Document:

EXHIBIT 4.18

             CERTIFICATE GUARANTY INSURANCE POLICY ENDORSEMENT

Attached to and forming                    Effective Date of Endorsement:
part of Policy No. AB0336 BE               February 15, 2000
issued to:

Wilmington Trust Company
not in its individual capacity but solely as Subordination
Agent under the Agreement

Citibank, N.A., as Class G Liquidity Provider
and Class C Liquidity Provider,
solely with respect to Deficiency Amounts
described in item (g) of the
definition of "Deficiency Amount"

          For all purposes of this Policy, the following terms shall have
the following meanings:

          "Agreement" shall mean the Intercreditor Agreement, dated as of
February ___, 2000, by and among Wilmington Trust Company, as Class G
Trustee and Class C Trustee, Citibank, N.A., as Class G Liquidity Provider
and Class C Liquidity Provider, Ambac Assurance Corporation, as Policy
Provider, and Wilmington Trust Company, as Subordination Agent, without
regard to any amendment or supplement thereto unless such amendment or
supplement has been executed, or otherwise approved in writing, by the
Insurer.

          "Business Day" shall mean any day other than a Saturday, a Sunday
or a day on which banking institutions in New York City or in the city in
which the corporate trust office of the Subordination Agent or the office
of the Insurer specified pursuant to Section 10.3 of the Agreement is
located are authorized or obligated by law or executive order to close.

          "Class G Trustee" shall mean Wilmington Trust Company, not in its
individual capacity but solely as trustee under the Trust Agreement, or any
successor thereto under the Trust Agreement.

          "Deficiency Amount" shall mean:

          (a) with respect to any Regular Distribution Date other than the
Final Legal Distribution Date, any shortfall in amounts available to the
Subordination Agent for the payment of accrued and unpaid interest at the
Stated Interest Rate on the Pool Balance of the Class G Certificates on
such Distribution Date (after giving effect to the subordination provisions
of the Agreement and to the application on such date of (i) any amounts
received by the Escrow Agent in the Class G Paying Agent Account in respect
of accrued interest on the Class G Deposits, (ii) any drawing paid under
the Class G Liquidity Facility in respect of interest due on the Class G
Certificates and (iii) any amounts withdrawn from the Class G Cash
Collateral Account in respect of interest due on the Class G Certificates);

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          (b) with respect to any Special Distribution Date (other than an
Election Distribution Date) established by reason of receipt of a Special
Payment constituting the proceeds of any Series G Equipment Notes or the
related Collateral, as the case may be, any shortfall in amounts available
to the Subordination Agent to pay to the Holders an amount equal to the
outstanding principal amount of such Series G Equipment Note (determined
immediately prior to the receipt of such proceeds) plus interest on such
principal amount accrued at the Stated Interest Rate on the Class G
Certificates from the immediately preceding Regular Distribution Date to
such Special Distribution Date (after giving effect to the subordination
provisions of the Agreement and to the application on such date of (i) any
amounts received by the Escrow Agent in the Class G Paying Agent Account in
respect of accrued interest on the Class G Deposits, (ii) any drawing paid
under the Class G Liquidity Facility in respect of interest due on the
Class G Certificates and (iii) any amounts withdrawn from the Class G Cash
Collateral Account in respect of interest due on the Class G Certificates,
in each case, attributable to interest on such Series G Equipment Note);

          (c) with respect to any Special Distribution Date established by
reason of the failure of the Subordination Agent to have received a Special
Payment constituting the proceeds of any Series G Equipment Note or the
related Collateral, as the case may be, on or before the date which is
twenty-four (24) months after the last date on which any payment was made
on such Series G Equipment Note as to which there has subsequently been a
failure to pay principal or that has subsequently been accelerated, the
amount equal to the outstanding principal amount of such Series G Equipment
Note plus accrued interest thereon at the Stated Interest Rate for the
Class G Certificates from the immediately preceding Regular Distribution
Date to such Special Distribution Date; provided, however, if the Insurer
shall have duly given a Notice of Insurer Election at any time prior to
such Special Distribution Date, the Deficiency Amount with respect to such
Special Distribution Date shall be an amount equal to the shortfall in
amounts available to the Subordination Agent for the payment of the
scheduled principal (without regard to the acceleration thereof) and
interest at the Stated Interest Rate for the Class G Certificates on such
Series G Equipment Note during such twenty-four (24) month period (after
giving effect to the subordination provisions of the Agreement and to the
application on such date of (i) any drawing paid under the Class G
Liquidity Facility in respect of interest due on the Class G Certificates,
and (ii) any withdrawal from the Class G Cash Collateral Account in respect
of interest due on the Class G Certificates, in each case, attributable to
interest on such Series G Equipment Note);

          (d) with respect to each Regular Distribution Date following the
Special Distribution Date as to which any Notice of Insurer Election
described in (c) above has been given in respect of any Series G Equipment
Note, and prior to the establishment of an Election Distribution Date with
respect to such Series G Equipment Note, an amount equal to the scheduled
principal (without regard to the acceleration thereof) and (without
duplication of any payments that may be required to be made under item (a)
above) interest payments that were to become due on such Regular
Distribution Date on such Series G Equipment Note;

          (e) with respect to any Special Distribution Date which is an
Election Distribution Date, an amount equal to the shortfall in amounts
available to the Subordination Agent to pay in full the then outstanding
principal balance of the Series G Equipment Note as to which such Election
Distribution Date relates and accrued interest thereon at the Stated
Interest Rate for the Class G Certificates from the immediately preceding
Regular Distribution Date to such Election Distribution Date less any
Insured Amounts paid by the Insurer in respect of principal on such Series
G Equipment Note and less any drawings paid on such Special Distribution
Date under the Class G Liquidity Facility and withdrawals made on such
Special Distribution Date from the

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Class G Cash Collateral Account attributable to such Series G Equipment
Note (after giving effect to the subordination provisions of the
Agreement);

          (f) with respect to the Final Legal Distribution Date, any
shortfall in amounts available to the Subordination Agent for the payment
in full of the Final Distribution (calculated as of such date but excluding
any accrued and unpaid premium) on the Class G Certificates (after giving
effect to the subordination provisions of the Agreement and to the
application on such date of (i) any amounts received by the Escrow Agent in
the Class G Paying Agent Account in respect of accrued interest on the
Class G Deposits, (ii) any drawing paid under the Class G Liquidity
Facility in respect of interest included in the Final Distribution and
(iii) any withdrawal from the Class G Cash Collateral Account in respect of
interest due on the Class G Certificates; and

          (g) with respect to any Distribution Date (including an Election
Distribution Date) which occurs during any Excess Interest Period, the
amount equal to the Excess Interest unpaid on such date.

