Document:

<PAGE>

                                                                    Exhibit 4.10

                         TRUST SUPPLEMENT NO. 2001-1B
                                      TO
                         PASS THROUGH TRUST AGREEMENT

                          dated as of August 22, 2001

                                    between

                            UNITED AIR LINES, INC.

                                      and

                      STATE STREET BANK AND TRUST COMPANY
                     OF CONNECTICUT, NATIONAL ASSOCIATION,
                                  as Trustee

                                 $150,168,000

      United Airlines Enhanced Pass Through Certificates, Series 2001-1B

<PAGE>

                               TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                    Page
<S>                                                                 <C>
Article I    Declaration of Trust.................................     1
             Section 1.01 Declaration of Trust....................     1
Article II   The Certificates.....................................     2
             Section 2.01 The Certificates........................     2
Article III  Definitions..........................................     3
             Section 3.01 Definitions.............................     3
Article IV   The Trustee..........................................     3
             Section 4.01 The Trustee.............................     3
Article V    Miscellaneous Provisions.............................     3
             Section 5.01 Basic Agreement Ratified................     3
             Section 5.02 Governing Law...........................     3
             Section 5.03 Execution in Counterparts...............     4
</TABLE>

Exhibit A     Form of Certificate
Exhibit B     DTC Letter of Representations
Exhibit C     Scheduled Payments of Principal on Class B Certificates
Exhibit D     Notes, Principal Amounts and Maturities
Exhibit E     Aircraft, Registration Numbers and Maturities
Exhibit F     Note Documents

                         TRUST SUPPLEMENT NO. 2001-1B

                          Dated as of August 22, 2001

              Enhanced Pass Through Certificates, Series 2001-1B

                                       i
<PAGE>

                         TRUST SUPPLEMENT NO. 2001-1B

     THIS TRUST SUPPLEMENT NO. 2001-1B, dated as of August 22, 2001 (herein
called the "Trust Supplement"), between UNITED AIR LINES, INC., a Delaware
corporation (the "Company"), and STATE STREET BANK AND TRUST COMPANY OF
CONNECTICUT, NATIONAL ASSOCIATION, a national banking association (the
"Trustee"), to the Pass Through Trust Agreement, dated as of August 22, 2001
(the "Basic Agreement"), between the Company and the Trustee.

     WHEREAS, the Basic Agreement, which is unlimited as to the aggregate
principal amount of Certificates that may be issued thereunder, has heretofore
or concurrently herewith been executed and delivered;

     WHEREAS, pursuant to each Indenture with respect to the Aircraft, United
proposes to issue on a recourse basis the Notes to refinance its current
indebtedness originally incurred to finance the Aircraft;

     WHEREAS, the Trustee intends to declare the creation of this 2001-1B Trust
(the "Class B Trust") for the benefit of the Certificateholders of the Class B
Certificates to be issued in respect of such Class B Trust, and the initial
Certificateholders of the Class B Certificates, as grantors of such Class B
Trust, by their respective acceptances of the Class B Certificates, shall join
in the creation of the Class B Trust with the Trustee;

     WHEREAS, all Certificates to be issued by the Class B Trust will evidence
fractional undivided interests in the Class B Trust created hereby and will
convey no rights, benefits or interests in respect of any property other than
the Trust Property of the Class B Trust;

     WHEREAS, pursuant to the terms and conditions of the Basic Agreement, as
supplemented by this Trust Supplement, and the Note Purchase Agreement, the
Trustee on behalf of the Class B Trust shall purchase the Notes issued by the
Company, in each case having the identical interest rate as, and final maturity
dates not later than the final Regular Distribution Date of, the Class B
Certificates issued hereunder and shall hold such Notes in trust for the benefit
of the Class B Certificateholders;

     WHEREAS, 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;

     NOW, THEREFORE, in consideration of the premises herein, it is agreed
between the Company and the Trustee as follows:

                                   ARTICLE I
                             DECLARATION OF TRUST

     Section 1.01  Declaration of Trust. The Trustee hereby declares the
                   --------------------
creation of this Class B Trust for the benefit of the Certificateholders of the
Certificates issued hereunder, and
<PAGE>

                                                  [Trust Supplement No. 2001-1B]

the initial Certificateholders, as the grantors of the Class B Trust, by their
respective acceptances of the Certificates issued hereunder, join in the
creation of this Class B Trust with the Trustee.

                                  ARTICLE II
                               THE CERTIFICATES

     Section 2.01  The Certificates. There is hereby created a class of
                   ----------------
Certificates to be issued under the Agreement, designated and to be
distinguished and known as "United Airlines Enhanced Pass Through Certificates,
Series 2001-1B" (the "Class B Certificates"). Each Certificate represents a
Fractional Undivided Interest in the Class B Trust created hereby. The terms and
conditions applicable to the Class B Certificates are as follows:

             1.    The maximum aggregate principal amount of the Class B
Certificates that shall be authenticated under the Agreement (except for Class B
Certificates authenticated and delivered pursuant to Sections 3.04, 3.07 and
3.10 of the Basic Agreement) upon their initial issuance is $150,168,000.

             2.    The Cut-off Date is August 22, 2001.

             3.    The Regular Distribution Dates with respect to any payment of
Scheduled Payments means each March 1 and September 1, commencing on March 1,
2002, until payment of all of the Scheduled Payments to be made under the Notes
described in Exhibit D.
             ---------

             4.    The Special Distribution Dates with respect to the Class B
Certificates are any Business Day on which a Special Payment is to be
distributed pursuant to the Agreement.

             5.    The Class B Certificates shall be in the form attached hereto
as Exhibit A, shall be Global Certificates and shall be subject to the
   ---------
conditions set forth in the Letter of Representations between the Company and
The Depository Trust Company, as initial Clearing Agency, attached hereto as
Exhibit B.
---------

             6.    The Scheduled Payments of principal shall be as set forth in
Exhibit C.
---------

             7.    The proceeds of the Class B Certificates issued under the
Class B Trust shall be used to purchase the Notes described in Exhibit D.
                                                               ---------

             8.    The Notes described in paragraph 7 relate to the Aircraft
listed in Exhibit E.
          ---------

             9.    The related Note Documents are listed in Exhibit F.
                                                            ---------

             10.   The Class B Certificates shall bear the following legend:

     EITHER: (A) THE HOLDER IS NOT ACQUIRING THIS CERTIFICATE OR AN INTEREST
HEREIN WITH PLAN ASSETS OF ANY PLAN OR AN INDIVIDUAL RETIREMENT PLAN SUBJECT TO
TITLE I OF THE EMPLOYEE RETIREMENT INCOME SECURITY ACT OF 1974, AS AMENDED
("ERISA"), OR SECTION 4975 OF THE INTERNAL REVENUE CODE OF 1986, AS AMENDED (THE
"CODE"); OR (B) THE

                                       2
<PAGE>

                                                  [Trust Supplement No. 2001-1B]

HOLDER'S PURCHASE AND HOLDING OF THIS CERTIFICATE OR AN INTEREST HEREIN ARE
EXEMPT FROM THE PROHIBITED TRANSACTION RESTRICTIONS OF SECTION 406(A) OF ERISA
AND SECTION 4975 OF THE CODE BY AN ADMINISTRATIVE CLASS PROHIBITED TRANSACTION
EXEMPTION GRANTED BY THE DEPARTMENT OF LABOR.

