<PAGE>

EXHIBIT 10.6

                          AMENDMENT TO CREDIT AGREEMENT
                          -----------------------------

         This AMENDMENT TO CREDIT AGREEMENT (this "Amendment") is made as of the
30th day of April, 2003, between ENVIRONMENTAL TECTONICS CORPORATION (the
"Borrower") and PNC BANK, NATIONAL ASSOCIATION (the "Bank").

                                   BACKGROUND

         A. The Bank and the Borrower are parties to a Credit Agreement dated as
of February 18, 2003 (the "Credit Agreement"), pursuant to which the Bank agreed
to make Revolving Credit Loans and issue Letters of Credit to and on behalf of
the Borrower.

         B. The Borrower has requested that the Bank amend the Credit Agreement,
and the Bank has agreed to do so on and subject to the terms and conditions set
forth herein.

         NOW, THEREFORE, in consideration of the foregoing and for good and
valuable consideration, the legality and sufficiency of which are hereby
acknowledged, the parties hereto, intending to be legally bound hereby, agree as
follows:

         1. Definitions. Capitalized terms used herein and not otherwise defined
herein shall have the meanings assigned to them in the Credit Agreement.

         2. Amendments to Credit Agreement.

         The Credit Agreement is hereby amended as follows:

              (a) The definition of "Borrowing Base" is hereby amended and
restated to read in full as follows:

         "Borrowing Base": the sum of (i) 80% of Eligible Receivables plus (ii)
         the lesser of (A) 50% of Eligible Inventory and (B) $2,000,000, plus
         (iii) the lesser of (A) 50% of Eligible Costs and Earnings and (B)
         $4,000,000, provided, however, that for purposes of determining the
         Borrowing Base, the Existing Centrifuge shall be included therein as
         Eligible Costs and Earnings at 50% of its actual cost plus profit if it
         is subject to a binding agreement of sale and is carried as "costs in
         excess of billings" on the books of the Borrower or, during the period
         commencing on the Closing Date and ending six months thereafter, (x) as
         Eligible Inventory at 25% of its actual cost if it is not subject to a
         binding agreement of sale or letter of intent for sale or (y) as
         Eligible Inventory at 50% of its actual cost if it is subject to a
         binding agreement of sale or letter of intent for sale and is carried
         as "inventory" on the books of the Borrower, plus (iv) the amount on
         deposit in the Cash Collateral Account, less (v) any Permitted
         Overadvance, all as set forth in the most recent Borrowing Base
         Certificate delivered to the Bank."


<PAGE>

              (b) The definitions of the terms "Cash Collateralized Letters of
Credit," "Cash Collateralized Letters of Credit Commitment," "Cash
Collateralized Letters of Credit Commitment Period," "Cash Collateralized
Letters of Credit Obligations" and "Cash Collateralized Letters of Credit
Termination Date" appearing in Section 1.1 of the Credit Agreement are hereby
deleted;

              (c) The definition of "Commitments" appearing in Section 1.1 of
the Credit Agreement is hereby amended by deleting the phrase "and the Cash
Collateralized Letter of Credit Commitment" appearing therein;

              (d) The definition of "Letters of Credit" appearing in Section 1.1
of the Credit Agreement is hereby deleted and all other references in the Loan
Documents to "Letters of Credit" shall be changed to "Revolving Credit Letters
of Credit;"

              (e) The definition of "Revolving Credit Commitment" appearing in
Section 1.1 of the Credit Agreement is hereby amended by deleting the dollar
amount "Twelve Million Dollars ($12,000,000)" appearing therein and inserting
the amount "Fourteen Million Eight Hundred Thousand Dollars ($14,800,000)" in
lieu thereof;

              (f) The definition of "Reimbursement Obligation" appearing in
Section 1.1 of the Credit Agreement is hereby amended and restated to read in
full as follows:

         "Reimbursement Obligation": the obligation of the Borrower to reimburse
         the Bank pursuant to subsection 2.1(d) for amounts drawn under the
         Revolving Credit Letters of Credit.

