Exhibit
10.15


February 24, 2006


W. Nicholas Howley

Chief Executive Officer

TransDigm Group Incorporated

1301 East 9th Street, Suite 3710

Cleveland, Ohio 44114


Dear Nick:


The purpose of this letter is to confirm our
mutual understanding regarding the interpretation of the Company’s Third
Amended and Restated Stock Option Plan (the “Plan”) as it relates to the
potential vesting of stock options upon the occurrence of a change in control
or other sale event.


As was agreed upon by you, Warburg Pincus Private
Equity VIII, L.P. (“Warburg Pincus”) and the Company at the time the Plan was
initially conceived, the vesting provision contained Section 8(b)(ii)(C) was
intended to apply “upon a change of control or other sale if the investors
received a [specified] return on their invested equity....”  The determining factor in each event is the
extent to which the Warburg Pincus and its investor group has realized the
targeted NRR (as described in the Plan) on the shares of the Company acquired
on July 22, 2003 (with respect to such shares, Warburg Pincus and its investor
group are referred to below as the “Investor Group”).  This understanding was memorialized in a
letter dated June 6, 2003, stating the intentions of the parties, from Warburg
Pincus to Mr. W. Nicholas Howley, then President and Chief Executive Officer of
TransDigm Holding Company.  This letter
was signed by both Warburg Pincus and Mr. Howley.


The Compensation Committee of the Board of
Directors has reviewed the intentions of the parties and, by this letter, as the
administrator of the Plan, is confirming that the NRR vesting provisions
contained in Section 8(b)(ii)(C) apply to any sale of Company stock by members
of the Investor Group.


Specifically, including for purposes of
making clear the mechanics of implementing this understanding, the Compensation
Committee has determined that:  if the
NRR equals, or is in excess of, 25% upon any sale of stock by the Investor
Group on the shares so sold, a percentage (not to exceed 100%) of the unvested
Performance Vested Options as of the date of this letter (the “Unvested
Performance Vested Options”) equal to the shares then sold by the Investor
Group as a percentage of all outstanding shares of stock of the Company
originally acquired by the Investor Group shall vest.  If the NRR is 20%, a percentage (not to
exceed 100%) of the Unvested Performance Vested Options as of the date of this
letter equal to the shares then sold by the Investor Group as a percentage of
all outstanding shares of stock of the Company originally acquired by the
Investor Group, multiplied by .75, shall vest. 
For each additional 1% of NRR in excess of 20% (to and including 24.9%)
earned on shares sold by the Investor Group, an additional percentage (not to
exceed 100%) of the Unvested Performance Vested Options as of the date of this
letter equal to the shares then sold by the Investor Group as a percentage of
all outstanding shares of stock of the Company originally acquired by the
Investor Group, multiplied by .05, shall vest. 
The foregoing is intended to apply in the event of distributions of
stock to the Investor Group’s respective partners and limited partners, but not
in the event of any direct or indirect distributions from any investment
vehicle in which the Investor Group holds Company stock to the members of such
Investor Group in proportion to their ownership position in such investment
vehicle.


The understanding addressed in this letter
does not amend or modify any provision contained in the Plan.


Sincerely,


/s/ David Barr


David Barr


Member of the Compensation Committee

of the Board of Directors of TransDigm Group Incorporated