diamondaviators.net

I'm curious if there is a specified amount of gearbox oil that must be visible in the small glass viewport, or if any visible oil is sufficient. The AFM simply says "check visually" and also says "if the gearbox oil quantity is too low, an unscheduled maintenance is necessary" without further explanation on what "too low" means. From reading this other thread, I'm assuming that it doesn't need to be all the way to the top of the window.

The question came up today during pre-flight when my instructor noticed that the bubble of air above the oil seemed a little larger today than last time. The difference seems slight and the level is still probably 80% of the way up the glass, so I'm not particularly worried about it at this point. When we returned from flying, it appeared completely full, so I assume the level changes with engine / ambient temperatures (also referenced in the other thread).

On a related note, would "topping off" this oil require supervision and a sign-off from a licensed mechanic or is it something an owner is allowed to do? It doesn't seem like it should really fall under the "changing oil" portion of 14 CFR Part 43, though it also seems much less complicated than servicing the fluid for landing gear struts.

According to the Austro Maintenance Manual, section 85-10-53, the proper gearbox oil level depends on the gearbox part revision number installed in your plane. We have revision 114 in our school DA42NG. In our case, as long as we can see oil in the window we are fine.

If you have revision 60 or lower, then you need a higher level, about .5 liter more (not sure where that level is indicated on the window).

When I instructed at a flight school with an affiliated Diamond service center, we were told that if the oil level was at or above the black dot in the center, we were okay. Not sure what all the part numbers were on those planes.

I concur. As long as you can see some liquid in the window, you are fine.

I like seeing that little window. For some reason it feels very high-tech when I open that port and peek in. I also asked my mechanic how often they had a plane at the flight school grounded because someone spotted that level low on the pre-flight. Never. It also changed levels depending on which spot on the ramp the DA42 was parked on.

Chris wrote: ↑Sat Jan 23, 2021 4:11 amOn a related note, would "topping off" this oil require supervision and a sign-off from a licensed mechanic or is it something an owner is allowed to do? It doesn't seem like it should really fall under the "changing oil" portion of 14 CFR Part 43, though it also seems much less complicated than servicing the fluid for landing gear struts.

I routinely service the gearbox oil in Austro engines on my DA62, since it should be no different from engine oil as far as Part 43 is concerned. It's no harder than any other "oil change" including checking of the gearbox oil filter -- in fact it's really easy on Diamond twins because everything is so readily accessible.

But I'm less sure that Part 43 applies to DA40NG aircraft, where it's necessary to also remove multiple hose clamps on the high-pressure duct leading to the intake manifold -- in order to access the gearbox oil fill port. Multiple licensed A&P shops have apparently gotten this wrong (re-using hose clamps or not tightening them properly after 100 hour servicing), causing hoses to come loose in-flight, engine loss of power, and emergency landings. Anyone servicing DA40NG gearbox oil needs to be VERY CAREFUL when replacing those hose clamps.

Chris, I had the same question when I first got into our 42. My maintenance guy at the time explained to me that the oil fills up the gearbox quite a bit. If it makes it up to the sight glass, you have more than enough.

In other words, any variance in the sight glass is a nominal amount of of oil.

More likely (like mentioned before) it's an uneven ramp or strut inflation that will show a difference.

The important thing is to see it.


Sent from my iPhone using Tapatalk

In my experience it’s very sensitive to the pitch of the ramp.

As a follow-on to the post I made above:

I recently talked to a mechanic who helps maintain a fleet of DA40NG aircraft for a flight school. He rigged up a funnel/filler (I didn't get to see it) to add gearbox oil WITHOUT needing to remove the hose clamps on the pressurized intake manifold that normally blocks the gearbox oil filler port. This not only saves time and effort, but should eliminate the potential for partial loss of engine power due to mis-installed clamps during DA40NG 100 hour servicing.