<PAGE>

                                                                    EXHIBIT 10.4

                                                                  EXECUTION COPY


                                 GATX GUARANTEE

                           dated as of April 30, 2002

                                       by

                                GATX CORPORATION
                                      and
                           GATX FINANCIAL CORPORATION
                                  as Guarantors

                                   in favor of

                        WELLS FARGO BANK NORTHWEST, N.A.
                               as Security Trustee

                     Ten (10) Boeing Model 737-800 Aircraft
            Eximbank Guarantee No. AP077971XX - United States - GATX

<PAGE>

                                TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                                              Pages
                                                                                              -----
<S>                                                                                            <C>
1.     DEFINITIONS........................................................................      2
2.     GUARANTEE..........................................................................      2
3.     RIGHT OF SET-OFF...................................................................      4
4.     NO SUBROGATION.....................................................................      4
5.     AMENDMENTS WITH RESPECT TO THE OBLIGATIONS; WAIVER OF RIGHTS.......................      4
6.     GUARANTEE ABSOLUTE AND UNCONDITIONAL...............................................      5
7.     REINSTATEMENT; BANKRUPTCY, ETC.....................................................      6
8.     PAYMENTS...........................................................................      6
9.     REPRESENTATIONS AND WARRANTIES.....................................................      7
       (a)    Corporate Existence.........................................................      7
       (b)    Authorization...............................................................      7
       (c)    Obligation..................................................................      7
       (d)    No Violation; Lien..........................................................      7
       (e)    Approvals...................................................................      7
       (f)    Litigation..................................................................      8
       (g)    Financial Statements........................................................      8
       (h)    Ranking.....................................................................      8
       (i)    Disclosure..................................................................      8
       (j)    Debarment Regulations.......................................................      8
10.    COVENANTS..........................................................................      9
       (a)     Existence; Conduct of Business.............................................      9
       (b)     Compliance with Laws, Etc..................................................      9
       (c)     Payment of Obligations.....................................................      9
       (d)     Authorizations.............................................................      9
       (e)     Submission to Jurisdiction; Service of Process.............................      9
       (f)     Bankruptcy Waiver..........................................................     10
       (g)     No Commencement of Bankruptcy Proceedings..................................     11
       (h)     Merger; Sale, etc.-GFC and Relevant Subsidiaries...........................     11
       (i)     Merger-GATX Corp. GATX Corp................................................     12
       (j)     Sale, etc.-GATX Corp. GATX Corp............................................     12
       (k)     Transactions with Affiliates...............................................     12
       (1)     Confirmations..............................................................     13
       (m)     Further Assurances.........................................................     13
11.    NOTICES............................................................................     13
12.    SEVERABILITY.......................................................................     14
</TABLE>

                                      -i-







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<TABLE>
<S>                                                                                           <C>
13.    INTEGRATION........................................................................    14
14.    AMENDMENTS IN WRITING; NO WAIVER; CUMULATIVE REMEDIES..............................    14
15.    RIGHTS AND REMEDIES................................................................    15
16.    SECTION HEADINGS...................................................................    15
17.    SUCCESSORS AND ASSIGNS.............................................................    15
18.    GOVERNING LAW......................................................................    15
19.    WAIVER OF JURY TRIAL...............................................................    15
</TABLE>

Schedule I - Form of Guarantee Confirmation

                                      -ii-

<PAGE>

                                 GATX GUARANTEE

      THIS GATX GUARANTEE dated as of April 30, 2002 (this "Guarantee") is made
by GATX CORPORATION, a corporation organized and existing under the laws of the
State of New York ("GATX Corp"), and GATX FINANCIAL CORPORATION, a corporation
organized and existing under the laws of the State of Delaware ("GFC" and,
together with GATX Corp, the "Guarantors", and each a "Guarantor"), in favor of
WELLS FARGO BANK NORTHWEST, N.A., not in its individual capacity, but solely as
security trustee for and on behalf of the Secured Parties, under the
Participation Agreement and the other Operative Documents.

                                   WITNESSETH:

      WHEREAS, USEB Aircraft Limited, a limited liability company duly organized
and validly existing under the laws of the Cayman Islands (the "Initial Borrower
Party") has entered into the Participation Agreement (as defined below), the
Loan Agreement and certain other of the Operative Documents.

      WHEREAS, other Persons may from time to time, in accordance with the terms
and conditions of the Participation Agreement, and together with the Initial
Borrower Party, become "Borrower Parties" for the purposes of the Operative
Documents (hereinafter collectively the "Borrower Parties").

      WHEREAS, the Borrower Parties may from time to time borrow Loans upon and
subject to the terms and conditions of the Loan Agreement and the other
Operative Documents (each of such Borrower Parties which are borrowers of Loans
from time to time are hereinafter collectively referred to as the "Borrowers").

      WHEREAS, each of Jackson Leasing Limited, a limited liability company duly
incorporated and validly existing under the laws of the Cayman Islands ("Cayman
Lessee No. 1"); Geary Leasing Limited, a limited liability company duly
incorporated and validly existing under the laws of the Cayman Islands ("Cayman
Lessee No. 2"); Jackson Leasing Corporation, a Delaware corporation ("Delaware
Lessee"); Jackson Leasing (Ireland) Limited, a company duly organized and
validly existing under the laws of Ireland ("Irish Lessee"); Jackson Leasing
(Cyprus) Limited, a company duly organized and validly existing under the laws
of the Republic of Cyprus ("Cypriot Lessee" and, together with Cayman Lessee No.
1, Cayman Lessee No. 2, Delaware Lessee and Irish Lessee, the "Initial Lessee
Parties", and each an "Initial Lessee Party"), has entered into the
Participation Agreement and certain other of the Operative Documents.

      WHEREAS, other Persons may from time to time, in accordance with the terms
and conditions of the Participation Agreement, and together with the Initial
Lessee Parties, become Lessees Parties for the purposes of the Operative
Documents (hereinafter collectively the "Lessee Parties").

      WHEREAS, the Lessee Parties may from time to time lease Aircraft upon and
subject to the terms and conditions of the Lease Agreements and the other
Operative Documents (each of

<PAGE>

such Lessee Parties which are lessees of Aircraft from time to time are
hereinafter collectively referred to as the "Lessees").

