1 EXHIBIT 4.3 TRUST SUPPLEMENT NO. 1998-A DATED AS OF MAY 1, 1998 TO PASS THROUGH TRUST AGREEMENT DATED AS OF FEBRUARY 1, 1993 SOUTHWEST AIRLINES CO. AND WILMINGTON TRUST COMPANY, AS TRUSTEE $95,531,435 2 TRUST SUPPLEMENT This Trust Supplement No. 1998-A, dated as of May 1, 1998 (the "Trust Supplement") between Southwest Airlines Co., a Texas corporation (the "Company") and Wilmington Trust Company, a Delaware banking corporation (the "Trustee"), to the Pass Through Trust Agreement dated as of February 1, 1993, between the Company and the Trustee (the "Basic Agreement"), WITNESSETH: WHEREAS, the Company and the Trustee have heretofore executed and delivered the Basic Agreement, unlimited as to the aggregate principal amount of Certificates (unless specified herein capitalized terms used herein without definition having the respective meanings specified heretofore in the Basic Agreement) which may be issued thereunder; WHEREAS, each of four Owner Trustees, each acting on behalf of an Owner Participant, has agreed to issue, on a non-recourse basis, Equipment Notes, among other things, to finance the outstanding debt portion of the purchase price of the aircraft heretofore purchased by such Owner Trustee and leased to the Company pursuant to the related Lease; WHEREAS, pursuant to the terms and conditions of the Basic Agreement as supplemented by this Trust Supplement (the "Agreement"), the Trustee shall purchase such Equipment Notes issued by such Owner Trustees of the same tenor as the Certificates issued hereunder and shall hold such Equipment Notes in trust for the benefit of the Certificateholders; WHEREAS, the Trustee hereby declares the creation of this Trust (the "1998-A Trust") for the benefit of the Certificateholders, and the initial Certificateholders as the grantors of the 1998-A Trust, by their respective acceptances of the Certificates, join in the creation of this 1998-A Trust with the Trustee; WHEREAS, all of the conditions and requirements necessary to make this Trust Supplement, when duly executed and delivered, a valid, binding and legal instrument in accordance with its terms and for the purposes herein expressed, have been done, performed and fulfilled, and the execution and delivery of this Trust Supplement in the form and with the terms hereof have been in all respects duly authorized; WHEREAS, this Trust Supplement is subject to the provisions of the Trust Indenture Act and shall, to the extent applicable, be governed by such provisions; NOW, THEREFORE, in consideration of the premises herein, it is agreed between the Company and the Trustee as follows: TRUST SUPPLEMENT NO. 1998-A -1- 3 ARTICLE I THE CERTIFICATES Section 1.01 The Certificates. Pursuant to Section 2.01 of the Basic Agreement, there is hereby created a series of Certificates to be issued under the Agreement to be distinguished and known as "Pass Through Certificates, Series 1998-A" (hereinafter defined as the "Series 1998-A Certificates"). Each Certificate represents a Fractional Undivided Interest in the 1998-A Trust created hereby. The terms and conditions applicable to the Series 1998-A Certificates are as follows: 1. The aggregate principal amount of the Series 1998-A Certificates that shall be authenticated under the Agreement (except for Series 1998-A Certificates authenticated and delivered pursuant to Section 3.03, 3.04 or 3.05 of the Basic Agreement) upon their initial issuance is $95,531,435. 2. The Cut-off Date is June 15, 1998. 3. The Regular Distribution Dates with respect to any payment of Scheduled Payments are January 2 and July 2 in each year, commencing July 2, 1998, until payment of all of the Scheduled Payments to be made under the Equipment Notes have been made. 4. The Scheduled Payments shall be as set forth in Exhibit C hereto. 5. The Special Distribution Dates are as follows: (i) in the case of an early redemption of Equipment Note arising out of an Event of Loss, a refinancing of the Equipment Notes or a purchase or early redemption by the related Owner Participant or Owner Trustee of such Equipment Notes, an early redemption of Equipment Notes arising out of a voluntary termination of the related Lease pursuant to Section 9.1 thereof, or exercise by Lessee of a purchase option, the date of the receipt of the applicable redemption or purchase price therefor, which shall be a Business Day, and (ii) otherwise, the earliest Business Day of a month for which it is practicable for the Trustee to give notice pursuant to Section 4.02(c) of the Basic Agreement 20 days prior thereto. 