Exhibit 10.23 CERTAIN IDENTIFIED INFORMATION HAS BEEN EXCLUDED FROM THE EXHIBIT BECAUSE IT IS BOTH NOT MATERIAL AND IS THE TYPE THAT THE REGISTRANT TREATS AS PRIVATE OR CONFIDENTIAL. OMITTED INFORMATION HAS BEEN REPLACED WITH ASTERISKS. Supplemental Agreement No. 5 to Purchase Agreement No. 3860 between The Boeing Company and United Airlines, Inc. Relating to Boeing Model 787 Aircraft THIS SUPPLEMENTAL AGREEMENT, entered into as of April 30, 2015, by and between THE BOEING COMPANY (Boeing) and UNITED AIRLINES, INC. (a Delaware corporation formerly known as Continental Airlines, Inc. and successor by merger to United Air Lines, Inc.) (Customer); WHEREAS, the parties hereto entered into Purchase Agreement No. 3860 dated September 27, 2012, as amended and supplemented (Purchase Agreement), relating to the purchase and sale of Boeing model 787 aircraft (Aircraft). This Supplemental Agreement is an amendment to the Purchase Agreement; WHEREAS, Boeing and Customer wish to *** the following firm 787-9 Aircraft *** this Purchase Agreement: Model MSN Delivery Month 787-9 *** *** WHEREAS, Boeing and Customer agree to *** the following *** firm 787-*** Aircraft and *** them with *** 787-*** Aircraft in the same delivery months: Model *** Firm Aircraft MSN *** Aircraft MSN Delivery Month *** *** TBD *** *** *** TBD *** WHEREAS, Boeing and Customer agree to apply *** firm Aircraft *** under this Supplemental Agreement No. 05 *** for the *** new model 787-*** Aircraft added under this Supplemental Agreement No. 05 and *** Customer’s *** for 787 aircraft. UAL-PA-3860 SA-5 Page 1 BOEING / UNITED AIRLINES, INC. PROPRIETARY NOW THEREFORE, in consideration of the mutual covenants herein contained, the parties agree to amend the Purchase Agreement as follows: 1. Table of Contents and Articles. The “Table of Contents” is deleted in its entirety and replaced with the attached “Table of Contents” (identified by “SA-5”). 2. Tables. 2.1. “Table 1”, 787-9 Aircraft Delivery, Description, Price and Advance Payments is deleted in its entirety. 2.2. “Table 1”, 787-10 Aircraft with GENX-1B76 Engines Delivery, Description, Price and Advance Payments, is deleted in its entirety and replaced with the attached “Table 1”, 787-10 Aircraft with GENX-1B76 Engines Delivery, Description, Price and Advance Payments, (identified by “SA-5”). 3. Letter Agreements. 3.1. “Attachment B-1 to Letter Agreement UAL-PA-03860-LA-120965R1”, 787-10 Option Aircraft with GENX-1B*** Engines Delivery, Description, Price and Advance Payments, is deleted in its entirety and replaced with the attached “Attachment B1 to Letter Agreement UAL-PA-03860-LA- 120965R1”, 787-10 Option Aircraft with GENX-1B*** Engines Delivery, Description, Price and Advance Payments, (identified by “SA-5”). 3.2. Letter agreement “UAL-PA-03860-LA-1209413A1”, Special Matters — Amendment 1, is deleted in its entirety and replaced with the attached “UAL-PA-03860-LA-1209413A1R1”, Special Matters — Amendment 1, (identified by “SA-5”). The Purchase Agreement will be deemed to be supplemented to the extent herein provided as of the date hereof and as so supplemented will continue in full force and effect. UAL-PA-3860 SA-5 Page 2 BOEING / UNITED AIRLINES, INC. PROPRIETARY EXECUTED IN DUPLICATE as of the day and year first written above. THE BOEING COMPANY UNITED AIRLINES, INC. /s/ Patrick McKelvey /s/ Gerald Laderman Signature Signature Attorney-in-Fact Senior Vice President – Finance, Procurement and Treasurer Title Title UAL-PA-3860 SA-5 Page 3 BOEING / UNITED AIRLINES, INC. PROPRIETARY TABLE OF CONTENTS SA NUMBER ARTICLES Article 1. Quantity, Model and Description SA-1 Article 2. Delivery Schedule SA-1 Article 3. Price SA-1 Article 4. Payment SA-1 Article 5. Additional Terms SA-1 TABLE 1. 