          "Due for Payment" shall mean the portion of the Insured Amounts
which is "Due for Payment" on any Distribution Date under this Policy; such
portion shall be equal to the Deficiency Amount existing for such
Distribution Date.

          "Election Distribution Date" shall mean any Special Distribution
Date established (i) by the Subordination Agent in response to a notice
given to the Subordination Agent by the Insurer not less than 20 days prior
thereto that it desires to establish an Election Distribution Date and
specifying such date, (ii) by reason of the occurrence and continuation of
a Policy Provider Default occurring after a Notice of Insurer Election or
(iii) by reason of the receipt of a Special Payment constituting the
proceeds of a Series G Equipment Note as to which a Notice of Insurer
Election has been given or of the related Collateral.

          "Excess Interest" shall mean interest accrued on all outstanding
Drawings under the Liquidity Facility of each Liquidity Provider (together
with interest previously accrued thereon), exclusive of any default
interest, from and after the first day of any Excess Interest Period to the
date of determination.

          "Excess Interest Period" shall mean, with respect to any Series G
Equipment Note, the period commencing on the day immediately following the
end of the twenty-four (24) month period referred to in clause (c) of the
definition of "Deficiency Amount" with respect to any such Series G
Equipment Note, and ending on the later to occur of (i) the Final Legal
Distribution Date and (ii) the date on which all obligations owed to any
Liquidity Provider have been paid in full.

          "Final Legal Distribution Date" shall mean July 15, 2017.

          "Holder" shall mean any person who is the registered owner or
beneficial owner of any of the Class G Certificates and who, on the
applicable Distribution Date, is entitled under the terms of the Class G
Certificates to payment thereunder.

          "Insurance Agreement" shall mean the Insurance and Indemnity
Agreement (as may be amended, modified or supplemented from time to time),
dated as of February 15, 2000, by and among the Insurer, American Trans
Air, Inc. and Wilmington Trust Company, not in its individual capacity, but
solely as Subordination Agent.

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<PAGE>

          "Insurance Policy" or "Policy" shall mean the Certificate
Guaranty Insurance Policy of which this Endorsement is a part together with
each and every endorsement thereto.

          "Insured Amount" shall mean, with respect to any Distribution
Date, the Deficiency Amount for such Distribution Date.

          "Insured Obligations" shall mean the Class G Certificates.

          "Insured Payments" shall mean, (i) with respect to any
Distribution Date, the aggregate amount actually paid by the Insurer to the
Subordination Agent (or, with respect to Insured Amounts in respect of
Deficiency Amounts described in item (g) of the definition of "Deficiency
Amount" to the Liquidity Provider) in respect of the Insured Amount for
such Distribution Date, and (ii) the Preference Amount for any given
Business Day.

          "Insurer" shall mean Ambac Assurance Corporation, or any
successor thereto, as issuer of the Insurance Policy.

          "Nonpayment" shall mean, with respect to any Distribution Date, a
shortfall in the amounts available to the Subordination Agent for
distribution to the Holders in respect of such Distribution Date, resulting
in a Deficiency Amount.

          "Notice of Avoided Payment" shall mean the telephonic or
telegraphic notice, promptly confirmed in writing by telecopy substantially
in the form of Exhibit B to the Policy, in each instance delivered or
performed on a Business Day and sent to the contact person at the address
and/or fax number set forth in Section 10.3 of the Agreement, the original
of which is subsequently delivered by registered or certified mail from the
Subordination Agent specifying the Preference Amount which shall be due and
owing on the applicable Distribution Date.

          "Notice of Insurer Election" shall mean a notice given by the
Insurer when no Policy Provider Default shall have occurred and be
continuing, stating that the Insurer elects to make payments of Deficiency
Amounts as defined under the proviso to clause (c) and the provisions of
clause (d) and, if applicable, clause (e) of the definition of Deficiency
Amounts in respect of any Series G Equipment Note in lieu of applying
clause (c) (without the proviso) of the definition of Deficiency Amount,
which notice shall be given to the Subordination Agent not less than five
(5) days prior to the Special Distribution Date established for payment of
a Deficiency Amount under clause (c) of the definition thereof.

          "Notice of Nonpayment" shall mean the telephonic or telegraphic
notice, promptly confirmed in writing by telecopy substantially in the form
of Exhibit A to the Policy, in each instance delivered or performed on a
Business Day and sent to the contact person at the address and/or fax
numbers set forth in Section 10.3 of the Agreement, the original of which
is subsequently delivered by registered or certified mail from the
Subordination Agent (or, with respect to Insured Amounts in respect of
Deficiency Amounts described in item (g) of the definition of "Deficiency
Amount," from any Liquidity Provider) specifying the Insured Amount which
shall be due and owing to the Class G Trustee (or, with respect to Insured
Amounts in respect of Deficiency Amounts described in item (g) of the
definition of "Deficiency Amount," to any Liquidity Provider) for
distribution to the Holders or any Liquidity Provider, as applicable, on
the applicable Distribution Date.

          "Order" shall mean a final, non-appealable order of a court of
competent jurisdiction exercising jurisdiction in an insolvency proceeding.

