If the lubrication system of a helicopter reducer is compromised, its gears and bearings will be in a working state without lubricating oil, which causes the reducer to be damaged in a very short time. Various 2% additives of T307, T321, T202, and T391 were injected and mixed with DOD-L-85734 aeronautical oil to produce 45-min oil–air lubrication experiments performed upon 12Cr2Ni4A aeronautical steel tribo-pairs. The results show that the best anti-wear effect is produced by oil–air lubrication containing T391: its wear width under jetting oil–air just three times and quantity of oil used only 0.015 mL in 45 min was only 421.32 µm but that of dry friction for 48 s was 629.20 µm. The technology of oil–air lubrication that contains an extreme-pressure and anti-wear additive is thus a feasible way to improve the operational ability of a helicopter transmission system that is out of oil.