When is it permissible to go behind a jet aircraft?

The scenario focuses on safety protocols around jet aircraft due to the potential dangers associated with jet blast and the aircraft's operating systems. The anti-collision light is a critical indication of an aircraft's operational status. When the anti-collision light is on, it signifies that the aircraft is either active or about to become active, which means it could be in the process of starting engines, taxiing, or preparing for takeoff. Approaching or going behind a jet aircraft under these conditions poses significant risks due to engine thrust and potential jet blast, which can cause injuries or damage.

Therefore, it is indeed never permissible to go behind a jet aircraft if the anti-collision light is on. This protocol is established to ensure the safety of personnel and other operations in the vicinity of the aircraft. Understanding this safety measure is crucial for anyone working around such environments, which is why option C is the correct answer in this context.