Document:

<PAGE>   1
                                                                   EXHIBIT 10.15

                                 FIFTH AMENDMENT
                                       TO
                       AMENDED AND RESTATED LOAN AGREEMENT

         This FIFTH AMENDMENT TO AMENDED AND RESTATED LOAN AGREEMENT (this
"AMENDMENT") is being entered into as of October 30, 2000, by and among
PETROLEUM HELICOPTERS, INC., a Louisiana corporation (the "COMPANY"), BANK OF
AMERICA, N.A., a national banking association (f/k/a Bank of America National
Trust and Savings Association, successor by merger to Bank of America, N.A.,
f/k/a NationsBank, N.A., successor by merger to NationsBank of Texas, N.A.
("NATIONSBANK") ("BANK OF AMERICA"), WHITNEY NATIONAL BANK, a national banking
association ("WHITNEY"), BANK ONE, LOUISIANA, N.A., a national banking
association ("BANK ONE" (as successor by merger to First National Bank of
Commerce, a national banking association ("FNBC")) and together with NationsBank
and Whitney, being hereinafter referred to collectively as the "Banks", and Bank
of America as agent for the Banks (in such capacity, the "AGENT").

                             PRELIMINARY STATEMENTS

         (1) The Company, NationsBank, Whitney, FNBC and the Agent have entered
into that certain Loan Agreement, originally dated as of January 31, 1986, as
amended and restated in its entirety as of March 31, 1997, and as amended by
that certain First Amendment to Amended and Restated Loan Agreement, dated as of
December 31, 1997, that certain Second Amendment to Amended and Restated Loan
Agreement, dated as of November 30, 1998, that certain Limited Waiver and Third
Amendment to Amended and Restated Loan Agreement, dated as of June 30, 1999, and
that certain Fourth Amendment to Amended and Restated Loan Agreement, dated as
of June 30, 2000 (such Loan Agreement, as so amended and restated and as the
same may be further amended from time to time, being hereinafter referred to as
the "LOAN AGREEMENT"). Terms used herein, unless otherwise defined herein, shall
have the meanings set forth in the Loan Agreement.

         (2) The Company has requested that the Banks agree to amend, and the
Banks now wish to amend, subject to the terms and conditions specified herein,
Section 1.01 of the Loan Agreement as provided below.

         NOW, THEREFORE, in consideration of the premises and for other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the Company, the Banks and the Agent hereby agree as follows:

         1. Pursuant to Section 12.02 of the Loan Agreement, the Company and the
Banks hereby agree that, effective as of the date hereof, Section 1.01 of the
Loan Agreement is hereby amended as follows:

                  (a) The definition of "Conversion Date" in Section 1.01 of the
         Loan Agreement is hereby amended in its entirety to read as follows:

<PAGE>   2

                 "Conversion Date" shall mean November 30, 2000.

         2. Other than as specifically provided for herein, the amendment
provided for in Section 1 above shall not operate as a consent to any other
action, event or circumstance or as a waiver or amendment of any right, power or
privilege of the Banks under the Loan Agreement or the Notes or of any other
term or condition of the Loan Agreement or the Notes nor shall the entering into
this Amendment preclude any of the Banks from refusing to enter into any further
consents, waivers or amendments with respect to the Loan Agreement or the Notes.

         3. Each reference in the Loan Agreement to "this Agreement",
"hereunder", "herein" or words of like import shall mean and be a reference to
the Loan Agreement as amended to date. Unless otherwise indicated, terms used in
this Amendment have the same meanings herein as in the Loan Agreement.

         4. The Loan Agreement, as amended to date, is in all respects ratified
and confirmed, and all of the rights and powers created thereby or thereunder
shall be and remain in full force and effect.

