Exhibit 4.2

TRUST SUPPLEMENT NO. 2009-1A-S

dated as of October 13, 2009

between

WILMINGTON TRUST COMPANY

as Trustee,

and

UNITED AIR LINES, INC.

to

PASS THROUGH TRUST AGREEMENT

dated as of June 26, 2007

$659,107,000

United Air Lines Pass Through Trust 2009-1A-S

United Air Lines

Pass Through Certificates,

Series 2009-1A-S

Vedder Price P.C.

Chicago, Illinois

TABLE OF CONTENTS

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THIS TRUST SUPPLEMENT NO. 2009-1A-S , dated as of October 13, 2009 (herein called the “ Trust Supplement ”), between United Air Lines, Inc., a Delaware corporation (the “ Company ”), and Wilmington Trust Company (the “ Trustee ”), to the Pass Through Trust Agreement, dated as of June 26, 2007, between the Company and the Trustee (the “ Basic Agreement ”).

W I T N E S S E T H :

WHEREAS , the Basic Agreement, unlimited as to the aggregate principal amount of Certificates (unless otherwise specified herein, capitalized terms used herein without definition having the respective meanings specified in the Basic Agreement) which may be issued thereunder, has heretofore been executed and delivered;

WHEREAS , as of the Transfer Date (as defined below), the Company will have financed the acquisition of all or a portion of such Aircraft through separate secured loan transactions, under which the Company owns such Aircraft (collectively, the “ Aircraft ”);

WHEREAS , as of the Transfer Date, in the case of each Aircraft, the Company will have issued pursuant to an Indenture, on a recourse basis, Equipment Notes to finance a portion of the purchase price of such Aircraft;

WHEREAS , as of the Transfer Date, the Related Trustee will assign, transfer and deliver all of such trustee’s right, title and interest to the trust property held by the Related Trustee to the Trustee pursuant to the Assignment and Assumption Agreement (as defined below);

WHEREAS , the Trustee, effective only, but automatically, upon execution and delivery of the Assignment and Assumption Agreement, will be deemed to have declared the creation of the United Air Lines Pass Through Trust 2009-1A-S (the “ Applicable Trust ”) for the benefit of the Applicable Certificateholders, and the initial Applicable Certificateholders as the grantors of the Applicable Trust, by their respective acceptances of the Applicable Certificates, join in the creation of the Applicable Trust with the Trustee;

WHEREAS , all Certificates deemed issued by the Applicable Trust will evidence fractional undivided interests in the Applicable Trust and will convey no rights, benefits or interests in respect of any property other than the Trust Property except for those Certificates to which an Escrow Receipt has been affixed;

WHEREAS , upon the execution and delivery of the Assignment and Assumption Agreement, 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 of 1939, as amended, 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:

ARTICLE I

THE CERTIFICATES

Section 1.01. The Certificates . The Applicable Certificates shall be known as “United Air Lines Pass Through Certificates, Series 2009-1A-S”. Each Applicable Certificate represents a fractional undivided interest in the Applicable Trust created hereby. The Applicable Certificates shall be the only instruments evidencing a fractional undivided interest in the Applicable Trust.

The terms and conditions applicable to the Applicable Certificates are as follows:

(a) The aggregate principal amount of the Applicable Certificates that shall be authenticated under the Agreement (except for Applicable Certificates authenticated and delivered under Sections 3.03, 3.04, 3.05 and 3.06 of the Basic Agreement) is $659,107,000.

(b) The Regular Distribution Dates with respect to any payment of Scheduled Payments means May 1 and November 1 of each year, commencing on May 1, 2010, until payment of all of the Scheduled Payments to be made under the Equipment Notes has been made.

(c) The Special Distribution Dates with respect to the Applicable Certificates means any Business Day on which a Special Payment is to be distributed pursuant to the Agreement.

(d) At the Escrow Agent’s request under the Escrow Agreement, the Trustee shall affix the corresponding Escrow Receipt to each Applicable Certificate. In any event, any transfer or exchange of any Applicable Certificate shall also effect a transfer or exchange of the related Escrow Receipt. Prior to the Final Withdrawal Date, no transfer or exchange of any Applicable Certificate shall be permitted unless the corresponding Escrow Receipt is attached thereto and also is so transferred or exchanged. By acceptance of any Applicable Certificate to which an Escrow Receipt is attached, each Holder of such an Applicable Certificate acknowledges and accepts the restrictions on transfer of the Escrow Receipt set forth herein and in the Escrow Agreement.