6. The Series 1998-A Certificates shall be in the form attached hereto as Exhibit A. The Series 1998-A Certificates shall be Book-Entry Certificates and shall be subject to the conditions set forth in the Letter of Representations between the Company and the Clearing Agency attached hereto as Exhibit B. 7. The proceeds of the Series 1998-A Certificates shall be used to purchase the Equipment Notes in the principal amounts specified below: Equipment Note Principal Amount Maturity -------------- ---------------- -------- Series SWA 1998 N620SW $23,882,858.75 July 2, 2019 Series SWA 1998 N621SW $23,882,858.75 July 2, 2019 Series SWA 1998 N622SW $23,882,858.75 July 2, 2019 Series SWA 1998 N623SW $23,882,858.75 July 2, 2019 TRUST SUPPLEMENT NO. 1998-A -2- 4 8. Each of four Owner Trustees, each acting on behalf of an Owner Participant, will issue on a non- recourse basis the Equipment Notes, the proceeds of which shall be used to finance the debt portion of the purchase price of the following Aircraft: Registration Manufacturer's Aircraft Number Serial Number -------- ------------- ------------- 1 Boeing 737-3H4 N620SW 28036 1 Boeing 737-3H4 N621SW 28037 1 Boeing 737-3H4 N622SW 27932 1 Boeing 737-3H4 N623SW 27933 9. The related Note Documents are as follows (with the trust relating to each Note Document being indicated in parentheses for purposes of identification): (a) Each of the following Indentures: Trust Indenture and Security Agreement (Southwest Airlines 1998 Trust N620SW) dated as of June 1, 1996, as supplemented; Trust Indenture and Security Agreement (Southwest Airlines 1998 Trust N621SW) dated as of June 1, 1996, as supplemented; Trust Indenture and Security Agreement (Southwest Airlines 1998 Trust N622SW) dated as of June 1, 1996, as supplemented; Trust Indenture and Security Agreement (Southwest Airlines 1998 Trust N623SW) dated as of June 1, 1996, as supplemented; (b) Each of the following Leases: Sale and Lease Agreement (Southwest Airlines 1998 Trust N620W), dated as of June 1, 1996, as supplemented; Sale and Lease Agreement (Southwest Airlines 1998 Trust N621SW), dated as of June 1, 1996, as supplemented; Sale and Lease Agreement (Southwest Airlines 1998 Trust N622SW), dated as of June 1, 1996, as supplemented; Sale and Lease Agreement (Southwest Airlines 1998 Trust N623SW), dated as of June 1, 1996, as supplemented; (c) Each of the following Participation Agreements: TRUST SUPPLEMENT NO. 1998-A -3- 5 Participation Agreement (Southwest Airlines 1998 Trust N620SW), dated as of June 1, 1996; Participation Agreement (Southwest Airlines 1998 Trust N621SW), dated as of June 1, 1996; Participation Agreement (Southwest Airlines 1998 Trust N622SW), dated as of June 1, 1996; Participation Agreement (Southwest Airlines 1998 Trust N623SW), dated as of June 1, 1996; (d) Each of the following Trust Agreements: Trust Agreement (Southwest Airlines 1998 Trust N620SW) dated as of June 1, 1996, as supplemented; Trust Agreement (Southwest Airlines 1998 Trust N621SW) dated as of June 1, 1996, as supplemented; Trust Agreement (Southwest Airlines 1998 Trust N622SW) dated as of June 1, 1996, as supplemented; Trust Agreement (Southwest Airlines 1998 Trust N623SW) dated as of June 1, 1996, as supplemented; ARTICLE II THE TRUSTEE Section 2.01. The Trustee. The Trustee shall not be responsible in any manner whatsoever for or in respect of the validity or sufficiency of this Trust Supplement or the due execution hereof by the Company, or for or in respect of the recitals and statements contained herein, all of which recitals and statements are made solely by the Company. Except as herein otherwise provided, no duties, responsibilities or liabilities are assumed, or shall be construed to be assumed by the Trustee by reason of this Trust Supplement other than as set forth in the Basic Agreement, and this Trust Supplement is executed and accepted on behalf of the Trustee, subject to all the terms and conditions set forth in the Basic Agreement, upon the effectiveness thereof, as fully to all intents as if the same were herein set forth at length. ARTICLE III MISCELLANEOUS PROVISIONS Section 3.01. Basic Agreement Ratified. Except and so far as herein expressly provided, all of the provisions, terms and conditions of the Basic Agreement are in all respects ratified and TRUST SUPPLEMENT NO. 1998-A -4- 6 confirmed; and the Basic Agreement and this Trust Supplement shall be taken, read and construed as one and the same instrument. Section 3.02. GOVERNING LAW. THIS TRUST SUPPLEMENT AND THE SERIES 1998-A CERTIFICATES SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF DELAWARE. Section 3.03. Execution in Counterparts. This Trust Supplement may be executed in any number of counterparts, each of which shall be an original, but such counterparts shall together constitute but one instrument. TRUST SUPPLEMENT NO. 1998-A -5- 7 IN WITNESS WHEREOF, the Company and the Trustee have caused this Trust Supplement to be duly executed by their respective officers thereto duly authorized, as of the day and year first above written. SOUTHWEST AIRLINES CO. By ------------------------------------ Treasurer WILMINGTON TRUST COMPANY, not in its individual capacity, but solely as Trustee By ------------------------------------ Title: TRUST SUPPLEMENT NO. 1998-A -6- 8 EXHIBIT A CUSIP NO. 84474 WAA 8 [FORM OF CERTIFICATE] **Unless this certificate is presented by an authorized representative of The Depository Trust Company, a New York Corporation ("DTC"), to Issuer or its agent for registration of transfer, exchange or payment, and any certificate issued is registered in the name of Cede & Co. or in such other name as is requested by an authorized representative of DTC (and any payment is made to Cede & Co. or to such other entity as is requested by an authorized representative of DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL inasmuch as the registered owner hereof, Cede & Co., has an