AMENDMENT NO. 3 TO NOTE PURCHASE AGREEMENT

          AMENDMENT NO. 3 to NOTE PURCHASE AGREEMENT (this "Amendment No.
     3"), dated as of September [sic October]    , 1994, among AAI
                                              ---
     CORPORATION, a Maryland corporation (the "Company"), and PRINCIPAL
     MUTUAL LIFE INSURANCE COMPANY and THE TRAVELERS INSURANCE COMPANY
     (collectively, the "Purchasers").


                              W I T N E S S E T H 
                              - - - - - - - - - -

          WHEREAS, the Company and the Purchasers have heretofore entered
     into a Note Purchase Agreement dated as of July 15, 1992 (the "Note
     Purchase Agreement");

          WHEREAS, the Company and the Purchasers have heretofore entered
     into Amendment No. 1 to the Note Purchase Agreement dated as of July
     15, 1993 (the "Amendment No. 1");

          WHEREAS, the Company and the Purchasers have heretofore entered
     into an Amendment to the Note Purchase Agreement dated as of December
     30, 1993 (the "Amendment No. 2");

          WHEREAS, the Company has requested that the Purchasers agree to
     amend certain of the provisions and covenants contained in the Note
     Purchase Agreement, as amended; and

          WHEREAS, the Purchasers are willing to amend such provisions and
     covenants upon the terms and conditions herein provided.

          NOW, THEREFORE, in consideration of the mutual promises and
     consideration set forth herein, the sufficiency of which is hereby
     acknowledged, the parties hereto agree as follows:

          Section 1.     Definitions; References.  Unless otherwise
                         ------------------------
     specifically defined herein, each term used herein which is defined in
     the Note Purchase Agreement, as amended, shall have the meaning
     assigned to such term in the Note Purchase Agreement, as amended. 
     Each reference to "hereof," "hereunder," "herein" and "hereby" and
     each other similar reference to "this Agreement" and each other
     similar reference contained in the Note Purchase Agreement or
     Amendment No. 1 or Amendment No. 2, and each reference in the Notes to
     "the Note Purchase Agreement" or "Amendment No. 1" or " Amendment No.
     2," "thereunder," "thereof" or words of like import referring to the
     Note Purchase Agreement and Amendment No. 1 and Amendment No. 2, shall
     from and after the
























     



     

     date hereof refer to the Note Purchase Agreement as amended by
     Amendment No. 1, Amendment No. 2 and this Amendment No. 3.

          Section 1.1.   Definitions.   The following definitions are
                         ------------
     hereby amended, modified or added to the definitions set forth in the
     Note Purchase Agreement, as amended:


               "Accounts Credit Percentage":  eighty percent
               (80%) in the case of Eligible Accounts which did
               not arise from progress billings, and fifty
               percent (50%) in the case of Eligible Accounts
               which arose from progress billings, or in either
               case, such lesser percentage or percentages as
               shall from time to time be established by the
               Required Lenders, in the discretion of the
               Required Lenders exercised in good faith, and
               communicated to the Borrower in writing by the
               Agent, with respect to Eligible Accounts, specific
               Eligible Accounts or categories, types or
               components of Eligible Accounts.  Such less
               percentage or percentages may be based upon
               evaluations of risk by the Lenders or any other
               factors deemed relevant by the Lenders, whether or
               not such factors have theretofore been used,
               contemplated or foreseen as a basis for adjusting
               the Accounts Credit Percentage. 

               "Agent":  as of the date of the Credit Agreement,
               First Fidelity Bank, National Association in its
               capacity as party to the Credit Agreement as
               "Agent," and, after the date of the Credit
               Agreement, the person from time to time, party to
               the Credit Agreement as "Agent." 

               "Aggregate Borrowing Base Charge":  at a
               particular time, the sum of (a) the Aggregate
               Loans Outstanding of all Lenders as at such time
               and (b) L/C Exposure as at such time.

