<PAGE>   1
                                                                  EXHIBIT 10.50


                               JOINDER AGREEMENT

         THIS JOINDER AGREEMENT (the "AGREEMENT"), dated as of January 15,
1999, is by and between SOLAIR, INC., a Florida corporation (the "APPLICANT
BORROWER"), KELLSTROM INDUSTRIES, INC., a Delaware corporation, as agent for
the Borrowers ("KELLSTROM") , the financial institutions party from time to
time to the below-referenced Loan Agreement, and NATIONSBANK, N.A., as agent
for the Lenders (the "AGENT"), under that certain Amended and Restated Loan and
Security Agreement (as amended and modified, the "LOAN AGREEMENT"), dated as of
December 14, 1998, by and among Kellstrom and certain related borrowing
entities (the "BORROWERS"), the Lenders and the Agent. All of the defined terms
in the Loan Agreement are incorporated herein by reference.

         The Applicant Borrower has indicated its desire to become a Borrower
pursuant to the terms of the Loan Agreement.

         Accordingly, the Applicant Borrower hereby agrees as follows with the
Agent and the Lenders:

         1. The Applicant Borrower hereby acknowledges, agrees and confirms
that, by its execution of this Agreement, the Applicant Borrower will be deemed
to be a party to the Loan Agreement and a "Borrower" for all purposes of the
Loan Agreement and the other Loan Documents and a co-maker of each of the
Notes, and shall have all of the obligations of a Borrower thereunder as if it
had executed the Loan Agreement and the other Loan Documents. The Applicant
Borrower hereby ratifies, as of the date hereof, and agrees to be bound by, all
of the terms, provisions and conditions contained in the Loan Agreement and in
the Loan Documents which are binding upon the Borrowers, including, without
limitation (a) all of the representations and warranties of the Borrowers set
forth in Article 6 of the Loan Agreement, as supplemented from time to time in
accordance with the terms thereof, and (b) all of the covenants set forth in
Articles 7, 8, 9, 10 and 11 of the Loan Agreement.

         2. Without limiting the generality of the foregoing terms of paragraph
1, the Applicant Borrower hereby grants to the Agent for the benefit of the
Secured Parties a continuing security interest in, and a right of set off
against, any and all right, title and interest of the Applicant Borrower in and
to the Collateral (as such term is defined in Section 1.1 of the Loan
Agreement) of the Applicant Borrower.

<PAGE>   2


         3. The Applicant Borrower acknowledges and confirms that it has
received a copy of the Loan Agreement and the Schedules and Exhibits thereto.
The Schedules to the Loan Agreement are amended to include the information
shown on the attached SCHEDULE A.

         4. Kellstrom confirms that all of the other Borrowers' obligations
under the Loan Agreement are, and upon the Applicant Borrower becoming a
Borrower shall continue to be, in full force and effect. Kellstrom further
confirms that immediately upon the Applicant Borrower becoming a Borrower the
term "Secured Obligations", as used in the Loan Agreement, shall include all
Secured Obligations of such Applicant Borrower under the Loan Agreement and
under each other Loan Document.

         5. Each of Kellstrom and the Applicant Borrower agrees that at any
time and from time to time, upon the written request of the Agent, it will
execute and deliver such further documents and do such further acts and things
as the Agent may reasonably request in order to effect the purposes of this
Agreement.

         6. This Agreement may be executed in two or more counterparts, each of
which shall constitute an original but all of which when taken together shall
constitute one contract.

         7. This Agreement shall be governed by and construed and interpreted
in accordance with the laws of the State of Georgia.


                                      -2-

<PAGE>   3


         IN WITNESS WHEREOF, each of Kellstrom and the Applicant Borrower has
caused this Agreement to be duly executed by its authorized officers, and the
Agent has caused the same to be accepted by its authorized officer, as of the
day and year first above written.

                                  Solair, Inc.


