CONVENTION ON OFFENCES AND CERTAIN OTHER ACTS COMMITTED ON BOARD AIRCRAFT, SIGNED AT TOKYO, ON 14 SEPTEMBER 1963 (TOKYO CONVENTION)
http://www.mcgill.ca/files/iasl/tokyo1963.pdf
THE STATES Parties to this Convention HAVE AGREED as follows:
CHAPTER I
SCOPE OF THE CONVENTION
Article 1
1. This Convention shall apply in respect of:
(a) offences against penal law;
(b) acts which,
whether or not they are offences, may or do jeopardize the safety of the aircraft or of persons or property therein or which jeopardise good order and discipline on board.
2. Except as provided in Chapter III, this Convention shall apply in respect of offences committed or acts done by a person on board any aircraft registered in a Contracting State, while that aircraft is in flight or on the surface of the high seas or of any other area outside the territory of any State.
3. For the purposes of this Convention, an aircraft is considered to be in flight from the moment when power is applied for the purpose of take- off until the moment when the landing run ends.
4. This Convention shall not apply to aircraft used in military, customs or police services.
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Article 11
1. When a person on board has unlawfully committed by force or threat thereof an act of interference, seizure, or other wrongful exercise of control of an aircraft in flight or when such an act is about to be committed, Contracting States shall take all appropriate measures to restore control of the aircraft to its lawful commander or to preserve his control of the aircraft.
2. In the cases contemplated in the preceding paragraph, the Contracting State in which the aircraft lands shall permit its passengers and crew to continue their journey as soon as practicable, and shall return the aircraft and its cargo to the persons lawfully entitled to possession.
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Article 14
1. When any person has been disembarked in accordance with Article 8, paragraph 1, or delivered in accordance with Article 9, paragraph 1, or has disembarked after committing an act contemplated in Article 11, paragraph 1, and when such person cannot or does not desire to continue his journey and the State of landing refuses to admit him, that State may, if the person in question is not a national or permanent resident of that State, return him to the territory of the State of which he is a national or permanent resident or to the territory of the State in which he began his journey by air.
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Article 16
1. Offences committed on aircraft registered in a Contracting State shall be treated, for the purpose of extradition, as if they had been committed not only in the place in which they have occurred but also in the territory of the State of registration of the aircraft.
2. Without prejudice to the provisions of the preceding paragraph, nothing in this Convention shall be deemed to create an obligation to grant extradition.
A lot of gobbledygook but Switzerland can, but is not compelled to, return the copilot to Ethiopia.