               "Aggregate Loans Outstanding":  as to any Lender
               at a particular time, the aggregate principal
               amount of the Revolving Credit Loans of such
               Lender outstanding as at such time.





























     NYFS11...:\95\78495\0001\7120\EXH02894.E00



     

               "Borrower":  shall mean AAI Corporation, a
               Maryland corporation.

               "Borrower Pledge Agreement":  shall mean, as the
               same may be waived, amended, modified, extended,
               renewed, supplemented or replaced from time to
               time, that certain Pledge and Security Agreement
               of even date herewith executed and delivered by
               Borrower in favor of Collateral Agent. 

               "Borrower Security Agreement":  shall mean, as the
               same may be waived, amended, modified, extended,
               renewed, supplemented or replaced from time to
               time, that certain Security Agreement of even date
               herewith executed and delivered by Borrower in
               favor of Collateral Agent.

               "Borrowing Base":  at a particular time, the
               product of (a) Eligible Accounts as at such time,
               and (b) the Accounts Credit Percentage.

               "Borrowing Base Certificate":  a report or
               schedule, certified by Borrower's Chief Financial
               Officer, in form and content satisfactory to the
               Required Lenders containing such information as
               the Required Lenders may require from time to time
               concerning the Borrowing Base, collections or
               other proceeds of accounts of the Borrower or its
               Subsidiaries and/or any other matter or matters as
               the Required Lenders may require from time to
               time, including with respect to accounts or
               contracts of the Borrower or its Subsidiaries and
               information concerning the cost to complete
               contracts of the Borrower or its Subsidiaries.

               "Collateral Agent":  shall mean as of the date of
               this Amendment No. 3, First Fidelity Bank,
               National Association in its capacity as party to
               the Intercreditor Agreement as "Collateral Agent,"
               and, after the date of this Amendment No. 3, the
               person from time to time, party to the
               Intercreditor Agreement as "Collateral Agent."
      































     



     

               "Collateral Agent Liens" shall mean, as the same
               may be amended, waived, modified, extended,
               renewed, supplemented or replaced from time to
               time, all security interests, liens, assignments
               and other encumbrances in or upon any property
               (real, personal or mixed) granted in favor of
               Collateral Agent pursuant to the Security
               Documents.

               "Credit Agreement":  shall mean, as the same may
               be amended, waived, modified, extended, renewed,
               supplemented or replaced from time to time, that
               certain Credit Agreement of even date herewith
               among Agent, Borrower, Lenders and Issuing Bank.

               "Collateral":  shall mean the property, rights and
               interests with are subject to the Collateral Agent
               Liens.

               "Eligible Accounts":  shall mean at a particular
               time, the aggregate amount, as at such time, of
               accounts of the Borrower and Eligible Affiliates
               which have been billed to the account debtors
               thereon, which are payable in conformity with such
               billings and which are, but only in the amounts
               such accounts are, acceptable to the Agent as at
               such time, in the discretion of the Agent
               exercised in good faith, as a basis for extensions
               of credit to the Borrower under this Agreement. 
               Except as otherwise agreed by the Agent from time
               to time, Eligible Accounts shall not include:  (a)
               any account which has remained unpaid for ninety
               (90) days or more after the billing thereof; (b)
               any account due from any Person other than the
               United States of America if fifty percent (50%) or
               more of all of the accounts due to the Borrower
               and Eligible Affiliates from such Person has
               remained unpaid for ninety (90) days or more after
               the billing thereof; (c) any account which arose
               out of any contract with the United States of
               America if fifty percent (50%) or more of the
               total amount due under such contract has remained
               unpaid for ninety (90) days or more after the
               billing thereof; (d) any account which is not






























     



