Claimant's request for review to provide the Claimant with
                  written notice of its decision.

                           The Committee shall have the right to request of and
                  receive from Claimant such additional information, documents
                  or other evidence as the Committee may reasonably require. In
                  the event that the Committee requests such additional
                  information from the Claimant, the period for making the
                  benefit determination on review shall not take into account
                  the period beginning on the date on which the Committee
                  notifies the Claimant in writing of the need for additional
                  information and ending on the date on which the Claimant
                  responds to the request for additional information.

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                           If the claim is denied upon review, in whole or in
                  part, the notice of disposition shall include the specific
                  reason for the denial, identify the specific provision of the
                  Plan upon which the denial is based, include a statement
                  advising the Claimant of his or her right to receive, upon
                  written request and free of charge, reasonable access to and
                  copies of all documents, records and other information which
                  are relevant to the Claimant's claim. The notice shall also
                  include a statement advising the claimant of his or her right
                  to bring a civil action under Section 502(a) of the Employee
                  Retirement Income Security Act of 1974, as amended, if his or
                  her claim is denied, in whole or in part, upon review.

                           For purposes of this Section 14.1, a document, record
                  or information will be considered "relevant" if it (a) was
                  relied upon by the Employee Benefits Department or Committee,
                  as applicable, in making the benefit decision, (b) was
                  submitted, considered or generated in the course of making
                  such decisions, even if it was not relied upon in making those
                  decisions, or (c) demonstrates compliance with the
                  administrative processes and safeguards established by the
                  Plan to insure that the terms of the Plan have been followed
                  and applied consistently.

                           To the extent permitted by law, a decision on review
                  by the Committee shall be binding and conclusive upon all
                  persons whomsoever. Completion of the claims procedure
                  described in this Section 14.1 shall be a mandatory
                  precondition that must be complied with prior to commencement
                  of a legal or equitable action in connection with the Plan by
                  a person claiming rights under the Plan, or by another person
                  claiming rights through such a person. The Committee may, in
                  its sole discretion, waive these procedures as a mandatory
                  precondition to such an action.

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         6.       Except as otherwise expressly provided herein, this Amendment
         shall be effective January 1, 2003.

         Except as amended hereby, the Company ratifies and confirms the Plan as
amended and restated effective January 1, 1995 and as thereafter amended.

                           Dated: December 18, 2003

                                    PINNACLE WEST CAPITAL CORPORATION

                                    By /s/ Jack E. Davis
                                       -----------------------------------------

                                    Its   President & Chief Operating Officer of
                                          Pinnacle West Capital Corporation and
                                          President & Chief Executive Officer of
                                          Arizona Public Service Company

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