      WHEREAS, all of the issued and outstanding shares of GFC are owned by GATX
Corp, all of the issued and outstanding shares of the Initial Lessee Parent are
owned by GFC and all of the issued and outstanding shares of each Initial Lessee
Party are owned by the Initial Lessee Parent.

      WHEREAS, the Guarantors expect to derive benefit from the making of Loans
to the Borrowers and the leasing of Aircraft to the Lessees.

      WHEREAS, the Secured Parties are unwilling to consummate the transactions
contemplated by the Participation Agreement and, in respect of the financing of
an Aircraft, the transactions contemplated by the Aircraft Financing Documents
for such Aircraft, unless the Guarantors issue this Guarantee and, with respect
to the financing of an Aircraft, issue a GATX Guarantee Confirmation in respect
of such Aircraft on the Borrowing Date for such Aircraft.

      NOW, THEREFORE, in consideration of the premises and for other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged by the Guarantors, the Guarantors hereby agree as follows:

      1. Definitions. Unless otherwise defined herein, capitalized terms used
herein shall have the meanings set forth in Appendix A to the participation
agreement dated as of April 30, 2002 among USEB Aircraft Limited, Geary Leasing
Limited, Jackson Leasing Limited, Jackson Leasing Corporation, Jackson Leasing
(Ireland) Limited, Jackson Leasing (Cyprus) Limited, Walkers SPV Limited,
Barclays Bank PLC, as the Initial Lender and Facility Agent, GATX Financial
Corporation, Export - Import Bank of the United States and Wells Fargo Bank
Northwest, N.A., as Security Trustee.

      2. Guarantee

            (a) Guaranteed Documents. Each Guarantor acknowledges that (i) it is
fully aware of the terms and conditions of the Participation Agreement, the Loan
Agreement and the other Operative Documents in effect on the date hereof to
which the Initial Borrower Party, each Initial Lessee Party or GFC is a party
and, (ii) in respect of an Aircraft, upon delivery of a GATX Guarantee
Confirmation, it will be fully aware of the terms of each of the Aircraft
Financing Documents and other Operative Documents to which any Borrower or
Lessee (each, an "Obligor" and collectively, the "Obligors") may become a party
in connection with the financing of such Aircraft (the documents described in
clauses (i) and (ii) if this Section 2(a) are collectively referred to herein as
the "Guaranteed Documents").

            (b) Obligations. Each Guarantor hereby unconditionally and
irrevocably guarantees, jointly with the other Guarantor and severally, as a
primary obligor and not merely as a surety, to the Security Trustee and the
other the Secured Parties:

            (i) each Borrower's prompt payment of the principal of and interest
      on any and all Loans, when and as due (whether scheduled, at maturity, by
      acceleration, upon one or more dates set for pre-payment or otherwise) in
      accordance with the terms of the

                                      -2-

<PAGE>

      Loan Agreement and all other amounts payable at any time by each Borrower
      to the Secured Parties under each Guaranteed Document to which any
      Borrower is, or from time to time becomes, a party including the
      obligation to pay fees, expenses, post-default interest and indemnity
      payments;

            (ii) in respect of each Aircraft and the Lessee for such Aircraft,
      such Lessee's prompt payment in full of all Rent when due (whether
      scheduled, upon demand under the Lease or otherwise) in accordance with
      the Lease for each Aircraft, and all other amounts payable at any time by
      such Lessee to the Secured Parties under the Guaranteed Document
      including, without limitation, the obligation to pay fees, expenses,
      post-default interest and indemnity payments;

            (iii) the due and punctual performance by each Obligor of all of its
      other obligations and covenants under the Participation Agreement, the
      Loan Agreement, each Lease and each other Guaranteed Document, together
      with all claims for damages arising from or in connection with the failure
      to pay or perform any such obligations or covenants,

in each case, as determined without reference to any limitation of the
obligations of any Obligor pursuant to Section 30 of the Participation Agreement
(or any analogous provision of any other Operative Document). All of the
foregoing obligations in clauses (i), (ii) and (iii) being collectively referred
to herein as the "Obligations".

            (c) If any Obligor shall fail to pay in full when due for any
reason, or timely perform, any of the Obligations, each Guarantor is obligated
promptly to pay or perform or to cause to be paid or performed the same as
stated in the relevant Guaranteed Document without any demand or notice
whatsoever. In respect of the Obligations, this Guarantee is an absolute,
present and continuing guarantee of payment and performance and not collection
and is in no way conditional or contingent upon any attempt to collect from any
Obligor any unpaid amounts due or otherwise to enforce performance by any
Obligor.

            (d) Each Guarantor further agrees to pay any and all expenses
(including, without limitation, all fees and disbursements of counsel) which may
be paid or incurred by the Security Trustee in enforcing this Guarantee.

            (e) Each Guarantor agrees that whenever, at any time, or from time
to time, it shall make any payment to the Security Trustee on account of its
liability hereunder, it will notify the Security Trustee in writing that such
payment is made under this Guarantee for such purpose.

            (f) The obligations of each of the Guarantors under this Guarantee
shall be joint and several and the failure or inability of any one such
Guarantor to pay or perform, or the release of any such Guarantor from, its
obligations under this Guarantee shall have no effect on the other Guarantor's
obligations under this Guarantee.

            (g) Without limiting Section 2(c) above, any demand, step or
proceeding to enforce this Guarantee may be made by the Security Trustee or the
Instructing Group from time to time, and the liabilities and obligations of any
Guarantor under this Guarantee may be

                                      -3-

<PAGE>

enforced, irrespective of whether any demands, steps or proceedings are being or
have been made or taken against the Obligors and/or the Guarantors and/or any
other Person.