787-8 with GENX-1B*** Engines Aircraft Information Table *** SA-3 1. 787-9 with GENX-1B*** Engines Aircraft Information Table *** SA-5 1. 787-10 with GENX-1B*** Engines Aircraft Information Table SA-5 EXHIBITS A1. 787-8 Aircraft Configuration A2. 787-9 Aircraft Configuration SA-4 A3. 787-10 Aircraft Configuration SA-1 B. Aircraft Delivery Requirements and Responsibilities SUPPLEMENTAL EXHIBITS AE1. Escalation Adjustment/Airframe and Optional Features BFE1. BFE Variables SA-1 CS1. Customer Support Document EE1. Engine Escalation/Engine Warranty *** SLP1. Service Life Policy Components P.A. 3860 TABLE OF CONTENTS, Page 1 of 5 SA-5 BOEING / UNITED AIRLINES, INC. PROPRIETARY

TABLE OF CONTENTS, CONTINUED SA NUMBER LETTER AGREEMENTS UAL-PA-03860-LA-1209247 787 e-Enabling UAL-PA-03860-LA-1209264 Open Configuration Matters UAL-PA-03860-LA-1209265R1 Option Aircraft SA-1 Attachment A, 787-*** Option Aircraft Delivery, Description, Price and Advance Payments (DELETED) SA-1 Attachment B-1, 787-*** with GENX-1B*** Engines: Option Aircraft Delivery, Description, Price and Advance Payments SA-5 Attachment B-2, 787-*** with TRENT1000-*** Engines: Option Aircraft Delivery, Description, Price and Advance Payments (DELETED) SA-3 UAL-PA-03860-LA-1209409 Spare Parts Initial Provisioning UAL-PA-03860-LA-1209410 Special Matters Relating to COTS Software and End User License Agreements UAL-PA-03860-LA-1209411 Special Terms – Seats and In-flight Entertainment UAL-PA-03860-LA-1209417 Model 787 Post-Delivery Software & Data Loading CONFIDENTIAL LETTER AGREEMENTS UAL-PA-03860-LA-1209236R1 Model Substitution SA-1 Attachment A, 787-9 Airframe Pricing of Substitution Aircraft with General Electric GEnx- 1B*** and Rolls Royce Trent 1000-*** engines SA-1 Attachment B, 787-10 with General Electric GEnx-1B*** and Rolls Royce TRENT 1000- *** Engines SA-1 Attachment C, 787-8 with General Electric GEnx-1B*** and Rolls Royce TRENT 1000-*** SA-1 P.A. 3860 TABLE OF CONTENTS, Page 2 of 5 SA-5 BOEING / UNITED AIRLINES, INC. PROPRIETARY TABLE OF CONTENTS, CONTINUED SA NUMBER CONFIDENTIAL LETTER AGREEMENTS, continued UAL-PA-03860-LA-1209412 Spare Parts Commitment UAL-PA-03860-LA-1209413R1 Special Matters SA-1 UAL-PA-03860-LA-1209413A1R1 Special Matters – Amendment 1 SA-5 UAL-PA-03860-LA-1209414 Other Special Matters UAL-PA-03860-LA-1209413A1 Other Special Matters - Amendment 1 SA-1 UAL-PA-03860-LA-1209416R1 Promotional Support SA-2 UAL-PA-03860-LA-1209430 Performance Guarantees UAL-PA-03860-LA-1209455 *** – TERMINATED SA-1 UAL-PA-03860-LA-1209429 *** UAL-PA-03860-LA-1209618R1 Alternate Engine Selection SA-1 6-1162-ELP-0794 *** Program- *** Aircraft 6-1162-ELP-0795 *** Program- *** Aircraft UAL-PA-03860-LA-1301368 Performance Guarantees (787-10) SA-1 UAL-PA-03860-LA-1301373 787-10 Aircraft Open Configuration and Other Matters SA-1 UAL-PA-03860-LA-1301375 Provisions Relating to Customer’s *** for 787-10 Aircraft SA-1 UAL-PA-03860-LA-1301377 787-10 *** SA-1 UAL-PA-03860-LA-1301377A1 787-10 *** – Amendment 1 SA-4 UAL-PA-03860-LA-1301380 787-10 Program Launch SA-1 UAL-PA-03860-LA-1500017 Demonstration Flight Waiver SA-4 UAL-PA-03860-LA-1500059 Installation of Cabin Systems Equipment SA-4 P.A. 3860 TABLE OF CONTENTS, Page 3 of 5 SA-5 BOEING / UNITED AIRLINES, INC. PROPRIETARY SUPPLEMENTAL AGREEMENTS DATED AS OF Supplemental Agreement No. 1 June 17, 2013 Supplemental Agreement No. 2 December 16, 2013 Supplemental Agreement No. 3 July 22, 2014 Supplemental Agreement No. 4 January 14, 2015 Supplemental Agreement No. 5 April 30, 2015 P.A. 3860 TABLE OF CONTENTS, Page 4 of 5 SA-5 BOEING / UNITED AIRLINES, INC. PROPRIETARY Table 1 to Purchase Agreement No. 3860 787-10 Aircraft with GENX-1B*** Engines Delivery, Description, Price and