There are several solutions to prevent a fuel system from sucking air from a fuel tank while in a steep turn when the fuel level is low.   This has been a hot debate on other forums.

I am curious to hear from folks who are actually flying their planes on which design you use to address this risk.  

1) Header tanks?

2) Check valves?

3) Limit fuel selector valve to only use R or L tank but not both?

4) None, I use "both" on my selector valve and do not have a header tank and have not had any issues. 

Could you you please comment which model you are flying and what engine, and if it is F.I. or carburated and if you have fuel return lines. 

Thank you !!!!!


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You start the post by stating "There are several solutions to prevent a fuel system from sucking air from a fuel tank while in a steep turn when the fuel level is low".  Unporting a fuel tank and sucking air is not necessarily the same.  The fuel pumps in our header tank will not suck air until the header tank is dry, and that can only happen after all fuel in both wing tanks is consumed.  


Some people use the term "unporting" to describe a dire situation where the fuel port (the exit out of the tank) is no longer covered  by fuel and as a result it is not delivering fuel, and as a result sucking air.   In the case where there is a header tank that has fuel, and the main tank(s) have run dry (God forbid) but the system is still delivering the header tank fuel for a few minutes, most people would not describe this as a system that is unported.   


I’ve not heard of this being a problem in the 701. I built the fuel system in my 701 following the Zenith drawing. A basic description is it’s a fuel tank in each wing, each line goes to the water separator at the system low point. From there a single line runs forward to the engine. No crossfeed, no L or R tank selector in the cockpit.  In the event one tank’s outlet has no fuel covering it, for whatever reason, the fuel from the other tank feeds the engine. If I ever find myself in a situation where I’m flying with only one tank with any fuel in it, and that tank is so low on fuel I uncover that tank’s port due to uncoordinated flight, then I suppose I will be dealing with a situation I created much earlier in the flight due to a lack of good judgement.


Well said!

I have 300+ hours on my 701 with a cont C85, gravity fed, standard Zenith gasolator and fuel valve, no issues. I’ve been down to only 3 gallons between both tanks and did not have any starvation problems during turns. 

Is anyone using this header tank system designed by Skytek Aircraft Services for the 912is?



Good question.   You might get a better audience in the 750 forum than in this thread in the Open Forum. 



You might post your question in the Rotax section. I know at least one happy flyer who uses their tank with a UL Engine. I fly behind a UL also, but have yet too see a need for me to install a header tank. 


Forgot to add as requested in the topic kickoff post, I fly behind a carbureted engine with a fuel return line (as required by Rotax).

I plan to use the Skytek tank, mounted on passenger side.  Continental 200A engine.  I think 750 STOL builder David Beaulieu used the Skytek tank with his UL engine.

Not sure if anyone is still discussing this, but I just had an unporting event in my STOL CH 750 Amphib.  And, I have read about other similar incidence/accidents.  I lost power on short final at 100ft and landed short of the runway on rough gopher holed grass.  Unfortunately, 100ft didn't allow me to bring the amphib gear back up before landing on the rough surface.

Aircraft Details:

CH 750 Amphibian (lower pitch on approach)


Gravity feeder lines

L/R fuel selector (not both)

Under wing fuel vents

4 gallons remaining in each tank (8 gallons total)

Flight Conditions:

Very turbulent (+- 10 knots)

Crosswind on final

Those who are saying that if you stay coordinated you won't unport the tanks are not providing a solution.  Anybody that says they are coordinated in all flight conditions is not telling the truth, and quite frankly is not using all the tools in the pilots flight bag (Slips, etc.)

I believe the combination of the turbulence, a long final approach, and a side slip (uncoordinated flight) to counter the crosswind for a more stabilized approach caused the fuel to unport, and power loss.

These flat bottom tanks have one port on the inboard rear of the tank.  That is a good position for takeoff and climb, where you absolutely do not want it to unport.  However, it is a bad position in my circumstance: sideslip on final approach with a higher approach speed (lower angle of attack).

So, there you go.  You can unport your fuel tank with as much as 4 gallons of fuel in it.

This circumstance is an instance where having "both" on the fuel selector would have fixed the issue.

Based on all the reading of this debate that I have done, the header tank seems like the best option.  Also, I don't understand why people think not having "both" on the fuel selector is a good idea.

"Based on all the reading of this debate that I have done, the header tank seems like the best option.  Also, I don't understand why people think not having "both" on the fuel selector is a good idea."

Ryan, I hope neither you nor your airplane got to beat up. Thanks for the report.

With regards to fuel valves on Zenith high wing designs, I think it is difficult to argue against a simple ON/OFF fuel selector (as Zenith specifies) perhaps with a single ball valve in the line coming from one of the tanks if you are concerned about cross feeding when parked on an uneven surface. I agree that a header tank is a good thing to ensure that the fuel keeps flowing.


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