             11.   The Class B Certificates shall have the benefit of the Class
B Liquidity Facility.

                                  ARTICLE III
                                  DEFINITIONS

     Section 3.01  Definitions. Unless otherwise specified herein, capitalized
                   -----------
terms used herein without definition shall have the respective meanings
specified heretofore in the Basic Agreement or in the Intercreditor Agreement.

                                  ARTICLE IV
                                  THE TRUSTEE

     Section 4.01  The Trustee. The Trustee shall not be responsible in any
                   -----------
manner whatsoever for or in respect of the validity or sufficiency of this Trust
Supplement or the due execution hereof by the Company or for or in respect of
the recitals and statements contained herein, all of which recitals and
statements are made solely by the Company.

     Except as herein otherwise provided, no duties, responsibilities or
liabilities are assumed, or shall be construed to be assumed by the Trustee by
reason of this Trust Supplement other than as set forth in the Basic Agreement,
and this Trust Supplement is executed and accepted on behalf of the Trustee,
subject to all the terms and conditions set forth in the Basic Agreement, upon
the effectiveness thereof, as fully to all intents as if the same were herein
set forth at length.

                                   ARTICLE V
                           MISCELLANEOUS PROVISIONS

     Section 5.01  Basic Agreement Ratified. Except and so far as herein
                   ------------------------
expressly provided, all of the provisions, terms and conditions of the Basic
Agreement are in all respects ratified and confirmed; and the Basic Agreement
and this Trust Supplement shall be taken, read and construed as one and the same
instrument.

     Section 5.02  GOVERNING LAW. THIS TRUST SUPPLEMENT AND THE CLASS B
                   -------------
CERTIFICATES SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF
THE STATE OF NEW YORK (WITHOUT REGARD TO THE PRINCIPLES OF CONFLICTS OF LAWS
THEREOF (OTHER THAN SECTION 5-1401 OF THE NEW YORK GENERAL OBLIGATIONS LAW)) AND
THE OBLIGATIONS, RIGHTS AND REMEDIES OF THE PARTIES UNDER THIS AGREEMENT SHALL
BE DETERMINED IN ACCORDANCE WITH SUCH LAWS.

                                       3
<PAGE>

                                                  [Trust Supplement No. 2001-1B]

     Section 5.03  Execution in Counterparts. This Trust Supplement may be
                   -------------------------
executed in any number of counterparts, each of which shall be an original, but
such counterparts shall together constitute but one and the same instrument.

                                       4
<PAGE>

                                                  [Trust Supplement No. 2001-1B]

     IN WITNESS WHEREOF, the Company and the Trustee have caused this Trust
Supplement to be duly executed by their respective officers thereto duly
authorized, as of the day and year first written above.

                                        UNITED AIR LINES, INC.

                                        By: /s/ Jeffrey T. Kawalsky
                                            -----------------------------------
                                        Name:  Jeffrey T. Kawalsky
                                        Title: Assistant Treasurer

                                        STATE STREET BANK AND TRUST
                                        COMPANY OF CONNECTICUT,
                                        NATIONAL ASSOCIATION, as Trustee

                                        By: /s/ John G. Correia
                                            -----------------------------------
                                        Name:  John G. Correia
                                        Title: Assistant Vice President

                                       5
<PAGE>

                                                  [Trust Supplement No. 2001-1B]

                                   EXHIBIT A

                              FORM OF CERTIFICATE

                              CLASS B CERTIFICATE

                          REGISTERED $______________
                         Fractional Undivided Interest

No. R - __                                          CUSIP NO. ________________

     UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE
DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION ("DTC"), TO THE TRUSTEE OR ITS
                                                   ---
AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY CERTIFICATE
ISSUED IN EXCHANGE FOR THIS CERTIFICATE IS REGISTERED IN THE NAME OF CEDE & CO.
OR IN SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC
(AND ANY PAYMENT HEREON IS MADE TO CEDE & CO. OR TO SUCH OTHER ENTITY AS IS
REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER
USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS
THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

     TRANSFERS OF THIS CERTIFICATE SHALL BE LIMITED TO TRANSFERS IN WHOLE, BUT
NOT IN PART, TO NOMINEES OF DTC OR TO A SUCCESSOR THEREOF OR SUCH SUCCESSOR'S
NOMINEE AND TRANSFERS OF PORTIONS OF THIS CERTIFICATE SHALL BE LIMITED TO
TRANSFERS MADE IN ACCORDANCE WITH THE RESTRICTIONS SET FORTH IN SECTION 3.05 OF
THE PASS THROUGH TRUST AGREEMENT REFERRED TO HEREIN.

     EITHER: (A) THE HOLDER IS NOT ACQUIRING THIS CERTIFICATE OR AN INTEREST
HEREIN WITH PLAN ASSETS OF ANY PLAN OR AN INDIVIDUAL RETIREMENT PLAN SUBJECT TO
TITLE I OF THE EMPLOYEE RETIREMENT INCOME SECURITY ACT OF 1974, AS AMENDED
("ERISA"), OR SECTION 4975 OF THE INTERNAL REVENUE CODE OF 1986, AS AMENDED (THE
"CODE"); OR (B) THE HOLDER'S PURCHASE AND HOLDING OF THIS CERTIFICATE OR AN
INTEREST HEREIN ARE EXEMPT FROM THE PROHIBITED TRANSACTION RESTRICTIONS OF
SECTION 406(A) OF ERISA AND SECTION 4975 OF THE CODE BY AN ADMINISTRATIVE CLASS
PROHIBITED TRANSACTION EXEMPTION GRANTED BY THE DEPARTMENT OF LABOR.

                                   Exhibit A
                                    Page 1
<PAGE>

                                                  [Trust Supplement No. 2001-1B]

              UNITED AIRLINES 2001-1B ENHANCED PASS THROUGH TRUST

                     UNITED AIRLINES ENHANCED PASS THROUGH
                          CERTIFICATE, SERIES 2001-1B

           Final Expected Regular Distribution Date: ______________

evidencing a fractional undivided interest in a trust, the property of which
includes certain equipment notes each secured by an Aircraft owned by United Air
Lines, Inc.

     THIS CERTIFIES THAT CEDE & CO., for value received, is the registered owner
of a _________________________________ ($______________) Fractional Undivided
Interest in the United Airlines 2001-1B Pass Through Trust (the "Trust") created
by State Street Bank and Trust Company of Connecticut, National Association, as
trustee (the "Trustee") pursuant to a Pass Through Trust Agreement, dated as of
August 22, 2001 (the "Basic Agreement"), as supplemented by Trust Supplement No.
2001-1B (collectively, the "Agreement") between the Trustee and United Air
Lines, Inc., a Delaware corporation (the "Company"), a summary of certain of the
pertinent provisions of which is set forth below. To the extent not otherwise
defined herein, the capitalized terms used herein have the meanings assigned to
them in the Agreement. This Certificate is one of the duly authorized
Certificates designated as "United Airlines Enhanced Pass Through Certificates,
Series 2001-1B" (the "Certificates"). This Certificate is issued under and is
subject to the terms, provisions and conditions of the Agreement.

