Commanders Responsibility
 

Hi. When does a commander actually assume command of an aircraft, & when does he relinquish it at the end of the flight??

I`m in command when I step aboard, until I disembark.

How very modest of you static.

Legally once you have signed the tech log you have accepted the aircraft. However once you have been assigned an aircraft you effectively take command when you take over the aircraft from the engineer or from the previous crew. Likewise on disembarking the aircraft you relinquish command when the engineer takes the aircraft or the next crew take over.

Hence if there is no one to take over the aircraft you make very sure that the chocks are in, the APU is shutdown and the aircraft is properly 'put to bed' before you leave it!

Thanks FLAP 5

Flap 5, no deeper meanings intended.

Essentially, what you are saying is the same thing.
Only at my company we don`t sign the tech log before the flight. We accept the aircraft by signing the flightplan. This is often done at a location away from the aircraft, and thus I don`t yet "assume command of the aircraft" at the same moment I sign the flightplan.