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                                                                Exhibit 10.13(a)

               AMENDMENT NUMBER 1 TO PURCHASE AGREEMENT GCT-025/98

This Amendment Number 1 To Purchase Agreement GCT-025/98, dated as of November
12th, 1998 ("Amendment No.1") relates to the Purchase Agreement GCT-025/98
between EMBRAER-Empresa Brasileira de Aeronautica S.A. ("EMBRAER") and Solitair
Corp. ("SOLITAIRBUYER") (the "Purchase Agreement"), dated June 17, 1998. This
Amendment No.1 is between EMBRAER and BUYER, collectively referred to herein as
the "Parties".

This Amendment No.1 constitutes an amendment and modification regarding the
incorporation of Changes and other modifications, pursuant to Article 11, items
"a" and "g" of the Purchase Agreement. All terms defined in the Purchase
Agreement and not defined herein shall have the meaning given in the Purchase
Agreement when used herein, and in case of any conflict between this Amendment
No.1 and the Purchase Agreement, this Amendment No.1 shall control.

NOW, THEREFORE, in consideration of the foregoing, EMBRAER and BUYER do hereby
agree as follows:

1.    CONFIGURATION CHANGES

      1.1   Item 2.1 of Attachment A to the Purchase Agreement, "OPTIONS TO THE
            STANDARD AVIONICS CONFIGURATION" is hereby amended to read as
            follows:

          " a)    CAT-II
            b)    2nd Radio Altimeter
            c)    2nd DME
            d)    2nd ADF
            e)    2nd Transponder Mode S
            f)    Selcal - Trimble
            g)    FMS/GPS - Honeywell
            h)    EGPWS
            i)    VHF (1st and 2nd) 8,33 khz spacing"

      1.2   Item 2.2 of Attachment A to the Purchase Agreement, "OPTIONAL
            SYSTEM/OTHER EQUIPMENT" is hereby amended by inserting after item
            "b" the following:

            ".....
            c)    Cockpit Floodlight
            d)    External Painting (with capability to be reverted to polished)
            e)    Service Door Sill Protection
            f)    Cargo Door Sill Protection
            g)    Cargo Door Light"

      1.3   Item 2.3 of Attachment A to the Purchase Agreement, "INTERIOR
            OPTIONAL ITEMS" is hereby amended to read as follows:

          " a) Interior Option 1
            b)    Audio Entertainment (CD player)

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            c)    2nd Attendant kit (include Handset/Cradle)
            d)    Blue Sterile Light
            e)    Baggage Compartment Class C
            f)    Standard main door
            g)    Passenger Seats - Customized Cushion Version Top w/
                  Ultra-leather
            h)    Baggage Restraint Net
            i)    Extra Oxygen Mask (3 mask for each double seat)"

      1.4   The Aircraft Basic Price described in Article 3 of the Purchase
            Agreement will be increased in the amount of US$ 455,532.00 (Four
            hundred fifty five thousand five hundred thirty two United States
            dollars) in July 1997 economic conditions.

2.    MISCELLANEOUS

All other provisions of the Purchase Agreement which have not been specifically
amended or modified by this Amendment shall remain valid in full force and
effect without any change.

IN WITNESS WHEREOF, EMBRAER and BUYER, by their duly authorized officers, have
entered into and executed this Amendment No.1 to be effective as of the date
first written above.

EMBRAER - Empresa Brasileira de                  Solitair Corp.
Aeronautica S.A.

By   /s/ Frederico Fleury Curado                 By  /s/ Frederick Simon
     ----------------------------                    ----------------------

Name:  Frederico Fleury Curado                   Name  Frederick Simon
     ----------------------------                     ---------------------

Title: E.V.P.--Commercial                        Title: President
     ----------------------------                      --------------------

By  /s/ Satoshi Yokota                           Date:  11-24-98
    -----------------------------                      --------------------

Name:  /s/ Satoshi Yokota                        Place: Greenwich, CT
    -----------------------------                      --------------------

Title: E.V.P.--Industrial
      ---------------------------

Date: November 24, 1998
      ---------------------------

Place: Sao Jose dos Campos, Brazil
       ---------------------------<Page>

                                                                Exhibit 10.13(b)

               AMENDMENT NUMBER 2 TO PURCHASE AGREEMENT GCT-025/98

This Amendment Number 2 to Purchase Agreement GCT-025/98, dated as of December
2nd, 1998 ("Amendment No. 2") relates to the Purchase Agreement GCT-025/98
between EMBRAER-Empresa Brasileira de Aeronautica S.A. ("EMBRAER") and Solitair
Corp. ("BUYER") dated June 17, 1998 as amended by Amendment No. 1 to the
Purchase Agreement GCT-025/98, dated November 12, 1998 (together referred to
herein as the "Agreement"). This Amendment No. 2 is between EMBRAER and BUYER,
collectively referred to herein as the "Parties".

This Amendment No. 2 constitutes an amendment and modification regarding the
incorporation of Changes and other modifications, pursuant to Article 11, items
"a" and "g" of the Agreement. All terms defined in the Agreement and not defined
herein shall have the meaning given in the Agreement when used herein, and in
case of any conflict between this Amendment No.2 and the Agreement, this
Amendment No.2 shall control.