     

               lawfully owned by the Borrower or an Eligible Affiliate,
               which has been assigned to the Borrower or an Eligible
               Affiliate, which is subject to any Lien except for permitted
               liens under the Credit Agreement, or in which the Borrower
               or the Eligible Affiliate, as the case may be, does not have
               the right and power to grant a security interest to the
               Collateral Agent in conformity with the Borrower Security
               Agreement, the Guarantor Security Agreement or the
               applicable Subsidiary Security Agreement, as the case may
               be, including any account the assignment of which is
               prohibited, limited or conditioned under any underlying or
               related contract; (e) any account with respect to which any
               transaction giving rise to or relating to the account was
               unlawful or not solicited and entered into in compliance
               with Requirements of Law; (f) any account which is not valid
               or enforceable or does not represent bona fide, undisputed
               indebtedness to the Borrower or an Eligible Affiliate of
               each obligor thereon; (g)  any account in which the
               Collateral Agent does not have a perfected first priority
               security interest; (h) any account evidenced in whole or in
               part by any instrument or chattel paper unless such
               instrument or chattel paper has been delivered to the
               Collateral Agent, together with such endorsements or
               assignments as the Collateral Agent may reasonably require;
               (i) any account to the extent that the account is subject to
               any defense, set-off, counterclaim, credit, discount,
               allowance, adjustment, deduction or reduction of any kind;
               (j) any account to the extent that such account includes any
               finance or similar charges on account of past due amounts;
               (k) any account with respect to which any obligor thereon is
               a Person of whom the Borrower or the Eligible Affiliate, as
               the case may be, is or becomes any account debtor or obligor
               by virtue of any obligation of the Borrower or such Eligible
               Affiliate to such Person not relating to accounts due or to
               become due from such Person to the Borrower or such Eligible
               Affiliate; (l) any account to the






































     



     

               extent that any goods, the sale or lease of which gave rise
               to the account, have been returned, rejected, lost or
               damaged prior to acceptance of such goods by the purchaser
               or lessee thereof; (m) any account which arose from the sale
               of goods, if such sale was not an absolute sale or was a
               sale on consignment, on approval or on a sale-or-return
               basis, or if such sale is subject to any repurchase or
               return agreement, or if such sale is subject to any other
               term by reason of which the obligation of any obligor
               thereon is contingent or conditional; (n) any account which
               did not arise in the ordinary course of business of Borrower
               or the Eligible Affiliate, as the case may be; (o) any
               account which arose out of a contract with the United States
               of America or any state, county, municipality or other
               Governmental Authority, or any department or agency thereof,
               to the extent that sums due or to become due in connection
               therewith have not been duly assigned to the Agent in
               accordance with the Federal Assignment of Claims Act and/or
               any other applicable federal, state and local laws, rules
               and regulations, relating to the assignment or payment of
               such contract and sums; (p) any account with respect to
               which any obligor thereon is insolvent (as defined in
               Section 101 (32) of the United States Bankruptcy Code), is
               unable to pay its debts as they mature, or is the subject of
               any pending, imminent or threatened bankruptcy,
               reorganization, insolvency, readjustment of debt,
               trusteeship, receivership, dissolution or liquidation law,
               statute or proceeding; (q) any account which arose out of a
               contract which is subject to any bonding or other similar
               arrangement as security for any obligations of the Borrower,
               any of its Subsidiaries or any Guarantor in connection   
               with which any Lien has been granted, incurred or assumed
               upon any property, assets or revenues, whether now owned or
               hereafter acquired, of any of Borrower, any of its
               Subsidiaries or any Guarantor; (r) any account with respect
               to which any obligor






































     



