GUARANTEE

Exhibit 4.9

GUARANTEE

dated as of October 13, 2009

from

UAL CORPORATION

Ten (10) Airbus A319-131 Aircraft

Six (6) Airbus A320-232 Aircraft

Seven (7) Boeing 767-322ER Aircraft

Three (3) Boeing 777-222ER Aircraft and

Five (5) Boeing 747-422 Aircraft

TABLE OF CONTENTS

i

GUARANTEE

THIS GUARANTEE , dated as of October 13, 2009 (as amended, modified or supplemented from time to time, this “ Guarantee ”), from UAL CORPORATION , a Delaware corporation (together with its permitted successors and assigns, the “ Guarantor ”), to the parties listed in Schedule I hereto (collectively, together with their successors and permitted assigns, the “ Parties ”, and, individually, a “ Party ”).

WHEREAS , United Air Lines, Inc., a Delaware corporation (“ Owner ”), a direct wholly-owned subsidiary of the Guarantor, has entered into that certain Note Purchase Agreement dated as of October 13, 2009 (the “ Note Purchase Agreement ”) among Owner, Wilmington Trust Company, as pass through trustee under the Pass Through Trust Agreement (the “ Pass Through Trustee ”), Wilmington Trust Company, as Escrow Agent, Wilmington Trust Company, as Paying Agent and Wilmington Trust Company, as Subordination Agent (the “ Subordination Agent ”);

WHEREAS , capitalized used but not defined herein shall have the meanings set forth in the Note Purchase Agreement;

WHEREAS , in order to finance the aircraft identified on Schedule II hereto (the “ Aircraft ”), Owner will issue the Equipment Notes under the Indentures; and

WHEREAS , it is a condition to the purchase of the Equipment Notes by the Pass Through Trustee that the Guarantor execute and deliver this Guarantee.

NOW, THEREFORE , in order to induce the Pass Through Trustee to purchase the Equipment Notes and for other good and valuable consideration, receipt of which is hereby acknowledged, the parties hereto agree as follows:

Section 1.        Guarantee .

(a)      The Guarantor does hereby acknowledge that it is fully aware of the terms and conditions of the Indentures, the Participation Agreements, the Equipment Notes and the transactions and the other documents contemplated thereby, and does hereby irrevocably and fully and unconditionally guarantee, as primary obligor and not as surety merely, to the Parties, as their respective interests may appear, the payment by Owner of all payment obligations when due under the Indentures, the Participation Agreements and the Equipment Notes (such obligations of Owner guaranteed hereby being hereafter referred to, individually, as a “ Guaranteed Obligation ” and, collectively, as the “ Guaranteed Obligations ”) in accordance with the terms of the Financing Agreements. The Guarantor does hereby agree that in the event that Owner fails to pay any Guaranteed Obligation when due for any reason (including, without limitation, the liquidation, dissolution, receivership, insolvency, bankruptcy, assignment for the benefit of creditors, reorganization, arrangement, composition or readjustment of, or other similar proceedings affecting the status, existence, assets or obligations of Owner, or the disaffirmance with respect to Owner of any Indenture or any other Financing Agreement to which Owner is a party in any such proceeding) after the date on which such Guaranteed Obligation became due and payable and the applicable grace period has expired, the Guarantor shall pay or cause to be paid forthwith, upon the receipt of notice from the Loan Trustee (such notice to be sent to Owner

[Guarantee]

(to the extent the Loan Trustee is not stayed or prevented from doing so by operation of law) and the Guarantor) stating that such Guaranteed Obligation was not paid when due after the applicable grace period has expired and stating the amount of such Guaranteed Obligation.

(b)      The obligations of the Guarantor hereunder shall not be, to the fullest extent permitted by law, affected by: the genuineness, validity, regularity or enforceability (or lack thereof) of any of Owner’s obligations under any Indenture or any other Financing Agreement to which Owner is a party, any amendment, waiver or other modification of any Indenture or such other Financing Agreement (except that any such amendment or other modification shall be given effect in determining the obligations of the Guarantor hereunder), or by any substitution, release or exchange of collateral for or other guaranty of any of the Guaranteed Obligations (except to the extent that such substitution, release or exchange is not undertaken in accordance with the terms of the Financing Agreements) without the consent of the Guarantor, or by any priority or preference to which any other obligations of Owner may be entitled over Owner’s obligations under any Indenture and the other Financing Agreements to which Owner is a party, or by any other circumstance that might otherwise constitute a legal or equitable defense to or discharge of the obligations of a surety or guarantor including, without limitation, any defense arising out of any laws of the United States of America of any State thereof which would excuse, discharge, exempt, modify or delay the due or punctual payment and performance of the obligations of the Guarantor hereunder. Without limiting the generality of the foregoing, it is agreed that the occurrence of any one or more of the following shall not, to the fullest extent permitted by law, affect the liability of the Guarantor hereunder: (a) the extension of the time for or waiver of, at any time or from time to time, without notice to