Exhibit 4.12

                       THIRD AMENDMENT TO CREDIT AGREEMENT


                  THIRD AMENDMENT TO CREDIT AGREEMENT (this "Amendment"), 
dated as of April 23, 1999, among TRANSDIGM HOLDING COMPANY, a Delaware 
corporation ("Holdings"), TRANSDIGM INC., a Delaware corporation (the 
"Borrower"), the various lending institutions party to the Credit Agreement 
referred to below (each, a "Lender" and, collectively, the "Lenders"), and 
BANKERS TRUST COMPANY, as Administrative Agent for the Lenders (the 
"Administrative Agent"). All capitalized terms used herein and not otherwise 
defined herein shall have the meanings provided such terms in the Credit 
Agreement.

                              W I T N E S S E T H :


                  WHEREAS, Holdings, the Borrower, the Lenders and the
Administrative Agent are parties to a Credit Agreement, dated as of December 3,
1998 (as amended through, but not including, the date hereof, the "Credit
Agreement"); and

                  WHEREAS, the parties hereto wish to amend the Credit Agreement
as herein provided;

                  NOW, THEREFORE, it is agreed:

I.       AMENDMENT TO CREDIT AGREEMENT.

                  1. Section 11 of the Credit Agreement is hereby amended by
deleting the definitions of "Applicable Base Rate Margin" and "Applicable
Eurodollar Rate Margin" appearing therein and inserting the following new
definitions of "Applicable Base Rate Margin" and "Applicable Eurodollar Rate
Margin" in lieu thereof:

                  "Applicable Base Rate Margin" shall mean:

                  (a) in the case of A Term Loans, Revolving Loans and Swingline
         Loans maintained as Base Rate Loans, (i) for the period from the
         Initial Borrowing Date through but not including February 16, 1999,
         2.50%, (ii) for the period from February 16, 1999 through but including
         the first Start Date after the Initial Borrowing Date, 2.25% and (iii)
         from and after any Start Date to and including the corresponding End
         Date, the respective percentage per annum set forth in clause (A), (B),
         (C) or (D) below if, but only if, as of the Test Date for such Start
         Date the applicable condition set forth in clause (A), (B), (C), or (D)
         below, as the case may be, is met:

                           (A) 2.25% if, but only if, as of the Test Date for
                  such Start Date the Total Leverage Ratio for the Test Period
                  ended on such Test Date shall be greater than or equal to
                  4.00:1.00;





                           (B) 2.00% if, but only if, as of the Test Date for
                  such Start Date the Total Leverage Ratio for the Test Period
                  ended on such Test Date shall be less than 4.00:1.00 and
                  greater than or equal to 3.00:1.00;

                           (C) 1.75% if, but only if, as of the Test Date for
                  such Start Date the Total Leverage Ratio for the Test Period
                  ended on such Test Date shall be less than 3.00:1.00 but
                  greater than or equal to 2.50:1.00; or

                           (D) 1.50% if, but only if, as of the Test Date for
                  such Start Date the Total Leverage Ratio for the Test Period
                  ended on such Test Date shall be less than 2.50:1.00

         Notwithstanding anything to the contrary contained above in this clause
         (a), (x) each of the percentages set forth above in this definition
         which would otherwise be in effect for any Applicable Margin Period
         shall be reduced by .25% from and after the respective Start Date to
         and including the corresponding End Date for such Applicable Margin
         Period if, but only if, as of the Test Date for such Start Date both
         the Senior Leverage Ratio for the Test Period ended on such Test Date
         shall be less than 2.75:1.00 and the Consolidated Interest Coverage
         Ratio for such Test Period shall be greater than 1.80:1.00 and (y) the
         Applicable Base Rate Margin for A Term Loans, Revolving Loans and
         Swingline Loans shall be 2.25% at all times when a Default or an Event
         of Default shall exist; and

                  (b) in the case of B Term Loans maintained as Base Rate Loans,
         2.50%.

                  "Applicable Eurodollar Rate Margin" shall mean:

                  (a) in the case of A Term Loans and Revolving Loans maintained
         as Eurodollar Loans, (i) for the period from the Initial Borrowing Date
         through but not including February 16, 1999, 3.50%, (ii) for the period
         from February 16, 1999 through but including the first Start Date after
         the Initial Borrowing Date, 3.25% and (iii) from and after any Start
         Date to and including the corresponding End Date, the respective
         percentage per annum set forth in clause (A), (B), (C) or (D) below if,
         but only if, as of the Test Date for such Start Date the applicable
         condition set forth in clause (A), (B), (C) or (D) below, as the case
         may be, is met:

                           (A) 3.25% if, but only if, as of the Test Date for
                  such Start Date the Total Leverage Ratio for the Test Period
                  ended on such Test Date shall be greater than or equal to
                  4.00:1.00;

                           (B) 3.00% if, but only if, as of the Test Date for
                  such Start Date the Total Leverage Ratio for the Test Period
                  ended on such Test Date shall be less than 4.00:1.00 and
                  greater than or equal to 3.00:1.00;



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                           (C) 2.75% if, but only if, as of the Test Date for
                  such Start Date the Total Leverage Ratio for the Test Period
                  ended on such Test Date shall be less than 3.00:1.00 and
                  greater than or equal to 2.50:1.00; or

                           (D) 2.50% if, but only if, as of the Test Date for
                  such Start Date the Total Leverage Ratio for the Test Period
                  ended on such Test Date shall be less than 2.50:1.00.