     

               thereon is an Affiliate of the Borrower or any Other
               Obligor; (s) any account with respect to which the principal
               place of business of any obligor thereon is not located in
               the United States of America, except to the extent that such
               account is (i) secured by a letter of credit or bond
               satisfactory to the Collateral Agent issued or confirmed by
               a bank or provided by a surety which is satisfactory to the
               Collateral Agent and which is organized under the laws of
               the United sates or any state thereof or (ii) guaranteed by
               the United States of America or any agency thereof on terms
               and conditions satisfactory to the Collateral Agent; (t) any
               account which arose out of a contract with the United States
               of America or any other Governmental Authority to the extent
               that (i) funds for the payment of such account have not been
               appropriated by the United States of America or such other
               Governmental Authority or (ii) the Collateral Agent is not
               satisfied, in its discretion exercised in good faith, that
               such account and contract is enforceable against the full
               faith and credit of the United States of America or such
               other Governmental Authority and that funds for the payment
               of such account are available.  Notwithstanding the
               provisions of clause (s) of this definition, accounts of the
               Borrower due from Marubun Corporation, a Japanese
               corporation ("Marubun"), which otherwise qualify as Eligible
               Accounts may constitute Eligible Accounts even though they
               would otherwise be excluded by such clause (s), provided
               that, except as otherwise agreed by the Agent from time to
               time:  (i) notwithstanding the provisions of clause (a) of
               this definition, no account of the Borrower due from Marubun
               shall constitute an Eligible Account if such account has
               remained unpaid for thirty (30) days or more after the
               billing thereof; (ii) notwithstanding the provisions of
               clause (b) of this definition, no account of the Borrower
               due from Marubun shall constitute an Eligible Account if
               fifty percent (50%) or more of all of the accounts due the
               Borrower






































     



     

               and Eligible Affiliates from such Person has remained unpaid
               for thirty (30) days or more after the billing thereof; and
               (iii) the product of (x) the Accounts Credit Percentage and
               (y) the aggregate amount of accounts of the Borrower due
               from Marubun constituting Eligible Accounts, shall not at
               any time exceed Two Hundred Fifty Thousand Dollars
               ($250,000.00).  The Agent may determine from time to time in
               its discretion exercised in good faith and notwithstanding
               any previous contrary determinations made by the Collateral
               Agent, to exclude from or include in Eligible Accounts
               specific accounts (including accounts due from Marubun),
               categories or types of accounts (including accounts due from
               Marubun), or specific components of accounts (including
               accounts due from Marubun).  Such determinations may be
               based upon evaluations of risk by the Collateral Agent or
               any other factors deemed relevant by the Collateral Agent,
               whether or not such factors have theretofore been used,
               contemplated or foreseen as a basis for limiting Eligible
               Accounts.  Any such determinations by the Collateral Agent
               will be promptly communicated in writing to the Borrower.  
                                 
               "Eligible Affiliate":  shall mean at a particular
               time (a) each Eligible Borrower Subsidiary as at
               such time and (b) Symtron, provided that the
               Lender Guaranty is subsisting as at such time with
               respect to Symtron, the Guarantor Security
               Agreement is subsisting as at such time with
               respect to Symtron and that the security interests
               granted by Symtron pursuant to the Guarantor
               Security Agreement are duly perfected as at such
               time and subject only to permitted liens under the
               Credit Agreement.


               "Eligible Borrower Subsidiary":  shall mean at a
               particular time, a Subsidiary of the Borrower
               which has executed and delivered to the Collateral
               Agent a Subsidiary Guaranty subsisting as at such
               time, a Subsidiary



































     



     

               Security Agreement subsisting as at such time, such
               financing statements as may be required by the Agent and
               such other documents and instruments as may be required
               pursuant under the Credit Agreement or any Security
               Documents, provided that the security interests granted by
               such Subsidiary pursuant to such Subsidiary Security
               Agreement are duly perfected as at such time and subject
               only to permitted liens under the Credit Agreement.  

               "First Fidelity":  shall mean First Fidelity Bank,
               National Association.

               "Governmental Authority":  shall mean any nation
               or government, any state or other political
               subdivision thereof and any entity exercising
               executive, legislative, judicial, regulatory or
               administrative functions of or pertaining to
               government, and any Person owned or controlled
               directly or indirectly by any of the foregoing,
               whether domestic or foreign. 