                                     4

<PAGE>

          "Preference Amount" means any payment of principal of, or
interest at the Stated Interest Rate on, the Series G Equipment Notes made
to the Class G Trustee or the Subordination Agent or (without duplication)
any payment of the Pool Balance of, or interest at the Stated Interest Rate
on, the Class G Certificates (including payments under the Class G
Liquidity Facility) made to a Holder which has become recoverable or been
recovered from the Class G Trustee, the Subordination Agent or the Holders
(as the case may be) as a result of an Order determining or deeming such
payment to be a preferential transfer pursuant to the United States
Bankruptcy Code or otherwise rescinding such payment or requiring such
payment to be returned.

          "Subordination Agent" shall mean Wilmington Trust Company, not in
its individual capacity but solely as Subordination Agent under the
Agreement, or any successor thereto under the Agreement.

          "Trust Agreement" shall mean the Pass Through Trust Agreement,
dated as of February 15, 2000, among American Trans Air, Inc., Amtran, Inc.
and the Class G Trustee, pursuant to which the Class G Certificates have
been issued.

          Capitalized terms used herein and not otherwise defined shall
have the meaning assigned to them in the Agreement as of the date of
execution of this Policy.

          Notwithstanding the first sentence of the second paragraph of the
face of this Policy, the Insurer will pay any Insured Amount payable
hereunder no later than 4:00 p.m. (New York City time) to the Subordination
Agent (or, with respect to Insured Amounts in respect of Deficiency Amounts
described in item (g) of the definition of "Deficiency Amount," to any
Liquidity Provider) on the later of (i) the Distribution Date on which the
related Deficiency Amount occurs, or (ii) the Business Day on which the
Insurer receives a Notice of Nonpayment; provided that, if such Notice of
Nonpayment is received after 1:00 p.m. (New York City time) on such
Business Day, it will be deemed to be received on the following Business
Day. If any such Notice of Nonpayment is not in proper form or is otherwise
insufficient for the purpose of making a claim under the Policy, it shall
be deemed not to have been received for purposes of this paragraph, and the
Insurer shall promptly so advise the Subordination Agent (or any Liquidity
Provider, if applicable) and the Subordination Agent (or any Liquidity
Provider, if applicable) may submit an amended Notice of Nonpayment.

          Notwithstanding the third paragraph of the face of this Policy,
the Insurer shall pay any Preference Amount due to be paid pursuant to an
Order, no later than 4:00 p.m. on the earlier of (x) the Special
Distribution Date established for the payment of such Preference Amount and
(y) the third Business Day prior to the expiration of this Policy, but in
any event no earlier than the third Business Day following receipt by the
Insurer on a Business Day of (i) a certified copy of an Order, (ii) a
certificate by or on behalf of the Subordination Agent, the Class G Trustee
or the Holder that such Order has been entered and is not subject to any
stay, (iii) an assignment, in form and substance satisfactory to the
Insurer, duly executed and delivered by the Subordination Agent, the Class
G Trustee or the Holder, irrevocably assigning to the Insurer all rights
and claims of the Subordination Agent, the Subordination Agent, the Class G
Trustee or the Holder (provided such Preference Amount is received by the
Holder) with respect to such Preference Amount and (iv) a Notice of Avoided
Payment (in the form attached hereto as Exhibit B) appropriately completed
and executed by the Subordination Agent. Any Notice of Avoided Payment
received by the Insurer after 1:00 p.m. on a Business Day shall be deemed
to have been received on the next Business Day. If any Notice of Avoided
Payment is not in proper form or is otherwise insufficient for the purpose
of making a claim under the Policy, it shall be deemed not to have been
received for purposes of this paragraph and the Insurer shall promptly so
advise the

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<PAGE>

Subordination Agent and the Subordination Agent may submit an amended
Notice of Avoided Payment. Such payment shall be disbursed to the receiver,
conservator, debtor-in-possession or trustee in bankruptcy named in the
Order, and not to the Subordination Agent or the Holder directly, unless
the Holder has made a payment of the Preference Amount to the court or such
receiver, conservator, debtor-in-possession or trustee in bankruptcy named
in the Order, in which case the Insurer will make such payment to the
Subordination Agent for payment over to the Holder, subject to the delivery
of (a) the items referred to in clauses (i), (ii), (iii) and (iv) above to
the Insurer and (b) evidence satisfactory to the Insurer that payment has
been made to such court or receiver, conservator, debtor-in-possession or
trustee in bankruptcy named in the Order.

          No instrument of assignment shall be required notwithstanding the
second paragraph of the face of this Policy except in connection with
payment of a Preference Amount. Notwithstanding the second paragraph of the
face of this Policy, the Insurer shall not be subrogated to the Class G
Certificates, and shall be subrogated to the Series G Equipment Notes only
to the extent provided in the Agreement. For the avoidance of doubt, the
subrogation provisions in the Agreement include Sections 2.4, 3.2 and 3.3
thereof.

          A premium will be payable on this policy in accordance with the
terms of the Insurance Agreement.

          The face of the Policy to which this Endorsement is attached and
of which it forms a part is hereby amended to provide that the Insurer
shall have no obligation (i) to pay any Insured Amount or Preference Amount
except at the times and in the amounts expressly provided for in this
Policy or (ii) to pay any amount in excess of the aggregate original face
amount of the Class G Certificates plus interest at the Stated Interest
Rate for the Class G Certificates for the period during which the Class G
Certificates were outstanding. This Policy does not cover (i) premiums, if
any, payable in respect of the Class G Certificates, (ii) shortfalls, if
any, attributable to the Subordination Agent, the Class G Trust or the
Class G Trustee for withholding taxes, if any (including interest and
penalties in respect of any such liability) or (iii) any risk other than
the risk of Nonpayment and the risk of the occurrence of a Preference
Amount, including failure of the Subordination Agent or the Class G Trustee
to make any payment due to the Holders of the Class G Certificates from
funds received.

          This Policy and the obligations of the Insurer hereunder shall
terminate on the earlier of (i) July 16, 2018 and (ii) the date that is one
year and one day after the date that the Pool Balance of and all interest
at the Stated Interest Rate on the Class G Certificates has been paid in
full. Notwithstanding the foregoing, the Insurer shall continue, after
termination of this Policy, to be obligated to pay any Insured Amounts or
Preference Amounts with respect to which a Notice of Nonpayment or Notice
of Avoided Payment has been given prior to termination of this Policy.

