There is a vent drain tube that leads from the oil tank to the engine accessory case on the W-670. There is also a vent line from the left hand top of the accessory case that leads down the left hand gear leg and ends somewhere around the lower knuckle.
This vent line is necessary to prevent pressure building up inside the engine case.
In cold icing conditions, there was a problem with water vapor freezing in the drain tube and plugging it up. To help with this problem a technical order was generated in the military to run the tube straight down through a hole in the lower engine cowl instead of down the gear leg.
Fewer bends in the tubing seemed to generate less plugging. This is what the extra hole is for that you sometimes see in the left side of the bottom engine cowl. The problem with this method is that is spreads any oil coming out of the drain all over the engine cowl and back on to the fuselage.
The drain from the step-up drive should also tee into this line.
Even without freezing, this tube can plug up with gunk. See Terry Emig’s report on the Feedback Page in the Nov. 2001 Issue.
If the line going down the gear leg terminates too close to the brake backing plate and knuckle, the turbulence around that tube outlet makes a mess of the inboard side of the wheel.
If you put a final 90 degree bend in the tube and point about a four inch section to the rear, the oil exits without getting all over the wheel.