     By virtue of its acceptance hereof, the Certificateholder of this
Certificate assents to and agrees to be bound by the provisions of the
Agreement, the Intercreditor Agreement and the Note Purchase Agreement. The
property of the Trust includes (i) certain Notes and all monies at any time paid
thereon and all monies due and to become due thereunder, (ii) funds from time to
time deposited in the related Escrow Account, the related Certificate Account
and the related Special Payments Account, (iii) all rights of such Trust and the
Trustee, on behalf of such Trust, under the Intercreditor Agreement and the Note
Purchase Agreement, including all rights to receive certain payments thereunder
and all monies paid to such Trustee on behalf of such Trust pursuant to the
Intercreditor Agreement and the Note Purchase Agreement and (iv) all monies
receivable by the Subordination Agent under the Liquidity Facility for the Trust
(the "Trust Property"). Each issue of the Notes is secured directly or
indirectly by, among other things, a security interest in the Aircraft owned by
the Company.

     The Certificates represent Fractional Undivided Interests in the Trust and
the Trust Property, and have no rights, benefits or interest in respect of any
assets or property of any trust of another class.

     Interest applicable to this Certificate will be payable at a rate equal to
_____%.

     Subject to and in accordance with the terms of the Agreement, the
Intercreditor Agreement and the Note Purchase Agreement, from and to the extent
of funds then available to the Trustee, there shall be distributed on each [ ]
and [ ] (a "Regular Distribution Date"), commencing on [ ], to the Person in
whose name this Certificate is registered at

                                   Exhibit A
                                    Page 2
<PAGE>

                                                  [Trust Supplement No. 2001-1B]

the close of business on the 15th day preceding such Regular Distribution Date,
an amount in respect of the Scheduled Payments on the Notes due on such Regular
Distribution Date, the receipt of which has been confirmed by the Trustee, equal
to the product of the percentage interest in the Trust evidenced by this
Certificate and an amount equal to the sum of such Scheduled Payments. Subject
to and in accordance with the terms of the Agreement, the Intercreditor
Agreement and the Note Purchase Agreement, if Special Payments on the Notes are
received by the Trustee, from funds then available to the Trustee, there shall
be distributed on the applicable Special Distribution Date, to the Person in
whose name this Certificate is registered at the close of business on the 15th
day preceding the Special Distribution Date, an amount in respect of such
Special Payments on the Notes, the receipt of which has been confirmed by the
Trustee, equal to the product of the percentage interest in the Trust evidenced
by this Certificate and an amount equal to the sum of such Special Payments so
received. If a Regular Distribution Date or Special Distribution Date is not a
Business Day, distribution shall be made on the next Business Day with the same
force and effect as if made on such Regular Distribution Date or Special
Distribution Date and interest shall accrue during the intervening period. The
Trustee shall mail notice of each Special Payment and the Special Distribution
Date therefor to the Certificateholder of this Certificate.

     Except as otherwise provided in the Agreement and notwithstanding the
above, the final distribution on this Certificate shall be made after notice
mailed by the Trustee of the pendency of such distribution and only upon
presentation and surrender of this Certificate at the office or agency of the
Trustee specified in such notice.

     THE AGREEMENT AND THIS CERTIFICATE SHALL BE GOVERNED BY AND CONSTRUED IN
ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK (WITHOUT REGARD TO THE
PRINCIPLES OF CONFLICTS OF LAWS THEREOF (OTHER THAN SECTION 5-1401 OF THE NEW
YORK GENERAL OBLIGATIONS LAW)) AND THE OBLIGATIONS, RIGHTS AND REMEDIES OF THE
HOLDER OF THIS CERTIFICATE UNDER THE AGREEMENT SHALL BE DETERMINED IN ACCORDANCE
WITH SUCH LAWS.

     Reference is hereby made to the further provisions of this Certificate set
forth in the reverse hereof, which further provisions shall for all purposes
have the same effect as if set forth at this place.

     Unless the certificate of authentication hereon has been executed by the
Trustee, by manual signature, this Certificate shall not be entitled to any
benefit under the Agreement or be valid or obligatory for any purpose.

                                   Exhibit A
                                    Page 3
<PAGE>

                                                  [Trust Supplement No. 2001-1B]

         IN WITNESS WHEREOF, the Trustee, on behalf of the Issuer and not in its
individual capacity, has caused this Certificate to be duly executed.

                                      UNITED AIRLINES 2001-1B PASS THROUGH TRUST

                                      By:  STATE STREET BANK AND TRUST
                                           COMPANY OF CONNECTICUT,
                                           NATIONAL ASSOCIATION, not in its
                                           individual capacity
                                           but solely as Trustee

Dated: _______________________        By: ____________________________________
                                      Name: __________________________________
                                      Title: _________________________________

                                   Exhibit A
                                    Page 4
<PAGE>

                                                  [Trust Supplement No. 2001-1B]

                    TRUSTEE'S CERTIFICATE OF AUTHENTICATION

         This is one of the Certificates referred to in the within-mentioned
Trust Agreement.

STATE STREET BANK AND TRUST                  STATE STREET BANK AND TRUST
COMPANY OF CONNECTICUT,                      COMPANY OF CONNECTICUT,
NATIONAL ASSOCIATION, not in its             NATIONAL ASSOCIATION, not in its
individual capacity but solely as            individual capacity but solely as
Trustee                                      Trustee

By: _______________________________          By: _______________________________
                                                       Authenticating Agent
                                             By: _______________________________

                                  Exhibit A
                                    Page 5
<PAGE>

                                                  [Trust Supplement No. 2001-1B]

                           [REVERSE OF CERTIFICATE]

         The Certificates do not represent a direct obligation of, or an
obligation guaranteed by, or an interest in, the Company or the Trustee or any
of their Affiliates. The Certificates are limited in right or payment, all as
more specifically set forth on the face hereof and in the Agreement. All
payments or distributions made to Certificateholders under the Agreement shall
be made only from the Trust Property and only to the extent that the Trustee
shall have sufficient income or proceeds from the Trust Property to make such
payments in accordance with the terms of the Agreement. Each Certificateholder
of this Certificate, by its acceptance hereof, agrees that it shall look solely
to the income and proceeds from the Trust Property to the extent available for
distribution to such Certificateholder as provided in the Agreement. This
Certificate does not purport to summarize the Agreement and reference is made to
the Agreement for information with respect to the interests, rights, benefits,
obligations, proceeds and duties evidenced hereby. A copy of the Agreement may
be examined during normal business hours at the principal office of the Trustee,
and at such other places, if any, designated by the Trustee, by any
Certificateholder upon request.

         The Agreement permits, with certain exceptions therein provided, the
amendment thereof and the modification of the rights and obligations of the
Company and the rights of the Certificateholders under the Agreement at any time
by the Company and the Trustee with the consent of the Certificateholders
holding Certificates evidencing Fractional Cumulative Interests aggregating not
less than a majority in interest in the Trust. Any such consent by the
Certificateholder of this Certificate shall be conclusive and binding on such
Certificateholder and upon all future Certificateholders of this Certificate and
of any Certificate issued upon the transfer hereof or in exchange hereof or in
lieu hereof whether or not notation of such consent is made upon this
Certificate. The Agreement also permits the amendment thereof, in certain
limited circumstances, without the consent of the Certificateholders of any of
the Certificates.

         As provided in the Agreement and subject to certain limitations therein
set forth, the transfer of this Certificate is registrable in the Register upon
surrender of this Certificate for registration of transfer at the offices or
agencies maintained by the Trustee in its capacity as Registrar, or by any
successor Registrar, at its Corporate Trust Office, duly endorsed or accompanied
by a written instrument of transfer in form satisfactory to the Trustee and the
Registrar duly executed by the Certificateholder hereof or such
Certificateholder's attorney duly authorized in writing, and thereupon one or
more new Certificates of authorized denominations evidencing the same aggregate
Fractional Undivided Interest in the Trust shall be issued to the designated
transferee or transferees.

