FIFTH AMENDMENT TO TERM AGREEMENT


         THIS FIFTH AMENDMENT TO TERM LOAN AGREEMENT  ("Amendment")  dated as of
December  19th,  1997, by and between AMSC  SUBSIDIARY  CORPORATION,  a Delaware
corporation  ("Borrower"),  with offices at 10802 Parkridge  Boulevard,  Reston,
Virginia 22091, and NTFC CAPITAL CORPORATION,  a Delaware corporation  (formerly
known as Northern Telecom Finance Corporation)  ("Lender"),  with offices at 220
Athens Way, Nashville, Tennessee 37228.

                                   BACKGROUND

         A. Borrower and Lender  executed that certain Term Loan Agreement dated
as of May 28, 1993,  as amended by the First  Amendment  to Term Loan  Agreement
dated as of April 8, 1994, the Second  Amendment to Term Loan Agreement dated as
of August  1,  1995,  the Third  Amendment  to Term Loan  Agreement  dated as of
November  7,  1995 and a Fourth  Amendment  dated as of  October  1, 1996 (as so
amended,  the "Original Loan Agreement")  providing for certain loans to be made
to Borrower by Lender (the  "Loans").  The Loans are  represented by the Amended
and Restated Equipment Note dated as of October 1, 1996,  amending and restating
the Note  originally  dated as of May 28,  1993 and as  previously  amended  and
restated as of April 8, 1994 (as so amended, the "Original Note").

         B. Borrower has requested Lender to make certain changes in the payment
schedule,  and  Lender  is  willing  to make  such  changes,  on the  terms  and
conditions set forth herein.

         NOW, THEREFORE, in consideration of the premises and for other good and
valuable   consideration,   the  receipt  and   adequacy  of  which  are  hereby
acknowledged, the parties hereto agree as follows:

         1.  Definitions:  All  capitalized  terms  used  herein  which  are not
otherwise  defined  shall have the meanings  given to such terms in the Original
Loan Agreement, as amended hereby.

         2.  Amendment  to  Section  1.01.  Section  1.01 of the  Original  Loan
Agreement is hereby  amended by amending  each of the following  definitions  to
read in its entirety as follows:

                           "Interest  Payment Date":  the First Interest Payment
                  date  for the  Loan  and (a) the  first  Business  Day of each
                  calendar month  thereafter  until  September 30, 1996, (b) the
                  first day of each Interest Period from October 1, 1996 through
                  October 1, 1997, and (c) December 31, 1997 and (d) February 1,
                  1998, March 1, 1998 and April 1, 1998.

                           "Interest  Rate":  a variable  interest rate equal to
                  (a) LIBOR plus 4.5% through and including  September 30, 1996,
                  (b) LIBOR plus 2.5% form and after  October  1, 1996,  and (c)
                  LIBOR plus 4.5% from and after December 31, 1997, in each case
                  adjusted on the first day of each Interest Period.


                           "Maturity  Date":  April 1, 1998, on which principal,
                  interest, premium, expenses, fees, penalties and other amounts
                  due under the Note shall be finally due and payable.

         3.  Amendment  to  Section  2.05.  Section  2.05 of the  Original  Loan
Agreement is hereby amended to read in its entirety as follows:

                           2.05.  Principal  Payments.  Borrower  shall make the
                  principal  payment  in  the  amount  of  One  Million  Dollars
                  ($1,000,000)  on December  31,  1997.  Thereafter,  the entire
                  outstanding  principal  amount of the Note and all accrued but
                  unpaid interest and all other unpaid amounts due thereunder
                  shall be paid on the Maturity Date.

         4. Amended and Restated Note.  Contemporaneously  with the execution of
this  Amendment,  Borrower  shall  execute  an  Amended  and  Restated  Note  to
incorporate the terms hereof, in form and substance satisfactory to Lender.

         5. Representations and Warranties of Borrower.  The Borrower represents
and  warrants to Lender that the  Borrower  has not  executed any other deeds of
trust,  mortgages,  security agreements or financing  statements in favor of any
other person or entity  affecting the  Collateral;  that no person or entity has
any rights to claim a lien upon the  Collateral  superior to the lien of Lender;
that no  Default  or Event of  Default  has  occurred  under the  Original  Loan
Agreement  (except  Defaults and Events of Default that are waived herein);  and
that no event has occurred and no claim,  offset or other condition exists which
would  relieve  the  Borrower  of any of its  obligations  to  Lender  under the
Original  Loan  Agreement  or  other  documents  executed  by  the  Borrower  in
connection therewith.

