<PAGE>   1







                                 EXHIBIT 10.6(d)

                  Amendment effective May 15, 1998, amending the Employment
                  Agreement between the Registrant and Michael Rubin, dated
                  February 8, 1990, as amended.


<PAGE>   2




                                  AMENDMENT TO
                              EMPLOYMENT AGREEMENT

         WHEREAS, Michael Rubin (the "Executive") and Hudson General
     Corporation, a Delaware corporation (the "Company"), entered into an
     Employment Agreement as of February 8, 1990, as amended from time to time
     (the "Agreement"); and

         WHEREAS, the Executive and the Company wish to further amend the 
     Agreement in certain respects;

         NOW, THEREFORE, for good and valuable consideration, the receipt of
     which is hereby acknowledged, the Executive and the Company agree that the
     Agreement shall be amended, effective as of May 15, 1998, as set forth
     herein.

         Unless otherwise defined herein, capitalized terms used herein shall
     have the meaning ascribed to such terms in the Agreement.

         1. Section 5(c) of the Agreement is hereby amended by adding the
     following new sentence after the first sentence thereof:

                  Without limiting the generality of the foregoing, the
                  Executive shall be entitled to (i) participate in (A) the
                  Company's Executive Incentive Bonus Program and (B) any plan
                  which is adopted as a replacement for the Executive Incentive
                  Bonus Program, and (ii) a percentage of the total allocation
                  under such plan with respect to a given year (the "Measurement
                  Year") which is no less than the average percentage of the
                  total allocation under any such plan (or any predecessor
                  thereto) with respect to the three years immediately prior to
                  the Measurement Year.



<PAGE>   3



         2. The second sentence of Section 7(a) of the Agreement is hereby
amended and restated to read as follows:

                  In addition, the Company shall make payments in substantially
                  equal periodic installments in accordance with the Company's
                  payroll practices then in effect for twelve months following
                  the Executive's date of death, which payments shall equal, in
                  the aggregate, the sum of (i) the Executive's Salary as in
                  effect on the date of the Executive's death and (ii) the
                  average of the annual bonuses (including awards under the
                  Company's Executive Incentive Bonus Program and any plan which
                  replaces it) earned by the Executive pursuant to any annual
                  bonus or incentive plan maintained by the Company in respect
                  of the three fiscal years ending immediately prior to the
                  fiscal year in which occurs the date of the Executive's death.

         3. Section 8(a) of the Agreement is hereby amended and restated to read
as follows:

                           (a) Severance payments made to the Executive pursuant
                  to Section 7(d) hereof shall continue for a period of 24
                  months following the Termination Date. Severance payments made
                  to the Executive pursuant to Section 7(e) hereof shall
                  continue for a period equal to the greater of (i) 24 months or
                  (ii) the period from the Termination Date to the Expiration
                  Date. The period during which severance payments are to be
                  made by the Company to the Executive as determined in this
                  subsection (a) is referred to herein as the "Severance Payment
                  Period." During the Severance Payment Period, the Company
                  shall make severance payments to the Executive, which payments
                  shall equal, in the aggregate, the product of (i) the
                  multiplier obtained by dividing the number of full months in
                  the Severance Payment Period by 12 multiplied by (ii) the sum
                  of (A) the Executive's Salary as in effect on the Termination
                  Date and (B) the average of the annual bonuses (including
                  awards under the Company's Executive Incentive Bonus Program
                  and any plan


<PAGE>   4



                  which replaces it) earned by the Executive pursuant to any
                  annual bonus or incentive plan maintained by the Company in
                  respect of the three fiscal years ending immediately prior to
                  the fiscal year in which occurs the Termination Date.
                  Severance payments shall be paid to the Executive in
                  substantially equal periodic installments in accordance with
                  the Company's payroll practices then in effect. In the event
                  of the death of the Executive during the Severance Payment
                  Period, then notwithstanding anything to the contrary
                  contained herein, the Severance Payment Period shall terminate
                  at the earlier of (x) twelve months following the date of
                  death or (y) the scheduled expiration of the Severance Payment
                  Period. The Executive may, at any time and at his sole
                  discretion, upon written notice to the Company, terminate the
                  Severance Payment Period, whereupon the Company shall have no
                  further obligations to the Executive to make severance
                  payments or provide benefits pursuant to Section 9 hereof that
                  were required to be provided during the Severance Payment
                  Period.

                  Except as amended hereby, the Agreement shall remain in full 
         force and effect.

                  IN WITNESS WHEREOF, the Company has caused this Amendment to 
         be executed by a duly authorized officer of the Company, and Executive
         has executed this Amendment, on this ____ day of ________, 1998,
         effective as of May 15, 1998.


                                    HUDSON GENERAL CORPORATION

                                    By:_______________________
                                       Name:  Jay B. Langner
                                       Title: Chief Executive
                                              Officer

                                    __________________________
                                          Michael Rubin