         The Certificates are issuable only as registered Certificates without
coupons in minimum denominations of $1,000 Fractional Undivided Interest and
integral multiples of $1,000 in excess thereof. As provided in the Agreement and
subject to certain limitations therein set forth, the Certificates are
exchangeable for new Certificates of authorized denominations evidencing the
same aggregate Fractional Undivided Interest in the Trust, as requested by the
Certificateholder surrendering the same.

                                   Exhibit A
                                    Page 6
<PAGE>

                                                  [Trust Supplement No. 2001-1B]

         No service charge shall be made for any such registration of transfer
or exchange, but the Trustee shall require payment by the Certificateholder of a
sum sufficient to cover any tax or governmental charge payable in connection
therewith.

         The Trustee, the Registrar, and any agent of the Trustee or the
Registrar may treat the person in whose name this Certificate is registered as
the owner hereof for all purposes, and neither the Trustee, the Registrar, nor
any such agent shall be affected by any notice to the contrary.

         The obligations and responsibilities created by the Agreement and the
Trust created thereby shall terminate upon the distribution to
Certificateholders of all amounts required to be distributed to them pursuant to
the Agreement and the disposition of all property held as part of the Trust
Property.

                                   Exhibit A
                                    Page 7
<PAGE>

                                                  [Trust Supplement No. 2001-1B]

                            FORM OF TRANSFER NOTICE

         FOR VALUE RECEIVED the undersigned registered holder hereby sell(s),
assign(s) and transfer(s) unto

Insert               Taxpayer             Identification                 No.

________________________________________________________________________________
please print or typewrite name and address including zip code of assignee

________________________________________________________________________________
the within Certificate and all rights thereunder, hereby irrevocably
constituting and appointing

________________________________________________________________________________
attorney to transfer said Certificate on the books of the Trustee with full
power of substitution in the premises.

Date:                                  [Name of Transferor]

                                       _________________________________________

                                       NOTE: The signature must correspond with
                                       the name as written upon the face of the
                                       within-mentioned instrument in every
                                       particular, without alteration or any
                                       change whatsoever.

Signature Guarantee: ________________

                                   Exhibit A
                                    Page 8
<PAGE>

                                                  [Trust Supplement No. 2001-1B]

                                   EXHIBIT B

                         DTC LETTER OF REPRESENTATIONS

                                   Exhibit B
                                    Page 1
<PAGE>

                                                  [Trust Supplement No. 2001-1B]

                                   EXHIBIT C

                        SCHEDULED PAYMENTS OF PRINCIPAL
                            ON CLASS B CERTIFICATES

           Payment Date                                 Principal Payment
-------------------------------------     --------------------------------------

                                   Exhibit C
                                    Page 1
<PAGE>

                                                  [Trust Supplement No. 2001-1B]

                                   EXHIBIT D

                       PRINCIPAL AMOUNTS AND MATURITIES

        Notes                   Principal Amount                Maturity
----------------------   ----------------------------  ------------------------

                                   Exhibit D
                                    Page 1
<PAGE>

                                                  [Trust Supplement No. 2001-1B]

                                   EXHIBIT E

                 AIRCRAFT, REGISTRATION NUMBERS AND MATURITIES

                                   Aircraft
                                 Registration
      Aircraft                      Number                   Maturity
----------------------   ----------------------------  ------------------------

                                   Exhibit E
                                    Page 1
<PAGE>

                                                  [Trust Supplement No. 2001-1B]

                                   EXHIBIT F

                                NOTE DOCUMENTS

                             Aircraft
                           Registration
      Aircraft                Number                   Note Document
--------------------  -----------------------  ------------------------------
      A319-131                N831UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-2
                                               Equipment Note, Series C
                                               Equipment Note, Series D

      A319-131                N833UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-2
                                               Equipment Note, Series C
                                               Equipment Note, Series D

      A319-131                N834UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-3
                                               Equipment Note, Series B
                                               Equipment Note, Series C
                                               Equipment Note, Series D

      A319-131                N835UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-3
                                               Equipment Note, Series B
                                               Equipment Note, Series C
                                               Equipment Note, Series D

                                   Exhibit F
                                    Page 1
<PAGE>

                                                  [Trust Supplement No. 2001-1B]

      A319-131                N836UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-3
                                               Equipment Note, Series B
                                               Equipment Note, Series C
                                               Equipment Note, Series D

      A319-131                N837UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-3
                                               Equipment Note, Series B
                                               Equipment Note, Series C
                                               Equipment Note, Series D

      A319-131                N838UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-3
                                               Equipment Note, Series B
                                               Equipment Note, Series C
                                               Equipment Note, Series D

      A319-131                N839UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-3
                                               Equipment Note, Series B
                                               Equipment Note, Series C
                                               Equipment Note, Series D

                                   Exhibit F
                                    Page 2
<PAGE>

                                                  [Trust Supplement No. 2001-1B]

      A319-131                N840UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-3
                                               Equipment Note, Series B
                                               Equipment Note, Series C
                                               Equipment Note, Series D

      A319-131                N841UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-3
                                               Equipment Note, Series B
                                               Equipment Note, Series C
                                               Equipment Note, Series D

      A320-232                N467UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-2
                                               Equipment Note, Series C
                                               Equipment Note, Series D

      A320-232                N468UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-2
                                               Equipment Note, Series C
                                               Equipment Note, Series D

      A320-232                N469UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-3
                                               Equipment Note, Series B
                                               Equipment Note, Series C
                                               Equipment Note, Series D

                                   Exhibit F
                                    Page 3
<PAGE>

                                                  [Trust Supplement No. 2001-1B]

      A320-232                N470UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-3
                                               Equipment Note, Series B
                                               Equipment Note, Series C
                                               Equipment Note, Series D

      A320-232                N471UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-3
                                               Equipment Note, Series B
                                               Equipment Note, Series C
                                               Equipment Note, Series D

      A320-232                N472UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-3
                                               Equipment Note, Series B
                                               Equipment Note, Series C
                                               Equipment Note, Series D

      B747-422                N117UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-2
                                               Equipment Note, Series C
                                               Equipment Note, Series D

      B747-422                N118UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-2
                                               Equipment Note, Series C
                                               Equipment Note, Series D

                                   Exhibit F
                                    Page 4
<PAGE>

                                                  [Trust Supplement No. 2001-1B]

      B747-422                N122UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-3
                                               Equipment Note, Series B
                                               Equipment Note, Series C
                                               Equipment Note, Series D

      B747-422                N127UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-3
                                               Equipment Note, Series B
                                               Equipment Note, Series C
                                               Equipment Note, Series D

      B747-422                N128UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-3
                                               Equipment Note, Series B
                                               Equipment Note, Series C
                                               Equipment Note, Series D

      B767-322                N664UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-2
                                               Equipment Note, Series C
                                               Equipment Note, Series D

      B767-322                N667UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-2
                                               Equipment Note, Series C
                                               Equipment Note, Series D

                                   Exhibit F
                                    Page 5
<PAGE>

                                                  [Trust Supplement No. 2001-1B]

      B767-322                N669UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-3
                                               Equipment Note, Series B
                                               Equipment Note, Series C
                                               Equipment Note, Series D

      B767-322                N670UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-3
                                               Equipment Note, Series B
                                               Equipment Note, Series C
                                               Equipment Note, Series D