              (g) The definition of "Total Funded Debt" appearing in Section 1.1
of the Credit Agreement is hereby amended by deleting the phrase "or Cash
Collateralized Letters of Credit" from the first parenthetical appearing
therein;

              (h) Section 2.1(d) of the Credit Agreement is hereby amended and
restated to read in full as follows:

         (d) Subject to the terms and conditions hereof, the Bank shall during
         the Revolving Credit Commitment Period issue or cause the issuance of
         letters of credit ("Revolving Credit Letters of Credit") on behalf of
         the Borrower; provided, however, that the Bank will not be required to
         issue or cause to be issued any Revolving Credit Letter of Credit which
         expires later than the Revolving Credit Termination Date or to the
         extent that the face amount of such Revolving Credit Letters of Credit
         would exceed the Available Revolving Credit Commitment; provided
         further, that the Bank shall not be required to issue any Revolving
         Credit Letter of Credit if, after giving effect to such issuance, the
         Borrower would not be in compliance with any of the applicable
         financial ratios set forth in Section 6.1. The maximum amount of
         outstanding Revolving Credit Letters of Credit shall not exceed
         $10,300,000 at any time; the maximum amount of outstanding Revolving
         Credit Letters of Credit which are standby letters of credit shall not


                                       2

<PAGE>

         exceed $7,800,000 at any time; and the maximum amount of outstanding
         Revolving Credit Letters of Credit which are trade letters of credit
         shall not exceed $2,500,000 at any time. The Borrower shall be required
         immediately to reimburse the Bank any amounts paid by the Bank pursuant
         to drawings on Revolving Credit Letters of Credit. All payments by the
         Bank of drawings on Revolving Credit Letters of Credit shall become, at
         the time such drawings are paid, Revolving Credit Loans and shall bear
         interest at the applicable Base Rate until repaid in full.

              (i) Section 2.1(e) of the Credit Agreement is hereby deleted in
its entirety and Section 2.1(f) of the Credit Agreement is hereby renumbered as
Section 2.1(e);

              (j) Section 2.9(a) is hereby amended by deleting the phrase "and
the Cash Collateralized Letters of Credit Commitment shall be automatically
terminated on the Cash Collateralized Letters of Credit Termination Date"
appearing in the first sentence therein; and

              (k) Section 2.9(b) is hereby amended by deleting the phrase "or
the Cash Collateralized Letter of Credit Commitment" appearing therein.

         3. Line of Credit Note. In order to evidence the increase in the
maximum principal amount available under the Revolving Credit Commitment to
$14,800,000, the Borrower shall execute and deliver to the Bank an Amended and
Restated Revolving Credit Note (the "Amended and Restated Revolving Credit
Note") in the form attached hereto as Exhibit A.

         4. Letters of Credit. As of the date hereof, any letter of credit other
than the Bond Letter of Credit issued and outstanding under the Credit
Agreement, including Cash Collateralized Letters of Credit issued under the
Credit Agreement as in effect prior to the execution of this Amendment, shall be
deemed to be Revolving Credit Letters of Credit subject to Section 2.1(d) of the
Credit Agreement, as amended by this Amendment.

         5. Amendments to Loan Documents. All references to the Credit Agreement
in any of the Loan Documents shall be deemed to refer to the Credit Agreement,
as amended by this Amendment and all references to the Revolving Credit Note in
any of the Loan Documents shall be deemed to refer to the Amended and Restated
Revolving Credit Note.

         6. Ratification. Except as the provisions thereof have been expressly
amended or waived by this Amendment, the Credit Agreement and the other Loan
Documents shall continue to be, and shall remain, unaltered and in full force
and effect in accordance with their terms. The Borrower hereby affirms all the
provisions of the Loan Documents, as amended or modified by this Amendment.


                                       3

<PAGE>

         7. Representations and Warranties.

              (a) The Borrower hereby certifies that (i) the representations and
warranties of the Borrower in the Credit Agreement are true and correct in all
material respects as of the date hereof, as if made on the date hereof and (ii)
no Event of Default and no event which could become an Event of Default with the
passage of time or the giving of notice, or both, under the Credit Agreement or
the other Loan Documents exists on the date hereof.

              (b) The Borrower further represents that it has all the requisite
power and authority to enter into and to perform its obligations under this
Amendment, and that the execution, delivery and performance of this Amendment
and the Amended and Restated Revolving Credit Note have been duly authorized by
all requisite action and will not violate or constitute a default under any
provision of any applicable law, rule, regulation, order, writ, judgment,
injunction, decree, determination or award presently in effect or of the
Articles of Incorporation or by-laws of the Borrower, or of any indenture, note,
loan or credit agreement, license or any other agreement, lease or instrument to
which the Borrower is a party or by which the Borrower or any of its properties
are bound.

              (c) The Borrower also further represents that its obligation to
repay the Loans, together with all interest accrued thereon, is absolute and
unconditional, and there exists no right of set off or recoupment, counterclaim
or defense of any nature whatsoever to payment of the Loans.