          Nothing herein contained shall be held to vary, alter, waive or
extend any of the terms, conditions, provisions, agreements or limitations
of the above mentioned Policy other than as specifically provided for
otherwise by this Endorsement.

          The obligations of the Insurer to make payments to any Liquidity
Provider hereunder may not be amended or modified without the consent of
such Liquidity Provider.

          This Policy is issued under and pursuant to, and shall be
construed under, the laws of the State of New York.

                                     6

<PAGE>

          IN WITNESS WHEREOF, the Insurer has caused this Endorsement to
the Policy to be signed by its duly authorized officers.

First Vice President                           Assistant Secretary

_______________________                        ____________________

                                    S-1

<PAGE>

                                EXHIBIT A-1
                TO THE CERTIFICATE GUARANTY INSURANCE POLICY

                            Policy No. AB0336BE

                      NOTICE OF NONPAYMENT AND DEMAND
                      FOR PAYMENT OF AN INSURED AMOUNT

                                 Date: [ ]

                        AMBAC ASSURANCE CORPORATION
                           One State Street Plaza
                          New York, New York 10004
                         Attention: General Counsel

          Reference is made to Certificate Guaranty Insurance Policy No.
AB0336BE (together with all endorsements thereto, the "Policy") issued by
Ambac Assurance Corporation ("Ambac"). Terms capitalized herein and not
otherwise defined shall have the meanings ascribed to such terms in or
pursuant to the Policy unless the context otherwise requires.

          The Subordination Agent hereby certifies as follows:

               1.   The Subordination Agent is an agent for the Class G
                    Trustee under the Intercreditor Agreement.

               2.   The relevant Distribution Date is __________. Such
                    Distribution Date is a [Regular Distribution Date, a
                    Special Distribution Date or the Final Legal
                    Distribution Date].

               [3.  Payment of interest at the Stated Interest Rate on the
                    Class G Certificates accrued to the Distribution Date
                    which is a Regular Distribution Date as determined
                    pursuant to paragraph (a) of the definition of
                    "Deficiency Amount" in the Policy is an amount equal to
                    $_________________.]

               [3.  The amount determined for payment to the Holders of the
                    Class G Certificates pursuant to paragraph (b) of the
                    definition of "Deficiency Amount" in the Policy on the
                    Distribution Date which is a Special Distribution Date
                    in respect of a reduction in the outstanding Pool
                    Balance of such Class G Certificates and interest on
                    the amount of such reduction at the Stated Interest
                    Rate from the immediately preceding Regular
                    Distribution Date to such Special Distribution Date is
                    $___________.]

               [3.  The Subordination Agent has not received a timely
                    Notice of Insurer Election pursuant to the Policy and
                    the amount determined for payment to the Holders of the
                    Class G Certificates pursuant to paragraph (c) of the
                    definition of "Deficiency Amount" in the Policy on the
                    Distribution Date which is a Special Distribution Date
                    in respect of the outstanding principal amount of the
                    relevant Series G Equipment Note(s) and interest
                    accrued thereon at the Stated Interest Rate for the
                    Class G Certificates from the

                                   A-1-1

<PAGE>

                    immediately preceding Regular Distribution Date to such
                    Special Distribution Date is $_______.]

               [3.  The Subordination Agent has received a timely Notice of
                    Insurer Election pursuant to the Policy and the amount
                    determined for payment to the Holders of the Class G
                    Certificates pursuant to the proviso in paragraph (c)
                    of the definition of "Deficiency Amount" in the Policy
                    on the Distribution Date which is a Special
                    Distribution Date in respect of scheduled principal
                    (without regard to acceleration thereof) and interest
                    at the Stated Interest Rate for the Class G
                    Certificates that is due on the relevant Series G
                    Equipment Note(s) during the twenty-four (24) month
                    period referred to in such paragraph (c) is
                    $_________.]

               [3.  The Subordination Agent has received a timely Notice of
                    Insurer Election pursuant to the Policy, no Election
                    Distribution Date has been established pursuant to the
                    Policy and the amount determined for payment to the
                    Holders of the Class G Certificates pursuant to
                    paragraph (d) of the definition of "Deficiency Amount"
                    in the Policy on the Distribution Date which is a
                    Regular Distribution Date in respect of scheduled
                    principal (without regard to acceleration thereof) and
                    (without duplication of any payments that may be
                    required to be made pursuant to paragraph (a) of such
                    definition) interest at the Stated Interest Rate for
                    the Class G Certificates due on the Regular
                    Distribution Date on the relevant Series G Equipment
                    Note(s) is $____________.]

               [3.  The amount determined for payment to the Holders of the
                    Class G Certificates pursuant to paragraph (e) of the
                    definition of "Deficiency Amount" in the Policy on the
                    Distribution Date which is an Election Distribution
                    Date in respect of the outstanding principal balance of
                    the relevant Series G Equipment Note(s) and accrued
                    interest thereon at the Stated Interest Rate for the
                    Class G Certificates from the immediately preceding
                    Regular Distribution Date to such Election Distribution
                    Date is $----------.]

               [3.  The amount determined for payment to the Holders of the
                    Class G Certificates pursuant to paragraph (f) of the
                    definition of "Deficiency Amount" in the Policy on the
                    Distribution Date which is the Final Legal Distribution
                    Date in respect of interest at the Stated Interest Rate
                    and the Pool Balance of such Certificates is
                    $__________.]

               4.   There is a Deficiency Amount in respect of such
                    Distribution Date of $__________________ in respect of
                    the Class G Certificates, which amount is an Insured
                    Amount pursuant to the terms of the Policy.

               5.   The sum of $__________________ is the Insured Amount
                    that is Due for Payment.

               6.   The Subordination Agent has not heretofore made a
                    demand for the Insured Amount in respect of such
                    Distribution Date.