      B767-322                N671UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-3
                                               Equipment Note, Series B
                                               Equipment Note, Series C
                                               Equipment Note, Series D

      B777-222                N794UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-2
                                               Equipment Note, Series C
                                               Equipment Note, Series D

      B777-222                N795UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-2
                                               Equipment Note, Series C
                                               Equipment Note, Series D

                                   Exhibit F
                                    Page 6
<PAGE>

                                                  [Trust Supplement No. 2001-1B]

      B777-222                N204UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-3
                                               Equipment Note, Series B
                                               Equipment Note, Series C
                                               Equipment Note, Series D

      B777-222                N205UA           Participation Agreement
                                               Trust Indenture and Mortgage
                                               Equipment Note, Series A-1
                                               Equipment Note, Series A-3
                                               Equipment Note, Series B
                                               Equipment Note, Series C
                                               Equipment Note, Series D

                                   Exhibit F
                                    Page 7<PAGE>

                                                                    Exhibit 4.11

                         TRUST SUPPLEMENT NO. 2001-1C
                                      TO
                         PASS THROUGH TRUST AGREEMENT

                          dated as of August 22, 2001

                                    between

                            UNITED AIR LINES, INC.

                                      and

                      STATE STREET BANK AND TRUST COMPANY
                     OF CONNECTICUT, NATIONAL ASSOCIATION,
                                  as Trustee

                                 $251,885,000

      United Airlines Enhanced Pass Through Certificates, Series 2001-1C

<PAGE>

                               TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                   Page
<S>                                                                <C>
Article I    Declaration of Trust................................     1
             Section 1.01 Declaration of Trust...................     1
Article II   The Certificates....................................     2
             Section 2.01 The Certificates.......................     2
Article III  Definitions.........................................     3
             Section 3.01 Definitions............................     3
Article IV   The Trustee.........................................     3
             Section 4.01 The Trustee............................     3
Article V    Miscellaneous Provisions............................     3
             Section 5.01 Basic Agreement Ratified...............     3
             Section 5.02 Governing Law..........................     3
             Section 5.03 Execution in Counterparts..............     4
</TABLE>

Exhibit A     Form of Certificate
Exhibit B     DTC Letter of Representations
Exhibit C     Scheduled Payments of Principal on Class C Certificates
Exhibit D     Notes, Principal Amounts and Maturities
Exhibit E     Aircraft, Registration Numbers and Maturities
Exhibit F     Note Documents

                         TRUST SUPPLEMENT NO. 2001-1C

                          Dated as of August 22, 2001

              Enhanced Pass Through Certificates, Series 2001-1C

                                       i
<PAGE>

                         TRUST SUPPLEMENT NO. 2001-1C

     THIS TRUST SUPPLEMENT NO. 2001-1C, dated as of August 22, 2001 (herein
called the "Trust Supplement"), between UNITED AIR LINES, INC., a Delaware
corporation (the "Company"), and STATE STREET BANK AND TRUST COMPANY OF
CONNECTICUT, NATIONAL ASSOCIATION, a national banking association (the
"Trustee"), to the Pass Through Trust Agreement, dated as of August 22, 2001
(the "Basic Agreement"), between the Company and the Trustee.

     WHEREAS, the Basic Agreement, which is unlimited as to the aggregate
principal amount of Certificates that may be issued thereunder, has heretofore
or concurrently herewith been executed and delivered;

     WHEREAS, pursuant to each Indenture with respect to the Aircraft, United
proposes to issue on a recourse basis the Notes to refinance its current
indebtedness originally incurred to finance the Aircraft;

     WHEREAS, the Trustee intends to declare the creation of this 2001-1C Trust
(the "Class C Trust") for the benefit of the Certificateholders of the Class C
Certificates to be issued in respect of such Class C Trust, and the initial
Certificateholders of the Class C Certificates, as grantors of such Class C
Trust, by their respective acceptances of the Class C Certificates, shall join
in the creation of the Class C Trust with the Trustee;

     WHEREAS, all Certificates to be issued by the Class C Trust will evidence
fractional undivided interests in the Class C Trust created hereby and will
convey no rights, benefits or interests in respect of any property other than
the Trust Property of the Class C Trust;

     WHEREAS, pursuant to the terms and conditions of the Basic Agreement, as
supplemented by this Trust Supplement, and the Note Purchase Agreement, the
Trustee on behalf of the Class C Trust shall purchase the Notes issued by the
Company, in each case having the identical interest rate as, and final maturity
dates not later than the final Regular Distribution Date of, the Class C
Certificates issued hereunder and shall hold such Notes in trust for the benefit
of the Class C Certificateholders;

     WHEREAS, 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;

     NOW, THEREFORE, in consideration of the premises herein, it is agreed
between the Company and the Trustee as follows:

                                   ARTICLE I
                             DECLARATION OF TRUST

     Section 1.01  Declaration of Trust. The Trustee hereby declares the
                   --------------------
creation of this Class C Trust for the benefit of the Certificateholders of the
Certificates issued hereunder, and
<PAGE>

                                                  [Trust Supplement No. 2001-1C]

the initial Certificateholders, as the grantors of the Class C Trust, by their
respective acceptances of the Certificates issued hereunder, join in the
creation of this Class C Trust with the Trustee.

                                  ARTICLE II
                               THE CERTIFICATES

     Section 2.01  The Certificates. There is hereby created a class of
                   ----------------
Certificates to be issued under the Agreement, designated and to be
distinguished and known as "United Airlines Enhanced Pass Through Certificates,
Series 2001-1C" (the "Class C Certificates"). Each Certificate represents a
Fractional Undivided Interest in the Class C Trust created hereby. The terms and
conditions applicable to the Class C Certificates are as follows:

             1.    The maximum aggregate principal amount of the Class C
Certificates that shall be authenticated under the Agreement (except for Class C
Certificates authenticated and delivered pursuant to Sections 3.04, 3.07 and
3.10 of the Basic Agreement) upon their initial issuance is $251,885,000.

             2.    The Cut-off Date is August 22, 2001.

             3.    The Regular Distribution Dates with respect to any payment of
Scheduled Payments means each March 1 and September 1, commencing on March 1,
2002, until payment of all of the Scheduled Payments to be made under the Notes
described in Exhibit D.
             ---------

             4.    The Special Distribution Dates with respect to the Class C
Certificates are any Business Day on which a Special Payment is to be
distributed pursuant to the Agreement.

             5.    The Class C Certificates shall be in the form attached hereto
as Exhibit A, shall be Global Certificates and shall be subject to the
   ---------
conditions set forth in the Letter of Representations between the Company and
The Depository Trust Company, as initial Clearing Agency, attached hereto as
Exhibit B.
---------

             6.    The Scheduled Payments of principal shall be as set forth in
Exhibit C.
---------

             7.    The proceeds of the Class C Certificates issued under the
Class C Trust shall be used to purchase the Notes described in Exhibit D.
                                                               ---------

             8.    The Notes described in paragraph 7 relate to the Aircraft
listed in Exhibit E.
          ---------

             9.    The related Note Documents are listed in Exhibit F.
                                                            ---------

             10.   The Class C Certificates shall bear the following legend:

     EITHER: (A) THE HOLDER IS NOT ACQUIRING THIS CERTIFICATE OR AN INTEREST
HEREIN WITH PLAN ASSETS OF ANY PLAN OR AN INDIVIDUAL RETIREMENT PLAN SUBJECT TO
TITLE I OF THE EMPLOYEE RETIREMENT INCOME SECURITY ACT OF 1974, AS AMENDED
("ERISA"), OR SECTION 4975 OF THE INTERNAL REVENUE CODE OF 1986, AS AMENDED (THE
"CODE"); OR (B) THE

                                       2
<PAGE>

                                                  [Trust Supplement No. 2001-1C]

HOLDER'S PURCHASE AND HOLDING OF THIS CERTIFICATE OR AN INTEREST HEREIN ARE
EXEMPT FROM THE PROHIBITED TRANSACTION RESTRICTIONS OF SECTION 406(A) OF ERISA
AND SECTION 4975 OF THE CODE BY AN ADMINISTRATIVE CLASS PROHIBITED TRANSACTION
EXEMPTION GRANTED BY THE DEPARTMENT OF LABOR.

