What are ferries

Is a single-engine ferry flight allowed on a twin-engine aircraft?

Civil aircraft are not designed for this, but some military aircraft are. The Antonov-70 can start without any problems with one engine out of operation (four in total), but can only do so to a limited extent two Engines on the same Take off the page! To do this, it has to be empty and can only carry minimal fuel.

This capability is the result of the Soviet Air Force's requirement that the An-70 be operated for 6 months with minimal maintenance. The Antonov design office, aware of the limited capabilities of the front-line troops in aircraft maintenance, designed this transporter with a lot of redundancy.

Edit: With an engine out of order, a twin-engine civil aircraft would not be legal trying to do a single-engine takeoff. I would expect there is a way to do this, but it does require the owner's approval and some documentation with the local authorities. If you can demonstrate that this particular ferry flight is safe, you are likely allowed to fly. However, I am sure that without lengthy preparation and paperwork, there is no way legal only to start with an engine.

This is in contrast to military aviation, for which this type of operation is planned.