Exhibit 10.19

6-1162-ELP-0790

United Air Lines, Inc.

P. O. Box 66100

Chicago, IL 60601-0100

This letter agreement (Letter Agreement) amends and supplements the Purchase Agreement. Unless otherwise defined, all terms used but not defined in this Letter Agreement have the same meaning as in the Purchase Agreement. The terms of this Letter Agreement will prevail in the event of any conflict between this Letter Agreement and any provision in the Purchase Agreement.

1. In consideration of Customer’s request for its ability to [CONFIDENTIAL MATERIAL OMITTED AND FILED SEPARATELY WITH THE SEC PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT] Customer’s Aircraft to [CONFIDENTIAL MATERIAL OMITTED AND FILED SEPARATELY WITH THE SEC PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT], Boeing consents to such [CONFIDENTIAL MATERIAL OMITTED AND FILED SEPARATELY WITH THE SEC PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT] under the following terms and conditions:

1.1 [CONFIDENTIAL MATERIAL OMITTED AND FILED SEPARATELY WITH THE SEC PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT]

1.2 Customer must notify Boeing its intent to exercise its right to [CONFIDENTIAL MATERIAL OMITTED AND FILED SEPARATELY WITH THE SEC PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT] in writing (the “Notice of Intent”) no less than [CONFIDENTIAL MATERIAL OMITTED AND FILED SEPARATELY WITH THE SEC PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT] months prior to the first day of the scheduled delivery month of [CONFIDENTIAL MATERIAL OMITTED AND FILED SEPARATELY WITH THE SEC PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT] Aircraft.

1.3 [CONFIDENTIAL MATERIAL OMITTED AND FILED SEPARATELY WITH THE SEC PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT]

P.A. No. 3427

[CONFIDENTIAL MATERIAL OMITTED AND FILED SEPARATELY WITH THE SEC PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT] Matters

BOEING / UNITED PROPRIETARY

United Air Lines, Inc.

6-1162-ELP-0790

1.4 Within thirty (30) days of Boeing’s receipt of the Notice of Intent, Boeing shall have the right [CONFIDENTIAL MATERIAL OMITTED AND FILED SEPARATELY WITH THE SEC PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT] under the Purchase Agreement for [CONFIDENTIAL MATERIAL OMITTED AND FILED SEPARATELY WITH THE SEC PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT].

1.5 [CONFIDENTIAL MATERIAL OMITTED AND FILED SEPARATELY WITH THE SEC PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT]

1.6 Any and all actual incremental costs associated with the [CONFIDENTIAL MATERIAL OMITTED AND FILED SEPARATELY WITH THE SEC PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT].

1.7 [CONFIDENTIAL MATERIAL OMITTED AND FILED SEPARATELY WITH THE SEC PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT]

1.8 Boeing shall not be subject to any additional liability as a result of [CONFIDENTIAL MATERIAL OMITTED AND FILED SEPARATELY WITH THE SEC PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT] under the terms and conditions of this Letter Agreement which Boeing would not otherwise be subject to under the Purchase Agreement.

2 [CONFIDENTIAL MATERIAL OMITTED AND FILED SEPARATELY WITH THE SEC PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT] shall mean the occurrence of any one or more of the following events: (i) any party taking any action to foreclose or otherwise exercise any right such party may have to control or otherwise direct [CONFIDENTIAL MATERIAL OMITTED AND FILED SEPARATELY WITH THE SEC PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT] pursuant to a material security agreement, pledge or otherwise; (ii) any [CONFIDENTIAL MATERIAL OMITTED AND FILED SEPARATELY WITH THE SEC PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT] whether through sale, merger, consolidation or otherwise or whether through foreclosure, enforcement of a security interest, or otherwise resulting from the acts of any party; (iii) the creation of any material lien upon the material assets of [CONFIDENTIAL MATERIAL OMITTED AND FILED SEPARATELY WITH THE SEC PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT] or any pledge of any ownership or other interest in [CONFIDENTIAL MATERIAL OMITTED AND FILED SEPARATELY WITH THE SEC PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT] to any party, or (iv) the bankruptcy (whether voluntary, involuntary or otherwise) or insolvency of the [CONFIDENTIAL MATERIAL OMITTED AND FILED SEPARATELY WITH THE SEC PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT].

P.A. No. 3427

[CONFIDENTIAL MATERIAL OMITTED AND FILED SEPARATELY WITH THE SEC PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT] Matters

BOEING / UNITED PROPRIETARY

United Air Lines, Inc.

6-1162-ELP-0790

3. Assignment.

The rights and obligations described in this Letter Agreement are provided to Customer in consideration of Customer becoming the operator of the Aircraft and can only be assigned, in whole or in part, pursuant to Article 9 of the AGTA as amended by Letter Agreement No. 6-1162-IRS-0184.

P.A. No. 3427

[CONFIDENTIAL MATERIAL OMITTED AND FILED SEPARATELY WITH THE SEC PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT] Matters

BOEING / UNITED PROPRIETARY

United Air Lines, Inc.

6-1162-ELP-0790

4. Confidential Treatment.

Customer and Boeing understand that certain commercial and financial information contained in this Letter Agreement are considered by Boeing and Customer as confidential and are subject to the terms and conditions set forth in Letter Agreement No. 6-1162-IRS-0182.

P.A. No. 3427

[CONFIDENTIAL MATERIAL OMITTED AND FILED SEPARATELY WITH THE SEC PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT] Matters

BOEING / UNITED PROPRIETARY