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                                                                    EXHIBIT 3.23

                          CERTIFICATE OF INCORPORATION

                                       OF

                             UNITED JET CENTER, INC.


                  I, THE UNDERSIGNED, in order to form a corporation for the
purposes hereinafter stated, under and pursuant to the provisions of the General
Corporation Law of the State of Delaware, do hereby certify as follows:

                  FIRST: The name of the corporation is

                             UNITED JET CENTER, INC.

                  SECOND: Its registered office is to be located at 229 South
State Street, in the City of Dover, in the County of Kent, in the State of
Delaware. The name of its registered agent at that address is The Prentice-Hall
Corporation System, Inc.

                  THIRD: The purpose of the corporation is to engage in any
lawful act or activity for which corporations may be organized under the General
Corporation Law of Delaware.

                  FOURTH: The total number of shares of stock which the
corporation is authorized to issue is one thousand (1,000) shares, and the par
value of each of such shares is one dollar ($1.00).

                  FIFTH: The name and address of the single incorporator is:

                     Madeline A. Stirber                 250 Park Avenue
                                                         New York, NY 10177

                  SIXTH: The By-Laws of the corporation may be made, altered,
amended, changed, added to or repealed by the Board of Directors without the
assent or vote of the stockholders. 
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Elections of directors need not be by ballot unless the By-Laws so provide.

                  SEVENTH: No director of the corporation shall be personally
liable to the corporation or to any of its stockholders for monetary damages for
breach of fiduciary duty as a director, provided that this Article SEVENTH shall
not eliminate or limit the liability of a director (i) for any breach of the
director's duty of loyalty to the corporation or its stockholders, (ii) for acts
or omissions not in good faith or which involve intentional misconduct or a
knowing violation of law, (iii) under Section 174 of the General Corporation Law
of Delaware, or (iv) for any transaction from which the director derived an
improper benefit.
                  EIGHTH: The corporation reserves the right to amend, alter,
change or repeal any provision contained in this certificate in the manner now
or hereafter prescribed by law, and all rights and powers conferred herein on
stockholders, directors and officers are subject to this reserved power.

                  IN WITNESS WHEREOF, I have hereunto set my hand and seal the
14th day of March, 1989.


                                              /s/  Madeline A. Stirber
                                         --------------------------------------
                                                 Madeline A. Stirber

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                            CERTIFICATE OF AMENDMENT

                                       OF

                          CERTIFICATE OF INCORPORATION

                                       OF

                             UNITED JET CENTER, INC.


                  Pursuant to the provisions of the General Corporation Law of
the State of Delaware, the undersigned hereby amend the Certificate of
Incorporation as follows:

FIRST:            The name of the Corporation is United Jet Center, Inc.

SECOND:           The Certificate of Incorporation was filed on March 16, 1989.

THIRD:            The Certificate of Incorporation shall be amended by adding a
                  new Article NINTH to the end thereof to read in its entirety
                  as follows:

                           "NINTH: The Corporation shall, to the fullest extent
                  permitted by Section 145 of the General Corporation Law of the
                  State of Delaware, as the same shall be amended and
                  supplemented, indemnify any and all persons whom it shall have
                  power to indemnify under said Section from and against any and
                  all of the expenses, liabilities or other matters referred to
                  in or covered by said Section, and the indemnification
                  provided for herein shall not be deemed exclusive of any other
                  rights to which those indemnified may be entitled under any
                  By-law, agreement, vote of shareholders or disinterested
                  directors or otherwise, both as to action in his official
                  capacity and as to action in another capacity while holding
                  such office and shall continue as to a person who has ceased
                  to be a director, officer, employee, or agent and shall inure
                  to the benefit of the heirs, executors and administrators of
                  such a person."

FOURTH:           The above amendment to the Certificate of Incorporation was
                  authorized and approved by the sole director and sole
                  stockholder of the Corporation pursuant to the provisions of
                  Section 242 of the General Corporation Law.
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                  We have subscribed this Certificate of Amendment to the
Certificate of Incorporation this 23rd day of October, 1989 and affirm the
statements contained herein are true under the penalties of perjury and that the
statements contained therein have been examined by us and are true and correct,
and that this Certificate of Amendment is the act and deed of the Corporation.


                                            /s/  John Catsimatidis
- -------------------                         -----------------------------------
                                            John Catsimatidis
                                            President




Attest:



/s/  James Devaney
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James Devaney, Secretary