         6. Lender's Fees and Expenses. Borrower shall pay to Lender, on demand,
all costs and expenses,  including  reasonable legal fees, incurred by Lender in
connection with the preparation,  negotiation,  execution or  implementation  of
this Amendment.

         7. Full Force and Effect.  Except as specifically  modified herein, the
Original Loan Agreement shall continue in full force and effect as written,  and
nothing  herein is  intended  to, nor shall it,  release,  diminish or waive the
rights of the parties under the Original Loan Agreement,  the Note or other Loan
Documents.

         8. Possible Extension. Borrower has represented to Lender that Borrower
expects to complete  certain  financing by March 31, 1998. If such  financing is
not  completed  by  that  date,   but  Borrower  can   demonstrate  to  Lender's
satisfaction  that significant  progress (as determined by Lender) has been made
towards such  completion and that such financing is scheduled and anticipated to
be  completed  in the  immediate  future,  and if no other  Default  or Event of
Default has then  occurred,  Lender will consider  extending the maturity due to
not later than May 1, 1998,  subject to the execution of such  documentation  as
Lender may deem  necessary  to implement or evidence  such  extension.  Lender's
agreement to consider  extending the maturity date is not a commitment to do so,
and Lender shall make any such decision in its sole and absolute discretion.






         9.  Counterparts.  This  Amendment  may be  executed  in any  number of
counterparts  (by  facsimile  transmission  or  otherwise)  and by the different
parties hereto on separate counterparts,  each of which, when so executed, shall
be deemed an original,  but all such  counterparts  shall constitute but one and
the same instrument.

         IN WITNESS WHEREOF, this Fifth Amendment to the Term Loan Agreement has
been  executed  as of the day first  above  written by the  parties'  authorized
representatives.

LENDER:                                       BORROWER:

NTFC CAPITAL CORPORATION                      AMSC SUBSIDIARY CORPORATION



By: /s/Henry Craig                            By: /s/Richard J. Burnheimer
    --------------                                 ------------------------

Title: VP-Chief Credit Officer                Title: Vice President & Treasurer
       -------------------------                     --------------------------





                            AMENDED AND RESTATED NOTE


$5,933,095.61                               Originally dated as of: May 28, 1993
                            Previously Amended and Restated as of: April 8, 1994
                                      Amended and Restated as of October 1, 1996
                                    Amended and Restated as of December 19, 1997


         FOR VALUE RECEIVED, AMSC SUBSIDIARY CORPORATION ("Borrower"),  promises
to pay to the order of NORTHERN  TELECOM FINANCE  CORPORATION  (the "Lender") at
its offices located at 220 Athens Way, Nashville,  Tennessee,  37228, or to such
other Person and such other location  specified in writing by the holder hereof,
in lawful  money of the United  States of America an din  immediately  available
funds the principal  amount of Five Million Nine Hundred  Thirty-Three  Thousand
Ninety Five Dollars and Sixty-One Cents ($5,933,095.61),  together with interest
thereon and other  amounts due as provided  below.  Notations  on the  Schedules
attached hereto are for convenience  only, and the failure of the Lender to make
any notation on any  Schedule,  or any  incorrect  notation by the Lender on any
Schedule,  shall not diminish the  obligations  of the Borrower under this Note.
This Note shall mature on April 1, 1998 (the "Maturity Date").

         The "Initial Payment Date" means the first Business Day of the calendar
month following the month in which the Termination  Date falls. The "Termination
Date" means the earliest of the  following  three dates:  (a) December 31, 1994,
but  only if  Final  Acceptance  (as  defined  in the  Loan  Agreement)  ("Final
Acceptance")  has  occurred on or before  such date;  or (b) the last day of the
month  of the  date of Final  Acceptance  occurs  between  January  1,  1995 and
February 28, 1995; and (c) March 31, 1995.