      3. Right of Set-off. Each of the Security Trustee and each Secured Party
is hereby irrevocably authorized at any time and from time to time without
notice to either Guarantor, any such notice being expressly waived by such
Guarantor to the extent permitted under Applicable Laws, to set off and
appropriate and apply any and all deposits (general or special, time or demand,
provisional or final), in any currency, and any other credits, indebtedness or
claims, in any currency, in each case whether direct or indirect, absolute or
contingent, matured or unmatured, at any time held or owing by the Security
Trustee or such Secured Party to or for the credit or the account of any
Guarantor, or any part thereof in such amounts as the Security Trustee or such
Secured Party may elect, against or on account of any Obligation that is not
paid when due and which remains owing at the time of such set-off, whether
arising hereunder, under the Loan Agreement, any Lease or any other Guaranteed
Document, as the Security Trustee or such Secured Party may elect, whether or
not the Security Trustee or such Secured Party has made any demand for payment.
The Security Trustee or such Secured Party, as the case may be, shall notify
such Guarantor of any such set-off and the application made by the Security
Trustee or such Secured Party, as the case may be, of the proceeds thereof, in
each case promptly after the same shall have occurred; provided that the failure
to give such notice shall not affect the validity of such set-off and
application. The rights of the Security Trustee and the Secured Parties under
this paragraph are in addition to other rights and remedies (including, without
limitation, other rights of set-off) which the Security Trustee and the Secured
Parties may have.

      4. No Subrogation. Each Guarantor shall be subrogated to the rights, if
any, of the Secured Parties in respect of any matter with respect to which an
amount has been paid by such Guarantor hereunder; provided always that any
subrogation rights to which such Guarantor becomes entitled by reason of
performance of any of its obligations hereunder shall be subject and subordinate
to the rights of the Secured Parties against any Obligor under any Guaranteed
Document and the exercise of any such subrogation rights of such Guarantor shall
be deferred until all Obligations have been paid in full and fully performed. If
any amount shall be paid to either Guarantor on account of such subrogation
rights at any time when all of the Obligations shall not have been paid in full,
such amount shall be held by such Guarantor in trust for the Security Trustee
segregated from other funds of such Guarantor, and shall, forthwith upon receipt
by such Guarantor, be turned over to the Security Trustee in the exact form
received by such Guarantor (duly indorsed by such Guarantor to the Security
Trustee, if required), to be applied against the Obligations, whether matured or
unmatured, in accordance with Section 21 of the Participation Agreement.

      5. Amendments with respect to the Obligations; Waiver of Rights.

            (a) Each Guarantor shall remain obligated hereunder notwithstanding
that, without any reservation of rights against either Guarantor, and without
notice to or further assent by either Guarantor, any demand for payment of any
of the Obligations made by the Security Trustee may be rescinded by the Security
Trustee and any of such Obligations continued, and the Obligations or the
liability of any other party for any part thereof, or any collateral security or
guarantee therefor or right of offset with respect thereto, may, from time to
time, in whole or in part, be renewed, extended, amended, modified, accelerated,
compromised, waived, surrendered

                                      -4-

<PAGE>

or released by the Security Trustee and any other documents executed and
delivered in connection therewith may be amended, modified, supplemented or
terminated, in whole or in part, as the Security Trustee may deem advisable from
time to time, and any collateral security, guarantee or right of offset at any
time held by the Security Trustee for the payment of the Obligations may be
sold, exchanged, waived, surrendered or released. The Security Trustee shall not
have any obligation to protect, secure, perfect or insure any Lien at any time
held by it as security for the Obligations or for this Guarantee or any property
subject thereto. When making any demand hereunder against either Guarantor, the
Security Trustee or Instructing Group, as the case may be, may, but shall be
under no obligation to, make a similar demand on any Obligor or any other
guarantor, and any failure by the Security Trustee or the Instructing Group to
make any such demand or to collect any payments from any Obligor or any such
other guarantor or any release of any Obligor or such other guarantor shall not
relieve either Guarantor of its obligations or liabilities hereunder, and shall
not impair or affect the rights and remedies, express or implied, or as a matter
of law, of the Security Trustee or Instructing Group against either Guarantor
(provided that such demand is made within any period required by any applicable
statute of limitations or similar law affecting the demand). For the purposes
hereof "demand" shall include the commencement and continuance of any legal
proceedings.

            (b) Notwithstanding the provisions of Section 5(a), no liability of
either Guarantor hereunder or any amount payable by either Guarantor hereunder
shall be increased as a result of any amendment to or variation of any of the
Guaranteed Documents to which any of the Secured Parties is a party, other than
any such amendment or variation which is permitted in accordance with the terms
thereof or is requested or consented to by either Guarantor.

      6. Guarantee Absolute and Unconditional. Subject to Section 5(b), (i) each
Guarantor waives any and all notice of the creation, renewal, extension,
amendment, variation, waiver or accrual of any of the Obligations (including the
delivery to and the acceptance by any Obligor of any Aircraft and the
effectiveness of any Lease) and notice of or proof of reliance by the Secured
Parties upon this Guarantee or acceptance of this Guarantee; and (ii) the
Obligations, and any of them, shall conclusively be deemed to have been created,
contracted or incurred, or renewed, extended, amended, varied or waived, in
reliance upon this Guarantee; and all dealings between any Obligor and either
Guarantor, on the one hand, and the Security Trustee and the other Secured
Parties on the other, shall likewise be conclusively presumed to have been had
or consummated in reliance upon this Guarantee. Each Guarantor waives diligence,
presentment, protest, demand for payment and notice of default or nonpayment to
or upon any Obligor or either Guarantor with respect to the Obligations. This
Guarantee shall be construed as a continuing, absolute and unconditional
guarantee of payment without regard to (a) the validity, regularity or
enforceability of any Guaranteed Document, any of the Obligations or any other
collateral security therefor or guarantee or right of offset with respect
thereto at any time or from time to time held by the Security Trustee or any
other Person, (b) any defense, set-off or counterclaim (other than a defense of
payment or performance) which may at any time be available to or be asserted by
any Obligor against the Security Trustee or any other Person, (c) any other
circumstance whatsoever (with or without notice to or knowledge of any Obligor
or either Guarantor) which constitutes, or might be construed to constitute, an
equitable or legal discharge of any Obligor for the Obligations, or of either
Guarantor under this Guarantee, in bankruptcy or in any other instance, (d) any
change in the ownership of any Obligor or any merger or consolidation of any
Obligor into any other Person, (e) any sale, transfer or disposal,

