Core Legal Answer & Context: The Convention for the Suppression of Unlawful Seizure of Aircraft (Hague Convention, 1970) is a key international treaty aimed at combating aircraft hijacking. The definition of 'in flight' is critical for determining the jurisdictional scope and applicability of the Convention's provisions.

Definition of 'In Flight' (Article 3):

1. An aircraft is considered to be 'in flight' from the moment when all its external doors are closed following embarkation until the moment when any such door is opened for disembarkation.
2. In the case of a forced landing, the flight is deemed to continue until the competent authorities take over responsibility for the aircraft and for persons and property on board.

Obligations Imposed on State Parties:

1. Criminalization of Offense (Article 1): Each State Party must make the unlawful seizure of an aircraft (hijacking) a grave offense punishable by severe penalties under its national law.
2. Establishment of Jurisdiction (Article 4): State Parties must establish jurisdiction over the offense when the offense is committed on board an aircraft registered in that State, when the aircraft lands in its territory with the offender on board, or when the offender is found in its territory.
3. Custody of Offenders (Article 6): Upon being satisfied that the circumstances so warrant, any State Party in whose territory the offender is found must take him into custody or take other measures to ensure his presence.
4. Prosecute or Extradite (Aut Dedere Aut Judicare) (Article 7): The State Party in whose territory the alleged offender is found, if it does not extradite him, must submit the case to its competent authorities for the purpose of prosecution, without exception whatsoever.
5. Restoration of Control and Facilitation of Journey (Article 9): State Parties must take all appropriate measures to restore control of the aircraft to its lawful commander or to preserve his control of the aircraft. They must also facilitate the continuation of the journey of the passengers and crew as soon as practicable.
6. Assistance in Return (Article 10): State Parties must assist the commander of the aircraft and the passengers and crew in the return of the aircraft and its cargo.

Relevant Statutes and Sections:

1. Convention for the Suppression of Unlawful Seizure of Aircraft (Hague Convention, 1970): Articles 1, 3, 4, 6, 7, 9, 10.

Clear Conclusion: An aircraft is 'in flight' under the Hague Convention from the closing of its external doors after embarkation until their opening for disembarkation, or until authorities assume responsibility after a forced landing. State Parties are obligated to criminalize hijacking, establish jurisdiction, take offenders into custody, prosecute or extradite them, and ensure the safe return of the aircraft, passengers, and cargo, thereby ensuring international cooperation against this grave offense.