         5. The Company hereby represents that (a) after giving effect to the
amendment contemplated herein, the representations and warranties contained in
the Loan Agreement, the Notes, the Security Documents, and any other documents
or instruments executed in connection with the Loan Agreement (collectively, the
"LOAN DOCUMENTS") are true and correct on and as of the date hereof as though
made on and as of such date, (b) upon execution of this Amendment, the Company
will not be in default in the due performance of any covenant on its part in the
Loan Documents, and (c) no Default or Event of Default has occurred and is
continuing or is imminent.

         6. The Company acknowledges, confirms, and warrants that the Security
Documents and any other security instruments executed at any time in connection
with the Loan Agreement continue to secure, inter alia, the payment of all
Indebtedness at any time created pursuant to the Loan Agreement, as amended to
date, and all obligations of the Company in respect of Swap Agreements.

         7. The effectiveness of this Amendment is subject to (i) the Company's
delivery to the Agent, for the account of the Banks, of a counterpart of this
Amendment executed by the Company; and (ii) the delivery to the Agent of
counterparts of this Amendment executed by each of the Banks.

         8. The Company agrees to do, execute, acknowledge, and deliver, all and
every such further acts and instruments as the Agent may request for the better
assuring and confirming unto the Agent and the Banks all and singular the rights
granted or intended to be granted hereby or hereunder.

         9. The Company agrees to pay on demand all reasonable costs and
expenses of the Banks in connection with the preparation, reproduction,
execution, and delivery of this

<PAGE>   3

Amendment and the other instruments and documents to be delivered hereunder
(including the reasonable fees and out-of-pocket expenses of counsel for the
Agent, and with respect to advising the Agent as to its rights and
responsibilities under the Loan Agreement, as hereby to date). In addition, the
Company shall pay any and all stamp and other taxes and fees payable or
determined to be payable in connection with the execution and delivery, filing,
or recording of this Amendment and the other instruments and documents to be
delivered hereunder, and agrees to save each Bank harmless from and against any
and all liabilities with respect to and resulting from any delay in paying or
omission to pay such taxes or fees.

         10. This Amendment may be executed in any number of counterparts
(including those transmitted by facsimile) and by different parties hereto in
separate counterparts, each of which when so executed and delivered shall be
deemed to be an original and all of which taken together shall constitute but
one and the same instrument. Delivery of this Amendment may be may be made by
telecopy transmission of a duly executed counterpart copy hereof.

         11. This Amendment shall be governed by and construed in accordance
with the laws of the State of Texas and shall be binding upon the Company, the
Agent, and the Banks and their respective successors and assigns.

         12. FINAL AGREEMENT. THIS AMENDMENT TOGETHER WITH THE FIRST AMENDMENT,
THE SECOND AMENDMENT, THE THIRD AMENDMENT, THE FOURTH AMENDMENT, THE LOAN
AGREEMENT, THE NOTES, THE SECURITY DOCUMENTS AND ANY OTHER DOCUMENTS OR
INSTRUMENTS EXECUTED IN CONNECTION WITH THE LOAN AGREEMENT REPRESENT THE FINAL
AGREEMENT BETWEEN THE PARTIES AND MAY NOT BE CONTRADICTED BY EVIDENCE OF PRIOR,
CONTEMPORANEOUS OR SUBSEQUENT ORAL AGREEMENTS OF THE PARTIES. THERE ARE NO
UNWRITTEN ORAL AGREEMENTS BETWEEN THE PARTIES.

      [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK; SIGNATURE PAGE FOLLOWS]

<PAGE>   4

         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
executed by their respective officers thereunto duly authorized as of the date
first above written.

                                      PETROLEUM HELICOPTERS, INC.

                                      By:
                                          ---------------------------------
                                      Name:
                                      Title:

                                      BANK OF AMERICA, N.A.,
                                      individually and as Agent

                                      By:
                                          ---------------------------------
                                      Name:
                                      Title:

                                      WHITNEY NATIONAL BANK

                                      By:
                                          ---------------------------------
                                      Name:
                                      Title:

                                      BANK ONE, LOUISIANA, N.A.