Advance Payments (787-10/GE/***) Airframe Model/MTOW: 787-10 *** pounds Detail Specification: *** Engine Model/Thrust: GENX-1B***¹ *** pounds Airframe Price Base Year/Escalation Formula: *** *** Airframe Price: $ *** Engine Price Base Year/Escalation Formula: *** *** Optional Features: $ *** Sub-Total of Airframe and Features: $ *** Airframe Escalation Data: Engine Price (Per Aircraft) : $ *** Base Year Index (ECI): *** Aircraft Basic Price (Excluding BFE/SPE): $ *** Base Year Index (CPI): *** Buyer Furnished Equipment (BFE) Estimate: $ *** Engine Escalation Data: In-Flight Entertainment (IFE) Estimate: $ *** Base Year Index (ECI): *** Base Year Index (CPI): *** Refundable Deposit/Aircraft at Proposal Accept: $ *** Escalation Escalation Escalation Estimate Advance Payment Per Aircraft (Amts. Due/Mos. Prior to Delivery): Delivery Number of Factor Factor Serial Adv Payment Base *** *** *** *** Date Aircraft (Airframe) (Engine) Number Price Per A/P *** *** *** *** *** *** *** *** * *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** * *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** * *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** * *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** * *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** * *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** * *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** * *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** * *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** * *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** * *** $ *** $ *** $ *** $ *** $ *** Boeing Proprietary 787-10 with GE Engines Table 1 to SA-5, Page 1

Table 1 to Purchase Agreement No. 3860 787-10 Aircraft with GENX-1B*** Engines Delivery, Description, Price and Advance Payments (787-10/GE/***) Escalation Escalation Escalation Estimate Advance Payment Per Aircraft (Amts. Due/Mos. Prior to Delivery): Delivery Number of Factor Factor Serial Adv Payment Base *** *** *** *** Date Aircraft (Airframe) (Engine) Number Price Per A/P *** *** *** *** *** *** *** *** * *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** * *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** * *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** * *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** * *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** ** *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** ** *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** ** *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** ** *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** ** *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** ** *** $ *** $ *** $ *** $ *** $ *** Total: 25 ¹ *** on a *** to delivery GEnx-1B*** thrust rating at the GEnx-1B***. * *** Escalation Factors *** ** *** Escalation Factors *** Boeing Proprietary 787-10 with GE Engines Table 1 to SA-5, Page 2 Attachment B-1 to Letter Agreement UAL-PA-03860-LA-120965R1 787-10 Option Aircraft with GENX-1B*** Engines Delivery, Description, Price and Advance Payments (787-10/GE/***) Airframe Model/MTOW: 787-10 *** pounds Detail Specification: *** Engine Model/Thrust: GENX-1B*** *** pounds Airframe Price Base Year/Escalation Formula: *** *** Airframe Price: $ *** Engine Price Base Year/Escalation Formula: *** *** Optional Features: $ *** Sub-Total of Airframe and Features: $ *** Airframe Escalation Data: Engine Price (Per Aircraft) : $ *** Base Year Index (ECI): *** Aircraft Basic Price (Excluding BFE/SPE): $ *** Base Year Index (CPI): *** Buyer Furnished Equipment (BFE) Estimate: $ *** Engine Escalation Data: In-Flight Entertainment (IFE) Estimate: $ *** Base Year Index (ECI): *** Base Year Index (CPI): *** *** Deposit/Aircraft