interest herein. SOUTHWEST AIRLINES 1998-A PASS THROUGH TRUST Pass Through Certificate, Series 1998-A Final Distribution Date: July 2, 2019 evidencing a fractional undivided interest in a trust, the property of which includes certain Equipment Notes each secured by an Aircraft leased to Southwest Airlines Co. Certificate No. ______ $ ________Fractional Undivided Interest representing _________% of the Trust per $1,000 face amount. THIS CERTIFIES THAT ___________________________________________, for value received, is the registered owner of a $__________________________ (_____________ dollars) Fractional Undivided Interest in the Southwest Airlines 1998-A Pass Through Trust (the "Trust") created by Wilmington Trust Company, as trustee (the "Trustee"), pursuant to a Pass Through Trust Agreement dated as of February 1, 1993 (the "Basic Agreement"), as supplemented by Trust Supplement No. 1998-A thereto dated as of May 1, 1998 (collectively, the "Agreement"), between the Trustee and Southwest Airlines Co., a corporation incorporated under Texas law (the "Company"), a summary of certain of the pertinent provisions of which is set forth below. To the extent not otherwise defined herein, the capitalized terms used herein have the meanings assigned to them in the Agreement. This Certificate is one of the duly authorized Certificates designated as "Pass Through Certificates, Series 1998-A" (herein called the "Certificates"). This Certificate is issued under and is subject to the terms, provisions, and conditions of the Agreement, to which Agreement the Certificateholder of this Certificate by virtue of the acceptance hereof assents and by which such Certificateholder is bound. The property of the Trust includes certain Equipment Notes or, pending the acquisition thereof, certain cash or Specified Investments (the "Trust Property"). Each issue of the Equipment Notes, when issued, will be secured by a security interest in an aircraft leased to the Company. The Certificates represent Fractional Undivided Interests in the Trust and the Trust Property, and have no rights, benefits or interest in respect of any other separate trust established pursuant to the terms of the Basic Agreement for any other series of certificates issued pursuant thereto. _ ** This legend to appear on Book-Entry Certificates to be deposited with The Depository Trust Company. One Certificate may be issued in a denomination of less than $1,000 which shall not have this legend. TRUST SUPPLEMENT NO. 1998-A A-1 9 Subject to and in accordance with the terms of the Agreement, from funds then available to the Trustee, there will be distributed on January 2 and July 2 in each year, commencing July 2, 1998 (a "Regular Distribution Date") to the Person in whose name this Certificate is registered at the close of business on the 15th day preceding the Regular Distribution Date, an amount in respect of the Scheduled Payments on the Equipment Notes due on such Regular Distribution Date, the receipt of which has been confirmed by the Trustee, equal to the product of the percentage interest in the Trust evidenced by this Certificate and an amount equal to the sum of such Scheduled Payments. Subject to and in accordance with the terms of the Agreement, in the event that Special Payments are received by the Trustee, from funds then available to the Trustee, there shall be distributed on the applicable Special Distribution Date, to the Person in whose name this Certificate is registered at the close of business on the 15th day preceding the Special Distribution Date, an amount in respect of such Special Payments, the receipt of which has been confirmed by the Trustee, equal to the product of the percentage interest in the Trust evidenced by this Certificate and an amount equal to the sum of such Special Payments so received. If a Regular Distribution Date or Special Distribution Date is not a Business Day, distribution shall be made on the immediately following Business Day with the same force and effect as if made on such Regular Distribution Date or Special Distribution Date and no interest shall accrue during the intervening period. The Trustee shall mail notice of each Special Payment and the Special Distribution Date therefor to the Certificateholder of this Certificate. Distributions on this Certificate will be made by the Trustee in immediately available funds to the Person entitled thereto, without the presentation or surrender of this Certificate or the making of any notation hereon. Except as otherwise provided in the Agreement and notwithstanding the above, the final distribution on this Certificate will be made after notice mailed by the Trustee of the pendency of such distribution and only upon presentation and surrender of this Certificate at the office or agency of the Trustee specified in such notice. The Certificates do not represent a direct obligation of, or an obligation guaranteed by, or an interest in, the Company or the Trustee or any affiliate thereof. The Certificates are limited in right or payment, all as more specifically set forth herein and in the Agreement. All payments or distributions made to Certificateholders under the Agreement shall be made only from the Trust Property and only to the extent that the Trustee shall have sufficient income or proceeds from the Trust Property to make such payments in accordance with the terms of the Agreement. Each Certificateholder of this Certificate, by its acceptance hereof, agrees that it will look solely to the income and proceeds from the Trust Property to the extent available for distribution to such Certificateholder as provided in the Agreement. This Certificate does not purport to summarize the Agreement and reference is made to the Agreement for information with respect to the interests, rights, benefits, obligations, proceeds, and duties, evidenced hereby. A copy of the Agreement may be examined during normal business hours at the principal office of the Trustee, and at such other places, if any, designated by the Trustee, by any Certificateholder upon request. The Agreement permits, with certain exceptions therein provided, the amendment thereof and the modification of the rights and obligations of the Company and the rights of the Certificateholders under the Agreement at any time by the Company and the Trustee with the consent TRUST SUPPLEMENT NO. 1998-A A-2 10 of the Certificateholders holding Certificates evidencing Fractional Undivided Interests aggregating not less than a majority in interest in the Trust. Any such consent by the Certificateholder of this Certificate shall be conclusive and binding on such Certificateholder and upon all future Certificateholders of this Certificate and of any Certificate issued upon the transfer hereof or in exchange hereof or in lieu hereof whether or not notation of such consent is made upon this Certificate. The Agreement also permits the amendment thereof, in certain limited circumstances, without the consent of the Certificateholders of any of the Certificates. As provided in the Agreement and subject to certain limitations therein set forth, the transfer of this Certificate is registrable in the Register upon surrender of this Certificate for registration of transfer at the offices or agencies maintained by the Trustee in its capacity as Registrar, or by any successor Registrar, duly endorsed or accompanied by a written instrument of transfer in form satisfactory to the Trustee and the Registrar duly executed by the Certificateholder hereof or such Certificateholder's attorney duly authorized in writing, and thereupon one or more new Certificates of authorized denominations evidencing the same aggregate Fractional Undivided Interest in the Trust will be issued to the designated transferee or transferees. The Certificates are issuable only as registered Certificates without coupons in minimum denominations of $1,000 or integral multiples thereof except that one Certificate may be in a denomination of less than $1,000. As provided in the Agreement and subject to certain limitations therein set forth, the Certificates are exchangeable for new Certificates of authorized denominations evidencing the same aggregate Fractional Undivided Interest in the Trust, as requested by the Certificateholder surrendering the same. No service charge will be made for any such registration of transfer or exchange, but the Trustee shall require payment of a sum sufficient to cover any tax or governmental charge payable in connection therewith. The Trustee, the Registrar, and any agent of the Trustee or the Registrar may treat the Person in whose name this Certificate is registered as the owner hereof for all purposes, and none of the Trustee, the Registrar, or any such agent shall be affected by any notice to the contrary. The obligations and responsibilities created by the Agreement and the Trust created thereby shall terminate upon the distribution to Certificateholders of all amounts required to be distributed to them pursuant to the Agreement and the disposition of all property held as part of the Trust Property. THE AGREEMENT AND THIS CERTIFICATE SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF DELAWARE. Unless the certificate of authentication hereon has been executed by the Trustee, by manual signature, this Certificate shall not be entitled to any benefit under the Agreement or be valid for any purpose. TRUST SUPPLEMENT NO. 1998-A A-3 11 IN WITNESS WHEREOF, the Trustee has caused this Certificate to be duly executed. SOUTHWEST AIRLINES 1998-A PASS THROUGH TRUST By: WILMINGTON TRUST COMPANY, not in its individual capacity but solely as Trustee By: -------------------------------------- Title: --------------------------------- Dated: May 29, 1998 TRUST SUPPLEMENT NO. 1998-A A-4 12 [FORM OF THE TRUSTEE'S CERTIFICATE OF AUTHENTICATION] This is one of the Certificates referred to in the within-mentioned Agreement. WILMINGTON TRUST COMPANY, not in its individual capacity, but solely as Trustee By: -------------------------------------- Authorized Officer TRUST SUPPLEMENT NO. 1998-A A-5 13 EXHIBIT B TRUST SUPPLEMENT NO. 1998-A Dated as of May 1, 1998 [DTC LETTER OF REPRESENTATIONS] TRUST SUPPLEMENT NO. 1998-A B-1 14 EXHIBIT C TRUST SUPPLEMENT NO. 1998-A Dated as of May 1, 1998 Scheduled Payments Percentage of Original Principal Payment Date Principal Amount - ---------------------- ---------------------- ----------------- 100.000000000 ================= TRUST SUPPLEMENT NO. 1998-A C-1