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
                                                                                  
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Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940
                      
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 (MM/DD/YYYY)
3/15/2021
(Street)
BOSTON, MA 02116
(City)       (State)       (Zip)
4. If Amendment, Date Original Filed (MM/DD/YYYY)
 
6. Individual or Joint/Group Filing (Check Applicable Line) _X _ Form filed by One Reporting Person
___ Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security
(Instr. 3)
2. Trans. Date 2A. Deemed Execution Date, if any 3. Trans. 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  3/15/2021    P    1  A $615.99  2410280  I  By Berkshire Entities (2)(3)
Common Stock                 165688  I  By Stockbridge Partners LLC (1)
Common Stock                 28074  I  By Family Trusts (4)
Common Stock                 50000  I  By Trust (5)
Common Stock                 23251  D (6)  

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivate Security
(Instr. 3)
2. Conversion or Exercise Price of Derivative Security 3. Trans. Date 3A. Deemed Execution Date, if any 4. Trans. 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 7. Title and Amount of Securities Underlying Derivative Security
(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

Explanation of Responses:
(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 VIII, L.P. ("VIII"), Berkshire Fund VIII-A, L.P. ("VIII-A"), Berkshire Fund IX, L.P. ("IX"), Berkshire Fund IX-A, L.P. ("IX-A"), 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 VIII, VIII-A, IX, IX-A, Investors III and Investors IV ("BP"), and SP, the registered investment adviser to SF and SARF. Eighth Berkshire Associates LLC ("8BA") is the general partner of each of VIII and VIII-A. Ninth Berkshire Associates LLC ("9BA") is the general partner of each of IX and IX-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, 9BA, SA, 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)  Represents shares of 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.
(5)  Represents shares of 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.
(6)  Represents shares of Common Stock held directly by the Reporting Person.

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 3/17/2021
**Signature of Reporting Person Date