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RV-12 Safety Directive SD-00017 published: Check fuel return line flow

greghughespdx

Well Known Member
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We have published Safety Directive SD-00017, which applies only to the original/legacy RV-12 (it does not apply to the RV-12iS).

This Safety Directive requires inspection before further flight of the fuel flow return line to ensure fuel is actually flowing through the return. This is a simple and quick check and can be accomplished by the owner/operator in about 5 minutes. No tools or parts are required and there is nothing you need to order to conduct the inspection.

In the event the return line is found to be blocked, the document contains the mandatory additional steps to rectify the issue.

https://www.vansaircraft.com/service-information-and-revisions/sd-00017/

Context: A blocked return line fitting was discovered on one RV-12 in the field. Due to the potential risk and impact of a fuel flow issue, we have issued this as a before-further-flight notice. Performing the check of this critical system is a quick and simple process.
 
As a matter of curiosity, how does a blocked fuel return line result in interruption of fuel to the engine?
 
I'll give it shot..probably be half right.

The fuel return line ensures a circulation of cooler (presumably) fuel to the engine fuel pump. If its blocked, the aircraft would be more susceptible to vaper lock.
 
I always do that during the condition inspection. No particular reason, just one little thing that only takes a minute to do. Now I?m glad I do it.
 
I'll give it shot..probably be half right.

The fuel return line ensures a circulation of cooler (presumably) fuel to the engine fuel pump. If its blocked, the aircraft would be more susceptible to vaper lock.

Pretty much totally right.
 
I will visually confirm return fuel flow before next flight and mark CW in the engine logbook.

I added an item to my pre-flight checklist that addresses this issue. I turn on the Master Switch before I climb into the airplane so I can hear how the electric fuel pumps starts. I listen to see if the rhythm of the pulses sounds correct and that the pump starts without hesitation. The item I added to the checklist is to verify fuel flow on the D-180 before engine start. For the few minutes the electric pump is running by itself I show something like 0.2 / 0.3 GPH flow that has returned to the fuel tank.

Good check before every flight...
 
Looking at the paperwork, it seems some faulty bulkhead fittings got through the system. Appears some weren't drilled all the way through.
Regards, DaveH
120485
 
With my fuel pump off I see a zero fuel flow. When I turn on the pump the fuel flow gradually increases to about 1.1 GPH. If I look into the filler neck I can see the end of the return line and there doesn't appear to be any flow.

So, is it possible to have a non-zero fuel flow with the return line blocked?
 
I used a video inspection scope down the filler neck and then turned the master switch on. There was a burst of fuel Initially and it then reduced to more of a gurgling out of the return line.

Regards
Bill Gardner
N969RV S12049
 
True AN fittings go through many inspections, its hard to imagine some getting through. But we know it happens.

Tom
 
Jim,

I had an aha moment when I read your post. I put a switch on my electric fuel pump. When I turn it on with th engine off I see the return flow indicated. Another reason to have a switch! ?- let the slings and arrows at me commence for my fuel pump switch heresy!😝

Rich
 
Tom,

I wouldn't trust the indicated fuel flow at all, at least for this purpose. I recommend you get someone to help you. Have them turn on the master while you are staring at the outlet in the filler tube. When I did this alone, the fuel level in my tank was just at the right level to see the ripples as the fuel ran down the return line into the tank but I couldn't discern whether or not fuel was flowing just by looking at the end of the tube. So, take a good look at the outlet with fuel pump not on, then again with it on. I think you'll find it is flowing, just hard to see. A small probe mirror helps.
 
Tom,

I wouldn't trust the indicated fuel flow at all, at least for this purpose. I recommend you get someone to help you. Have them turn on the master while you are staring at the outlet in the filler tube. When I did this alone, the fuel level in my tank was just at the right level to see the ripples as the fuel ran down the return line into the tank but I couldn't discern whether or not fuel was flowing just by looking at the end of the tube. So, take a good look at the outlet with fuel pump not on, then again with it on. I think you'll find it is flowing, just hard to see. A small probe mirror helps.

Thanks Steve, I ended up pretty much doing what you suggested. Couldn't find anyone around to help but was able to use a long stick to turn on the fuel pump switch while I watched the tube. Thx
 
Jim,

I had an aha moment when I read your post. I put a switch on my electric fuel pump. When I turn it on with th engine off I see the return flow indicated. Another reason to have a switch! ?- let the slings and arrows at me commence for my fuel pump switch heresy!😝

Rich

Just wondering, if you have the K-factor set close to correct, then there would be very little fuel flow indicated since the engine is off. In fact, I remember some guys setting their K-factor so with the engine off the indicated flow is zero.;)
 
Safety Directive SD-00017

I took the idea of using the endoscope and used it. I could see the fuel coming out of the tube inside the filler neck. I could not see anything without the endoscope.

Thanks to the gentlemen who posted that idea.
 
Fuel tank leak test should have found it

I bought a pre-built fuel tank but did the leak test anyway. The air to inflate the tank as well as the balloon goes through the return fuel line connector. If it's plugged then no air will go into the tank. Correct me if I'm wrong.
 
Air can get through a lot smaller hole than fuel can.
The air test might not indicate a partially plugged fuel line.
 
There is also a AN832-4D fitting for the return line in the center section bulkhead (28-06). Would that not also be suspect if there is insufficient return fuel flow?
 
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