                                       -5-

<PAGE>

by any Obligor, of all, or substantially all, of its assets, (f) any change in
any Lessee or Borrower under, or with respect to, any Aircraft, Lease, Loan or
Note as contemplated in the Operative Documents or (g) any change in or of the
Operating Lessee or Sublessee for an Aircraft or its State of Registration or
any Aircraft being Off-Lease. When pursuing its rights and remedies hereunder
against either Guarantor, the Security Trustee or the Instructing Group may, but
shall be under no obligation to, pursue such rights and remedies as it may have
against any Obligor or any other Person or against any collateral security or
guarantee for the Obligations or any right of offset with respect thereto, and
any failure by the Security Trustee or the Instructing Group to pursue such
other rights or remedies or to collect any payments from any Obligor or any such
other Person or to realize upon any such collateral security or guarantee or to
exercise any such right of offset, or any release of any Obligor or any such
other Person or of any such collateral security, guarantee or right of offset,
shall not relieve either Guarantor of any liability hereunder, and shall not
impair or affect the rights and remedies, whether express, implied or available
as a matter of law, of the Secured Parties against either Guarantor. This
Guarantee shall remain in full force and effect and be binding in accordance
with and to the extent of its terms upon either Guarantor and its successors and
assigns thereof, and shall inure to the benefit of the Security Trustee, each of
the other Secured Parties and their respective successors and permitted
endorsees, transferees and assigns, until all the Obligations and the
obligations of both Guarantors under this Guarantee shall have been satisfied in
full.

      7. Reinstatement; Bankruptcy, etc. This Guarantee shall continue to be
effective, or be reinstated, as the case may be, if at any time payment, or any
part thereof, of any of the Obligations is rescinded or must otherwise be
restored or returned by any Secured Party upon the insolvency, bankruptcy,
dissolution, liquidation or reorganization of any Obligor or upon or as a result
of the appointment of a receiver, intervenor or conservator of, or trustee or
similar officer for, any Obligor or any substantial part of its property, or
otherwise, all as though such payments had not been made. If an event permitting
the declaration of default under a Guaranteed Document exists at any time, and
such declaration of default is prevented by the pendency against any Obligor or
any other Person of a case or proceeding under a bankruptcy or insolvency law,
then for purposes of this Guarantee and the Guarantors' obligations hereunder,
such Guaranteed Document shall be deemed to have been declared in default with
the same effect as if such Guaranteed Document had been enforceable in
accordance with the terms thereof, and the Guarantors shall forthwith pay the
amounts due hereunder as specified by any Secured Party, any interest thereon,
and any other amounts guaranteed hereunder, without further notice or demand.

      8. Payments. (a) Each Guarantor hereby agrees that the Obligations will be
paid without set-off or counterclaim in Dollars (or, in the case of indemnity
obligations, in such currency as such Claim was incurred) to the account
specified for such Obligation in accordance with the relevant Guaranteed
Document. All payments hereunder shall be made free and clear of, and without
deduction or withholding for or on account of any Taxes. If any Taxes shall be
required by law to be deducted or withheld from any payment to any Secured Party
hereunder, each Guarantor shall increase the amount paid so that such Secured
Party receives, after deduction or withholding on account of such Taxes, the
full amount of the payments provided for in this Guarantee. Whenever any Taxes
are payable by a Guarantor in respect of payments hereunder, as promptly as
possible thereafter such Guarantor shall send to the applicable Secured

                                      -6-

<PAGE>

Party a certified copy of an original official receipt received by such
Guarantor showing payment thereof.

      (b) If, as a result of any assignment or transfer by any Secured Party
(other than Ex-Im Bank) of all or any part of its rights and/or obligations
under any of the Guaranteed Documents or change in any Lending Office or other
office through which such Secured Party participates in any of the transactions
contemplated by the Guaranteed Documents (excluding any such assignment or
transfer by or to Ex-Im Bank or change in office by Ex-Im Bank) there arises an
obligation on the part of either Guarantor to pay any amount in excess of the
amount it would at such time have been obliged to pay hereunder (other than with
respect to any amount payable hereunder to Ex-Im Bank or for the benefit of
Ex-Im Bank) but for such assignment, transfer or change, as the case may be,
such Guarantor shall not be obliged to pay the amount of such excess unless such
assignment, transfer or change, as the case may be, is made at the request of
either Guarantor in connection with any mitigation action taken under any
Operative Document.

      9. Representations and Warranties. Each Guarantor represents and warrants
to the Security Trustee and each other Secured Party as follows:

            (a) Corporate Existence. Each Guarantor is a corporation duly
organized and validly existing under (in the case of GATX Corp) the laws of the
State of New York or (in the case of GFC) the laws of Delaware and it has the
corporate power and authority to carry on its business as now conducted, to own
or to hold under lease the properties it holds itself out as owning or leasing.

            (b) Authorization. Each Guarantor has the corporate power and
authority and the legal right to execute and deliver, and to perform its
obligations under, this Guarantee, and has taken all necessary corporate action
to authorize its execution, delivery and performance of this Guarantee.

            (c) Obligation. This Guarantee constitutes a legal, valid and
binding obligation of each Guarantor enforceable in accordance with its terms,
except as affected by bankruptcy, insolvency, fraudulent conveyance,
reorganization, moratorium and other similar laws relating to or affecting the
enforcement of creditors' rights generally, general equitable principles and an
implied covenant of good faith and fair dealing. This Guarantee is in proper
form for enforcement in the United States of America.

            (d) No Violation; Lien. The execution, delivery and performance of
this Guarantee will not violate any provision of any Applicable Law or
contractual obligation of either Guarantor and will not result in or require the
creation or imposition of any Lien on any of the properties or revenues of
either Guarantor pursuant to any Applicable Law or contractual obligation of
either Guarantor.

            (e) Approvals. Neither the execution and delivery by either
Guarantor of this Guarantee, nor the consummation of any of the transactions by
either Guarantor contemplated hereby, requires the consent or approval of, or
the giving of notice to, or the registration with, or

                                      -7-

<PAGE>

the taking of any other action in respect of, any Government Body. It is not
necessary to ensure the legality, validity, enforceability or admissibility in
evidence of this Guarantee that this Guarantee or any other instrument be filed,
recorded, registered or enrolled in any court or public office or elsewhere, or
that any stamp, registration or similar tax be paid, in each case in the United
States of America, on or in relation to this Guarantee.