               "Guarantor Security Agreement":  shall mean as
               waived, amended, modified, extended, renewed,
               supplemented or replaced from time to time, the
               Security Agreement to be executed and delivered by
               the Lender Guarantors (other than UIC) in favor of
               the Collateral Agent, for the ratable benefit of
               the Lenders, the Issuing Bank and the Noteholders,
               pursuant to which each of the Lender Guarantors
               (other than UIC) shall, among other things, grant
               to the Collateral Agent a security interest in all
               of its present and future accounts, chattel paper,
               instruments, documents of title, general
               intangibles, equipment, inventory and other
               assets.  

               "Indemnified Letters of Credit":  the collective
               reference to letters of credit issued by Signet
               Bank/Maryland for the account of the Borrower and
               subject to the Issuing Bank L/C Indemnification
               Agreement.

































     



     

               "Intercreditor Agreement":  shall mean, as the
               same may be amended, waived, modified, extended,
               renewed, supplemented or replaced from time to
               time, that certain Intercreditor Agreement of even
               date herewith by and among The Travelers Insurance
               Company, a Connecticut corporation, Principal
               Mutual Life Insurance Company, an Iowa
               corporation, First Fidelity Bank, National
               Association in its capacity as Lender, in its
               capacity as Agent, in its capacity as Issuing
               Bank, and in its capacity (in such capacity,
               "Collateral Agent") as grantee and beneficiary of
               the Collateral Agent Liens, and the Bank of
               Baltimore in its capacity as Lender.

               "Issuing Bank":  shall mean, as of the date of the
               Credit Agreement, First Fidelity Bank, National
               Association, in its capacity as party to the
               Credit Agreement as "Issuing Bank," and, after the
               date of the Credit Agreement, the person from time
               to time party to the  Credit Agreement as "Issuing
               Bank."

               "Issuing Bank L/C Indemnification Agreement":  as
               amended, modified, extended, renewed, supplemented
               or replaced from time to time, a letter agreement
               to be executed and delivered between the Issuing
               Bank and Signet Bank/Maryland, satisfactory in
               form and content to the Issuing Bank, pursuant to
               which the Issuing Bank shall indemnify Signet
               Bank/Maryland in connection with certain letters
               of credit issued by Signet Bank/Maryland for the
               account of the Borrower.

               "L/C Aggregate Undrawn Amount":  at a particular
               date, the aggregate undrawn amount, as at such
               date, of all Letters of Credit and all Indemnified
               Letters of Credit issued and outstanding.

               "L/C Agreements":  shall mean, as amended,
               modified, extended, renewed, supplemented or
               replaced from time to time, applications and
               reimbursement and other agreements in form































     



     

               and content and executed by Persons satisfactory to the
               Issuing Bank requesting issuance of one or more Letters of
               Credit and setting forth reimbursement obligations and other
               terms and conditions relating thereto.

               "L/C Exposure":  at a particular time, the sum of
               (a) the L/C Aggregate Undrawn Amount as at such
               time and (b) L/C Reimbursement Obligations as at
               such time.

               "L/C Reimbursement Obligations":  at a particular
               time, the aggregate amount of all drawings made
               under Letters of Credit and Indemnified Letters of
               Credit which, as at such time, have not been
               reimbursed by the Borrower to the Issuing Bank or
               Signet Bank/Maryland, as the case may be.

               "Lenders":  shall mean, as of the date of the
               Credit Agreement, First Fidelity Bank, National
               Association, and Bank of Baltimore, each in its
               capacity as party to the Credit Agreement as a
               "Lender," and, after the date of this Agreement,
               all persons from time to time parties to the
               Credit Agreement, as "Lenders."

               "Lender Guarantors":  shall mean, collectively,
               the Guarantor, UIC-Del. Corporation, a Delaware
               corporation, and the Restricted Subsidiaries.
      
               "Lender Guaranty":  shall mean, as the same may be
               amended, waived, modified, extended, renewed,
               supplemented or replaced from time to time, that
               certain Guaranty of even date herewith executed
               and delivered by Lender Guarantors in favor of
               Agent, Lenders and Issuing Bank.