             11.   The Class C Certificates shall have the benefit of the Class
C Liquidity Facility.

                                  ARTICLE III
                                  DEFINITIONS

     Section 3.01  Definitions. Unless otherwise specified herein, capitalized
                   -----------
terms used herein without definition shall have the respective meanings
specified heretofore in the Basic Agreement or in the Intercreditor Agreement.

                                  ARTICLE IV
                                  THE TRUSTEE

     Section 4.01  The Trustee. The Trustee shall not be responsible in any
                   -----------
manner whatsoever for or in respect of the validity or sufficiency of this Trust
Supplement or the due execution hereof by the Company or for or in respect of
the recitals and statements contained herein, all of which recitals and
statements are made solely by the Company.

     Except as herein otherwise provided, no duties, responsibilities or
liabilities are assumed, or shall be construed to be assumed by the Trustee by
reason of this Trust Supplement other than as set forth in the Basic Agreement,
and this Trust Supplement is executed and accepted on behalf of the Trustee,
subject to all the terms and conditions set forth in the Basic Agreement, upon
the effectiveness thereof, as fully to all intents as if the same were herein
set forth at length.

                                   ARTICLE V
                           MISCELLANEOUS PROVISIONS

     Section 5.01  Basic Agreement Ratified. Except and so far as herein
                   ------------------------
expressly provided, all of the provisions, terms and conditions of the Basic
Agreement are in all respects ratified and confirmed; and the Basic Agreement
and this Trust Supplement shall be taken, read and construed as one and the same
instrument.

     Section 5.02  GOVERNING LAW. THIS TRUST SUPPLEMENT AND THE CLASS C
                   -------------
CERTIFICATES SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF
THE STATE OF NEW YORK (WITHOUT REGARD TO THE PRINCIPLES OF CONFLICTS OF LAWS
THEREOF (OTHER THAN SECTION 5-1401 OF THE NEW YORK GENERAL OBLIGATIONS LAW)) AND
THE OBLIGATIONS, RIGHTS AND REMEDIES OF THE PARTIES UNDER THIS AGREEMENT SHALL
BE DETERMINED IN ACCORDANCE WITH SUCH LAWS.

                                       3
<PAGE>

                                                  [Trust Supplement No. 2001-1C]

     Section 5.03  Execution in Counterparts. This Trust Supplement may be
                   -------------------------
executed in any number of counterparts, each of which shall be an original, but
such counterparts shall together constitute but one and the same instrument.

                                       4
<PAGE>

                                                  [Trust Supplement No. 2001-1C]

     IN WITNESS WHEREOF, the Company and the Trustee have caused this Trust
Supplement to be duly executed by their respective officers thereto duly
authorized, as of the day and year first written above.

                                        UNITED AIR LINES, INC.

                                        By:  /s/ Jeffrey T. Kawalsky
                                             ----------------------------------
                                        Name:  Jeffrey T. Kawalsky
                                        Title: Assistant Treasurer

                                        STATE STREET BANK AND TRUST
                                        COMPANY OF CONNECTICUT,
                                        NATIONAL ASSOCIATION, as Trustee

                                        By:  /s/  John G. Correia
                                             ----------------------------------
                                        Name:  John G. Correia
                                        Title: Assistant Vice President

                                       5
<PAGE>

                                                  [Trust Supplement No. 2001-1C]

                                   EXHIBIT A

                              FORM OF CERTIFICATE

                              CLASS C CERTIFICATE

                          REGISTERED $______________
                         Fractional Undivided Interest

No. R - __                                           CUSIP NO. ________________

     UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE
DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION ("DTC"), TO THE TRUSTEE OR ITS
                                                   ---
AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY CERTIFICATE
ISSUED IN EXCHANGE FOR THIS CERTIFICATE IS REGISTERED IN THE NAME OF CEDE & CO.
OR IN SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC
(AND ANY PAYMENT HEREON IS MADE TO CEDE & CO. OR TO SUCH OTHER ENTITY AS IS
REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER
USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS
THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

     TRANSFERS OF THIS CERTIFICATE SHALL BE LIMITED TO TRANSFERS IN WHOLE, BUT
NOT IN PART, TO NOMINEES OF DTC OR TO A SUCCESSOR THEREOF OR SUCH SUCCESSOR'S
NOMINEE AND TRANSFERS OF PORTIONS OF THIS CERTIFICATE SHALL BE LIMITED TO
TRANSFERS MADE IN ACCORDANCE WITH THE RESTRICTIONS SET FORTH IN SECTION 3.05 OF
THE PASS THROUGH TRUST AGREEMENT REFERRED TO HEREIN.

     EITHER: (A) THE HOLDER IS NOT ACQUIRING THIS CERTIFICATE OR AN INTEREST
HEREIN WITH PLAN ASSETS OF ANY PLAN OR AN INDIVIDUAL RETIREMENT PLAN SUBJECT TO
TITLE I OF THE EMPLOYEE RETIREMENT INCOME SECURITY ACT OF 1974, AS AMENDED
("ERISA"), OR SECTION 4975 OF THE INTERNAL REVENUE CODE OF 1986, AS AMENDED (THE
"CODE"); OR (B) THE HOLDER'S PURCHASE AND HOLDING OF THIS CERTIFICATE OR AN
INTEREST HEREIN ARE EXEMPT FROM THE PROHIBITED TRANSACTION RESTRICTIONS OF
SECTION 406(A) OF ERISA AND SECTION 4975 OF THE CODE BY AN ADMINISTRATIVE CLASS
PROHIBITED TRANSACTION EXEMPTION GRANTED BY THE DEPARTMENT OF LABOR.

                                   Exhibit A
                                    Page 1
<PAGE>

                                                  [Trust Supplement No. 2001-1C]

              UNITED AIRLINES 2001-1C ENHANCED PASS THROUGH TRUST

                     UNITED AIRLINES ENHANCED PASS THROUGH
                          CERTIFICATE, SERIES 2001-1C

           Final Expected Regular Distribution Date: ______________

evidencing a fractional undivided interest in a trust, the property of which
includes certain equipment notes each secured by an Aircraft owned by United Air
Lines, Inc.

     THIS CERTIFIES THAT CEDE & CO., for value received, is the registered owner
of a _________________________________ ($______________) Fractional Undivided
Interest in the United Airlines 2001-1C Pass Through Trust (the "Trust") created
by State Street Bank and Trust Company of Connecticut, National Association, as
trustee (the "Trustee") pursuant to a Pass Through Trust Agreement, dated as of
August 22, 2001 (the "Basic Agreement"), as supplemented by Trust Supplement No.
2001-1C (collectively, the "Agreement") between the Trustee and United Air
Lines, Inc., a Delaware corporation (the "Company"), a summary of certain of the
pertinent provisions of which is set forth below. To the extent not otherwise
defined herein, the capitalized terms used herein have the meanings assigned to
them in the Agreement. This Certificate is one of the duly authorized
Certificates designated as "United Airlines Enhanced Pass Through Certificates,
Series 2001-1C" (the "Certificates"). This Certificate is issued under and is
subject to the terms, provisions and conditions of the Agreement.