            (f) Litigation. Save as may be disclosed pursuant to the Disclosure
Letter, no litigation, investigation or proceeding of or before any arbitrator
or Government Body is pending or, to the knowledge of either Guarantor,
threatened by or against either Guarantor or against any of its properties or
revenues, which has any reasonable likelihood of having a Material Adverse
Effect on such Guarantor.

            (g) Financial Statements. The audited financial statements of each
Guarantor as of December 31, 2001 heretofore delivered to the Secured Parties
are complete and correct and fairly present the financial condition of such
Guarantor as of and for the fiscal year ending on such date and were prepared in
accordance with GAAP, consistently applied, and (save as may be disclosed
pursuant to the Disclosure Letter) since such date no material adverse change
has occurred in the financial condition, business, prospects or operations of
either Guarantor from that set forth in such balance sheet of such Guarantor.

            (h) Ranking. The obligations of each Guarantor under this Guarantee
rank, and until discharged in full will continue to rank, in right of payment
and security at least pari passu in all respects with all other unsecured
unsubordinated indebtedness of each Guarantor now or hereafter outstanding
except for such indebtedness as shall be preferred solely by operation of law
and not by contract or default of any Person.

            (i) Disclosure. No document, certificate or statement furnished to
the Security Trustee by or on behalf of either Guarantor in connection with the
transactions contemplated hereby contains any untrue statement of a material
fact or omits to state a material fact necessary in order to make the statements
contained therein not misleading; and there is no fact, to the best knowledge of
any member of such Guarantor's board of directors or any executive officer of
such Guarantor, which has not been disclosed to the Security Trustee, the
Facility Agent or Ex-Im Bank in writing on or before the date of this Guarantee
or in the Disclosure Letter and which materially adversely affects or will
materially adversely affect the ability of such Guarantor to carry on its
business or to perform its obligations hereunder.

            (j) Debarment Regulations. Neither Guarantor nor its Principals (as
defined below) is (i) debarred, suspended, proposed for debarment with a final
determination still pending, declared ineligible or voluntarily excluded (as
such terms are defined in any of the Debarment Regulations referred to below)
from participating in procurement or nonprocurement transactions with any United
States federal government department or agency pursuant to any of the Debarment
Regulations (as defined below) or (ii) indicted, convicted or had a civil
judgment rendered against it or any of its Principals for any of the offenses
listed in any of the Debarment Regulations and unless authorized by Ex-Im Bank,
it will not knowingly enter into any transactions in connection with any
Aircraft with any Person who is debarred, suspended, declared ineligible or
voluntarily excluded from participation in procurement or nonprocurement

                                      -8-

<PAGE>

transactions with any United States federal government department or agency
pursuant to any of the Debarment Regulations; it will provide immediate written
notice to Ex-Im Bank if at any time it learns that the certification set forth
in this Clause 9(j) was erroneous when made or has become erroneous by reason of
changed circumstances. (For the purposes hereof, (A) "Principals" shall mean any
officer, director, owner, partner, key employee, or other Person with primary
management or supervisory responsibilities with respect to the relevant
Guarantor; or any other Person (whether or not an employee) who has critical
influence on or substantive control over the transactions contemplated herein
and in the other Operative Documents and (B) the "Debarment Regulations" shall
mean (1) the Government-wide Debarment and Suspension (Nonprocurement)
regulations (Common Rule), 53 Fed. Reg. 19204 (May 26, 1988), (2) Subpart 9.4
(Debarment, Suspension, and Ineligibility) of the Federal Acquisition
Regulations 48 C.F.R. 9.400 - 9.409 and (3) the revised Government-wide
Debarment and Suspension (Nonprocurement) regulations (Common Rule), 60 Fed.
Reg. 33037 (June 26, 1995)).

      10. Covenants. Each Guarantor hereby covenants and agrees with the
Security Trustee and other Secured Parties that, from and after the date of this
Guarantee until the Obligations are paid in full and fully performed:

            (a) Existence; Conduct of Business. It will preserve, renew and keep
in full force and effect its legal existence and the rights, licenses, permits,
privileges and franchises material to the conduct of its business (provided that
the foregoing shall not prohibit any act matter or thing permitted under
Sections 10(h), (i) and (])).

            (b) Compliance with Laws, Etc. It will comply with the requirements
of all Applicable Laws applicable to it or its property, except where the
failure to do so, individually or in aggregate, could not reasonably be expected
to have a Material Adverse Effect on such Guarantor.

            (c) Payment of Obligations. It will pay and discharge all Taxes
imposed on it or on its income or profits or on any of its property prior to the
date on which penalties attach thereto, except where (i) the validity or amount
thereof is being contested in good faith and by proper proceedings, (ii) it has
set aside on its books adequate reserves with respect thereto in accordance with
GAAP and (iii) the failure to make payment pending such contest could not
reasonably be expected to have a Material Adverse Effect on it.

            (d) Authorizations. It will promptly obtain at any time and from
time to time all governmental approvals, authorizations, licenses, consents,
registrations and filings as shall now or hereafter be necessary under
Applicable Laws for such Guarantor to make and perform this Guarantee and will
promptly furnish copies thereof to the Security Trustee upon request.

