Originally Posted by Tom NJ
AeroShell 555 is a high load carrying version of MIL-PRF-23699 and AS5780 spec oils and contains an extreme pressure additive, so it is designed to handle highly loaded gearboxes in helicopters and turboprops. Oils like Eastman 2380 and Mobil 254 do not contain an EP additive, only anti-wear (TCP). I would be wary of running an engine or transmission on these oils. It may take time for the damage to be noticeable, but with no ZDDP, detergents, or dispersants you are not doing an engine any good.
Thanks, that's great information. We are now required to use a specific lubricant in our heli gearboxes called Castrol "Transmax". I don't know anything about it, other than it's $2300 initial cost. It came in nondescript grey bottles with no mil spec. (not the automotive stuff) I'd guess it contains the EP additives, as the gear wear patterns are one of the things they were trying to address.
The Pratt PT-6 often comes from the factory, serviced with 2380. They don't seem to experience any gearbox related failures, even over decades of 2380 use (on our PC-12's) . Our Helicopter engines, Troublemeca Arrius 2B1's have internal gearboxes that reduce the free turbine's 56,000 RPM to 6000 RPM. We use 254, not for gearbox protection, but to help reduce coking. In over 20 years of operating these engines, the gearbox is the least of the worries with these junkers, er engines ....
(3 catastrophic engine failures within 1000 hours)