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Exhibit 10.15 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 XXXXXXXXX. Supplemental Agreement No. 11 to Purchase Agreement No. 03776 between The Boeing Company and United Airlines, Inc. Relating to Boeing Model 737 *** Aircraft THIS SUPPLEMENTAL AGREEMENT, entered into as of September 25, 2018, by and between THE BOEING COMPANY (Boeing) and UNITED AIRLINES, INC. (Customer) (SA-11); WHEREAS, the parties hereto entered into Purchase Agreement No. 3776 dated July 12, 2012, as amended and supplemented (Purchase Agreement), relating to the purchase and sale of Boeing model 737 *** aircraft (Aircraft). This Supplemental Agreement is an amendment to the Purchase Agreement; WHEREAS, the parties wish to *** from the Purchase Agreement; *** scheduled for delivery in ***, inclusive, from the Purchase Agreement; and *** in the event of *** for 737-*** Aircraft into the Purchase Agreement; NOW THEREFORE, in consideration of the mutual covenants herein contained, the parties agree to amend the Purchase Agreement as follows: 1. Table of Contents. The "Table of Contents" is deleted in its entirety and replaced with the attached "Table of Contents" (identified by "SA-11"). 2. Tables. Table 1 A entitled "737-*** Aircraft Delivery, Description, Price and ***" is deleted in its entirety and replaced with the attached similarly titled "Table 1A" (identified by "SA-11") to *** 737-*** Aircraft scheduled for delivery in ***, inclusive. 3. Letter Agreements. 3.1. Letter Agreement UAL-PA-03776-LA-1207644R1 entitled "*** Aircraft - 737-***" is *** as a result of *** from the Purchase Agreement. 3.2. Letter Agreement No. UAL-PA-03776-LA-1807469 entitled "*** From ***" (identified by "SA- 11") is added to the Purchase Agreement to incorporate the *** in the event of *** from the *** for 737-*** Aircraft. UAL-PA-03776 SA-11, Page 1 BOEING / UNITED AIRLINES, INC. PROPRIETARY � ! " # $ % & ' ( " " % " " ")*+ ,+-. /0 .*1- 234+ 1- 5+0. 16.+6.1/6357 85369:;<== �=> ?@ABCDE F GDCHBI JCKLCDBMN CDOP QKAQKCBHJKR � ! " # $ # $ "% & % '()*+ ,-+./0 1-234/5 6/.)+7 4.89./+:; ./1<== ! > == ? # ! # �% �% ! > ? # ! # %# %# $@%@A B%( C% %# #%" A% % D"% % %!@@ �@E ,-+./0 F 6/.)+7 4.89./+:; ./1< 38-38.+)485 � � �� !!"#$ % "&'(! ) * + *, - !! .,# � /)/01112"&"#$ *!111 '03 111/)/01112"&"#$ *!111 '0456 7879:::;<=<>?@ABC;DB<EFABG=<;H@;IJFK<;=B>JL::: 955MN � 0 /)/0111O111/)/01112P 2Q '0R0% /)/01112P 2Q 0) /)/01112P 2Q 0+ /)/01112P 2Q '03S 2"&TU,#!T#$ #V# KK �MN � W 111!X#,Y2,!111 W% 111!X#,Y2,!1112 (/)/01112 '03SZW SZW[V#/)/011120 '0/SZW% SZW[V#/)/01112 '03P' P# ,'$$ [V# '03WW WQ\!111 ']* '&]2* P ,$ # ̂]0*04)//_ .S]ẀZP̀ a.Wa.' '0*Q 2) bc �A F 6KK �d

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