            (e) Submission to Jurisdiction; Service of Process. Each Guarantor
(i) hereby irrevocably submits itself to the jurisdiction of the Supreme Court
of the State of New York, New York County and the United States District Court
for the Southern District of New York for the purposes of any suit, action or
other proceeding arising out of this Guarantee, or the subject matter hereof or
any of the transactions contemplated hereby, brought by any Secured Party or its
successors, subrogees or permitted assigns, (ii) hereby irrevocably agrees that
all claims in

                                      -9-

<PAGE>

respect of such action or proceeding may be heard and determined in such courts,
and (iii) to the extent that it has or hereafter may acquire any immunity from
jurisdiction of any court or from any legal process, hereby waives such
immunity, and agrees not to assert, by way of motion, as a defense, or
otherwise, in any such suit, action or proceeding the defense of sovereign
immunity, any claim that it is not personally subject to the jurisdiction of the
above-named courts by reason of sovereign immunity or otherwise, that it is
immune from any legal process (whether through service or notice, attachment
prior to judgment, attachment in aid of execution, execution or otherwise) with
respect to itself or its property, or attachment either prior to judgment or in
aid of execution, by reason of any immunity, that the suit, action or proceeding
is brought in an inconvenient forum, that the venue of the suit, action or
proceeding is improper, or that this Guarantee or the subject matter hereof may
not be enforced in or by such courts or under any Applicable Laws. Each
Guarantor hereby consents to service of process in any suit, action or other
proceeding arising out of this Guarantee or the subject matter hereof or any of
the transactions contemplated hereby and hereby appoints the New York office of
Corporation Service Company (the "Process Agent") as its attorney-in-fact to
receive service of process in such action, suit or proceeding, it being agreed
that service upon such Process Agent shall constitute valid service upon such
Guarantor and its permitted successors and permitted assigns. Each Guarantor
hereby agrees to pay to the Process Agent such compensation as shall be agreed
upon from time to time by it and such Process Agent for such Process Agent's
services hereunder. Each Guarantor hereby agrees that its submission to
jurisdiction and its designation of each Process Agent set forth above is made
for the express benefit of the Secured Parties and their respective successors,
subrogees, and assigns. Each Guarantor agrees that it will at all times
continuously maintain an agent to receive service of process in the City, County
and State of New York on behalf of itself and its properties with respect to
this Guarantee, and in the event that, for any reason, the agent named pursuant
to this Section 10(e) shall no longer serve as agent to receive service of
process on such Guarantor's behalf, such Guarantor shall promptly appoint a
successor Process Agent. Each Guarantor further agrees that a final judgment
against such Guarantor in any such action or proceeding shall be inclusive, and
may be enforced in other jurisdictions by suit on the judgment or in any other
manner provided by law, a certified or true copy of which final judgment shall
be conclusive evidence of the fact and of the amount of any indebtedness or
liability of therein described; provided that nothing in this Section 10(e)
shall affect the right of the Secured Parties or their respective successors,
subrogees or assigns to serve legal process in any other manner permitted by law
or affect the right of the Secured Parties or their respective successors,
subrogees or assigns to bring any action or proceeding against either Guarantor
or its property in the courts of other jurisdictions. In the event of the
transfer of all or substantially all the assets and business of the Process
Agent to any other corporation, by consolidation, merger, sale of assets or
otherwise, such other corporation shall be substituted hereunder for such
Process Agent with the same effect as if named herein in place of such Process
Agent.

            (f) Bankruptcy Waiver. To the extent permitted by Applicable Law,
each Guarantor hereby irrevocably waives, to the extent it may do so under any
bankruptcy law or other Applicable Law, in the event of any voluntary or
involuntary bankruptcy, insolvency, reorganization, liquidation, debt
moratorium, surseance of payment or arrangement proceeding or case with respect
to any Obligor or the other Guarantor (a "Bankruptcy"), any right it may have
under any such law to assert that this Guarantee cannot be enforced as a result
of such

                                      -10-
<PAGE>

Bankruptcy. If a Bankruptcy shall occur, each Guarantor agrees, after the
occurrence of the Bankruptcy, to reconfirm in writing, to the extent permitted
by applicable law, its pre-petition waiver of any such protection it may be
entitled to under applicable bankruptcy laws.

            (g) No Commencement of Bankruptcy Proceedings.

            (i) Neither Guarantor shall give its permission to, consent to or
      authorize:

                  (A) (1) the appointment of a receiver, trustee or liquidator
            of any Obligor of a substantial part of such Obligor's property, (2)
            the admission in writing by any Obligor, submitted in connection
            with judicial or other similar procedures with respect to such
            Obligor, of its inability to pay its debts generally as they come
            due, (3) the making of a general assignment by any Obligor for the
            benefit of creditors (excluding the Secured Parties) or (4) the
            exercise by any creditor of any Obligor (other than the Secured
            Parties) of a contractual right to assume the operations or
            financial management of such Obligor; or

                  (B) (1) the filing by an Obligor of (x) a voluntary petition
            in bankruptcy or a voluntary petition, (y) an answer seeking
            reorganization in a proceeding under any bankruptcy laws (as now or
            hereafter in effect) or (z) an answer admitting the material
            allegations of a petition filed against such Obligor in any such
            proceedings, (2) the answering, or the consenting to or seeking of
            relief, by any Obligor by voluntary petition, under the provisions
            of any other now existing or future bankruptcy, insolvency or other
            similar law providing for the reorganization or winding-up of
            corporations or (3) the providing for an agreement, composition,
            extension or adjustment with the creditors of any Obligor or
            otherwise for the relief of distressed debtors, in each case other
            than the Secured Parties.

            (ii) Save as may be requested by the Security Trustee or the
      Instructing Group, the Guarantors shall not commence or join with any
      other Person in commencing any case, proceeding or action described in the
      preceding paragraph (i) of this Section 10(g) with respect to an Obligor,
      or seek an order, judgment or decree appointing a receiver, trustee or
      liquidator of any Obligor of all or substantial part of such Obligor's
      property, or sequestrating of all or any substantial part of the property
      of any Obligor or otherwise filing a petition against any Obligor in a
      proceeding under any bankruptcy, insolvency or other similar laws as now
      or hereafter in effect.