               "Letter of Credit":  shall mean, commercial and
               standby letters of credit issued for the account
               of the Borrower, for such purposes, in such
               amounts, for the benefit of such Persons and
               subject to such terms and conditions as may be
               acceptable to the Issuing Bank and the Required
               Lenders in































     



     

               their discretion exercised in good faith (individually, as
               amended, modified, extended, renewed, supplemented or
               replaced from time to time, a "Letter of Credit," and
               collectively, the "Letters of Credit").

               "Lien":  shall mean any mortgage, pledge,
               hypothecation, assignment, deposit arrangement,
               encumbrance, lien (statutory or other) or
               preference, priority or other security agreement
               or preferential arrangement of any kind or nature
               whatsoever (including, without limitation, any
               conditional sale or other title retention
               agreement, any financing lease of any property
               (real, personal or mixed) as in conformity with
               generally accepted accounting principles would be
               required to be capitalized on a balance sheet of
               such Person having substantially the same economic
               effect as any of the foregoing, and the filing of
               any financing statement under the Uniform
               Commercial Code or comparable law or any
               jurisdiction in respect of any of the foregoing).

               "Other Obligor":  shall mean each of the Lender
               Guarantors and each other Person other than the
               Borrower that is now or hereafter primarily or
               secondarily, or contingently or noncontingently,
               liable for or obligated upon or in connection with
               any obligations of Borrower to Agent, any Lender
               or Issuing Bank, whether or not so liable, that
               has granted any lien or security interest to the
               Collateral Agent as security for any of such
               obligations or any obligations of any other Person
               in connection with any of such obligations. 

               "Person":  an individual, partnership,
               corporation, limited liability company, business
               trust, joint stock company, trust, unincorporated
               association, joint venture, Governmental Authority
               or other entity of whatever nature. 



































     



     

               "Required Lenders":  at a particular time, a
               Lender or Lenders holding more than sixty percent
               (60%) of the Aggregate Loans Outstanding of all
               Lenders under the Credit Agreement as at such time
               or, if no Lender has any Revolving Credit Loans
               outstanding under the Credit Agreement from time
               to time, a Lender or Lenders whose commitment
               percentages as identified in the Credit Agreement
               aggregate more than sixty percent (60%) as at such
               time.

               "Requirements of Law":  shall mean as to any
               Person, the certificate of incorporation and by-
               laws or other organizational or governing
               documents of such Person, and any law, treaty,
               rule or regulation or determination of an
               arbitrator or a court or other Governmental
               Authority, in each case applicable to or binding
               upon such Person or any of its property or to
               which such Person or any of its property is
               subject.

               "Restricted Subsidiaries":  mean (i) AAI
               Engineering Support, Inc., a Maryland corporation,
               AAI Microflite Simulation International
               Corporation, a Maryland Corporation, AAI/ACL
               Technologies, Inc., a Maryland corporation, Seti,
               Inc., a Pennsylvania corporation, AAI Systems
               Management, Inc., a Maryland corporation and AAI
               California Carshell, Inc., a Maryland corporation;
               (ii) any other Subsidiary with respect to which
               the Company has notified the Noteholders that it
               has been designated as such by the Board of
               Directors of the Company or by an Executive
               Officer of the Company who has been authorized by
               such Board of Directors to make such designation;
               and (iii) Symtron Systems, Inc., a New Jersey
               corporation, a wholly owned subsidiary of UIC.

               "Revolving Credit Loans":  at a particular time
               and from time to time the revolving credit loans
               made by the Lender or Lenders to the Borrower
               under Section 2.1 of the Credit Agreement.































     



     

               "Revolving Credit Notes":  shall mean the
               promissory notes of the Borrower evidencing the
               revolving credit loan or loans made under the
               Credit Agreement, from time to time, appropriately
               completed, as amended, modified, extended,
               renewed, supplemented or replaced from time to
               time, payable to the order of such Lender and
               further evidencing the obligation of the Borrower
               to pay with interest the aggregate loans
               outstanding under the Credit Agreement to such
               Lender from time to time. 
      