NOW, THEREFORE, in consideration of the foregoing, EMBRAER and BUYER do hereby
agree as follows:

1.    CONFIGURATION CHANGES

      1.1   Item 2.2 of Attachment A to the Agreement, "OPTIONAL SYSTEM / OTHER
            EQUIPMENT" is hereby amended by inserting after item "g" the
            following:

            "....
            h)    Wiring provision on the panel lamps for Filament Test
            i)    Structural provision for 10(degree)rudder deflection
            j)    Wiring provision for the nose landing gear door position
                  indication in the EICAS
            k)    Provision for warning of the selection of Flaps 22(degree)to
                  take-off
            l)    Provision for limitation of the hydraulic pressure on the
                  speed brake actuator when the aircraft is above 200 knots"

      1.2   Item 2.3.f of Attachment A to the Agreement, "OPTIONAL SYSTEM/OTHER
            EQUIPMENT" is hereby deleted and replaced with:
            ".....
            f)    Standard main door with structural provisions for plug type
                  door
            ..... "

      1.3   Due to the changes described in item 1.1 and 1.2 herein, the
            Aircraft Basic Price described in Article 3 of the Agreement will be

                                     [*]

--------------------
* Confidential

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2.    MISCELLANEOUS

All other provisions of the Agreement which have not been specifically amended
or modified by this Amendment shall remain valid in full force and effect
without any change.

IN WITNESS WHEREOF, EMBRAER and BUYER, by their duly authorized officers, have
entered into and executed this Amendment No. 2 to be effective as of the date
first written above.

EMBRAER - Empresa Brasileira de                  Solitair Corp.
Aeronautica S.A.

By     /s/ Satoshi Yokota                        By     /s/ Frederick Simon
      -----------------------------                  ---------------------------
Name:  Satoshi Yokota                            Name:   Frederick Simon
Title: E.V.P. Industrial                         Title:  President

By     /s/ Frederico Fleury Curado               Date:  _______________________
      -----------------------------              Place: _______________________
Name:   Frederico Fleury Curado
Title:  E.V.P. Commercial

Date:  December 8, 1998
Place: Sao Jose dos Campos, Brazil<Page>

                                                                Exhibit 10.13(c)

               AMENDMENT NUMBER 3 TO PURCHASE AGREEMENT GCT-025/98

This Amendment Number 3 to Purchase Agreement GCT-025/98, dated as of August 18,
1999 ("Amendment No. 3") relates to the Purchase Agreement GCT-025/98 between
EMBRAER - Empresa Brasileira de Aeronautica S.A. ("EMBRAER") and Solitair Corp.
("BUYER") dated June 17, 1998 as amended from time to time (together referred to
herein as the "Agreement"). This Amendment No. 3 is between EMBRAER and BUYER,
collectively referred to herein as the "Parties".

This Amendment No. 3 constitutes an amendment and modification regarding the
incorporation of Changes and other modifications, pursuant to Article 11, items
"a" and "g" of the Agreement, with respect to the inclusion of the plug type
passenger door. All terms defined in the Agreement and not defined herein shall
have the meaning given in the Agreement when used herein, and in case of any
conflict between this Amendment No.3 and the Agreement, this Amendment No.3
shall control.

NOW, THEREFORE, in consideration of the foregoing, EMBRAER and BUYER do hereby
agree as follows:

1.    CONFIGURATION CHANGES

      1.1   Item 2.2 of Attachment A to the Agreement, "OPTIONAL SYSTEM / OTHER
            EQUIPMENT" for the FOURTH AIRCRAFT and all subsequent Aircraft is
            hereby amended by inserting after item "l" the following:
            "....
            m)    Plug type passenger door"

      1.2   Due to the changes described in item 1.1, the Aircraft Basic Price
            described in Article 3 of the Agreement for the FOURTH AIRCRAFT and
            all subsequent Aircraft will be [*]. Therefore, the Aircraft
            Basic Price for the FOURTH AIRCRAFT and all subsequent Aircraft
            shall be [*]

2.    MISCELLANEOUS

All other provisions of the Agreement which have not been specifically amended
or modified by this Amendment shall remain valid in full force and effect
without any change.

----------
* Confidential

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IN WITNESS WHEREOF, EMBRAER and BUYER, by their duly authorized officers, have
entered into and executed this Amendment No. 3 to be effective as of the date
first written above.

EMBRAER - Empresa Brasileira de                  Solitair Corp.
Aeronautica S.A.

By     /s/ Frederico Fleury Curado               By     /s/ Frederick Simon
       -----------------------------                    -----------------------
Name:   Frederico Fleury Curado                  Name:  Frederick Simon
Title:  E.V.P. Commercial                        Title: President

By     /s/ Flavio Rimoli                         Date:  8/18/99
       -----------------------------             Place: Greenwich, CT
Name:  Flavio Rimoli
Title: Director of Contracts

Date:  August 18, 1999
Place: Sao Jose dos Campos, Brazil

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