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                                                                 Exhibit 4(d)(1)

                                                          December 9, 1999

Northwest Airlines Pass Through Trust 1999-3G

Ladies and Gentlemen:

      In consideration of the Revolving Credit Agreement (the "Agreement") dated
as of December 9, 1999 between Morgan Stanley Capital Services Inc., a Delaware
corporation (hereinafter "MSCS") and State Street Bank and Trust Company, as
Subordination Agent, as agent and trustee for the Northwest Airlines Pass
Through Trust 1999-3G ("Counterparty"), Morgan Stanley Dean Witter & Co., a
Delaware corporation (hereinafter "MSDW"), hereby irrevocably and
unconditionally guarantees to Counterparty, with effect from the date of the
Agreement, the due and punctual payment of all amounts payable by MSCS under the
Agreement when the same shall become due and payable, whether on scheduled
payment dates, upon demand, upon declaration of termination or otherwise, in
accordance with the terms of the Agreement and giving effect to any applicable
grace period. Upon failure of MSCS punctually to pay any such amounts, and upon
written demand by Counterparty to MSDW at its address set forth in the signature
block of this Guarantee (or to such other address as MSDW may specify in
writing), MSDW agrees to pay or cause to be paid such amounts; provided that
delay by Counterparty in giving such demand shall in no event affect MSDW's
obligations under this Guarantee.

      MSDW hereby agrees that its obligations hereunder shall be unconditional
and will not be discharged except by complete payment of the amounts payable
under the Agreement, irrespective of any claim as to the Agreement's validity,
regularity or enforceability or the lack of authority of MSCS to execute or
deliver the Agreement; or any change in or amendment to the Agreement; or any
waiver or consent by Counterparty with respect to any provisions thereof; or the
absence of any action to enforce the Agreement or the recovery of any judgment
against MSCS or of any action to enforce a judgment against MSCS under the
Agreement; or any similar circumstance which might otherwise constitute a legal
or equitable discharge or defense of a guarantor generally. MSDW hereby waives
diligence, presentment, demand on MSCS for payment or otherwise (except as
provided hereinabove), filing of claims, requirement of a prior proceeding
against MSCS and protest or notice, except as provided for in the Agreement with
respect to amounts payable by MSCS. If at any time payment under the Agreement
is rescinded or must be otherwise restored or returned by Counterparty upon the
insolvency, bankruptcy or reorganization of MSCS or MSDW or otherwise, MSDW's
obligations hereunder with respect to such payment shall be reinstated upon such
restoration or return being made by Counterparty.

      MSDW represents to Counterparty as of the date hereof, which
representations will be deemed to be repeated by MSDW on each date on which a
Transaction is entered into, that:

      (1) it is duly organized and validly existing under the laws of the
jurisdiction of its incorporation and has full power and legal right to execute
and deliver this Guarantee and to perform the provisions of this Guarantee on
its part to be performed;

      (2) its execution, delivery and performance of this Guarantee have been
and remain duly authorized by all necessary corporate action and do not
contravene any provision of its certificate of incorporation or by-laws or any
law, regulation or contractual restriction binding on it or its assets;

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                                   Northwest Airlines Pass Through Trust 1999-3G
                                                                 December 9 1999
                                                                          Page 2

      (3) all consents, authorizations, approvals and clearances (including,
without limitation, any necessary exchange control approval) and notifications,
reports and registrations requisite for its due execution, delivery and
performance of this Guarantee have been obtained from or, as the case may be,
filed with the relevant governmental authorities having jurisdiction and remain
in full force and effect and all conditions thereof have been duly complied with
and no other action by, and no notice to or filing with, any governmental
authority having jurisdiction is required for such execution, delivery or
performance; and

      (4) this Guarantee is its legal, valid and binding obligation enforceable
against it in accordance with its terms except as enforcement hereof may be
limited by applicable bankruptcy, insolvency, reorganization or other similar
laws affecting the enforcement of creditors' rights or by general equity
principles.

      By accepting this Guarantee and entering into the Agreement, Counterparty
agrees that MSDW shall be subrogated to all rights of Counterparty against MSCS
in respect of any amounts paid by MSDW pursuant to this Guarantee, provided that
MSDW shall be entitled to enforce or to receive any payment arising out of or
based upon such right of subrogation only to the extent that it has paid all
amounts payable by MSCS under the Agreement.

      This Guarantee shall be governed by and construed in accordance with the
laws of the State of New York. All capitalized terms not otherwise defined
herein shall have the respective meanings assigned to them in the Agreement.

                                        MORGAN STANLEY DEAN WITTER & CO.


                                        By:_____________________________________
                                        Name:  Eileen S. Wallace
                                        Title: Assistant Treasurer

                                        Address:    1585 Broadway
                                                    3rd Floor
                                                    New York, NY  10036
                                        Attention:  Swap Group
                                        Fax No.:    (212) 761-0162