Under the Securities Exchange Act of 1934
(Amendment No. 4)*

(Name of Issuer)

(Title of Class of Securities)

(CUSIP Number)

(Name, Address and Telephone Number of Person
Authorized to Receive Notices and Communications)

(Date of Event Which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box. o

Note: Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See Rule 13d-7 for other parties to whom copies are to be sent.

^* The remainder of this cover page shall be filled out for a reporting person's initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

SCHEDULE 13D

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SCHEDULE 13D

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SCHEDULE 13D

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SCHEDULE 13D

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SCHEDULE 13D

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Introduction.

This Amendment No. 4 to Schedule 13D (this “Amendment”) amends the Schedule 13D filed with the Securities and Exchange Commission on March 30, 2006, as amended by Amendment No. 1 thereto filed with the Securities and Exchange Commission on May 29, 2007, amended by Amendment No. 2 thereto filed with the Securities and Exchange Commission on November 29, 2007 and further amended by Amendment No. 3 thereto filed with the Securities and Exchange Commission on December 12, 2007 (as so amended, the “Current Schedule 13D”), on behalf of TD Group Holdings, LLC, a Delaware limited liability company (“TD LLC”), Warburg Pincus Private Equity VIII, L.P., a Delaware limited partnership (together with two affiliated entities, “WP VIII”), Warburg Pincus LLC, a New York limited liability company (“WP LLC”), Warburg Pincus & Co., a New York general partnership (“WP”), and Warburg Pincus Partners, LLC, a New York limited liability company and a subsidiary of WP (“WP Partners LLC”, and together with WP VIII, WP LLC and WP, the “Warburg Pincus Reporting Persons”).  Charles R. Kaye and Joseph P. Landy are each Managing General Partners of WP and Co-Presidents and Managing Members of WP LLC.  This Amendment relates to the common stock, par value $0.01 per share (the “Common Stock”), of TransDigm Group Incorporated, a Delaware corporation (the “Company”).

TD LLC and the Warburg Pincus Reporting Persons (together with TD LLC, the “Reporting Persons”) are making this single, joint filing because they may be deemed to constitute a “group” within the meaning of Section 13(d)(3) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”).  Each Reporting Person disclaims

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beneficial ownership of all shares of Common Stock to which such Reporting Person does not have a pecuniary interest.

Unless otherwise indicated herein, each capitalized term used but not otherwise defined herein shall have the meaning ascribed to such term in the Current Schedule 13D.

Item 5.                                                         Interest in Securities of the Issuer.

Item 5 of the Current Schedule 13D is hereby amended and replaced in its entirety as set forth below.

(a)                                On May 12, 2008, TD LLC distributed an aggregate of 3,027,636 shares of Common Stock to its members (the “TD LLC Distribution”).  The TD LLC Distribution was made on a pro rata basis to all members of TD LLC and no consideration was received by TD LLC in connection therewith.   WP VIII is a member of TD LLC and, in connection with the TD LLC Distribution, received an aggregate of 2,556,509 shares of Common Stock.  Immediately following the completion of the TD LLC Distribution, WP VIII distributed all of the shares of Common Stock received by it in connection with the TD LLC Distribution to its limited partners and WP Partners LLC on a pro rata basis (the “WP Distribution” and, together with the TD LLC Distribution, the “Distributions”).  WP VIII did not receive any consideration in connection with the WP Distribution.

Immediately following the completion of the Distributions, each of the Reporting Persons may be deemed to beneficially own 11,383,201 shares of Common Stock, representing approximately 23.8% of the outstanding Common Stock, based on the 47,882,903 shares of Common Stock outstanding as of April 25, 2008 as reported in the Company’s Form 10-Q filed on May 8, 2008.

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(b)                                 Each of the Reporting Persons share the power to vote or to direct the vote and to dispose or to direct the disposition of the 11,383,201 shares of Common Stock it may be deemed to beneficially own.  The Reporting Persons are making this single, joint filing because they may be deemed to constitute a “person” or “group” within the meaning of Section 13(d)(3) of the Exchange Act.  The filing of this Schedule 13D shall not be construed as an admission of such beneficial ownership or that the Reporting Persons constitute a person or group.

(c)                                  Other than the Distributions, no transactions in the Common Stock were effected by any Reporting Person during the past sixty days.

(d)                                 Not applicable.

(e)                                  Not applicable.

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SIGNATURES

After reasonable inquiry and to the best of our knowledge and belief, the undersigned certify that the information set forth in this statement is true, complete and correct.