                                  By:
                                      -----------------------------------------

                                  Name: 
                                       ----------------------------------------

                                  Title:                      
                                         --------------------------------------


                                  KELLSTROM INDUSTRIES, INC., for itself and 
                                  for the other Borrowers



                                  By:
                                      -----------------------------------------

                                  Name: 
                                       ----------------------------------------

                                  Title:                      
                                         --------------------------------------


                                  NATIONSBANK, N.A., as Agent for itself and 
                                  for the other Lenders

                                  By:
                                      -----------------------------------------

                                  Name: 
                                       ----------------------------------------

                                  Title:                      
                                         --------------------------------------

                                      -3-


<PAGE>   4


                                   SCHEDULE A


<PAGE>   5


                         NOTARY JURAT FOR EXECUTION OF
                        WRITTEN OBLIGATIONS TO PAY MONEY
                              BY FLORIDA BORROWERS

         On this the ____ day of _____________, 199_, before me, the
undersigned, a Notary Public in and for the State of _______________, County of
_____________, Michael W. Wallace personally appeared, personally known to me
or proved to me on the basis of satisfactory evidence to be the Vice President
of Solair, Inc., a Florida corporation, who, being by me first duly sworn,
stated that:

1.   He executed the foregoing Joinder Agreement on behalf of Solair, Inc.
     pursuant to its by-laws or a resolution of its board of directors, said
     execution taking place in the State of _______________, County of
     _____________; and

2.   He has this day delivered the foregoing instrument to NationsBank, N.A.,
     as agent for the Lenders, at Fulton County, Georgia.

                                               Signature of Borrower's Officer:

                                               By:                             
                                                  -----------------------------
                                                  Michael W. Wallace


Sworn to and subscribed before me this ___ day of _____________, 199_:


----------------------------------
        Notary Signature


My Commission Expires:


---------------------------------

     [Affix Notarial Seal]


<PAGE>   6



                         NOTARY JURAT FOR EXECUTION OF
                        WRITTEN OBLIGATIONS TO PAY MONEY
                              BY FLORIDA BORROWERS

         On this the ____ day of ____________, 199_, before me, the
undersigned, a Notary Public in and for the State of _______________, County of
_____________, Michael W. Wallace personally appeared, personally known to me
or proved to me on the basis of satisfactory evidence to be the Chief Financial
Officer of Kellstrom Industries, Inc., a Delaware corporation, who, being by me
first duly sworn, stated that:

1.   He executed the foregoing Joinder Agreement on behalf of Kellstrom
     Industries, Inc., as agent for the Borrowers, pursuant to its by-laws or a
     resolution of its board of directors, said execution taking place in the
     State of _______________, County of _____________; and

2.   He has this day delivered the foregoing instrument to NationsBank, N.A.,
     as agent for the Lenders, at Fulton County, Georgia.

                                              Signature of Borrower's Officer:

                                              By:                            
                                                 ------------------------------
                                                       Michael W. Wallace


Sworn to and subscribed before me this ___ day of _____________, 199_:


----------------------------------
          Notary Signature


My Commission Expires:

---------------------------------

      [Affix Notarial Seal]


<PAGE>   7





                          AFFIDAVIT REGARDING DELIVERY

         On this the ____ day of ______________, 199_, before me, the
undersigned, a Notary Public in and for the State of Georgia, County of Cobb,
M. Steven Liff personally appeared, personally known to me or proved to me on
the basis of satisfactory evidence to be a Vice President of NationsBank, N.A.,
who, being by me first duly sworn, stated that NationsBank, N.A. has received
delivery of the foregoing Joinder Agreement in the State of Georgia, County of
Fulton.

                                     ----------------------------------------
                                     Signature of Officer of NationsBank, N.A.


Sworn to and subscribed before me this ___ day of ________________, 1999:


----------------------------------
         Notary Signature


My Commission Expires:

---------------------------------

       [Affix Notarial Seal]