Exhibit 4.10

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                        NEW NEXTLINK COMMUNICATIONS, INC.
                 (to be known as NEXTLINK Communications, Inc.)

                                       AND

                             NEXTLINK CAPITAL, INC.
                                     Issuers

                                       and

                     UNITED STATES TRUST COMPANY OF NEW YORK
                                     Trustee



                    ----------------------------------------

                                     SECOND
                             SUPPLEMENTAL INDENTURE
                            Dated as of June 3, 1998

                                    Amending

                                    INDENTURE
                           Dated as of April 25, 1996

                    ----------------------------------------


                                  $350,000,000

                              12-1/2% Senior Notes
                               Due April 15, 2006




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         THIS SECOND SUPPLEMENTAL INDENTURE, dated as of June 3, 1998 (herein
called the "Supplement"), is between NEW NEXTLINK COMMUNICATIONS, INC., a
corporation organized and existing under the laws of the State of Delaware
(herein called the "Company"), and NEXTLINK CAPITAL, INC., a corporation
organized and existing under the laws of the State of Washington which will
become a wholly owned subsidiary of the Company following the Merger
("Capital"), as joint and several obligors (collectively, the "Issuers"), each
having its principal office at 155 108th Avenue N.E., 8th Floor, Bellevue,
Washington 98004, and UNITED STATES TRUST COMPANY OF NEW YORK, duly organized
and existing under the laws of the State of New York, as Trustee (herein called
the "Trustee").

                             RECITALS OF THE ISSUERS

         WHEREAS, pursuant to the terms of the Indenture, dated as of April 25,
1996 (as supplemented by the First Supplemental Indenture, herein called the
"Original Indenture"), between NEXTLINK Communications, L.L.C., a limited
liability company formed under the laws of the State of Washington, Capital and
the Trustee, $350,000,000 principal amount of 12-1/2% Senior Notes due April 15,
2006 (herein called the "Securities") were issued; and

         WHEREAS, pursuant to the terms of the First Supplemental Indenture,
dated as of January 31, 1997 (the "First Supplemental Indenture"), NEXTLLINK
Communications, Inc., a corporation organized and existing under the laws of the
State of Washington ("NEXTLINK-WA"), became the successor to NEXTLINK
Communications, L.L.C. as the result of the merger of NEXTLINK Communications,
L.L.C. with and into NEXTLINK-WA; and

         WHEREAS, pursuant to the terms of that certain Agreement and Plan of
Merger, dated as of May 29, 1998, by and among the Company and NEXTLINK-WA,
NEXTLINK-WA will be merged with and into the Company, with the Company as the
surviving corporation (the "Merger"); and

         WHEREAS, as a result of the Merger, the Company will change its name to
NEXTLINK Communications, Inc.; and

         WHEREAS, Section 901 of the Original Indenture provides for the
execution and delivery by the Issuers and, subject to the provisions of Section
903 of the Original Indenture, by the Trustee of one or more supplemental
indentures, without the consent of the Holders of the Securities, for the
purposes specified therein; and

         WHEREAS, pursuant to the provisions of Section 801 and assuming the
requirements of such Section are satisfied, NEXTLINK-WA is permitted to become a
Delaware corporation through a merger transaction in which NEXTLINK-WA is not
the surviving corporation, and under the Original Indenture, the Issuers and the
Trustee may enter into a supplemental indenture, "to evidence the succession of
another Person to either of the Issuers and the assumption by such successor of
the covenants of the Issuers contained in the Securities," which supplement,
pursuant to Section 901 of the Original Indenture, does not require the consent
of the Holders of the Securities; and




         WHEREAS, pursuant to the provisions of Section 801(b) the Company
wishes by this Supplemental Indenture to evidence its succession to NEXTLINK-WA
and its assumption of the covenants of NEXTLINK-WA contained in the Original
Indenture and the Securities and pursuant to the provisions of Section 802 the
Company shall succeed to, and be substituted for, and may exercise every right
and power of, NEXTLINK-WA under the Original Indenture; and

         WHEREAS, all things necessary to make this Supplement, when executed
and delivered by the Trustee, the valid agreement of the Issuers in accordance
with its terms have been done.