         This Note has been made and  delivered  pursuant to that  certain  Term
Loan  Agreement  dated as of May 28, 1993 by and between  the  Borrower  and the
Lender,  as amended by the First  Amendment to Term Loan  Agreement  dated as of
August 1, 1995, the Third  Amendment to Term Loan Agreement dated as of November
7, 1995, the Fourth  Amendment to Term Loan Agreement  dated October 1, 1996 and
the Fifth  Amendment to Term Loan  Agreement of even date  herewith (as the same
may  be  modified,  amended  or  supplemented  from  time  to  time,  the  "Loan
Agreement") and is the Note described in Section 2.03(a)  thereof.  Any term not
otherwise defined in this Note shall have the meaning ascribed to it in the Loan
Agreement.  Reference  is made to the Loan  Agreement,  which among other things
provides for the  acceleration  of the maturity  hereof upon the  occurrence  of
certain  events and for  prepayments in certain  circumstances  and upon certain
terms and  conditions.  This Note is secured by the Collateral  described in the
Security Documents.

         All advances  hereunder  shall bear  interest at the Interest  Rate (as
defined  below)  from the date of such  Advance  until  such  amount  is due and
payable (whether on any Payment Date, at the Maturity Date, by acceleration,  or
otherwise).

         The  "Interest  Rate"  shall be a variable  interest  rate equal to (a)
LIBOR plus 4.5% through and  including  September  30, 1996,  and (b) LIBOR plus
2.5% from and after October 1, 1996,  through and  including  December 31, 1997,
and (c) LIBOR plus 4.5%  thereafter,  in each case  adjusted on the first day of
each Interest Period.







         "LIBOR":  in respect of any Interest  Period,  the rate of interest per
annum  shall be the rate quoted in the "money  rates"  column of The Wall Street
Journal for the three-month LIBOR (London Interbank Offered Rates). This rate is
to be  determined  on the second  Business Day before the  commencement  of such
Interest  Period (each such second  Business Day before the  commencement  of an
Interest  Period being  hereinafter  referred to as an  "Interest  Determination
Date").

         "Interest  Period":  each three (3)  calendar  month  period  beginning
January 1, April 1, July 1 and October 1 of each calendar year provided that:

         (A) if any Interest Period  pertaining to a Loan would otherwise end on
a day which is not a Business Day, that Interest Period shall be extended to the
next  succeeding  Business Day unless the result of such  extension  would be to
carry such  Interest  Period into another  calendar  month,  in which event such
Interest Period shall end on the immediately preceding Business Day;

         (B) any Interest  Period  pertaining  to a Loan that begins on the last
Business Day of a calendar  month (or on a day for which there is no numerically
corresponding  day in the  calendar  month at the end of such  Interest  Period)
shall end on the last Business Day of the last  calendar  month of such Interest
Period;

         (C) no Interest Period shall extend beyond the Maturity Date; and

         (D) no Interest  Period shall extend  beyond any date upon which is due
any  scheduled  principal  payment in respect of the Loan  unless the  aggregate
principal  amount  of the Loan is equal to or in  excess  of the  amount of such
principal payment.

         Interest  shall accrue at the Interest  Rate on all  principal  amounts
outstanding hereunder.  Commencing on January 1, 1997, interest shall be payable
quarterly in arrears,  on the first day of each Interest Period until October 1,
1997 and on December 31, 1997.  Thereafter,  accrued  interest  shall be payable
monthly  in  arrears  on  February  1,  1998,  March 1, 1998 and April 1,  1998.
Interest  shall  also be  payable  on the date of any  prepayment  of this  Loan
pursuant to Section  2.07 of the Loan  Agreement  for the portion of the Loan so
prepaid and upon payment  (including  prepayment) in full thereof and, after the
occurrence and during the continuance of any Event of Default, interest shall be
payable on demand.



         Borrower  shall  make one  payment  of  principal  in the amount of One
Million Dollars ($1,000,000) on December 31, 1997 and thereafter all outstanding
principal,  together with all accrued  interest and all other amounts  otherwise
payable hereunder, shall be due and payable on the Maturity Date.

         Notwithstanding  the  foregoing,  if the Borrower shall fail to pay any
then due  principal  amount or interest or other amount  payable by the Borrower
under the Loan  Agreement  or under this Note within ten (10) days after the due
date,  such amount shall bear  interest from the original due date at a rate per
annum that is equal to the lesser of (i) five  percent (5%) higher than the then
applicable  Interest  Rate or (ii) the maximum  permissible  interest rate under
applicable Law until such overdue principal amount,  interest or other amount is
paid in full  (both  before  and after  judgment)  whether  or not any notice of
default in the payment thereof has been delivered under the Loan Agreement.