     By virtue of its acceptance hereof, the Certificateholder of this
Certificate assents to and agrees to be bound by the provisions of the
Agreement, the Intercreditor Agreement and the Note Purchase Agreement. The
property of the Trust includes (i) certain Notes and all monies at any time paid
thereon and all monies due and to become due thereunder, (ii) funds from time to
time deposited in the related Escrow Account, the related Certificate Account
and the related Special Payments Account, (iii) all rights of such Trust and the
Trustee, on behalf of such Trust, under the Intercreditor Agreement and the Note
Purchase Agreement, including all rights to receive certain payments thereunder
and all monies paid to such Trustee on behalf of such Trust pursuant to the
Intercreditor Agreement and the Note Purchase Agreement and (iv) all monies
receivable by the Subordination Agent under the Liquidity Facility for the Trust
(the "Trust Property"). Each issue of the Notes is secured directly or
indirectly by, among other things, a security interest in the Aircraft owned by
the Company.

     The Certificates represent Fractional Undivided Interests in the Trust and
the Trust Property, and have no rights, benefits or interest in respect of any
assets or property of any trust of another class.

     Interest applicable to this Certificate will be payable at a rate equal to
_____%.

     Subject to and in accordance with the terms of the Agreement, the
Intercreditor Agreement and the Note Purchase Agreement, from and to the extent
of funds then available to the Trustee, there shall be distributed on each [ ]
and [ ] (a "Regular Distribution Date"), commencing on [ ], to the Person in
whose name this Certificate is registered at

                                   Exhibit A
                                    Page 2
<PAGE>

                                                  [Trust Supplement No. 2001-1C]

the close of business on the 15th day preceding such Regular Distribution Date,
an amount in respect of the Scheduled Payments on the Notes due on such Regular
Distribution Date, the receipt of which has been confirmed by the Trustee, equal
to the product of the percentage interest in the Trust evidenced by this
Certificate and an amount equal to the sum of such Scheduled Payments. Subject
to and in accordance with the terms of the Agreement, the Intercreditor
Agreement and the Note Purchase Agreement, if Special Payments on the Notes are
received by the Trustee, from funds then available to the Trustee, there shall
be distributed on the applicable Special Distribution Date, to the Person in
whose name this Certificate is registered at the close of business on the 15th
day preceding the Special Distribution Date, an amount in respect of such
Special Payments on the Notes, the receipt of which has been confirmed by the
Trustee, equal to the product of the percentage interest in the Trust evidenced
by this Certificate and an amount equal to the sum of such Special Payments so
received. If a Regular Distribution Date or Special Distribution Date is not a
Business Day, distribution shall be made on the next Business Day with the same
force and effect as if made on such Regular Distribution Date or Special
Distribution Date and interest shall accrue during the intervening period. The
Trustee shall mail notice of each Special Payment and the Special Distribution
Date therefor to the Certificateholder of this Certificate.

     Except as otherwise provided in the Agreement and notwithstanding the
above, the final distribution on this Certificate shall be made after notice
mailed by the Trustee of the pendency of such distribution and only upon
presentation and surrender of this Certificate at the office or agency of the
Trustee specified in such notice.

     THE AGREEMENT AND THIS CERTIFICATE SHALL BE GOVERNED BY AND CONSTRUED IN
ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK (WITHOUT REGARD TO THE
PRINCIPLES OF CONFLICTS OF LAWS THEREOF (OTHER THAN SECTION 5-1401 OF THE NEW
YORK GENERAL OBLIGATIONS LAW)) AND THE OBLIGATIONS, RIGHTS AND REMEDIES OF THE
HOLDER OF THIS CERTIFICATE UNDER THE AGREEMENT SHALL BE DETERMINED IN ACCORDANCE
WITH SUCH LAWS.

     Reference is hereby made to the further provisions of this Certificate set
forth in the reverse hereof, which further provisions shall for all purposes
have the same effect as if set forth at this place.

     Unless the certificate of authentication hereon has been executed by the
Trustee, by manual signature, this Certificate shall not be entitled to any
benefit under the Agreement or be valid or obligatory for any purpose.

                                   Exhibit A
                                    Page 3
<PAGE>

                                                  [Trust Supplement No. 2001-1C]

      IN WITNESS WHEREOF, the Trustee, on behalf of the Issuer and not in its
individual capacity, has caused this Certificate to be duly executed.

                                        UNITED AIRLINES 2001-1C PASS
                                        THROUGH TRUST

                                        By:  STATE STREET BANK AND TRUST
                                             COMPANY OF CONNECTICUT,
                                             NATIONAL ASSOCIATION, not in its
                                             individual capacity
                                             but solely as Trustee

Dated:_________________________         By:__________________________________
                                        Name:________________________________
                                        Title:_______________________________

                                   Exhibit A
                                    Page 4
<PAGE>

                                                  [Trust Supplement No. 2001-1C]

                    TRUSTEE'S CERTIFICATE OF AUTHENTICATION

   This is one of the Certificates referred to in the within-mentioned Trust
                                  Agreement.

STATE STREET BANK AND TRUST             STATE STREET BANK AND TRUST
COMPANY OF CONNECTICUT,                 COMPANY OF CONNECTICUT,
NATIONAL ASSOCIATION, not in its        NATIONAL ASSOCIATION, not in its
individual capacity but solely as       individual capacity but solely as
Trustee                                 Trustee

By:________________________________     By:________________________________
                                                 Authenticating Agent

                                        By:________________________________

                                   Exhibit A
                                    Page 5
<PAGE>

                                                  [Trust Supplement No. 2001-1C]

                           [REVERSE OF CERTIFICATE]

         The Certificates do not represent a direct obligation of, or an
obligation guaranteed by, or an interest in, the Company or the Trustee or any
of their Affiliates. The Certificates are limited in right or payment, all as
more specifically set forth on the face hereof and in the Agreement. All
payments or distributions made to Certificateholders under the Agreement shall
be made only from the Trust Property and only to the extent that the Trustee
shall have sufficient income or proceeds from the Trust Property to make such
payments in accordance with the terms of the Agreement. Each Certificateholder
of this Certificate, by its acceptance hereof, agrees that it shall look solely
to the income and proceeds from the Trust Property to the extent available for
distribution to such Certificateholder as provided in the Agreement. This
Certificate does not purport to summarize the Agreement and reference is made to
the Agreement for information with respect to the interests, rights, benefits,
obligations, proceeds and duties evidenced hereby. A copy of the Agreement may
be examined during normal business hours at the principal office of the Trustee,
and at such other places, if any, designated by the Trustee, by any
Certificateholder upon request.

         The Agreement permits, with certain exceptions therein provided, the
amendment thereof and the modification of the rights and obligations of the
Company and the rights of the Certificateholders under the Agreement at any time
by the Company and the Trustee with the consent of the Certificateholders
holding Certificates evidencing Fractional Cumulative Interests aggregating not
less than a majority in interest in the Trust. Any such consent by the
Certificateholder of this Certificate shall be conclusive and binding on such
Certificateholder and upon all future Certificateholders of this Certificate and
of any Certificate issued upon the transfer hereof or in exchange hereof or in
lieu hereof whether or not notation of such consent is made upon this
Certificate. The Agreement also permits the amendment thereof, in certain
limited circumstances, without the consent of the Certificateholders of any of
the Certificates.