               "Security Documents":  shall mean, as the same may
               be amended, waived, modified, extended, renewed,
               supplemented or replaced from time to time, that
               certain Pledge and Security Agreement of even date
               herewith executed and delivered by the Borrower in
               favor of Collateral Agent, that certain Security
               Agreement of even date herewith executed and
               delivered by the Borrower in favor of the
               Collateral Agent, that certain Security Agreement
               of even date herewith executed and delivered by
               the Restricted Subsidiaries, et al in favor of
               Collateral Agent, that certain Deed of Trust and
               Security Agreement of even date herewith executed
               and delivered by the Borrower in favor of certain
               trustees for the benefit of Collateral Agent, that
               certain Assignment of Leases and Rents of even
               date herewith executed and delivered by the
               Borrower in favor of the Collateral Agent, that
               certain Pledge and Security Agreement of even date
               herewith executed and delivered by Guarantor in
               favor of Collateral Agent, that certain Collateral
               Assignment of Trademarks Agreement of even date
               herewith executed and delivered by the Borrower in
               favor of the Collateral Agent, that certain
               Collateral Assignment of Patents of even date
               herewith executed and delivered by the Borrower in
               favor of the Collateral Agent, that certain
               Collateral Assignment of Trademarks of even date
               herewith executed and delivered by Symtron
               Systems, Inc. in favor of the Collateral Agent,
               that certain Collateral Assignment of































     



     

               Patents of even date herewith executed and delivered by
               Symtron Systems, Inc. in favor of Collateral Agent, that
               certain Collateral Assignment of Trademarks of even date
               herewith executed and delivered by AAI/ACL Technologies,
               Inc. in favor of the Collateral Agent, that certain
               Collateral Assignment of Copyrights of even date herewith
               executed and delivered by AAI/ACL Technologies, Inc. in
               favor of the Collateral Agent, and that certain Collateral
               Assignment of Patents of even date herewith executed and
               delivered by AAI/ACL Technologies, Inc. in favor of
               Collateral Agent.

               "Subsidiary":  of a Person means (i) any
               corporation or other entity of which securities or
               other ownership interests having ordinary voting
               power to elect a majority of the board of
               directors or other persons performing similar
               functions are at the time, directly or indirectly,
               owned by such Person, or (ii) the management of
               which is otherwise controlled, directly or
               indirectly, through one or more intermediaries, by
               such Person.

               "Subsidiary Guaranty":  shall mean as waived,
               amended, modified, extended, renewed, supplemented
               or replaced from time to time a guaranty in form
               substantially similar to the Lender Guaranty, but
               in form and content satisfactory to the Required
               Lenders, pursuant to which a Subsidiary of the
               Borrower shall, among other things guarantee
               payment of the obligations of the Borrower to the
               Agent, the Lenders and the Issuing Bank.

               "Subsidiary Security Agreement":  shall mean as
               waived, amended, modified, extended, renewed,
               supplemented or replaced from time to time, a
               security agreement in form substantially similar
               to the Guarantor Security Agreement, but in form
               and content satisfactory to Required Lenders,
               executed and delivered between the Agent and a
               Subsidiary of Borrower pursuant to which such
               Subsidiary shall, among other things, grant
































     



     

               to the Collateral Agent, for the ratable benefit of the
               Lenders, the Issuing Bank and the Noteholders, a security
               interest in all accounts, chattel paper documents of title,
               general intangibles, instruments, equipment, inventory and
               other assets of such Subsidiary.

               "Symtron":  shall mean Symtron Systems, Inc., a
               New Jersey corporation." 

