|In case of a hostile repossession:
De-registration of an aircraft should be applied for by the Owner of the aircraft or his authorized representative / agent. There is no specific timing for making such a request for de-registration, however, it is recommended that a de-registration request should be made only after possession of all aircraft records and other vital documents have been received by the Owner from the (presumably defaulting) Lessee.
In case of cooperation by the Lessee:
De-registration of your aircraft should be timed just right, i.e. a few days before the inspectors of the safety agency arrive (from the jurisdiction where your aircraft will be registered) to inspect the aircraft.