              (d) The Borrower also further represents that there have been no
changes to the Articles of Incorporation, by-laws or other organizational
documents of the Borrower since the most recent date true and correct copies
thereof were delivered to the Bank.

         8. Conditions Precedent. The effectiveness of this Amendment is subject
to the fulfillment, to the satisfaction of the Bank and its counsel, of the
following conditions precedent:

              (a) The Borrower shall have delivered to the Bank the following,
all of which shall be in form and substance satisfactory to the Bank and shall
be duly completed and executed:

                    (i) This Amendment, executed by the Borrower;

                    (ii) The executed original of the Amended and Restated
              Revolving Credit Note; and

                    (iii) Such additional documents, certificates and
              information as the Bank may require pursuant to the terms hereof
              or otherwise reasonably request.

              (b) After giving effect to the amendments contained herein, the
representations and warranties set forth in the Credit Agreement shall be true
and correct on and as of the date hereof.

                                       4


<PAGE>


              (c) After giving effect to the amendments contained herein, no
Event of Default hereunder, and no event which, with the passage of time or the
giving of notice, or both, would become such an Event of Default shall have
occurred and be continuing as of the date hereof.

         9. No Waiver. Except as expressly provided herein, this Amendment does
not and shall not be deemed to constitute a waiver by the Bank of any Event of
Default, or of any event which with the passage of time or the giving of notice
or both would constitute an Event of Default, nor does it obligate the Bank to
agree to any further modifications to the Loan Agreement or any other Loan
Document or constitute a waiver of any of the Bank's other rights or remedies.

         10. Release and Indemnity. Recognizing and in consideration of the
Bank's agreement to the amendments set forth herein, the Borrower hereby waives
and releases the Bank and its officers, attorneys, agents, and employees from
any liability, suit, damage, claim, loss or expense of any kind or nature
whatsoever and howsoever arising the Borrower ever had or now has against any of
them arising out of or relating to the Bank's acts or omissions with respect to
this Amendment, the Credit Agreement, the other Loan Documents or any other
matters described or referred to herein or therein. The Borrower further hereby
agrees to indemnify and hold the Bank and its officers, attorneys, agents and
employees harmless from any loss, damage, judgment, liability or expense
(including counsel fees) suffered by or rendered against the Bank on account of
anything arising out of this Amendment, the Credit Agreement, the other Loan
Documents or any other document delivered pursuant thereto up to and including
the date hereof; provided that, the Borrower shall not have any obligation
hereunder to the Bank with respect to indemnified liabilities arising from the
gross negligence or willful misconduct of the Bank.

         11. Severability. Any provision of this Amendment which is prohibited
or unenforceable in any jurisdiction shall, as to such jurisdiction, be
ineffective to the extent of such prohibition or unenforceability without
invalidating the remaining provisions hereof, and any such prohibition or
unenforceability in any jurisdiction shall not invalidate or render
unenforceable such provision in any other jurisdiction.

         12. Miscellaneous.

              (a) Expenses. The Borrower agrees to pay all of the Bank's
out-of-pocket fees and expenses incurred in connection the preparation,
negotiation and execution of this Amendment and the other documents executed in
connection.

              (b) Governing Law. This Amendment shall be governed by and
construed in accordance with the laws of the Commonwealth of Pennsylvania.

              (c) Successor and Assigns. The terms and provisions of this
Amendment shall be binding upon and shall inure to the benefit of the Borrower
and the Bank and their respective successors and assigns.


                                       5

<PAGE>

              (d) Counterparts. This Amendment may be executed in one or more
counterparts, each of which shall be deemed to be an original, and all of which
shall constitute one and the same instrument.

              (e) Headings. The headings of any paragraph of this Amendment are
for convenience only and shall not be used to interpret any provision hereof.

              (f) Modifications. No modification hereof or any agreement
referred to herein shall be binding or enforceable unless in writing and signed
on behalf of the party against whom enforcement is sought.

         IN WITNESS WHEREOF, the parties hereto have executed this Amendment as
of the day and year first above written.