         Notwithstanding any provision of this Note or the Loan Agreement to the
contrary, it is the intent of the Lender and the Borrower that the Lender or any
subsequent  holder of this Note shall never be  entitled  to  receive,  collect,
reserve  or apply,  as  interest,  any amount in excess of the  maximum  rate of
interest permitted to be charged by applicable Law, as amended or enacted,  from
time to time. In the event Lender,  or any subsequent  holder of this Note, ever
receives,  collects,  reserves or applies,  as interest,  any such excess,  such
amount which would be excessive interest shall be deemed a partial prepayment of
principal and treated as such, or, if the principal  indebtedness  and all other
amounts due are paid in full,  any remaining  excess funds shall  immediately be
paid  to the  Borrower.  In  determining  whether  or not the  interest  paid or
payable,  under any specific  contingency,  exceeds the highest lawful rate, the
Bor rower and the Lender shall, to the maximum extent permitted under applicable
law, (a) exclude voluntary  prepayments and the effects thereof as it may relate
to any fees charged by the Lender,  and (b)  amortize,  prorate,  allocate,  and
spread, in equal parts, the total amount of interest  throughout the entire term
of the Note;  provided  that if the Note is paid and  performed in full prior to
the end of the full contemplated  term hereof,  and if the interest received for
the actual  period of existence  hereof  exceeds the maximum  lawful  rate,  the
Lender or any  subsequent  holder of the Note shall  refund to the  Borrower the
amount of such excess or credit the amount of such excess  against the principal
portion of the Note,  as of the date it was  received,  and, in such event,  the
Lender  shall  not be  subject  to  any  penalties  provided  by  any  laws  for
contracting  for,  charging,  reserving or  receiving  interest in excess of the
maximum lawful rate.

         Upon the  occurrence of any one or more Events of Default  specified in
the Loan Agreement,  all amounts then remaining unpaid on this Note shall be, or
may be  declared  to be,  immediately  due and  payable as  provided in the Loan
Agreement,  without  further  notice,  at the option of the holder  hereof.  The
holder may waive any Event of Default before or after the same has been declared
and  restore  this Note to full force and effect  without  impairing  any rights
hereunder,  such  right of waiver  being a  continuing  one,  but one waiver not
implying any additional or subsequent waiver.

         Demand,  presentment,  notice and protest are expressly waived,  except
for notices otherwise expressly required in the Loan Agreement.

         In the event this Note is placed in the hands of one or more  attorneys
for collection or enforcement or protection of the holder's rights  described in
the Loan Agreement,  the Borrower  agrees to pay all reasonable  attorney's fees
and all court and other out-of-pocket costs incurred by the holder hereof (which
shall be due on demand).

         This Note may be prepaid in accordance  with the  provisions of Section
2.07 of the Loan Agreement.



         This Note is governed by and shall be construed in accordance  with the
internal laws of the State of New York.

         This Note may not be changed, extended or terminated except in writing.

         This Note may be assigned in  accordance  with Section 8.18 of the Loan
Agreement.  In the  event  of any  conflict  between  this  Note  and  the  Loan
Agreement, the provisions of the Loan Agreement shall control.

         This  Amended  and  Restated  Note is an  amendment,  modification  and
restatement of that certain Note in the original  principal amount of $3,750,000
(plus  capitalized  interest),  dated as of May 28, 1993,  issued by Borrower to
Lender,  previously  amended and restated by an Amended and  Restated  Equipment
Note in the original principal amount of $7,500,000 (plus capitalized  interest)
dated as of April 8, 1994 and by an Amended and Restated  Note in the  principal
amount of  $5,933,095.61  dated  October  1, 1996 (as  previously  amended,  the
"Original Note"). The principal amount of this Note is the outstanding principal
amount  of the  Original  Note,  including  interest  capitalized  and  added to
principal as provided therein. This Note is not a novation, release or discharge
of the indebtedness evidenced by the Original Note.

         Executed as of December 19th, 1997.

                                                  AMSC SUBSIDIARY CORPORATION


                                              By:/s/Richard J. Burnheimer
                                                 ------------------------

                                              Title:  Vice President & Treasurer
                                                      --------------------------