                                      By:
                                          ---------------------------------
                                      Name:
                                      Title:<PAGE>   1
                                                                   EXHIBIT 10.16

                                 SIXTH AMENDMENT
                                       TO
                       AMENDED AND RESTATED LOAN AGREEMENT

         This SIXTH AMENDMENT TO AMENDED AND RESTATED LOAN AGREEMENT (this
"AMENDMENT") is being entered into as of November 30, 2000, by and among
PETROLEUM HELICOPTERS, INC., a Louisiana corporation (the "COMPANY"), BANK OF
AMERICA, N.A., a national banking association (f/k/a Bank of America National
Trust and Savings Association, successor by merger to Bank of America, N.A.,
f/k/a NationsBank, N.A., successor by merger to NationsBank of Texas, N.A.
("NATIONSBANK") ("BANK OF AMERICA"), WHITNEY NATIONAL BANK, a national banking
association ("WHITNEY"), BANK ONE, LOUISIANA, N.A., a national banking
association ("BANK ONE" (as successor by merger to First National Bank of
Commerce, a national banking association ("FNBC")) and together with NationsBank
and Whitney, being hereinafter referred to collectively as the "Banks", and Bank
of America as agent for the Banks (in such capacity, the "AGENT").

                             PRELIMINARY STATEMENTS

         (1) The Company, NationsBank, Whitney, FNBC and the Agent have entered
into that certain Loan Agreement, originally dated as of January 31, 1986, as
amended and restated in its entirety as of March 31, 1997, and as amended by
that certain First Amendment to Amended and Restated Loan Agreement, dated as of
December 31, 1997, that certain Second Amendment to Amended and Restated Loan
Agreement, dated as of November 30, 1998, that certain Limited Waiver and Third
Amendment to Amended and Restated Loan Agreement, dated as of June 30, 1999,
that certain Fourth Amendment to Amended and Restated Loan Agreement, dated as
of June 30, 2000, and that certain Fifth Amendment to Amended and Restated Loan
Agreement, dated as of October 30, 2000 (such Loan Agreement, as so amended and
restated and as the same may be further amended from time to time, being
hereinafter referred to as the "LOAN AGREEMENT"). Terms used herein, unless
otherwise defined herein, shall have the meanings set forth in the Loan
Agreement.

         (2) The Company has requested that the Banks agree to amend, and the
Banks now wish to amend, subject to the terms and conditions specified herein,
Section 1.01 of the Loan Agreement as provided below.

         NOW, THEREFORE, in consideration of the premises and for other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the Company, the Banks and the Agent hereby agree as follows:

         1. Pursuant to Section 12.02 of the Loan Agreement, the Company and the
Banks hereby agree that, effective as of the date hereof, Section 1.01 of the
Loan Agreement is hereby amended as follows:

<PAGE>   2

                  (a) The definition of "Conversion Date" in Section 1.01 of the
         Loan Agreement is hereby amended in its entirety to read as follows:

                 "Conversion Date" shall mean December 29, 2000.

         2. Other than as specifically provided for herein, the amendment
provided for in Section 1 above shall not operate as a consent to any other
action, event or circumstance or as a waiver or amendment of any right, power or
privilege of the Banks under the Loan Agreement or the Notes or of any other
term or condition of the Loan Agreement or the Notes nor shall the entering into
this Amendment preclude any of the Banks from refusing to enter into any further
consents, waivers or amendments with respect to the Loan Agreement or the Notes.

         3. Each reference in the Loan Agreement to "this Agreement",
"hereunder", "herein" or words of like import shall mean and be a reference to
the Loan Agreement as amended to date. Unless otherwise indicated, terms used in
this Amendment have the same meanings herein as in the Loan Agreement.

         4. The Loan Agreement, as amended to date, is in all respects ratified
and confirmed, and all of the rights and powers created thereby or thereunder
shall be and remain in full force and effect.

