How is smoke detected in the cabin when flying without passengers?
The threat for a cabin compartment smoke or fire comes from paying passengers &amp; baggage.
On a ferry flight, you have neither, so the threat is greatly reduced or eliminated.
The FAA authorizes ferry permits for only 1 or a few  segments to get an aircraft to a facility where maintenance can be performed, these ferry permits take into account the risks involved and thus why no revenue cargo / passengers can be carried.