EXHIBIT 10.5.6

                                                                  EXECUTION COPY

           AMENDMENT NO. 4 TO SECURITY AGREEMENT AND CHATTEL MORTGAGE
                            (AIR CRAFT NO. N355MC)(1)

            THIS FOURTH AMENDMENT TO THE SECURITY AGREEMENT AND CHATTEL MORTGAGE
is dated as of November 30, 2004,  (this  "AMENDMENT"),  and entered into by and
between ATLAS AIR INC., a Delaware  corporation  ("COMPANY"),  and DEUTSCHE BANK
TRUST COMPANY  AMERICAS,  as agent for and  representative  of  ("ADMINISTRATIVE
AGENT") the financial  institutions  ("LENDERS")  party to the Credit  Agreement
referred to below.  Unless otherwise defined herein,  all capitalized terms used
herein and defined in the Credit Agreement  referred to below are used herein as
therein defined.

                              W I T N E S S E T H:

            WHEREAS, Company is party to that certain Fifth Amended and Restated
Credit Agreement, dated as of July 27, 2004, among Company, Atlas Air Worldwide
Holdings, Inc., the Lenders from time to time party thereto and the
Administrative Agent (as amended, modified and/or supplemented from time to
time, the "CREDIT AGREEMENT").

            WHEREAS,  Company and the  Administrative  Agent are parties to that
certain First Security Agreement and Chattel Mortgage with respect to one Boeing
747-341, U.S. Registration No. N355MC, Manufacturer's Serial Number 23395, dated
May 18, 2000,  between Atlas Air, Inc. as debtor and Deutsche Bank Trust Company
Americas (formerly Bankers Trust Company) as Agent for and Representative of the
Lenders referred to therein,  recorded by the Federal Aviation Administration on
July 5, 2000,  as Conveyance  No.  XX015579,  amended by the First  Amendment to
First Security  Agreement and Chattel Mortgage  (Aircraft No. 23395) dated as of
May 1, 2002,  recorded May 29, 2002, as Conveyance No. M000709,  further amended
by the  Second  Amendment  to First  Security  Agreement  and  Chattel  Mortgage
(Aircraft  No.  N355MC)  dated as of April 30, 2004,  recorded May 27, 2004,  as
Conveyance No.  MM026454,  further  amended by Amendment No. 3 to First Security
Agreement and Chattel Mortgage  (Aircraft No. N355MC) dated as of July 27, 2004,
recorded  August 25, 2004,  as Conveyance  No.  Q073443 (the  "AIRCRAFT  CHATTEL
MORTGAGE") and

            WHEREAS, subject to the terms and conditions set forth below, the
parties hereto wish to amend certain provisions of the Aircraft Chattel Mortgage
as provided herein.

            NOW THEREFORE, it is agreed:

- ----------
(1) This Amendment to the First Security Agreement and Chattel Mortgage has been
executed in several counterparts.  To the extent, if any, that this Amendment to
the First Security Agreement and Chattel Mortgage  constitutes chattel paper (as
such  term  is  defined  in the  Uniform  Commercial  Code as in  effect  in any
applicable  jurisdiction)  no security  interest in this  Amendment to the First
Security  Agreement and Chattel  Mortgage may be created through the transfer or
possession of any  counterpart  other than the original.  The  counterpart to be
deemed the original shall be the counterpart  that contains the receipt therefor
executed by Deutsche Bank Trust Company Americas,  as  Administrative  Agent, on
the  signature  page thereof and no security  interest in this  Amendment to the
First  Security  Agreement  and  Chattel  Mortgage  may be created  through  the
transfer of any counterpart other than said original counterpart.



      1. Section 1(b)(i) of the Aircraft  Chattel  Mortgage is hereby amended by
deleting such  subsection  in its entirety and  inserting the following  text in
lieu thereof:

      (i) all the tolls, rents,  issues,  profits,  revenues and other income of
the property subject or required to be subject to the lien of this Mortgage;

      2. Section 1(b)(xvi) of the Aircraft Chattel Mortgage is hereby amended by
deleting the period and inserting a semi-colon at the end thereof;

      3. Section 1(b) is hereby  amended by inserting the  following  text after
Section 1(b)(xvi):

      "PROVIDED,   HOWEVER,  that  in  no  event  shall  such  Aircraft  Related
      Collateral  include or be deemed or  construed to include any accounts (as
      such term is defined in the  Uniform  Commercial  Code as in effect in any
      applicable  jurisdiction)  or other  rights to  payment  arising  from the
      rendition of any ACMI Contract."

      4. This Amendment may be executed in any number of counterparts and by the
different parties hereto on separate  counterparts,  each of which  counterparts
when  executed  and  delivered  shall be an  original,  but all of  which  shall
together constitute one and the same instrument.  A complete set of counterparts
executed  by all the  parties  hereto  shall  be  lodged  with  Company  and the
Administrative Agent.

      5. This  Amendment  is limited as  specified  and shall not  constitute  a
modification,  acceptance  or  waiver  of any other  provision  of the  Aircraft
Chattel Mortgage.

      6. From and after the date hereof,  all references in the Aircraft Chattel
Mortgage  shall be deemed to be references to the Aircraft  Chattel  Mortgage as
modified hereby.

                                      * * *



            IN WITNESS  WHEREOF,  the  parties  hereto  have  caused  their duly
authorized  officers to execute and deliver this  Amendment as of the date first
above written.

                                        ATLAS AIR, INC.


                                        By: /s/ Dorinda Pannozzo
                                            ---------------------------------
                                            Name: Dorinda Pannozzo
                                            Title: Assistant Treasurer

                                                  Security Agreement and Chattel
                                        Mortgage Amendment to the First Security
                                                  Agreement and Chattel Mortgage
                                                           (Aircraft No. N355MC)



                                        DEUTSCHE BANK TRUST COMPANY
                                        AMERICAS,

                                        as Administrative Agent


                                        By: /s/ David J Bell
                                            ---------------------------------
                                            Name: David J Bell
                                            Title: Managing Director

                                                  Security Agreement and Chattel
                                        Mortgage Amendment to the First Security
                                                  Agreement and Chattel Mortgage
                                                           (Aircraft No. N355MC)






                           Schedule to Exhibit 10.5.6

The agreements listed below are substantially identical to this exhibit and are
not being filed separately as exhibits pursuant to instruction 2 to Regulation
S-K, Item 601.



- -------------------- ------------------------ ---------------- ------------------------- -----------------------------
REGISTRATION         MANUFACTURER'S SERIAL    AGENT            BORROWER                  AGREEMENT
NUMBER               NUMBER(S)
- -------------------- ------------------------ ---------------- ------------------------- -----------------------------
                                                                             
N540MC               22508                    Deutsche Bank    Atlas Air, Inc.           Amendment No. 2 to First
                                              Trust Company                              Security Agreement (N540MC)
                                              Americas                                   dated as of November 30,
                                                                                         2004 to secure obligations
                                                                                         under the Aircraft Credit
                                                                                         Facility.
- -------------------- ------------------------ ---------------- ------------------------- -----------------------------

N536MC               21576                    Deutsche Bank    Atlas Air, Inc.           Amendment No. 3 to First
                                              Trust Company                              Security Agreement (N536MC)
                                              Americas                                   dated as of November 30,
                                                                                         2004 to secure obligations
                                                                                         under the Aircraft Credit
                                                                                         Facility.
- -------------------- ------------------------ ---------------- ------------------------- -----------------------------