         NOW, THEREFORE, THIS SUPPLEMENTAL INDENTURE WITNESSETH:

         SECTION 101. Definitions. Except as otherwise expressly provided
herein, all capitalized words and terms used herein shall have the respective
meanings ascribed thereto in Article One of the Original Indenture.

         SECTION 102. Representations of the Company. The Company hereby
represents and warrants to the Trustee that as of the date hereof:

         (a) The Company is a corporation validly existing and in good standing
under the laws of the State of Delaware; and

         (b) no Default or Event of Default will result from the Merger or the
execution and delivery of this Supplement.

         SECTION 103. Assumption of Obligations. The Company hereby assumes all
of the obligations of NEXTLINK-WA in its capacity as the Company under the
Original Indenture.

         SECTION 104. Construction with Original Indenture. All of the
covenants, agreements and provisions of this Supplement shall be deemed to be
and construed as part of the Original Indenture and VICE VERSA to the same
extent as if fully set forth verbatim therein and herein and shall be fully
enforceable in the manner provided in the Original Indenture. Except as provided
in this Supplement, the Original Indenture shall remain in full force and effect
and the terms and conditions thereof are hereby confirmed.

         SECTION 105. Conflict with Trust Indenture Act. If any provision hereof
limits, qualifies or conflicts with a provision of the Trust Indenture Act that
is required under such Act to be part of and govern the Original Indenture or
this Supplement, the latter provision shall control. If any provision hereof
modifies or excludes any provision of the Trust Indenture Act that may be so
modified or excluded, the latter provision shall be deemed to apply to this
Supplement as so modified or to be excluded, as the case may be.

         SECTION 106. Effect of Headings. The Section headings herein are for
convenience only and shall not affect the construction hereof.

         SECTION 107. Separability Clause. In case any provision in this
Supplement shall be invalid, illegal or unenforceable, the validity, legality
and enforceability of the remaining 




provisions shall not in any way be affected or impaired thereby, it being
intended that all of the provisions hereof shall be enforceable to the full
extent permitted by law.

         SECTION 108. Benefits of Supplement and Original Indenture. Nothing in
this Supplement or the Original Indenture or in the Securities, express or
implied, shall give to any Person other than the parties hereto and thereto and
their successors hereunder and thereunder and the Holders of Securities, any
benefit or any legal or equitable right, remedy or claim under this Supplement
or the Original Indenture. Neither this Supplement nor the Original Indenture
may be used to interpret another indenture, loan agreement or debt agreement of
the Issuers or any of their respective Subsidiaries. No such other indenture or
loan or debt agreement may be utilized to interpret this Supplement or the
Original Indenture.

         SECTION 109. GOVERNING LAW. THIS SUPPLEMENT SHALL BE GOVERNED BY AND
CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK.

         SECTION 110. No Recourse Against Others. A director, member, managing
member officer, employee, stockholder or incorporator, as such, of the Issuers
shall not have any liability for any obligations of the Issuers under this
Supplement or for any claim based on, in respect or by reason of such
obligations or their creation.

         SECTION 111. Duplicate Originals. All parties may sign any number of
copies or counterparts of this Supplement. Each signed copy or counterpart shall
be an original, but all of them together shall represent the same agreement.

         SECTION 112. Effectiveness. This Supplement shall become effective in
accordance with the provisions of Article Nine of the Original Indenture.

         IN WITNESS WHEREOF, the parties hereto have caused this Supplement to
be duly executed as of the day and year first above written.

                                             NEW NEXTLINK COMMUNICATIONS, INC.