         As provided in the Agreement and subject to certain limitations therein
set forth, the transfer of this Certificate is registrable in the Register upon
surrender of this Certificate for registration of transfer at the offices or
agencies maintained by the Trustee in its capacity as Registrar, or by any
successor Registrar, at its Corporate Trust Office, duly endorsed or accompanied
by a written instrument of transfer in form satisfactory to the Trustee and the
Registrar duly executed by the Certificateholder hereof or such
Certificateholder's attorney duly authorized in writing, and thereupon one or
more new Certificates of authorized denominations evidencing the same aggregate
Fractional Undivided Interest in the Trust shall be issued to the designated
transferee or transferees.

         The Certificates are issuable only as registered Certificates without
coupons in minimum denominations of $1,000 Fractional Undivided Interest and
integral multiples of $1,000 in excess thereof. As provided in the Agreement and
subject to certain limitations therein set forth, the Certificates are
exchangeable for new Certificates of authorized denominations evidencing the
same aggregate Fractional Undivided Interest in the Trust, as requested by the
Certificateholder surrendering the same.

                                   Exhibit A
                                    Page 6
<PAGE>

                                                  [Trust Supplement No. 2001-1C]

         No service charge shall be made for any such registration of transfer
or exchange, but the Trustee shall require payment by the Certificateholder of a
sum sufficient to cover any tax or governmental charge payable in connection
therewith.

         The Trustee, the Registrar, and any agent of the Trustee or the
Registrar may treat the person in whose name this Certificate is registered as
the owner hereof for all purposes, and neither the Trustee, the Registrar, nor
any such agent shall be affected by any notice to the contrary.

         The obligations and responsibilities created by the Agreement and the
Trust created thereby shall terminate upon the distribution to
Certificateholders of all amounts required to be distributed to them pursuant to
the Agreement and the disposition of all property held as part of the Trust
Property.

                                   Exhibit A
                                    Page 7
<PAGE>

                                                  [Trust Supplement No. 2001-1C]

                            FORM OF TRANSFER NOTICE

     FOR VALUE RECEIVED the undersigned registered holder hereby sell(s),
assign(s) and transfer(s) unto

Insert             Taxpayer                Identification                  No.

________________________________________________________________________________
please print or typewrite name and address including zip code of assignee

________________________________________________________________________________
the within Certificate and all rights thereunder, hereby irrevocably
constituting and appointing

________________________________________________________________________________
attorney to transfer said Certificate on the books of the Trustee with full
power of substitution in the premises.

Date:                                 [Name of Transferor]

                                      ________________________________________

                                      NOTE: The signature must correspond with
                                      the name as written upon the face of the
                                      within-mentioned instrument in every
                                      particular, without alteration or any
                                      change whatsoever.

Signature Guarantee: _______________

                                  Exhibit A
                                    Page 8
<PAGE>

                                                  [Trust Supplement No. 2001-1C]

                                   EXHIBIT B

                         DTC LETTER OF REPRESENTATIONS

                                   Exhibit B
                                    Page 1
<PAGE>

                                                  [Trust Supplement No. 2001-1C]

                                   EXHIBIT C

                        SCHEDULED PAYMENTS OF PRINCIPAL
                            ON CLASS C CERTIFICATES

           Payment Date                            Principal Payment
-----------------------------------    -----------------------------------------

                                   Exhibit C
                                    Page 1
<PAGE>

                                                  [Trust Supplement No. 2001-1C]

                                   EXHIBIT D

                       PRINCIPAL AMOUNTS AND MATURITIES

       Notes                  Principal Amount                  Maturity
--------------------   ------------------------------   ------------------------

                                  Exhibit D
                                    Page 1
<PAGE>

                                                  [Trust Supplement No. 2001-1C]

                                   EXHIBIT E

                 AIRCRAFT, REGISTRATION NUMBERS AND MATURITIES

                                   Aircraft
                                 Registration
      Aircraft                      Number                      Maturity
--------------------   ------------------------------   ------------------------

                                  Exhibit E
                                    Page 1
<PAGE>

                                                  [Trust Supplement No. 2001-1C]

                                   EXHIBIT F

                                NOTE DOCUMENTS

                                Aircraft
                              Registration
       Aircraft                  Number                    Note Document
----------------------   ----------------------   ------------------------------
      A319-131                   N831UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-2
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

      A319-131                   N833UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-2
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

      A319-131                   N834UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-3
                                                  Equipment Note, Series B
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

      A319-131                   N835UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-3
                                                  Equipment Note, Series B
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

                                   Exhibit F
                                    Page 1
<PAGE>

                                                  [Trust Supplement No. 2001-1C]

      A319-131                   N836UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-3
                                                  Equipment Note, Series B
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

      A319-131                   N837UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-3
                                                  Equipment Note, Series B
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

      A319-131                   N838UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-3
                                                  Equipment Note, Series B
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

      A319-131                   N839UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-3
                                                  Equipment Note, Series B
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

                                   Exhibit F
                                    Page 2
<PAGE>

                                                  [Trust Supplement No. 2001-1C]

      A319-131                   N840UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-3
                                                  Equipment Note, Series B
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

      A319-131                   N841UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-3
                                                  Equipment Note, Series B
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

      A320-232                   N467UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-2
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

      A320-232                   N468UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-2
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

      A320-232                   N469UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-3
                                                  Equipment Note, Series B
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

                                   Exhibit F
                                    Page 3
<PAGE>

                                                  [Trust Supplement No. 2001-1C]

      A320-232                   N470UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-3
                                                  Equipment Note, Series B
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

      A320-232                   N471UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-3
                                                  Equipment Note, Series B
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

      A320-232                   N472UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-3
                                                  Equipment Note, Series B
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

      B747-422                   N117UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-2
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

      B747-422                   N118UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-2
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

                                   Exhibit F
                                    Page 4
<PAGE>

                                                  [Trust Supplement No. 2001-1C]

      B747-422                   N122UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-3
                                                  Equipment Note, Series B
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

      B747-422                   N127UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-3
                                                  Equipment Note, Series B
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

      B747-422                   N128UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-3
                                                  Equipment Note, Series B
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

      B767-322                   N664UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-2
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

      B767-322                   N667UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-2
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

                                   Exhibit F
                                    Page 5
<PAGE>

                                                  [Trust Supplement No. 2001-1C]

      B767-322                   N669UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-3
                                                  Equipment Note, Series B
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

      B767-322                   N670UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-3
                                                  Equipment Note, Series B
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

      B767-322                   N671UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-3
                                                  Equipment Note, Series B
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

      B777-222                   N794UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-2
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

      B777-222                   N795UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-2
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

                                   Exhibit F
                                    Page 6
<PAGE>

                                                  [Trust Supplement No. 2001-1C]

      B777-222                   N204UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-3
                                                  Equipment Note, Series B
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

      B777-222                   N205UA           Participation Agreement
                                                  Trust Indenture and Mortgage
                                                  Equipment Note, Series A-1
                                                  Equipment Note, Series A-3
                                                  Equipment Note, Series B
                                                  Equipment Note, Series C
                                                  Equipment Note, Series D

                                   Exhibit F
                                    Page 7

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