         Notwithstanding anything to the contrary contained above in this clause
         (a), (x) each of the percentages set forth above in this definition
         which would otherwise be in effect for any Applicable Margin Period
         shall be reduced by .25% from and after the respective Start Date to
         and including the corresponding End Date for such Applicable Margin
         Period if, but only if, as of the Test Date for such Start Date both
         the Senior Leverage Ratio for the Test Period ended on such Test Date
         shall be less than 2.75:1.00 and the Consolidated Interest Coverage
         Ratio for such Test Period shall be greater than 1.80:1.00 and (y) the
         Applicable Eurodollar Rate Margin for A Term Loans and Revolving Loans
         maintained as Eurodollar Loans shall be 3.25% at all times when a
         Default or an Event of Default shall exist; and

                  (b) in the case of B Term Loans maintained as Eurodollar
         Loans, 3.50%.

II.      MISCELLANEOUS PROVISIONS.

                  1. In order to induce the Lenders to enter into this
Amendment, each of Holdings and the Borrower hereby represents and warrants
that:

                  (a) no Default or Event of Default exists as of the Third
         Amendment Effective Date (as defined below), both before and after
         giving effect to this Amendment; and

                  (b) all of the representations and warranties contained in the
         Credit Agreement and the other Credit Documents are true and correct in
         all material respects on the Third Amendment Effective Date, both
         before and after giving effect to this Amendment, with the same effect
         as though such representations and warranties had been made on and as
         of the Third Amendment Effective Date (it being understood that any
         representation or warranty made as of a specific date shall be true and
         correct in all material respects as of such specific date).

                  2. This Amendment is limited as specified and shall not
constitute a modification, acceptance or waiver of any other provision of the
Credit Agreement or any other Credit Document.

                  3. This Amendment may be executed in any number of
counterparts and by the different parties hereto on separate counterparts, each
of which counterparts when executed and delivered shall be an original, but all
of which shall together constitute one and the same instrument. A complete set
of counterparts shall be lodged with the Borrower and the Administrative Agent.



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                  4. THIS AMENDMENT AND THE RIGHTS AND OBLIGATIONS OF THE
PARTIES HERETO SHALL BE CONSTRUED IN ACCORDANCE WITH AND GOVERNED BY THE LAW OF
THE STATE OF NEW YORK.

                  5. This Amendment shall become effective on the date (the
"Third Amendment Effective Date") when each of Holdings, the Borrower and each
Lender shall have signed a counterpart hereof (whether the same or different
counterparts) and shall have delivered (including by way of facsimile
transmission) the same to the Administrative Agent at the Notice Office.

                  6. From and after the Third Amendment Effective Date, all
references in the Credit Agreement and each of the other Credit Documents to the
Credit Agreement shall be deemed to be references to the Credit Agreement as
amended hereby.

                                      * * *



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                  IN WITNESS WHEREOF, the parties hereto have caused their duly
authorized officers to execute and deliver this Amendment as of the date first
above written.


                                  TRANSDIGM HOLDING COMPANY

                                  By /s/ Peter B. Radekevich
                                    --------------------------------------------
                                    Title: Chief Financial Officer

                                  TRANSDIGM INC.

                                  By /s/ Peter B. Radekevich
                                    --------------------------------------------
                                    Title: Chief Financial Officer

                                  BANKERS TRUST COMPANY, Individually and
                                  as Administrative Agent

                                  By /s/ Gregory Shefrin
                                    --------------------------------------------
                                    Title: Principal

                                  CREDIT SUISSE FIRST BOSTON,
                                  Individually and as Syndication Agent

                                  By /s/ Bill O'Daly
                                    --------------------------------------------
                                    Title: Vice President

                                  By /s/ Robert Hetu
                                    --------------------------------------------
                                    Title: Vice President

                                  BANK OF NOVA SCOTIA

                                  By /s/ Robert Gaviglio
                                    --------------------------------------------
                                    Title: Senior Relationship Manager

                                  FLEET NATIONAL BANK,
                                  Individually and as Documentation Agent

                                  By /s/ James C. Silva
                                    --------------------------------------------
                                    Title: Vice President


                                  NBD BANK

                                  By /s/ Gary C. Wilson
                                    ------------------------------------------
                                    Title: First Vice President


                                       5

                                    GENERAL ELECTRIC CAPITAL CORPORATION

                                    By
                                      ------------------------------------------
                                      Title:

                                    HELLER FINANCIAL, INC.

                                    By /s/ Scott Ziemke
                                      ------------------------------------------
                                      Title: Assistant Vice President

                                    NATIONAL CITY BANK

                                    By /s/ Joseph D. Robison
                                      ------------------------------------------
                                      Title: Vice President

                                    INDOSUEZ CAPITAL FUNDING II A, LIMITED
                                    By Indosuez Capital Luxembourg,
                                          as Collateral Agent

                                    By /s/ Melissa Marano
                                      ------------------------------------------
                                      Title: Vice President

                                    INDOSUEZ CAPITAL FUNDING IV, L.P.
                                    By Indosuez Capital Luxembourg,
                                          as Collateral Agent

                                    By /s/ Melissa Marano
                                      ------------------------------------------
                                      Title: Vice President

                                    PARIBAS CAPITAL FUNDING LLC

                                    By /s/ Jeffrey J. Youle
                                      ------------------------------------------
                                      Title:

                                    SANKATY HIGH YIELD ASSET PARTNERS, L.P.

                                    By /s/ Diane Exter
                                      ------------------------------------------
                                      Title: Portfolio Manager
 
                                    TORONTO DOMINION (NEW YORK), INC.

                                    By
                                      ------------------------------------------
                                      Title: