EX-99.4

Exhibit 99.4

TRANSDIGM UK HOLDINGS PLC

OFFER TO EXCHANGE

UP TO $500,000,000 IN AGGREGATE PRINCIPAL AMOUNT OF

6.875% SENIOR SUBORDINATED NOTES DUE 2026

FOR

ALL OF ITS OUTSTANDING

6.875% SENIOR SUBORDINATED NOTES DUE 2026

SOLD IN A TRANSACTION EXEMPT FROM REGISTRATION

UNDER THE SECURITIES ACT OF 1933, AS AMENDED

To Securities Dealers, Commercial Banks

Trust Companies And Other Nominees:

Enclosed for your consideration is a Prospectus dated , (as the same may be amended or supplemented from time to time, the “Prospectus”) and a form of Letter of Transmittal (the “Letter of Transmittal”) relating to the offer (the “Exchange Offer”) by TransDigm UK Holdings plc (“Company”) to exchange up to $500,000,000 in aggregate principal amount of its 6.875% Senior Subordinated Notes due 2026 (the “Exchange Notes”) for all of its outstanding 6.875% Senior Subordinated Notes due 2026 (the “Original Notes”), issued and sold in a transaction exempt from registration under the Securities Act of 1933, as amended. Capitalized terms used in this letter and not defined herein shall have the respective meanings ascribed to them in the Prospectus.

We are asking you to contact your clients for whom you hold Original Notes registered in your name or in the name of your nominee. In addition, we ask you to contact your clients who, to your knowledge, hold Original Notes registered in their own name. Company will not pay any fees or commissions to any broker, dealer or other person in connection with the solicitation of tenders pursuant to the Exchange Offer. You will, however, be reimbursed by Company for customary mailing and handling expenses incurred by you in forwarding any of the enclosed materials to your clients. Company will pay all transfer taxes, if any, applicable to the tender of Original Notes to it or its order, except as otherwise provided in the Prospectus and the Letter of Transmittal.

Enclosed are copies of the following documents:

1. The Prospectus;

2. A Letter of Transmittal for your use in connection with the tender of Original Notes and for the information of your clients;

3. A form of letter that may be sent to your clients for whose accounts you hold Original Notes registered in your name or the name of your nominee, with space provided for obtaining the clients’ instructions with regard to the Exchange Offer; and

4. A form of Notice of Guaranteed Delivery.

Your prompt action is requested. The Exchange Offer will expire at 5:00 p.m., New York City time, on , , unless extended (the “Expiration Date”). Original Notes tendered pursuant to the Exchange Offer may be withdrawn, subject to the procedures described in the Prospectus, at any time prior to the Expiration Date.

To tender Original Notes, certificates for Original Notes or a Book-Entry Confirmation, a duly executed and properly completed Letter of Transmittal or a facsimile thereof, and any other required documents, must be received by the Exchange Agent as provided in the Prospectus and the Letter of Transmittal.

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