Ownership Submission
FORM 4
Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).
UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940
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(Print or Type Responses)
1. Name and Address of Reporting Person *
SMALL ROBERT J
  2. Issuer Name and Ticker or Trading Symbol
TransDigm Group INC [TDG]
5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
__X__ Director _____ 10% Owner
_____ Officer (give title below) _____ Other (specify below)
(Last)
(First)
(Middle)
C/O BERKSHIRE PARTNERS LLC, 200 CLARENDON STREET, 35TH FLOOR
3. Date of Earliest Transaction (Month/Day/Year)
02/20/2019
(Street)

BOSTON, MA 02116
4. If Amendment, Date Original Filed(Month/Day/Year)
6. Individual or Joint/Group Filing(Check Applicable Line)
_X_ Form filed by One Reporting Person
___ Form filed by More than One Reporting Person
(City)
(State)
(Zip)
Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security
(Instr. 3)
2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code
(Instr. 8)
4. Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5)
5. Amount of Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 3 and 4)
6. Ownership Form: Direct (D) or Indirect (I)
(Instr. 4)
7. Nature of Indirect Beneficial Ownership
(Instr. 4)
Code V Amount (A) or (D) Price
Common Stock 02/20/2019   S   32,881 D $ 433.25 294,800 I By Stockbridge Partners LLC (1)
Common Stock 02/20/2019   S   104,119 D $ 433.25 3,181,940 I By Berkshire Entities (2) (3) (4)
Common Stock 02/20/2019   S   174,734 D $ 434.895 3,007,206 I By Berkshire Entities (2) (3) (4)
Common Stock 02/20/2019   S   55,206 D $ 434.895 239,594 I By Stockbridge Partners LLC (1)
Common Stock 02/20/2019   P   229,940 A $ 434.895 3,237,146 I By Berkshire Entities (2) (3) (5)
Common Stock               6,113 I By Family Trusts (6)
Common Stock               16,765 I By Trust (7)
Common Stock               37,175 D  

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security
(Instr. 3)
2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (Month/Day/Year) 3A. Deemed Execution Date, if any (Month/Day/Year) 4. Transaction Code
(Instr. 8)
5. Number of Derivative Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4, and 5)
6. Date Exercisable and Expiration Date
(Month/Day/Year)
7. Title and Amount of Underlying Securities
(Instr. 3 and 4)
8. Price of Derivative Security
(Instr. 5)
9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 4)
10. Ownership Form of Derivative Security: Direct (D) or Indirect (I)
(Instr. 4)
11. Nature of Indirect Beneficial Ownership
(Instr. 4)
Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares

Reporting Owners

Reporting Owner Name / Address Relationships
 Director  10% Owner  Officer  Other
SMALL ROBERT J
C/O BERKSHIRE PARTNERS LLC
200 CLARENDON STREET, 35TH FLOOR
BOSTON, MA 02116
  X      

Signatures

 /s/ Robert J. Small   02/22/2019
**Signature of Reporting Person Date

Explanation of Responses:

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1) Represents shares held by Stockbridge Partners LLC ("SP") on behalf of a managed account over which it has shared voting and sole dispositive power. This Form 4 has been filed because the Reporting Person is a director of the Issuer and a managing member of SP. As such, the Reporting Person may be deemed to share voting and dispositive power with respect to the shares of the Issuer's common stock held by SP. However, the Reporting Person disclaims beneficial ownership of these shares, except to the extent, if any, of his pecuniary interest therein, and the inclusion of these securities in this report shall not be deemed an admission of beneficial ownership of the reported securities for purposes of Section 16 or for any other purposes.
(2) Represents shares held directly or indirectly by Berkshire Fund VII, L.P. ("VII"), Berkshire Fund VII-A, L.P. ("VII-A"), Berkshire Fund VIII, L.P. ("VIII"), Berkshire Fund VIII-A, L.P. ("VIII-A"), Berkshire Investors LLC ("Investors"), Berkshire Investors III LLC ("Investors III"), Berkshire Investors IV LLC ("Investors IV"), Stockbridge Fund, L.P. ("SF") and Stockbridge Absolute Return Fund, L.P. ("SARF") (collectively, the "Berkshire Entities"). Berkshire Partners Holdings LLC ("BPH") is the general partner of BPSP, L.P. ("BPSP"), which is the managing member of each of Berkshire Partners LLC, the registered investment adviser to VII, VII-A, VIII, VIII-A, Investors, Investors III and Investors IV ("BP"), and SP, the registered investment adviser to SF and SARF. Seventh Berkshire Associates LLC ("7BA") is the general partner of each of VII and VII-A. Eighth Berkshire Associates LLC ("8BA") is the general partner of each of VIII and VIII-A.
(3) [Continued from Footnote 2] Stockbridge Associates LLC ("SA") is the general partner of each of SF and SARF. The Reporting Person is a managing member of each of BPH, BPSP, BP, SP, 8BA, 7BA, SA, Investors, Investors III and Investors IV. As such, the Reporting Person may be deemed to share voting and dispositive power with respect to the shares of the Issuer's common stock held by the Berkshire Entities. However, the Reporting Person disclaims beneficial ownership of these shares, except to the extent, if any, of his pecuniary interest therein, and the inclusion of these securities in this report shall not be deemed an admission of beneficial ownership of the reported securities for purposes of Section 16 or for any other purposes.
(4) On February 20, 2019, SF and SARF sold 278,805 and 48 shares, respectively, of the Issuer's common stock.
(5) On February 20, 2019, VIII, VIII-A, Investors III and Investors IV indirectly purchased an aggregate of 149,571, 62,148, 3,865 and 14,356 shares, respectively, of the Issuer's common stock.
(6) Represents shares of the Issuer's common stock beneficially owned by certain family trusts. The Reporting Person is a trustee and the Reporting Person's immediate family members are beneficiaries of such family trusts.
(7) Represents shares of the Issuer's common stock beneficially owned by a trust. The Reporting Person is a trustee and the Reporting Person's immediate family members are beneficiaries of such trust.

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