(e) (i) The Applicable Certificates shall be in the form attached as Exhibit A to the Related Pass Through Trust Supplement, with such appropriate insertions, omissions, substitutions and other variations as are required or permitted by the Related Pass Through Trust Agreement or the Agreement, as the case may be, or as the Trustee may deem appropriate, to reflect the fact that the Applicable Certificates are being issued under the Agreement as opposed to under the Related Pass Through Trust Agreement. Any Person acquiring or accepting an Applicable Certificate or an interest therein will, by such acquisition or acceptance, be deemed to represent and warrant to and for the benefit of the Company that either (i) the assets of an employee benefit plan subject to Title I of the Employee Retirement Income Security Act of 1974, as amended (“ ERISA ”), or of a plan subject to Section 4975 of the

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Internal Revenue Code of 1986, as amended (the “ Code ”), have not been used to purchase or hold Applicable Certificates or an interest therein or (ii) the purchase and holding of Applicable Certificates or an interest therein is exempt from the prohibited transaction restrictions of ERISA and the Code pursuant to one or more prohibited transaction statutory or administrative exemptions. In addition, the Applicable Certificates will bear a legend regarding ERISA compliance matters.

(ii) The Applicable 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 as Exhibit B to the Related Pass Through Trust Supplement.

(f) The “Participation Agreements” as defined in this Trust Supplement are the “Note Purchase Agreements” referred to in the Basic Agreement.

(g) The Applicable Certificates are subject to the Intercreditor Agreement, the Deposit Agreement and the Escrow Agreement.

(h) The Applicable Certificates are entitled to the benefits of the Liquidity Facility.

(i) The Equipment Notes to be acquired and held in the Applicable Trust, and the related Aircraft and Note Documents, are described in the Note Purchase Agreement.

ARTICLE II

DEFINITIONS

Section 2.01. Definitions . For all purposes of the Basic Agreement as supplemented by this Trust Supplement, the following capitalized terms have the following meanings (any capitalized term used herein but not defined shall have the meaning assigned to it in the Basic Agreement, and any term used herein which is defined in both this Trust Supplement and the Basic Agreement shall have the meaning assigned thereto in this Trust Supplement for purposes of the Basic Agreement as supplemented by this Trust Supplement):

Agreement : Means the Basic Agreement, as supplemented by the Trust Supplement.

Aircraft : Means each of the Aircraft in respect of which a Participation Agreement is entered into in accordance with the Note Purchase Agreement (or any substitute aircraft, including engines therefor, owned by the Company and securing one or more Equipment Notes).

Applicable Certificate : Means any of the “Applicable Certificates” issued by the Related Trust and that are “Outstanding” (as defined in the Related Pass Through Trust Agreement) as of the Transfer Date (the “ Transfer Date Certificates ”) and any Certificate issued in exchange therefor or replacement thereof pursuant to the Agreement.

Applicable Certificateholder : Means the Person in whose name an Applicable Certificate is registered on the Register for the Applicable Certificates.

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Applicable Closing Date : Has the meaning specified in Section 5.01(b) of this Trust Supplement.

Applicable Participation Agreement : Has the meaning specified in Section 5.01(b) of this Trust Supplement.

Applicable Trust : Has the meaning specified in the recitals hereto.

Assignment and Assumption Agreement : Means the assignment and assumption agreement substantially in the form of Exhibit C to the Related Pass Through Trust Supplement executed and delivered in accordance with Section 7.01 of the Related Trust Supplement.

Basic Agreement : Has the meaning specified in the first paragraph of this Trust Supplement.

Business Day : Means any day other than a Saturday, a Sunday or a day on which commercial banks are required or authorized to close in Chicago, Illinois, New York, New York, or, so long as any Applicable Certificate is outstanding, the city and state in which the Trustee, the Subordination Agent or any related Loan Trustee maintains its corporate trust office or receives and disburses funds.

Certificate : Has the meaning specified in the Intercreditor Agreement.

Certificate Buyout Event : Means that a United Bankruptcy Event has occurred and is continuing and the following events in either clause (A) or (B) have occurred: (A) (i) the 60-day period specified in Section 1110(a)(2)(A) of the U.S. Bankruptcy Code (the “ 60-Day Period ”) has expired and (ii) the Company has not entered into one or more agreements under Section 1110(a)(2)(A) of the U.S. Bankruptcy Code to perform all of its obligations under all of the Indentures or, if it has entered into such agreements, has at any time thereafter failed to cure any default under any of the Indentures in accordance with Section 1110(a)(2)(B) of the Bankruptcy Code; or (B) if prior to the expiry of the 60-Day Period, the Company shall have abandoned any Aircraft.

Class : Has the meaning specified in the Intercreditor Agreement.

Closing Notice : Has the meaning specified in the Note Purchase Agreement.

Company : Has the m