          Section 2.     Amendment of Section 6.8.  Restriction on Liens. 
                         -----------------------------------------------
     Subsections (vi), (vii) and (viii) be and hereby are added to Section
     6.8 of the Note Purchase Agreement, as amended, as follows:

               "(vi)     Liens in favor of the Collateral Agent
               created pursuant to the Security Documents
               securing the obligations under the Credit
               Agreement and the Revolving Credit Notes and under
               this Agreement and the Notes.

               (vii)     Liens in favor of or for the benefit of
               the Issuing Bank in or upon cash, cash equivalents
               or other liquid assets pledged to the Issuing Bank
               in connection with, or in or upon bills of lading
               or other shipping or transportation documents,
               warehouse receipts or similar rights arising in
               connection with, the L/C Agreements or the
               issuance and payment of drawings under Letters of
               Credit.

               (viii)    Liens in favor of or for the benefit of
               the Agent or any Lender in or upon cash, cash
               equivalents, marketable securities or other liquid
               assets and other rights relating to or in
               connection with overnight investments or other
               investments made or managed by the Agent or any
               Lender for or on behalf of the Borrower, any of
               its Subsidiaries or Symtron."

          Section 3.     Amendment of Section 6.11.  Guaranties.  Section
                         --------------------------------------
     6.11 of the Note Purchase Agreement is amended to read in its entirety
     as follows:































     



     

               "Section 6.11. Guaranties.    The Company will 
                              ----------
               not, and will not permit any Restricted Subsidiary to, at
               any time, make, suffer to exist or become liable with
               respect to guarantees of obligations of any Person or
               Persons in excess of an aggregate of $5,000,000.00, except
               that the Restricted Subsidiaries shall be permitted to
               guarantee the obligations of the Company under the Credit
               Agreement, the Revolving Credit Notes and the Lender
               Guaranty to the Lenders and to pledge their respective
               Collateral as security for such obligations by executing and
               delivering the Security Documents."

          Section 4.     Borrowing Base Certificate.  The following new
                         --------------------------
     subparagraph (c) be and hereby is added to Section 5.1, as follows:

               "(c)  The Company agrees to promptly deliver to
               each of the Noteholders a copy of any Borrowing
               Base Certificate that it shall hereafter deliver
               to the Required Lenders in the Company's capacity
               as Borrower under the Credit Agreement that states
               that (a) the Aggregate Borrowing Base Charge
               exceeds (b) the Borrowing Base, provided, however,
               that the Company shall have no monetary liability,
               whether direct, incidental, consequential or
               otherwise, to any Noteholder or any other Person
               on account of any failure of the Company to so
               give such written notification to any Noteholder."

          Section 5.     No Other Amendment.  Except as specifically set
                         ------------------
     forth herein, the Note Purchase Agreement shall remain in full force
     and effect in accordance with its terms.

          Section 6.     Governing Law.  This Amendment No. 3 shall be
                         -------------
     governed by and construed in accordance with the laws of the  State of
     New York.

          Section 7.     Counterparts.  This Amendment No. 3 may be
                         ------------
     executed in any number of counterparts and by different parties hereto
     in separate counterparts, each of which when so executed shall be
     deemed to be an original and all of which taken together shall
     constitute one and the same agreement.




























     



     

          IN WITNESS WHEREOF, the parties hereto have caused this Amendment
     No. 3 to Note Purchase Agreement to be executed by their respective
     officers thereunto duly authorized as of the date first above written.

                              AAI CORPORATION


                              By:                                   
                                 -----------------------------------
                              Name: Paul J. Michaud                   
                                   ---------------------------------
                              Title: Vice President, Chief Financial 
                                    --------------------------------
                                    Officer and Treasurer              
                                    --------------------------------

                              PRINCIPAL MUTUAL LIFE INSURANCE COMPANY


                              By:                                    
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                              Name:                                  
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                              Title:                                 
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                              By:                                    
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                              Name:                                  
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                              Title:                                 
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                              THE TRAVELERS INSURANCE COMPANY


                              By:                                     
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                              Name:                                   
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                              Title:                              
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