at Def Agreement $ *** Escalation Escalation Escalation Estimate Adv Payment Advance Payment Per Aircraft (Amts. Due/Mos. Prior to Delivery): Delivery Number of Factor Factor Manufacturer Base *** *** *** *** Date Aircraft (Airframe) (Engine) Serial Number Price Per A/P *** *** *** *** *** *** *** *** TBD $ *** $ *** $ *** $ *** $ *** *** *** *** *** TBD $ *** $ *** $ *** $ *** $ *** *** *** *** *** *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** *** $ *** $ *** $ *** $ *** $ *** APR 64695-1F.TXT Boeing Proprietary 787-10 with GE Engines Table 1 to SA-5, Page 1 Attachment B-1 to Letter Agreement UAL-PA-03860-LA-120965R1 787-10 Option Aircraft with GENX-1B*** Engines Delivery, Description, Price and Advance Payments (787-10/GE/***) Escalation Escalation Escalation Estimat Adv Payment Advance Payment Per Aircraft (Amts. Due/Mos. Prior to Delivery): Delivery Number of Factor Factor Manufacturer Base *** *** *** *** Date Aircraft (Airframe) (Engine) Serial Number Price Per A/P *** *** *** *** *** *** *** *** *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** *** $ *** $ *** $ *** $ *** $ *** *** *** *** *** *** $ *** $ *** $ *** $ *** $ *** Total: *** APR 64695-1F.TXT Boeing Proprietary 787-10 with GE Engines Table 1 to SA-5, Page 2 The Boeing Company P.O. Box 3707 Seattle, WA 98124-2207 UAL-PA-03860-LA-1209413A1R1 United Airlines, Inc. 233 South Wacker Drive Chicago, Illinois 60606 Subject: Special Matters — Amendment 1 Reference: Purchase Agreement No. 3860 (Purchase Agreement) between The Boeing Company (Boeing) and United Airlines, Inc. relating to Model 787 aircraft (Aircraft) This letter agreement UAL-PA-03860-LA-1209413A1R1 (Amending Letter Agreement) amends and supplements the Purchase Agreement, amends certain terms in Letter Agreement UAL-PA-03860-LA-1209413 (the Letter Agreement), and supersedes and replaces in its entirety letter agreement UAL- PA-03860-LA-1209413A1. All terms used and not defined in this Letter Agreement have the same meaning as in the Purchase Agreement. 1. Amendments to Article 4 of the Letter Agreement. Article 4.4 of the Letter Agreement is hereby deleted and replaced with the following: 4.4. Special *** Provisions for the Launch Aircraft. With respect to (i) the *** 787-10 Aircraft listed in Table 1 to the Purchase Agreement as of the effective date of Supplemental Agreement No. 5 to the Purchase Agreement and (ii) the *** 787-*** Aircraft with scheduled delivery dates of *** and ***; (each a Launch Aircraft), the parties agree that *** of the Article 4.1 *** obligation will be *** delivery of each Launch Aircraft (Launch Aircraft *** Obligation). At time of delivery of each Launch Aircraft, Boeing will *** to *** the Launch Aircraft *** Obligation. 2. Confidential Treatment. Boeing and Customer understand that certain information contained in this Letter Agreement, including any attachments hereto, is considered by both parties to be confidential. Boeing and Customer agree that each party will treat this Letter Agreement and the information contained herein as confidential and will not, without the other party’s prior written consent, disclose this Letter Agreement or any information contained herein to any other person or entity except as may be required by applicable law or governmental regulations. UAL-PA-03860-LA-1209413A1R1 Page 1 Special Matters SA-5 BOEING / UNITED AIRLINES, INC. PROPRIETARY

Very truly yours, THE BOEING COMPANY By /s/ Patrick McKelvey Its Attorney-In-Fact ACCEPTED AND AGREED TO this Date: April 30, 2015 UNITED AIRLINES, INC. By /s/ Gerald Laderman Its Senior Vice President – Finance, Procurement and Treasurer UAL-PA-03860-LA-1209413A1R1 Page 2 Special Matters SA-5 BOEING / UNITED AIRLINES, INC. PROPRIETARY