         5. The Company hereby represents that (a) after giving effect to the
amendment contemplated herein, the representations and warranties contained in
the Loan Agreement, the Notes, the Security Documents, and any other documents
or instruments executed in connection with the Loan Agreement (collectively, the
"LOAN DOCUMENTS") are true and correct on and as of the date hereof as though
made on and as of such date, (b) upon execution of this Amendment, the Company
will not be in default in the due performance of any covenant on its part in the
Loan Documents, and (c) no Default or Event of Default has occurred and is
continuing or is imminent.

         6. The Company acknowledges, confirms, and warrants that the Security
Documents and any other security instruments executed at any time in connection
with the Loan Agreement continue to secure, inter alia, the payment of all
Indebtedness at any time created pursuant to the Loan Agreement, as amended to
date, and all obligations of the Company in respect of Swap Agreements.

         7. The effectiveness of this Amendment is subject to (i) the Company's
delivery to the Agent, for the account of the Banks, of a counterpart of this
Amendment executed by the Company; and (ii) the delivery to the Agent of
counterparts of this Amendment executed by each of the Banks.

         8. The Company agrees to do, execute, acknowledge, and deliver, all and
every such further acts and instruments as the Agent may request for the better
assuring and confirming unto the Agent and the Banks all and singular the rights
granted or intended to be granted hereby or hereunder.

<PAGE>   3

         9. The Company agrees to pay on demand all reasonable costs and
expenses of the Banks in connection with the preparation, reproduction,
execution, and delivery of this Amendment and the other instruments and
documents to be delivered hereunder (including the reasonable fees and
out-of-pocket expenses of counsel for the Agent, and with respect to advising
the Agent as to its rights and responsibilities under the Loan Agreement, as
hereby to date). In addition, the Company shall pay any and all stamp and other
taxes and fees payable or determined to be payable in connection with the
execution and delivery, filing, or recording of this Amendment and the other
instruments and documents to be delivered hereunder, and agrees to save each
Bank harmless from and against any and all liabilities with respect to and
resulting from any delay in paying or omission to pay such taxes or fees.

         10. This Amendment may be executed in any number of counterparts
(including those transmitted by facsimile) and by different parties hereto in
separate counterparts, each of which when so executed and delivered shall be
deemed to be an original and all of which taken together shall constitute but
one and the same instrument. Delivery of this Amendment may be may be made by
telecopy transmission of a duly executed counterpart copy hereof.

         11. This Amendment shall be governed by and construed in accordance
with the laws of the State of Texas and shall be binding upon the Company, the
Agent, and the Banks and their respective successors and assigns.

         12. FINAL AGREEMENT. THIS AMENDMENT TOGETHER WITH THE FIRST AMENDMENT,
THE SECOND AMENDMENT, THE THIRD AMENDMENT, THE FOURTH AMENDMENT, THE LOAN
AGREEMENT, THE NOTES, THE SECURITY DOCUMENTS AND ANY OTHER DOCUMENTS OR
INSTRUMENTS EXECUTED IN CONNECTION WITH THE LOAN AGREEMENT REPRESENT THE FINAL
AGREEMENT BETWEEN THE PARTIES AND MAY NOT BE CONTRADICTED BY EVIDENCE OF PRIOR,
CONTEMPORANEOUS OR SUBSEQUENT ORAL AGREEMENTS OF THE PARTIES. THERE ARE NO
UNWRITTEN ORAL AGREEMENTS BETWEEN THE PARTIES.

      [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK; SIGNATURE PAGE FOLLOWS]

<PAGE>   4

         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
executed by their respective officers thereunto duly authorized as of the date
first above written.

                                      PETROLEUM HELICOPTERS, INC.

                                      By:
                                           -----------------------------
                                      Name:
                                      Title:

                                      BANK OF AMERICA, N.A.,
                                      individually and as Agent

                                      By:
                                           -----------------------------
                                      Name:
                                      Title:

                                      WHITNEY NATIONAL BANK

                                      By:
                                           -----------------------------
                                      Name:
                                      Title:

                                      BANK ONE, LOUISIANA, N.A.

                                      By:
                                           -----------------------------
                                      Name:
                                      Title:

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