Document:

EXHIBIT 10.5.5

                                                                  EXECUTION COPY

           AMENDMENT NO. 3 TO SECURITY AGREEMENT AND CHATTEL MORTGAGE
                            (AIRCRAFT NO. N355MC)(1)

            THIS THIRD  AMENDMENT TO THE SECOND  SECURITY  AGREEMENT AND CHATTEL
MORTGAGE is dated as of July 27, 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 Fifth Amended and
Restated Credit Agreement referred to below.

                              W I T N E S S E T H:

            WHEREAS,  Company  is  party  to that  certain  Fourth  Amended  and
Restated  Credit  Agreement,  dated as of April 25,  2000,  among  Company,  the
Lenders  from  time to time  party  thereto  and the  Administrative  Agent  (as
amended,  modified and/or  supplemented to, but not including,  the date hereof,
the "CREDIT AGREEMENT").

            WHEREAS,  pursuant to that certain Fifth Amended and Restated Credit
Agreement,  dated as of July 27, 2004,  among Company,  the Lenders from time to
time party thereto and the  Administrative  Agent (as amended,  modified  and/or
supplemented  from  time  to  time,  the  "FIFTH  AMENDED  AND  RESTATED  CREDIT
AGREEMENT"),  Company  has  agreed to  further  amend  and  restate  the  Credit
Agreement.

            WHEREAS,  Company and the  Administrative  Agent are parties to that
certain  Second  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. XX015580,  amended by
the First Amendment to Second Security  Agreement and Chattel Mortgage (Aircraft
No. 23395) dated as of May 1, 2002,  recorded  June 14, 2002, as Conveyance  No.
M000794,  further amended by the Second  Amendment to Second Security  Agreement
and Chattel Mortgage (Aircraft No. N355MC) dated as of April 30, 2004,  recorded
May 27, 2004, as Conveyance No. MM026455 (the "AIRCRAFT CHATTEL MORTGAGE").

----------
(1) This  Amendment to the Second  Security  Agreement and Chattel  Mortgage has
been  executed  in  several  counterparts.  To the  extent,  if any,  that  this
Amendment to the Second  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 Second 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 Second  Security  Agreement  and Chattel  Mortgage may be
created  through  the  transfer  of any  counterpart  other  than said  original
counterpart.

<PAGE>

            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. The  Aircraft  Chattel  Mortgage is hereby  amended,  by  deleting  all
references to the term "Credit  Agreement" and inserting the term "Fifth Amended
and Restated Credit Agreement" in lieu thereof.

      2. Section 1(a)(iii) of the Aircraft Chattel Mortgage is hereby deleted in
its entirety and the following is inserted in its place:

      "(iii) all appliances,  parts,  instruments,  appurtenances,  accessories,
furnishings and other equipment of whatever nature (other than complete  Engines
or  engines),  that may from time to time be  incorporated  or  installed  in or
attached to the Airframe or any Engine, together with (i) all appliances, parts,
instruments, appurtenances,  accessories, furnishings, other equipment purchased
or owned by the Borrower and identified for  incorporation or installation in or
attachment to the Airframe or any Engine  pursuant to the terms of any agreement
whether  or not  identified  in a  Supplemental  Chattel  Mortgage  and (ii) all
appliances,  parts,  instruments,  appurtenances,  accessories,  furnishings and
other equipment of whatever  nature removed from the Airframe or any Engine,  no
matter where located, until such time as it shall be replaced on the Airframe or
any  Engine  by  an  appliance,  part,  instrument,   appurtenance,   accessory,
furnishing or other equipment in as good operating condition as and with a value
and  utility  at  least  equal  to  the  item  removed.  Immediately  upon  such
replacement,   such  replacement  appliance,  part,  instrument,   appurtenance,
accessory,  furnishing or other  equipment  shall become subject to the lien and
security  interest of this  Mortgage and shall be deemed part of the Airframe or
such  Engine  for  all  purposes  hereof  to the  same  extent  as the  property
originally comprising or installed on the Airframe or any Engine and the removed
item  shall no longer  be  subject  to the lien and  security  interest  of this
Mortgage (collectively referred to herein as "PARTS"); and"

      3. Section 1(b) of the Aircraft  Chattel Mortgage is hereby amended (x) by
deleting  the text "and" from the end of clause  (xii) of section  1(b),  (y) by
renumbering  clause (xiii) of Section 1(b) as clause (xvi), and (z) by inserting
the following new clauses:

      "(xiii) the Holdings  Guaranty,  including without limitation all payments
of any kind  thereunder,  and  including  all rights of Company,  as  guaranteed
beneficiary,  to execute any election or option or to give any notice,  consent,
waiver or approval under or in respect of the Holdings Guaranty,  as well as any
rights,  powers or remedies on the part of Company,  whether  arising  under the
Holdings  Guaranty or by statute or at law or in equity,  or otherwise,  arising
out of any Event of Default or out of any breach of the Holdings Guaranty;

      (xiv) the Subsidiaries Guaranty, including without limitation all payments
of any kind  thereunder,  and  including  all rights of Company,  as  guaranteed
beneficiary,  to execute any election or option or to give any notice,  consent,
waiver or approval under or in respect of the Subsidiaries  Guaranty, as well as
any rights, powers or remedies on the part of Company, whether arising under the
Subsidiaries  Guaranty  or by  statute  or at law or in  equity,  or  otherwise,
arising  out of any Event of Default  or out of any  breach of the  Subsidiaries
Guaranty; and"

<PAGE>

      (xv) that certain  intercompany  claim owed by Polar Air to Company in the
amount  of not less  than  $5,285,660  in  unpaid  basic  rent  and  maintenance
reserves, plus an undetermined amount of other unpaid supplemental rent, in each
case under the Polar Air Lease (the  "INTERCOMPANY  CLAIM"),  which Intercompany
Claim survives the effective date of the Plan of Reorganization  pursuant to the
terms thereof; and"

      4.  Section  2 of the  Aircraft  Chattel  Mortgage  is hereby  amended  by
inserting the following new defined term in the appropriate alphabetical order:

      "FIFTH AMENDED AND RESTATED CREDIT AGREEMENT" shall mean the Fifth Amended
and Restated Credit  Agreement,  dated as of July 27, 2004,  among Company,  the
lenders  from time to time  party  thereto,  and the  Administrative  Agent,  as
amended, modified or supplemented from time to time.

      5.  Section  4 of the  Aircraft  Chattel  Mortgage  is hereby  amended  by
inserting the following section after Section (j):

      "(k) INTERCOMPANY CLAIM. Upon the occurrence and during the continuance of
an Event  of  Default,  Company  will  cause  all  payments  in  respect  of the
Intercompany  Claim  to  be  made  directly  to  the  Administrative  Agent  for
application  as set  forth in  Section  2.4B(iii)(b)  of the Fifth  Amended  and
Restated Credit Agreement."

      6. 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  (including  by way of  facsimile  or  electronic
transmission)  shall be an original,  but all of which shall together constitute
one and the same instrument. A complete set of counterparts shall be lodged with
Company and the Administrative Agent.

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

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

                                      * * *

<PAGE>

            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/ William C. Bradley
                                            ---------------------------------
                                            Name: William C. Bradley
                                            Title: Vice President & Treasurer

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

<PAGE>

                                        DEUTSCHE BANK TRUST COMPANY
                                        AMERICAS,

                                        as Administrative Agent

                                        By: /s/ Keith C. Braun
                                            ---------------------------------
                                            Name: Keith C. Braun
                                            Title: Director

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

<PAGE>

                           Schedule to Exhibit 10.5.5

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.

<TABLE>
<CAPTION>
-------------------- ------------------------ ---------------- ------------------------- -----------------------------
REGISTRATION         MANUFACTURER'S SERIAL    AGENT            BORROWER                  AGREEMENT
NUMBER               NUMBER(S)
-------------------- ------------------------ ---------------- ------------------------- -----------------------------
<S>                  <C>                      <C>              <C>                       <C>
N540MC               22508                    Deutsche Bank    Atlas Air, Inc.           Amendment No. 1 to Second
                                              Trust Company                              Security Agreement (N540MC)
                                              Americas                                   dated as of July 27, 2004
                                                                                         to secure obligations under
                                                                                         the Aircraft Credit
                                                                                         Facility.
-------------------- ------------------------ ---------------- ------------------------- -----------------------------
N536MC               21576                    Deutsche Bank    Atlas Air, Inc.           Amendment No. 2 to Second
                                              Trust Company                              Security Agreement (N536MC)
                                              Americas                                   dated as of July 27, 2004
                                                                                         to secure obligations under
                                                                                         the Aircraft Credit
                                                                                         Facility.
-------------------- ------------------------ ---------------- ------------------------- -----------------------------

</TABLE>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.

<PAGE>

      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.

                                      * * *

<PAGE>

            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)

<PAGE>

                                        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)

<PAGE>

                           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.

<TABLE>
<CAPTION>
-------------------- ------------------------ ---------------- ------------------------- -----------------------------
REGISTRATION         MANUFACTURER'S SERIAL    AGENT            BORROWER                  AGREEMENT
NUMBER               NUMBER(S)
-------------------- ------------------------ ---------------- ------------------------- -----------------------------
<S>                  <C>                      <C>              <C>                       <C>
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.
-------------------- ------------------------ ---------------- ------------------------- -----------------------------

</TABLE>

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