            (h) Merger; Sale, etc. - GFC and Relevant Subsidiaries. GFC will
not, and GATX Corp will not permit GFC or any other wholly owned direct or
indirect Subsidiary of GATX Corp (each such Subsidiary, excluding GFC, being
referred to herein as a "Relevant Subsidiary"), to merge into or consolidate
with any other Person, or permit any other Person to merge into or consolidate
with GFC or any Relevant Subsidiary, or sell, transfer, lease or otherwise
dispose of (in one transaction or in a series of transactions) all or
substantially all of the assets of GFC or any Relevant Subsidiary, or all or
substantially all of the stock of GFC or any Relevant Subsidiary (in each case,
whether now owned or hereafter acquired), or liquidate or dissolve, except that,
if at the time thereof and immediately after giving effect thereto no Lease

                                      -11-

<PAGE>

Default shall have occurred and be continuing, (i) any Person may merge into or
with GFC in a transaction in which GFC or GATX Corp is the surviving Person,
(ii) any Person may merge into or with any Relevant Subsidiary (other than a
Lessee) in a transaction in which a Guarantor or a Relevant Subsidiary is the
surviving Person, (iii) GFC may sell, transfer, lease or otherwise dispose of
all or substantially all of its assets to GATX Corp or any Relevant Subsidiary
on terms acceptable to it, or to any other Person on an arms length basis,
provided that if the purchaser, transferee, lessee or other acquiring entity
(each an "Acquiring Person") is not GATX Corp, the Acquiring Person assumes the
obligations of GFC hereunder and under the other Operative Documents to which it
is a party pursuant to documentation reasonably acceptable to the Security
Trustee, (iv) each Relevant Subsidiary (other than a Lessee or Sublessee) may
sell, transfer, lease or otherwise dispose of all or substantially all of its
assets to a Guarantor or any Relevant Subsidiary on terms acceptable to it, or
to any other Person on an arms length basis, (v) any Relevant Subsidiary (other
than a Lessee or Sublessee) may liquidate or dissolve if a Guarantor determines
in good faith that such liquidation or dissolution is in the best interest of
the Guarantors and is not materially disadvantageous to the Secured Parties and
(vi) each Lessee may sell, lease, transfer or dispose of its interest in any
Aircraft leased to it under the Lease for such Aircraft if (but only if) such
sale, lease, transfer or other disposal thereof is permitted under such Lease or
the Participation Agreement.

            (i) Merger - GATX Corp. GATX Corp will not merge into or consolidate
with any other Person, or permit any other Person to merge into or consolidate
with it, except that, if at the time thereof and immediately after giving effect
thereto no Lease Default shall have occurred and be continuing, GATX Corp may
merge or consolidate with any Person and permit any such merger or consolidation
if (i) either (1) GATX Corp or GFC is the surviving entity or (2) the surviving
entity assumed the obligations of GATX Corp hereunder pursuant to documentation
reasonably acceptable to the Security Trustee, and (ii) immediately after such
merger or consolidation the surviving entity is solvent and has a Net Worth of
at least equal to the Net Worth of the GATX Group immediately prior to such
merger or consolidation.

            (j) Sale, etc. - GATX Corp. GATX Corp will not sell, transfer, lease
or otherwise dispose of (in one transaction or in a series of transactions) all
or substantially all of its assets (whether now owned or hereafter acquired),
except that, if at the time thereof and immediately after giving effect thereto
no Lease Default shall have occurred and be continuing, GATX Corp may sell,
transfer, lease or otherwise dispose of all or substantially all of its assets
if the Acquiring Person (i) either (1) assumes the obligations of GATX Corp
hereunder pursuant to documentation reasonably acceptable to the Security
Trustee or (2) is GFC and (ii) immediately after such sale, transfer, lease or
disposition is solvent and has a Net Worth at least equal to the Net Worth of
the GATX Group immediately prior to such sale, transfer, lease or disposition.

            (k) Transactions with Affiliates. Neither Guarantor shall, nor will
it permit any of its Subsidiaries to, sell, lease or otherwise transfer any
property or assets to, or purchase, lease or otherwise acquire any property or
assets from, or otherwise engage in any transaction with, any of its Affiliates,
except (i) any such transactions in the ordinary course of its business at
prices and on terms and conditions not less favorable to such Guarantor or such
Subsidiary than could be obtained on an arm's length basis from unrelated third
parties, (ii) any such transactions between or among either Guarantor and any of
its Subsidiaries not involving any

                                      -12-

<PAGE>

other Affiliate, and (iii) any such transactions permitted by Sections 10(i),
(j) and (k); provided that the foregoing provisions of this Section 10(1) shall
not prohibit any such Person from declaring or paying any dividend so long as,
after giving effect thereto, no Lease Event of Default shall have occurred and
be continuing.

            (1) Confirmations. Without limiting any other provision hereof, the
Guarantors will, at the request of any Lessee in connection with the financing
or re-leasing of an Aircraft or any Designation contemplated by the
Participation Agreement, execute and deliver to the Security Trustee, a
confirmation of this Guarantee on or prior to the Borrowing Date or releasing
date for such Aircraft or the Designation Date for such Designation,
substantially in the form of Schedule 1 hereto.

            (m) Further Assurances. Each Guarantor shall from time to time, at
its own cost and expense, do and perform such other and further acts and duly
execute and deliver such further documents and assurances as may be required by
Applicable Law or reasonably requested by the Security Trustee or any Secured
Party to establish, maintain and protect the respective rights and remedies of
such party and to carry out the intent and purpose of this Guarantee or any
other Guaranteed Document.

      11. Notices. For the purposes of this Guarantee, all notices and other
communications shall be in writing, in English, and shall be given or made by
fax, mail or personal delivery and faxed, mailed or delivered to the intended
recipient at the address specified below; or, as to any party, at such other
address as shall be designated by such party in a notice to each other party
hereto. Except as otherwise provided in this Guarantee, all such communications
shall be deemed to have been duly given when transmitted by fax (provided such
transmission by fax is in legible form and is accompanied by or generates a
substantially simultaneous confirmation of transmission), or personally
delivered or, in the case of a mailed notice, upon receipt, in each case given
or addressed as aforesaid.

      (i)   If to the Security Trustee:

            Wells Fargo Bank Northwest, N.A.
            79 South Main Street
            Salt Lake City, Utah 84111
            U.S.A.

            Attention:       Corporate Trust Services
            Telephone:       +1 801 246 5630
            Fax:             +1 801 246 5053

                                      -13-

<PAGE>

      (ii)  if to GATX Financial Corporation:

            GATX Capital Division
            GATX Financial Corporation
            Four Embarcadero Center, Suite 2200
            San Francisco, California 94111
            U.S.A.

            Attention:   Aircraft Portfolio Management
            Telephone:   +1 415 995 3200
            Fax:         +1 415 955 3424

      (iii) if to GATX Corporation:

            GATX Corporation
            500 West Monroe
            Chicago, Illinois 60661-3676
            U.S.A.