                                   A-1-2

<PAGE>

               7.   The Subordination Agent hereby requests that payment of
                    such Insured Amount that is Due for Payment be made by
                    Ambac under the Policy and directs that payment under
                    the Policy be made to the following account by bank
                    wire transfer of federal or other immediately available
                    funds in accordance with the terms of the Policy to:

     [    ]
             ABA #[     ]
             Acct # [     ]
             FBO:   [     ]

     [Policy Account number.]

               8.   The Subordination Agent hereby agrees that, following
                    receipt of the Insured Amount from Ambac, it shall (a)
                    cause such funds to be deposited in the Policy Account
                    and not permit such funds to be held in any other
                    account, (b) cause such funds to be paid to the Class G
                    Trustee for distribution to the Holders in payment of
                    the Pool Balance of, or interest on, the Class G
                    Certificates (as applicable) and not apply such funds
                    for any other purpose and (c) maintain an accurate
                    record of such payments with respect to the Class G
                    Certificates and the corresponding claim on the Policy
                    and proceeds thereof.

                                          Wilmington Trust Company, not in its
                                          individual capacity but solely as
                                          Subordination Agent

                                          By:___________________________

                                          Title:_________________________
                                                   (Officer)

                                   A-1-3

<PAGE>

                                EXHIBIT A-2
                TO THE CERTIFICATE GUARANTY INSURANCE POLICY

                            Policy No. AB0336BE

                      NOTICE OF NONPAYMENT AND DEMAND
          FOR PAYMENT OF AN INSURED AMOUNT TO A LIQUIDITY PROVIDER

                                 Date: [ ]

                        AMBAC ASSURANCE CORPORATION
                           One State Street Plaza
                          New York, New York 10004
                         Attention: General Counsel

          Reference is made to Certificate Guaranty Insurance Policy No.
AB0336BE (together with all endorsements thereto, the "Policy") issued by
Ambac Assurance Corporation ("Ambac"). Terms capitalized herein and not
otherwise defined shall have the meanings ascribed to such terms in or
pursuant to the Policy unless the context otherwise requires.

               The  Liquidity Provider hereby certifies as follows:

               1.   The relevant Distribution Date is __________. Such
                    Distribution Date is a Distribution Date described in
                    item (g) of the definition of "Deficiency Amount" in
                    the Policy. The Excess Interest paid on such
                    Distribution Date to the Liquidity Provider is
                    $________.

               2.   There is a Deficiency Amount in respect of such
                    Distribution Date of $__________________ in respect of
                    amounts owed to the Liquidity Provider, which amount is
                    an Insured Amount pursuant to the terms of the Policy.

               3.   The sum of $__________________ is the Insured Amount
                    that is Due for Payment to the Liquidity Provider.

               4.   The Liquidity Provider has not heretofore made a demand
                    for the Insured Amount in respect of such Distribution
                    Date.

               5.   The Liquidity Provider hereby requests that payment of
                    such Insured Amount that is Due for Payment be made by
                    Ambac under the Policy and directs that payment under
                    the Policy be made to the following account by bank
                    wire transfer of federal or other immediately available
                    funds in accordance with the terms of the Policy to:

                           [    ]
                                   ABA #[     ]
                                   Acct # [     ]
                                   FBO:   [     ]

                           [Policy Account number.]

                                   A-2-1

<PAGE>

               6.   The Liquidity Provider hereby agrees that, following
                    receipt of the Insured Amount from Ambac, it shall
                    maintain an accurate record of such payments with
                    respect to all Liquidity Facilities of the Liquidity
                    Provider and the corresponding claim of the Liquidity
                    Provider on the Policy and proceeds thereof.

                                       Citibank, N.A., as Liquidity Provider

                                       By:_________________________

                                       Title:________________________
                                                   (Officer)

                                   A-2-2

<PAGE>

                                 EXHIBIT B
                TO THE CERTIFICATE GUARANTY INSURANCE POLICY

                            Policy No. AB0336BE

                    NOTICE OF AVOIDED PAYMENT AND DEMAND
                     FOR PAYMENT OF PREFERENCE AMOUNTS

                                 Date: [ ]

                        AMBAC ASSURANCE CORPORATION
                           One State Street Plaza
                          New York, New York 10004
                         Attention: General Counsel

          Reference is made to Certificate Guaranty Insurance Policy No.
AB0336BE (together with all endorsements thereto, the "Policy") issued by
Ambac Assurance Corporation ("Ambac"). Terms capitalized herein and not
otherwise defined shall have the meanings ascribed to such terms in or
pursuant to the Policy unless the context otherwise requires.

          The Subordination Agent hereby certifies as follows:

               1.   The Subordination Agent is an agent for the Class G
                    Trustee under the Intercreditor Agreement.

               2.   The Subordination Agent has established ______________
                    as a Special Distribution Date pursuant to the
                    Agreement for amounts claimed hereunder.

               3.   An Order providing for the recovery of a Preference
                    Amount of $___________________ has been issued.

               4.   $__________________ of the amount set forth in item No.
                    3 above has been paid by the Holders and
                    $________________ is required to be paid to the
                    receiver, conservator, debtor-in-possession or trustee
                    in bankruptcy named in the Order.

               5.   The Subordination Agent has not heretofore made a
                    demand for such Preference Amount.

               6.   The Subordination Agent hereby requests that payment of
                    $______________ of such Preference Amount be made to
                    the receiver, conservator, debtor-in- possession or
                    trustee in bankruptcy named in the Order and
                    $________________ of such Preference Amount be paid to
                    the Subordination Agent for payment over to the Class G
                    Trustee for distribution to the Holders, in each case,
                    by Ambac under the Policy and directs that payment
                    under the Policy be made to the following account by
                    bank wire transfer of federal or other immediately
                    available funds in accordance with the terms of the
                    Policy to:

               7.   For the portion to be paid to the receiver,
                    conservator, debtor-in-possession or trustee, to
                    ______________________:

                                    B-1

<PAGE>

  ABA  #[     ]
  Acct #[     ]
  FBO:  [     ]

               [relevant account number]
               For the portion to be paid to the Subordination Agent:

               ABA #[     ]
               Acct # [     ]
               FBO:   [     ]

         [Policy Account Number]

                                      Wilmington Trust Company, not in its
                                      individual capacity but solely as
                                      Subordination Agent

                                      By:__________________________

                                      Title:   _________________________
                                                   (Officer)

                                    B-2EXHIBIT 4.19

                        AMBAC ASSURANCE CORPORATION,

                         SALOMON SMITH BARNEY INC.,

                     MORGAN STANLEY & CO. INCORPORATED,

                           CHASE SECURITIES INC.,

                                    and

                       BANC ONE CAPITAL MARKETS, INC.

