<PAGE>

          CERTAIN PORTIONS OF THIS EXHIBIT HAVE BEEN OMITTED AND FILED
         SEPARATELY WITH THE SECURITIES AND EXCHANGE COMMISSION PURSUANT
                     TO A REQUEST FOR CONFIDENTIAL TREATMENT

                                                                   Exhibit 10.20

                          LETTER AGREEMENT DCT-008/2003

This Letter Agreement DCT-008/2003 ("Agreement" or "Letter Agreement") dated May
__, 2003 is an agreement between Regional Aircraft Holdings Ltd. ("Buyer") with
its address c/o Galindo, Arias y Lopez, Avenida Federico Boyd Numero 51 Piso 11,
Panama, Rep of Panama, and EMBRAER - Empresa Brasileira de Aeronautica S.A.
("Embraer" or "Embraer-Brazil"), with its principal place of business at Sao
Jose dos Campos, SP, Brazil (collectively the "Parties"), relating to Purchase
Agreement DCT-006/03 (the "Purchase Agreement") dated as of May ___,2003.

This Letter Agreement constitutes an amendment, supplement and modification of
the Purchase Agreement as it sets forth additional agreements of the Parties
with respect to the matters set forth therein. All terms defined in the Purchase
Agreement shall have the same meaning when used herein, and in case of any
conflict between this Agreement and the Purchase Agreement, this Letter
Agreement shall prevail.

WHEREAS:

a)    The Parties have entered into the Purchase Agreement, pursuant to, and
      subject to the terms and conditions of, which Buyer shall buy and Embraer
      shall sell ten (10) Firm Aircraft and up to twenty (20) Option Aircraft.

b)    The Parties wish to set forth the additional agreements of the Parties
      with respect to certain matters related to the purchase of the above
      referenced Aircraft.

NOW, THEREFORE, for good and valuable consideration, the Parties agree as
follows:

1 - **MATERIAL REDACTED**

2 - APPLICABLE LAW

      This Agreement shall be construed in accordance with and its performance
      shall be governed by the laws of the State of New York, USA without regard
      to any conflict of law rules other than General Obligations Law 5-1401 and
      5-1402.

3 - JURISDICTION

      All disputes arising in connection with this Agreement shall be finally
      settled in the courts of the United States District Court for the Southern
      District of New York located in the county of New York, provided that if
      such court lacks jurisdiction, disputes shall be resolved in the state
      courts for the state of New York. The Parties hereby waive any other court
      of Jurisdiction that may be competent for settlement of disputes arising
      from this Agreement. **Material Redacted**

4 - CONFIDENTIALITY

      Notwithstanding anything to the contrary in the Purchase Agreement,
      neither Buyer

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      nor Embraer shall disclose the terms of this Agreement except as needed to
      its officers, employees, auditors, insurers (brokers) and legal advisors
      and except (a) as required by law or legal process or (b) with the prior
      written consent of the other party. In addition, Buyer and Embraer may
      disclose the terms of this Agreement to shareholders who hold more than
      ten percent (10%) of their respective common shares, provided that (i)
      such shareholders are not, in the case of Buyer, competitors or affiliates
      of competitors of Embraer in the business of manufacturing aircraft, or in
      the case of Embraer, competitors or affiliates of competitors of Copa
      Airlines, S.A. in the business of a scheduled airline, and (ii) such
      shareholders, to the extent not officers of a Party shall have executed a
      confidentiality agreement with the other Party. Without limiting the
      foregoing, in the event either party is legally required to disclose the
      terms of this Agreement, each party hereto agrees to exert its best
      efforts to request confidential treatment of the Articles and conditions
      of this Agreement relevantly designated by the other as confidential.

5 - SEVERABILITY

      If any provision or part of a provision of this Letter Agreement or any of
      the Attachments shall be, or be found by any authority or court of
      competent jurisdiction to be, illegal, invalid or unenforceable, such
      illegality, invalidity or unenforceability shall not affect the other
      provisions or parts of such provisions of this Letter Agreement, all of
      which shall remain in full force and effect.

6 - NEGOTIATED AGREEMENT

      Buyer and Embraer agree that this Agreement has been the subject of
      discussion and negotiation and is fully understood by the Parties, and
      that the rights, obligations and other mutual agreements of the Parties
      contained in this Agreement are the result of such complete discussion and
      negotiation between the Parties.

7 - COUNTERPARTS

      This Agreement may be signed by the Parties hereto in any number of
      separate counterparts with the same effect as if the signatures thereto
      and hereto were upon the same instrument and all of which when taken
      together shall constitute one and the same instrument.

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