Exhibit 10.3

SUPPLEMENT NO. 4 dated as of September 14, 2012 (this “Supplement”) to the
Guarantee and Collateral Agreement dated as of June 23, 2006, as amended and
restated as of December 6, 2010, and as further amended and restated as of
February 14, 2011 (as amended and supplemented from time to time, the “Guarantee
and Collateral Agreement”), among TRANSDIGM INC., a Delaware corporation (the
“Borrower”), TRANSDIGM GROUP INCORPORATED, a Delaware corporation (“Holdings”),
each subsidiary of the Borrower listed on Schedule I thereto (each such
subsidiary individually a “Subsidiary Guarantor” and collectively, the
“Subsidiary Guarantors”; the Subsidiary Guarantors, Holdings and the Borrower
are referred to collectively herein as the “Grantors”) and CREDIT SUISSE AG, as
collateral agent for the Secured Parties and as administrative agent under each
of the 2010 Credit Agreement and the 2011 Credit Agreement (each as defined
below) (in such capacities, the “Agent”).

A. Reference is made to (a) the Credit Agreement dated as of December 6, 2010
(as amended, supplemented or otherwise modified from time to time, the “2010
Credit Agreement”), among the Borrower, Holdings, each subsidiary of the
Borrower from time to time party thereto, the lenders from time to time party
thereto (the “2010 Lenders”) and the Agent and (b) the Credit Agreement dated as
of February 14, 2011 (as amended, supplemented or otherwise modified from time
to time, the “2011 Credit Agreement” and, together with the 2010 Credit
Agreement, the “Credit Agreements”), among the Borrower, Holdings, each
subsidiary of the Borrower from time to time party thereto, the lenders from
time to time party thereto (the “2011 Lenders” and, together with the 2010
Lenders, the “Lenders”) and the Agent.

B. Capitalized terms used herein and not otherwise defined herein shall have the
meanings assigned to such terms in the 2010 Credit Agreement, the 2011 Credit
Agreement or the Guarantee and Collateral Agreement, as the context may require.

C. The Grantors have entered into the Guarantee and Collateral Agreement in
order to induce the Lenders to make Loans and the 2010 Issuing Banks to issue
Letters of Credit. Section 7.16 of the Guarantee and Collateral Agreement
provides that additional Domestic Subsidiaries of the Loan Parties may become
Subsidiary Guarantors and Grantors under the Guarantee and Collateral Agreement
by execution and delivery of an instrument in the form of this Supplement. The
undersigned Subsidiary (the “New Subsidiary”) is executing this Supplement in
accordance with the requirements of the applicable Credit Agreement to become a
Subsidiary Guarantor and a Grantor under the Guarantee and Collateral Agreement
in order to induce the Lenders to make additional Loans and the 2010 Issuing
Banks to issue additional Letters of Credit, and as consideration for Loans
previously made and Letters of Credit previously issued.

Accordingly, the Agent and the New Subsidiary agree as follows:

SECTION 1. In accordance with Section 7.16 of the Guarantee and Collateral
Agreement, the New Subsidiary by its signature below becomes a Grantor and
Subsidiary Guarantor under the Guarantee and Collateral Agreement with the same
force and effect as if originally named therein as a Grantor and Subsidiary
Guarantor, and the New Subsidiary hereby (a) agrees to all the terms and
provisions of the Guarantee and Collateral Agreement applicable to it as a
Grantor and Subsidiary Guarantor thereunder and (b) represents and warrants that
the

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representations and warranties made by it as a Grantor and Subsidiary Guarantor
thereunder are true and correct in all material respects on and as of the date
hereof (except for any representation or warranty that is limited by its terms
to an earlier specified date). In furtherance of the foregoing, the New
Subsidiary, as security for the payment and performance in full of the Secured
Obligations (as defined in the Guarantee and Collateral Agreement), does hereby
create and grant to the Agent, its successors and assigns, for the ratable
benefit of the Secured Parties, their successors and assigns, a security
interest in and lien on all of the New Subsidiary’s right, title and interest in
and to the Collateral (as defined in the Guarantee and Collateral Agreement) of
the New Subsidiary. Each reference to a “Grantor” or a “Subsidiary Guarantor” in
the Guarantee and Collateral Agreement shall be deemed to include the New
Subsidiary. The Guarantee and Collateral Agreement is hereby incorporated herein
by reference.

SECTION 2. The New Subsidiary represents and warrants to the Agent and the other
Secured Parties that this Supplement has been duly authorized, executed and
delivered by it and constitutes its legal, valid and binding obligation,
enforceable against it in accordance with its terms subject to applicable
bankruptcy, insolvency or similar laws affecting creditors’ rights generally and
to general principles of equity.

SECTION 3. This Supplement may be executed in counterparts (and by different
parties hereto on different counterparts), each of which shall constitute an
original, but all of which when taken together shall constitute a single
contract. This Supplement shall become effective when the Agent shall have
received counterparts of this Supplement that, when taken together, bear the
signatures of the New Subsidiary and the Agent. Delivery of an executed
signature page to this Supplement by facsimile or other electronic transmission
shall be as effective as delivery of a manually signed counterpart of this
Supplement.