                                             By /s/ R. Bruce Easter, Jr.
                                                ------------------------------
                                             Title: President
                                                    --------------------------

Attest:


/s/ Richard A. Montfort, Jr.
- ------------------------------
Name: Richard A. Montfort, Jr.
      ------------------------
Title: counsel
      -------------------------




                                               NEXTLINK CAPITAL, INC.



                                               By /s/ R. Bruce Easter, Jr.
                                                    ------------------------
                                                      Title: President
                                                            ------------
Attest:


/s/ Richard A. Montfort, Jr.
- -------------------------------
Name: Richard A. Montfort, Jr.
      -------------------------
Title: counsel
      -------------------------




                                               UNITED STATES TRUST COMPANY
                                                    OF NEW YORK, Trustee


                                                    By /s/ Patricia Stermer
                                                       ------------------------
                                                    Title: Asst. Vice President
                                                           --------------------

Attest:


/s/ Sirojni Dihdial
- ------------------------------
Name: Sirojni Dihdial
      ------------------------
Title: Asst. Secretary
      ------------------------





STATE OF WASHINGTON        )
                           )ss.:
COUNTY OF KING             )

         On the 2nd day of June, 1998, before me personally came R. BRUCE
EASTER, JR., to me known, who, being by me duly sworn, did depose and say that
he is the President of NEW NEXTLINK COMMUNICATIONS, INC., a Delaware
corporation, one of the corporations described in and which executed the
foregoing instrument, and duly acknowledged to me that he executed the same by
authority of the Board of Directors of said corporation.

         IN WITNESS WHEREOF, I have hereunto set my hand and official seal the
day and year first above written.


                                         /s/ Julia A. Aviles
                                         --------------------------------------
                                         NOTARY PUBLIC in and for the State of 
                                         Washington, residing at Bellvue, WA
                                                                ---------------
                                         My appointment expires 1-19-02
                                                                ---------------
                                         Print Name Julia A. Aviles
                                                    ---------------------------


STATE OF WASHINGTON        )
                           )ss.:
COUNTY OF KING             )

         On the 2nd day of June, 1998, before me personally came R. Bruce
Easter, Jr., to me known, who, being by me duly sworn, did depose and say that
he/she is the Vice President of NEXTLINK CAPITAL, INC., a Washington
corporation, one of the corporations described in and which executed the
foregoing instrument, and duly acknowledged to me that he/she executed the same
by authority of the Board of Directors of said corporation.

         IN WITNESS WHEREOF, I have hereunto set my hand and official seal the
day and year first above written.



                                         /s/ Julia A. Aviles
                                         --------------------------------------
                                         NOTARY PUBLIC in and for the State of 
                                         Washington, residing at Bellvue, WA
                                                                ---------------
                                         My appointment expires 1-19-02
                                                                ---------------
                                         Print Name Julia A. Aviles
                                                    ---------------------------




STATE OF NEW YORK          )
                           ) ss.:
COUNTY OF NEW YORK         )

         On the 3rd day of June, 1998, before me personally came Patricia
Stermer, to me known, who, being by me duly sworn, did depose and say that
he/she is Asst. Vice President of UNITED STATES TRUST COMPANY OF NEW YORK, one
of the corporations described in and which executed the foregoing instrument,
and duly acknowledged to me that he/she signed his/her name thereto by authority
of the By-Laws of said corporation.

         IN WITNESS WHEREOF, I have hereunto set my hand and official seal the
day and year first above written.


                                     /s/ Christine C. Collins
                                     ----------------------------------------
                                     NOTARY PUBLIC in and for the State of New
                                       York, residing at 
                                                        -----------------------
                                       My appointment expires
                                                             ------------------
                                       Print Name
                                                 ------------------------------

                                       Christine C. Collins
                                       Notary Public, State of New York
                                       No. 03-4624735
                                       Qualified in Bronx County
                                       Certificate Filed in New York County
                                       Commission Expires March 30, 2000