Borrower:                          ENVIRONMENTAL TECTONICS CORPORATION

                                   By:  Duane D. Deaner
                                        ----------------------------------------
                                   Name:  Duane D. Deaner
                                   Title: Chief Financial Officer


Bank:                              PNC BANK, NATIONAL ASSOCIATION

                                   By:  John G. Siegrist
                                        ----------------------------------------
                                   Name:  John G. Siegrist
                                   Title: Vice President




                                       6
<PAGE>

                                    EXHIBIT A
                   AMENDED AND RESTATED REVOLVING CREDIT NOTE

$14,800,000                                                      April ___, 2003
                                                                Philadelphia, PA


         FOR VALUE RECEIVED, ENVIRONMENTAL TECTONICS CORPORATION (the
"Borrower"), hereby unconditionally promises to pay to the order of PNC BANK,
NATIONAL ASSOCIATION (the "Bank"), at the office of the Bank located at 1600
Market Street, Philadelphia, Pennsylvania, 19103, on the Revolving Credit
Termination Date (as such term is defined in the Credit Agreement hereinafter
referred to) in lawful money of the United States of America and in immediately
available funds, the principal sum of (a) FOURTEEN MILLION EIGHT HUNDRED
THOUSAND DOLLARS ($14,800,000), or, if less, (b) the aggregate unpaid principal
amount of all Revolving Credit Loans made by the Bank to the Borrower pursuant
to the Credit Agreement. The Borrower further unconditionally agrees to pay
interest accrued on the unpaid principal amount outstanding hereunder from time
to time from the date hereof in like money at such office at the rates and on
the dates specified in the Credit Agreement together with all other costs, fees
and expenses as provided in the Credit Agreement.

         The holder of this Note is authorized to endorse on Schedule 1 annexed
hereto and made a part hereof or on a continuation thereof which shall be
attached hereto and made a part hereof the respective date, Type, and amount of
each Revolving Credit Loan made by the Bank to the Borrower, each continuation
thereof, each conversion of all or a portion thereof to another Type, the date
and amount of each payment or prepayment of principal thereof and, in the case
of Eurodollar Loans, the length of each Interest Period with respect thereto,
which endorsement shall constitute prima facie evidence of the accuracy of the
information endorsed absent manifest error; provided, however, that the failure
to make any such endorsement (or any error in such recordation) shall not affect
the obligations of the Borrower to make payments of principal, interest and
other amounts outstanding in accordance with the terms of this Note and the
Credit Agreement.

         This Note amends and completely restates and evidences the indebtedness
outstanding under and is substituted for, but not in payment, satisfaction,
cancellation or novation of, the Revolving Credit Note dated February 18, 2003
issued by the Borrower to the Bank and, as of the date hereof, shall be deemed
to be the Revolving Credit Note referred to in, evidences indebtedness incurred
under, and is entitled to the benefits of, the Credit Agreement, dated as of the
date hereof (as it may be amended, supplemented or otherwise modified from time
to time, the "Credit Agreement"), between the Borrower and the Bank. The Credit
Agreement, among other things, contains provisions for the acceleration of the
maturity hereof upon the happening of certain events, for optional or mandatory
prepayments of the principal hereof prior to the maturity thereof, for a higher
rate of interest upon the occurrence of an Event of Default and for certain
security interests granted by the Borrower and certain related entities.
Reference is made to the Credit Agreement and the other Loan Documents for a
statement of the terms and conditions under which the Revolving Credit Loans
evidenced hereby have been secured.

<PAGE>

         Upon the occurrence of any one or more of the Events of Default
specified in the Credit Agreement, all amounts then remaining unpaid on this
Note shall become, or may be declared to be, immediately due and payable, all as
provided therein.

         All parties now and hereafter liable with respect to this Note, whether
maker, principal, surety, guarantor, endorser or otherwise, hereby waive
presentment, demand, protest and notice (except as required under the Credit
Agreement) of any kind. No failure to exercise, and no delay in exercising, any
rights hereunder on the part of the holder hereof shall operate as a waiver of
such rights.

         Capitalized terms not otherwise defined herein shall have the meanings
set forth in the Credit Agreement. This Note shall be governed by, and construed
in accordance with, the laws of the Commonwealth of Pennsylvania.


                                    ENVIRONMENTAL TECTONICS CORPORATION


                                    By:____________________________________
                                       Name:
                                       Title:



<PAGE>
<TABLE>
<CAPTION>

                                                           Schedule 1

                                                 Loans, Conversions and Payments

====================================================================================================================================
                                                                      Amount of       Amount of
                                                                      Base Rate      Eurodollar
                                                                        Loans           Loans         Unpaid
                 Type of Loan                          Amount of      Converted     Converted To     Principal
                (Eurodollar or          Amount of      Principal    to Eurodollar     Base Rate     Balance of       Notation
  Date            Base Rate)              Loan          Repaid          Loans           Loans          Loans         Made By
====================================================================================================================================
<S>                <C>                    <C>            <C>            <C>             <C>             <C>             <C>

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</TABLE>