            Attention:    Chief Financial Officer
            Telephone:    +1 312 621 6200
            Fax:          +1 312 621 6665

      12. Severability. Any provision of this Guarantee which is prohibited or
unenforceable in any jurisdiction shall, as to such jurisdiction, be ineffective
to the extent of such prohibition or unenforceability without invalidating the
remaining provisions hereof, and any such prohibition or unenforceability in any
jurisdiction shall not invalidate or render unenforceable such provision in any
other jurisdiction.

      13. Integration. This Guarantee represents the agreement of each Guarantor
with respect to the subject matter hereof and there are no promises or
representations by the Secured Parties relative to the subject matter hereof not
reflected herein.

      14. Amendments in Writing; No Waiver; Cumulative Remedies. (a) None of the
terms or provisions of this Guarantee may be waived, amended, supplemented or
otherwise modified except by a written instrument executed by the Guarantors and
the Security Trustee.

            (b) The Security Trustee shall not by any act (except by a written
instrument pursuant to paragraph 14(a) hereof) of delay, indulgence, omission or
otherwise be deemed to have waived any right or remedy hereunder or to have
acquiesced in any Default or Event of Default or in any breach of any of the
terms and conditions hereof. No failure to exercise, nor any delay in
exercising, on the part of the Security Trustee, any right, power or privilege
hereunder shall operate as a waiver thereof. No single or partial exercise of
any right, power or privilege hereunder shall preclude any other or further
exercise thereof or the exercise of any other right, power or privilege. A
waiver by the Security Trustee of any right or remedy hereunder on any one
occasion shall not be construed as a bar to any right or remedy which the
Security Trustee would otherwise have on any future occasion.

                                      -14-

<PAGE>

      15. Rights and Remedies. The rights and remedies herein provided are
cumulative, may be exercised singly or concurrently and are not exclusive of any
other rights or remedies provided by law.

      16. Section Headings. The section headings used in this Guarantee are for
convenience of reference only and are not to affect the construction hereof or
be taken into consideration in the interpretation hereof.

      17. Successors and Assigns. This Guarantee shall be binding upon the
successors and assigns of each Guarantor and shall inure to the benefit of the
Secured Parties and their respective successors and permitted assigns.

      18. Governing Law. This Guarantee shall be governed by, and be construed
and interpreted in accordance with, the internal laws of the State of New York,
United States of America, without reference to principles of conflicts of law
other than Sections 5-1401 and 5-1402 of the New York General Obligations Law.

      19. WAIVER OF JURY TRIAL. EACH GUARANTOR IRREVOCABLY WAIVES ANY RIGHTS IT
MAY HAVE TO A JURY TRIAL IN RESPECT OF ANY CIVIL ACTION ARISING UNDER THIS
GUARANTEE OR ANY OTHER OPERATIVE DOCUMENT.

                                    *  *  *

                                      -15-

<PAGE>

      IN WITNESS WHEREOF, the undersigned has caused this Guarantee to be duly
executed and delivered by its duly authorized officer as of the day and year
first above written.

                                                   GATX FINANCIAL CORPORATION

                                                   By: /s/ Susan M. Yata
                                                       ----------------------
                                                       Name:  SUSAN M. YATA
                                                       Title: VICE PRESIDENT

                                                   GATX CORPORATION

                                                   By: /s/ Susan M. Yata
                                                       ----------------------
                                                       Name:  SUSAN M. YATA
                                                       Title: VICE PRESIDENT

<PAGE>

                                   SCHEDULE 1

                         FORM OF GUARANTEE CONFIRMATION

                                                                [    ], 20[ ](1)

TO: WELLS FARGO BANK NORTHWEST, N.A., AS SECURITY TRUSTEE

RE: GATX GUARANTEE CONFIRMATION

Ladies and Gentlemen,

      1. Transaction. Reference is made to (i) the Participation Agreement dated
as of April [ ], 2002 among, inter alios, USEB Aircraft Limited, Walkers SPV
Limited, Barclays Bank PLC, as the Initial Lender and Facility Agent, GATX
Financial Corporation, Export - Import Bank of the United States and Wells Fargo
Bank Northwest, N.A., as Security Trustee (the "Participation Agreement"); (ii)
the GATX Guarantee dated as of April 30, 2002 (the "GATX Guarantee") among GATX
Financial Corporation and GATX Corporation, as Guarantors and Wells Fargo Bank
Northwest, N.A., as Security Trustee; and (iii) the Aircraft Financing Documents
(as defined in the Participation Agreement) entered or to be entered into in
connection with the financing of the Aircraft with manufacturers serial number
[ ]. Capitalized terms not defined herein have the meanings assigned to such
terms in the Participation Agreement.

      2. Confirmation. The Guarantors hereby (i) confirm the GATX Guarantee in
all respects and [confirm that the Obligations (as defined in the GATX
Guarantee) include all of the obligations of each Obligor (as defined in the
GATX Guarantee) under and in connection with the Aircraft Financing Documents
for the Aircraft referred to in paragraph 1](2) [acknowledge that [ ](3) is
[Borrower and Lessor] [Lessor] [Lessee] for the purposes of the Operative
Documents and therefore an Obligor for the purposes of the GATX Guarantee] (4)
and (ii) confirm that the Guarantee remains in full force and effect
notwithstanding the matters referred to in paragraph 2(i).

[3. The Guarantors hereby confirm that the representations and warranties set
forth in

--------------
(1)   Insert for a Borrowing Date/re-leasing date.

(2)   Insert for a Borrowing Date/a re-leasing date.

(3)   Insert name of the applicable Acceptable Person.

(4)   Insert for a Designation Date.

<PAGE>

Section 9 of the GATX Guarantee are true and correct as of the date hereof.](5)

[3]/[4]. Condition Precedent. This is the GATX Guarantee Confirmation referred
to in Section [4A(e)][8C(v)][6(c)(iv)] of the Participation Agreement.

-------------
(5)   Insert for a Borrowing Date.

                                       -2-

<PAGE>

Yours faithfully,

GATX FINANCIAL CORPORATION

By:________________________________________
   Name:
   Title:

GATX CORPORATION

By:_________________________________________
   Name:
   Title:

                                       -3-