SECTION 4. The New Subsidiary hereby represents and warrants that (a) set forth
on Schedule I attached hereto is a true and correct schedule of all leased and
owned real property of the New Subsidiary and each other location where any
Collateral of the New Subsidiary with a value in excess of $300,000 is stored or
otherwise located, set forth on Schedule II is a true and correct schedule of
the Pledged Collateral of the New Subsidiary and set forth on Schedule III is a
true and correct schedule of the Intellectual Property of the New Subsidiary,
and (b) set forth under its signature hereto, is the true and correct legal name
of the New Subsidiary, its jurisdiction of formation and the location of its
chief executive office.

SECTION 5. Except as expressly supplemented hereby, the Guarantee and Collateral
Agreement shall remain in full force and effect.

SECTION 6. THIS SUPPLEMENT SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE
WITH, THE LAWS OF THE STATE OF NEW YORK.

SECTION 7. In case any one or more of the provisions contained in this
Supplement should be held invalid, illegal or unenforceable in any respect, the
validity, legality and enforceability of the remaining provisions contained
herein and in the Guarantee and Collateral Agreement shall not in any way be
affected or impaired thereby (it being understood that the invalidity of a
particular provision in a particular jurisdiction shall not in and of itself

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affect the validity of such provision in any other jurisdiction). The parties
hereto shall endeavor in good-faith negotiations to replace the invalid, illegal
or unenforceable provisions with valid provisions the economic effect of which
comes as close as possible to that of the invalid, illegal or unenforceable
provisions.

SECTION 8. All communications and notices hereunder shall be in writing and
given as provided in Section 7.01 of the Guarantee and Collateral Agreement. All
communications and notices hereunder to the New Subsidiary shall be given to it
at the address set forth under its signature below.

SECTION 9. The New Subsidiary agrees to reimburse the Agent for its reasonable
out-of-pocket expenses in connection with this Supplement, including the
reasonable fees, other charges and disbursements of counsel for the Agent.

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IN WITNESS WHEREOF, the New Subsidiary and the Agent have duly executed this
Supplement to the Guarantee and Collateral Agreement as of the day and year
first above written.

 

AERO-INSTRUMENTS CO., LLC, as the New
Subsidiary by  

/s/ Gregory Rufus

  Name: Gregory Rufus   Title: Treasurer and Secretary  

Address: 14901 Emery Avenue

  Cleveland, Ohio 44135

  Legal Name: Aero-Instruments Co., LLC   Jurisdiction of Formation: Ohio  

Location of Chief

Executive Office: 14901 Emery Avenue

Cleveland, Ohio 44135

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CREDIT SUISSE AG, CAYMAN

ISLANDS BRANCH, as Agent

by  

/s/ Robert Hetu

  Name: Robert Hetu   Title:   Managing Director by  

/s/ Kevin Buddhdew

  Name: Kevin Buddhdew   Title:   Associate

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Schedule I

Subsidiary Guarantors

 

Exact Legal Name

  

Jurisdiction

  

Organizational

Identification

Number

  

Federal Taxpayer

Identification

Number

Aero-Instruments Co., LLC

   Ohio    1242087    34-1961289

Locations of Collateral

 

  1. 14835 Emery Avenue, Cleveland, Ohio.

 

  2. 14901 Emery Avenue, Cleveland, Ohio.

 

  3. 1324 Hird Avenue, Lakewood, Ohio.

 

  4. 4081 W. 150th Street, Cleveland, Ohio.

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Schedule II

Capital Stock

None

Pledged Debt Securities

None

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Schedule III

Intellectual Property

Patents

 

COUNTRY

 

PATENT TITLE

 

PATENT NO.

 

ISSUE DATE

U.S.

  NOSE SECTION FOR A PITOT PROBE   7,549,331 B1   6/23/09

U.S.

  TEMPERATURE PROBE   8,100,582 B1   1/24/12

Trademarks

 

COUNTRY

 

TRADEMARK

 

APPL. NO.

 

APPL. DATE

 

REG. NO.

 

REG. DATE

U.S.

  FLY TRUE   77/215,267   6/26/07   3,437,419   5/27/08

U.S.

  AERO-INSTRUMENTS & DESIGN   77/223,165   7/6/07   3,465,951   7/15/08

Copyrights

None

Licenses

 

LICENSED PRODUCT

 

EFFECTIVE DATE

 

EXPIRATION DATE

 

LICENSOR NAME

ANSYS FLUENT

  9/28/11   9/27/12   ANSYS, Inc.

ANSYS Geometry Interface for Creo Parametric

  9/28/11   9/27/12   ANSYS, Inc.

ANSYS DesignModeler

  9/28/11   9/27/12   ANSYS, Inc.

ANSYS HPC Pack

  9/28/11   9/27/12   ANSYS, Inc.

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Schedule IV

Commercial Tort Claims

None.