                         INDEMNIFICATION AGREEMENT

                          AMERICAN TRANS AIR, INC.

                         PASS-THROUGH CERTIFICATES,
                               SERIES 2000-1G

                       Dated as of February 15, 2000

                                    -1-

<PAGE>

                             TABLE OF CONTENTS

          (This Table of Contents is for convenience of reference only and
shall not be deemed to be part of this Agreement. All capitalized terms
used in this Agreement and not otherwise defined shall have the meanings
set forth in Section 1 of this Agreement.)

                                                                          Page

Section 1. Defined Terms....................................................1
Section 2. Other Definitional Provisions....................................1
Section 3. Representations and Warranties of the Initial Purchasers.........2
Section 4. Representations and Warranties of the Policy Provider............2
Section 5. Indemnification..................................................3
Section 6. Amendments, Etc..................................................4
Section 7. Notices..........................................................5
Section 8. Severability.....................................................6
Section 9. Governing Law....................................................6
Section 10. Counterparts....................................................6
Section 11. Headings........................................................6

                                    -2-

<PAGE>

          INDEMNIFICATION AGREEMENT, dated as of February 15, 2000, (this
"Indemnification Agreement") by and among AMBAC ASSURANCE CORPORATION, (the
"Policy Provider"), and SALOMON SMITH BARNEY INC., MORGAN STANLEY & CO.
INCORPORATED, CHASE SECURITIES INC., and BANC ONE CAPITAL MARKETS, INC.
(the "Initial Purchasers").

          Section 1. Defined Terms. Unless the context clearly requires
otherwise, all capitalized terms used but not defined herein shall have the
respective meanings assigned to them in the Intercreditor Agreement for
purposes of this Indemnification Agreement; and the following terms shall
have the following meanings:

          "Initial Purchasers" means Salomon Smith Barney Inc., Morgan
Stanley & Co. Incorporated, Chase Securities Inc., and Banc One Capital
Markets, Inc.

          "Initial Purchaser Information" has the meaning given such term
in Section 3.

          "Insurance Agreement" means the Insurance and Indemnity Agreement
(as the same may be amended, modified or supplemented from time to time),
dated as of the Closing Date, by and among the Policy Provider, ATA and
WTC, not in its individual capacity, but solely as Subordination Agent.

          "Intercreditor Agreement" means the Intercreditor Agreement
(2000-1), dated as the date hereof by and among WTC, as Trustee under each
of the Class G Trust and the Class C Trust, the Liquidity Provider, the
Policy Provider and the Subordination Agent.

          "Offering Document" means collectively, the Offering Memorandum,
the Exchange Offer Registration Statement (as defined in the Registration
Rights Agreement), the Shelf Registration (as defined in the Registration
Rights Agreement) or any amendment or supplement thereto, all with respect
to the Class G Certificates, that makes reference to the Policy Provider or
the Policy.

          "Offering Memorandum" means the Offering Memorandum dated
February 8, 2000.

          "Policy Provider" means Ambac Assurance Corporation, as issuer of
the Policy.

          "Policy Provider Information" has the meaning given such term in
Section 4.

          "Securities Act" means the Securities Act of 1933, including,
unless the context otherwise requires, the rules and regulations
thereunder, as amended from time to time.

          "Securities Exchange Act" means the Securities Exchange Act of
1934, including, unless the context otherwise requires, the rules and
regulations thereunder, as amended from time to time.

          Section 2. Other Definitional Provisions. The words "hereof,"
"herein" and "hereunder" and words of similar import when used in this
Indemnification Agreement shall refer to this Indemnification Agreement as
a whole and not to any particular provision of this Indemnification
Agreement. Section and subsection references relate to this Indemnification
Agreement unless otherwise specified. The meanings given to terms defined
herein shall be equally applicable to both the singular and plural forms of
such terms. The words "include" and "including" shall be deemed to be
followed by the phrase "without limitation."

                                    -3-

<PAGE>

          Section 3. Representation, Warranties and Agreements of the
Initial Purchasers. Each of the Initial Purchasers represents, warrants and
agrees with respect to itself as follows:

               (a) Offering Document. The Initial Purchaser will not use,
          or distribute to other broker-dealers for use, any Offering
          Document in connection with the offer and sale of the Class G
          Certificates unless such Offering Document includes such
          information relating to the Policy Provider as has been furnished
          by the Policy Provider for inclusion therein and has been
          approved by the Policy Provider.

               (b) Initial Purchaser Information. All material provided by
          the Initial Purchaser for inclusion in the Offering Document (as
          revised from time to time, and as included in such Offering
          Document, the "Initial Purchaser Information"), insofar as such
          information relates to the Initial Purchaser, shall be true and
          correct in all material respects.

               (c) Compliance with Laws. The Initial Purchaser will comply
          in all material respects with all legal requirements in
          connection with its offers and sales of the Class G Certificates
          and will make such offers and sales in the manner provided in the
          Offering Document.

               (d) Organization, Power, Enforceability. Each Initial
          Purchaser is duly organized, validly existing and in good
          standing in the jurisdiction of its organization and has the
          corporate power and authority to execute and deliver this
          Indemnification Agreement and to perform its obligations
          hereunder. This Indemnification Agreement constitutes a legal,
          valid and binding obligation of each Initial Purchaser,
          enforceable in accordance with its terms, subject to bankruptcy,
          insolvency, reorganization, moratorium, receivership and other
          similar laws affecting creditors' rights generally and by general
          principles of equity and subject to principles of public policy
          limiting the right to enforce the indemnification provisions
          contained herein insofar as such provisions relate to
          indemnification for liabilities arising under federal securities
          laws.

          Section 4. Representations, Warranties and Agreements of the
Policy Provider. The Policy Provider represents and warrants to, and agrees
with, each of the Initial Purchasers as follows:

               (a) Organization and Licensing. The Policy Provider is duly
organized, validly existing and in good standing as a Wisconsin stock
insurance company duly qualified to conduct an insurance business in each
jurisdiction where qualification may be necessary to accomplish the
Transactions (as defined in the Insurance Agreement).

               (b) Corporate Power. The Policy Provider has the corporate
power and authority to issue the Policy and execute and deliver this
Indemnification Agreement and the Intercreditor Agreement and to perform
all of its obligations hereunder and thereunder.

               (c) Authorization; Approvals. Proceedings legally required
for the issuance of the Policy and the execution, delivery and performance
of this Indemnification Agreement have been taken and licenses, orders,
consents or other

                                    -2-

<PAGE>

authorizations or approvals of any governmental boards or bodies legally
required for the enforceability of the Policy have been obtained; any
proceedings not taken and any licenses, authorizations or approvals not
obtained are not material to the enforceability of the Policy.

               (d) Enforceability. The Policy, when issued, will
constitute, and each of this Indemnification Agreement and the
Intercreditor Agreement constitutes, a legal, valid and binding obligation
of the Policy Provider, enforceable in accordance with its terms, subject
to bankruptcy, insolvency, reorganization, moratorium, receivership and
other similar laws affecting creditors' rights generally and by general
principles of equity and subject to principles of public policy limiting
the right to enforce the indemnification provisions contained therein and
herein, insofar as such provisions relate to indemnification for
liabilities arising under federal securities laws.

               (e) Financial Information. The balance sheet of the Policy
Provider as of December 31, 1998, and the related statements of income,
stockholder's equity and cash flows for the three fiscal years ended
December 31, 1998, and the accompanying footnotes, together with an opinion
thereon dated January 27, 1999, of KPMG LLP, independent certified public
accountants, a copy of which is incorporated by reference into the Offering
Document relating to the Class G Certificates, fairly present in all
material respects the financial condition of the Policy Provider as of such
dates and for the periods covered by such statements in accordance with
generally accepted accounting principles consistently applied. The balance
sheet of the Policy Provider as of September 30, 1999, and the related
statements of operations, stockholder's equity and cash flows for the three
month period ended September 30, 1999, and the accompanying footnotes, a
copy of which is incorporated by reference into the Offering Document,
present fairly in all material respects the financial condition of the
Policy Provider as of such date and for such three month period in
accordance with generally accepted accounting principles consistently
applied. Since September 30, 1999, there has been no material change in
such financial condition of the Policy Provider that would materially and
adversely affect its ability to perform its obligations under the Policy,
this Indemnification Agreement or the Intercreditor Agreement.

               (f) Policy Provider Information. The information included
and incorporated by reference in the Offering Memorandum as of the date
hereof under the caption "DESCRIPTION OF THE POLICY PROVIDER"
(collectively, the "Policy Provider Information") is true and correct in
all material respects and does not contain any untrue statement of a
material fact or an omission of any material fact necessary in order to
make the statements therein, in light of the circumstances under which they
were made, not misleading. The Policy Provider will promptly inform ATA and
the Initial Purchasers of any information which would cause the Policy
Provider Information not to be true and correct in all material respects or
to contain an untrue statement of a material fact or an omission of any
material fact necessary in order to make the statements therein not
misleading on the Closing Date. The Policy Provider consents to the
inclusion in the Exchange Offer Registration Statement and the Shelf
Registration Statement of the Policy Provider Information and agrees to
cooperate with the Initial Purchasers and ATA in updating such information
in the manner required by the Securities Act or as may otherwise be
requested by the staff of the Securities and Exchange Commission in
connection with its review of the Exchange Offer Registration Statement or
the Shelf Registration Statement.

                                    -3-

<PAGE>

               (g) No Litigation. There are no actions, suits, proceedings
or investigations pending or, to the best of the Policy Provider's
knowledge, threatened against it at law or in equity or before or by any
court, governmental agency, board or commission or any arbitrator which, if
decided adversely, would materially and adversely affect its ability to
perform its obligations under the Policy, this Indemnification Agreement or
the Intercreditor Agreement.

          Section 5. Indemnification.

               (a) Each Initial Purchaser agrees, severally and not
jointly, to indemnify and save harmless the Policy Provider and its
officers, directors, shareholders, employees, agents and each Person, if
any, who controls the Policy Provider within the meaning of either Section
15 of the Securities Act or Section 20 of the Securities Exchange Act from
and against, any and all claims, losses, liabilities (including penalties),
actions, suits, judgments, demands, damages, costs or expenses (including
reasonable fees and expenses of attorneys, consultants and auditors and
reasonable costs of investigations) of any nature arising out of or by
reason of any untrue statement of a material fact contained in the Initial
Purchaser Information with respect to such Initial Purchaser, or arising
out of or by reason of any omission to state a material fact necessary in
order to make the statements therein, in the light of the circumstances
under which they were made, not misleading, or a breach of any of the
representations and warranties of such Initial Purchaser contained in
Section 3.

               (b) The Policy Provider agrees to indemnify and save
harmless each of the Initial Purchasers and its officers, directors,
shareholders, employees, agents and each Person, if any, who controls any
of the Initial Purchasers within the meaning of either Section 15 of the
Securities Act or Section 20 of the Securities Exchange Act from and
against, any and all claims, losses, liabilities (including penalties),
actions, suits, judgments, demands, damages, costs or expenses (including
reasonable fees and expenses of attorneys, consultants and auditors and
reasonable costs of investigations) of any nature arising out of or by
reason of any untrue statement of a material fact contained in the Policy
Provider Information, or arising out of or by reason of any omission to
state a material fact necessary in order to make the statements therein, in
the light of the circumstances under which they were made, not misleading,
or a breach of any of the representations and warranties of the Policy
Provider contained in Section 4.

               (c) If any action or proceeding (including any governmental
investigation) shall be brought or asserted against any Person
(individually, an "Indemnified Party" and, collectively, the "Indemnified
Parties") in respect of which the indemnity provided in this Section 5(a)
or (b) may be sought hereunder from any Initial Purchaser, on the one hand,
or the Policy Provider, on the other (each, an "Indemnifying Party"), each
such Indemnified Party shall promptly notify the Indemnifying Party in
writing, and the Indemnifying Party shall assume the defense thereof,
including the employment of counsel satisfactory to the Indemnified Party
and the payment of all expenses. The Indemnified Party shall have the right
to employ separate counsel in any such action and to participate in the
defense thereof at the expense of the Indemnified Party; provided, however,
that the fees and expenses of such separate counsel shall be at the expense
of the Indemnifying Party if (i) the Indemnifying Party has agreed to pay
such fees and expenses, (ii) the Indemnifying Party shall have failed to
assume the defense of such action or proceeding and employ counsel
reasonably satisfactory to the Indemnified Party in any such action or
proceeding or (iii) the named parties to any such action or

                                    -4-

<PAGE>

proceeding (including any impleaded parties) include both the Indemnified
Party and the Indemnifying Party, and the Indemnified Party shall have been
advised by counsel that there may be one or more legal defenses available
to it which are different from or additional to those available to the
Indemnifying Party (in which case, if the Indemnified Party notifies the
Indemnifying Party in writing that it elects to employ separate counsel at
the expense of the Indemnifying Party, the Indemnifying Party shall not
have the right to assume the defense of such action or proceeding on behalf
of such Indemnified Party, it being understood, however, that the
Indemnifying Party shall not, in connection with any one such action or
proceeding or separate but substantially similar or related actions or
proceedings in the same jurisdiction arising out of the same general
allegations or circumstances, be liable for the reasonable fees and
expenses of more than one separate firm of attorneys at any time for the
Indemnified Parties, which firm shall be designated in writing by the
Indemnified Parties). The Indemnifying Party shall not be liable for any
settlement of any such action or proceeding effected without its written
consent to the extent that any such settlement shall be prejudicial to the
Indemnifying Party, but, if settled with its written consent, or if there
is a final judgment for the plaintiff in any such action or proceeding with
respect to which the Indemnifying Party shall have received notice in
accordance with this subsection (c), the Indemnifying Party agrees to
indemnify and hold the Indemnifie Parties harmless from and against any
loss or liability by reason of such settlement or judgment. The Indemnified
Parties shall promptly on demand reimburse the Indemnifying Party for all
expenses incurred hereunder on behalf of the Indemnified Party in any
action or proceeding in which there shall have been a final determination
that the Indemnifying Party had not made a material misstatement or
omission or breached a representation or warranty.

               (d) To provide for just and equitable contribution if the
indemnification provided by the Indemnifying Party is determined to be
unavailable or insufficient to hold harmless any Indemnified Party (other
than due to application of this Section), each Indemnifying Party shall
contribute to the losses incurred by the Indemnified Party on the basis of
the relative fault of the Indemnifying Party, on the one hand, and the
Indemnified Party, on the other hand.

          Section 6. Amendments, Etc. This Indemnification Agreement may be
amended, modified, supplemented or terminated only by written instrument or
written instruments signed by the parties hereto.

          Section 7. Notices. All demands, notices and other communications
to be given hereunder shall be in writing (except as otherwise specifically
provided herein) and shall be mailed by registered mail or personally
delivered and telecopied to the recipient as follows:

               (a) To the Policy Provider:

                   Ambac Assurance Corporation
                   One State Street Plaza
                   New York, New York    10004
                   Attention:   Surveillance Department
                   Facsimile:  (212) 363-1459
                   Confirmation:  (212) 668-0340

                                    -5-

<PAGE>

               (b) To the Initial Purchasers:

                   c/o Salomon Smith Barney Inc.
                   390 Greenwich Street
                   New York, NY  10013
                   Attention:  Janice Warne
                   Facsimile:  (212) 723-8677
                   Confirmation:  (212) 723-6152

          A party may specify an additional or different address or
addresses by writing mailed or delivered to the other parties as aforesaid.
All such notices and other communications shall be effective upon receipt.

          Section 8. Severability. In the event that any provision of this
Indemnification Agreement shall be held invalid or unenforceable by any
court of competent jurisdiction, the parties hereto agree that such holding
shall not invalidate or render unenforceable any other provision hereof.
The parties hereto further agree that the holding by any court of competent
jurisdiction that any remedy pursued by any party hereto is unavailable or
unenforceable shall not affect in any way the ability of such party to
pursue any other remedy available to it.

          Section 9. Governing Law. This Indemnification Agreement shall be
governed by and construed in accordance with the laws of the State of New
York.

          Section 10. Counterparts. This Indemnification Agreement may be
executed in counterparts by the parties hereto, and all such counterparts
shall constitute one and the same instrument.

          Section 11. Headings. The headings of Sections and the Table of
Contents contained in this Indemnification Agreement are provided for
convenience only. They form no part of this Indemnification Agreement and
shall not affect its construction or interpretation.

                                    -6-

<PAGE>

          IN WITNESS WHEREOF, the parties hereto have executed this
Agreement, all as of the day and year first above mentioned.

                                 AMBAC ASSURANCE CORPORATION,
                                 as Policy Provider

                                 By:_______________________________
                                    Name:  David B. Nemschoff
                                    Title:   First Vice President

                                 SALOMON SMITH BARNEY INC., MORGAN
                                 STANLEY & CO. INCORPORATED, CHASE
                                 SECURITIES INC., and BANC ONE CAPITAL
                                 MARKETS, INC.,
                                 as Initial Purchasers

                                 By SALOMON SMITH BARNEY INC., acting
                                 on behalf of itself and as the representative
                                 of the other named Initial Purchasers

                                 By:_______________________________
                                    Name:
                                    Title:

                                    -7-

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