Fill to Tabs - what part of the tab?

When “filling to tabs” - do I fill the tank such that the fuel is just touching the bottom of the tab or do I submerge the top of the tab in fuel?

Russel, would you rely on the difference to say “I submerged the top then I can continue the flight” ?

Eric it’s a fair question and I don’t consider it pedantic - there’s a few gallons in the difference and considering each one costs 6 pounds if can make a difference for mgw if you can take that extra bag or not!

If it’s that critical I use the known fuel on board - from the totaliser - to determine how much I can add. The tab is there for sanity checking, not precise measurement.

via COPAme
Asus Nexus 7

1 Like

I am not sure if we are still taking applications for ARCOPA. [:)]

Seriously, though, a bigger problem might be is the tab in the proper position. It is not unusual for an over eager line guy to bend the tab with the nozzle. It can carefully be bent back, but if not, the end of the tab will be substantially below where it was and the next line guy might put in much fuel than you expect.

As to were to bend it, my assumption is that it is right when the bottom of the tab is level. Makes sense, but I don’t know for sure.

As to the original question, I fuel until the fuel just covers the tab.

Same here. And, I also use a calibrated fuel hawk to double check partial fuel loads.

Search calibrated dipstick and use that to confirm where u want to be with fuel load if it really matters …

1 Like

Assuming your Tab hasn’t been bent and is in the proper position, you are talking a fuel quantity that would be just ovr the thickness of the Tab itslef, plus a bit more to actuall cover the top, maybe we’re talking 1/8th of an inch, or .125 " ?

No more than 4 Milimeters… How much fuel could that be ? just guessing less than 1/2 gallon. I can’t imagine needing it that precise for myself.

In my 8 years of Cirrus ownership, I have never looked at the tab. I am in agreement with Clyde, you have a very accurate totalizer, just use it. Maybe I’m OCD, but I keep exact track of what I use out of each tank, and use that as the fuel I need.

If you were OCD you would trust but verify the totalizer with a quick glance and comparision of the tab (sanity check per Clyde). My totalizer doesn’t take into consideration a failing check-drain valve or other leak below the wing. I did have a bunch of blue stains though that offered another hint.

Fellow Cirrus Pilots,

Thank you for the great feedback. As I suspected, this problem is not universally understood.

Problems as I see it.

  1. Tab position may or may not be accurate depending on the quality of the maintenance personnel.

  2. Fuel to Tab relationship could become a big deal in enough or not enough fuel on board.

  3. My mechanic warned me not to rely on my cockpit fuel gauges. They are slightly better than sun dials or onboard compass.

  4. The OCD may accurately calculate fuel consumption, but the starting point is manually set at startup. One math error and you could be over weight.

As a result of this discussion, I will do the following:

Buy a Universal FuelHawk Gas Gauge.

Calibrate my tab placement, by filling each wing “to tabs” (fuel touching base of tab). Continue to fuel to full and calculate what “tabs” mean. 40.5 gal - post tabs fuel = fuel “at tabs”. Theoretical post tab fuel should be 17 gal.

I would say the problem is trying to use a tool- the tabs, for a purpose beyond its design. It’s a ‘close counts’ indicator. If a couple gallons of fuel or a couple pounds of wt matter, you’re cutting it too close.

1 Like

Russell, I think you’ve got a good strategy here but I also think you want to include a significant amount of windage in the calculation anyway. Lot’s of little variables that could stack as an unfavorable combination. Airplanes seem to grow heavier with use, accumulating tools, supplies, chocks, books, etc. and fuel weight varies considerably with temps (the weight of a gallon a side between a 60 degree day and 90 for instance). Moreover, I never see a scale for PAX or bags in an FBO or on a ramp. I suppose if you’re really cutting it exactly closely, it’s been rumored that a slightly over weight Cirrus will fly, and an under-fueled one eventually will not!

I need to contribute to receive updates. The Tabs that i have seen on Cirri are pretty close and they are just awash at Tab fuel volume if not bent. I have been pleasantly surprised. Nice Job Cirrus.

As a thought process take a gallon of water and pour it on the driveway, it will flow to an approx surface level of a Cirrus fuel tank. Now measure the height of the water with a stick.

You will find that it is not really an effective tool for determining accurate fuel level. Additionally, there is no standard reference position or angle for said stick.

… and if your pax lied about their wt. by 40 lbs, the plane is not going to fall out of the sky. You’ll never know the difference.

Hi Mark, bought my Cirrus in March, finished my lapsed PPL last week and am doing my conversion training starting this week. Have a fuel hawk, and a digital flow meter in my hangar, so obviously planning to calibrate the dip stick, just wondered if you can send your calibrate sheet, would be interesting to compare. What is the minimum you can measure before the fuel runs past the filler?


Congratulations on your Cirrus! I don’t still have that aircraft. It was a G3 with 46 gallon/side tanks. Due to tank geometry, the minimum I could measure was 20/ side (about 15mm according to my notes - but each aircraft will be a little different).

You have to be careful to measure on a level surface, with the stick exactly positioned. I upgraded to Cies digital gauges and found them accurate at this reduced fuel level, but needed recalibration in the 30/side range. I haven’t kept up with which generations these can be retrofitted on.

PS: There is a Cirrus Pilot Proficiency Program planned for South Africa in August. I hope you’ll consider attending. Enjoy the Cirrus.

This seems like a great idea, but now we need to determine what “full” is…

i can always get a few more gallons in each wing after a lineman says it’s full. I also feel like I can get more fuel in the wing on a cold day vs a hot day.

Sounds like a reasonable strategy to me.

I’d be interested to hear what is the result of your testing.

This thread reminds me of the flight tests Clyde did on early Cirrus best glide speed. He proved the POH was not accurate.

I hadn’t really considered the possibility of the tab being bent much.


Tis one is easy. Full is when you see no free space between the bottom of the filler neck and the fuel surface. In other words, the fuel touches the bottom of the ring in the filler. That is full. On a hot day some of that will expand and drain out the fuel vent. Many FBOs are reluctant to fill it to “real full” for a variety of reasons. Getting that last 1-2 gallons in there requires not having flow rate through the hose to be full speed.

Determining “fill to tabs” is a very inexact science. The tabs are not precisely the same in each tank and the airplane would have to be perfectly level. And it probably varies a bit plane to plane. I would say the only way to real know what visually is the exact amount of fuel at the tabs is to do this experiment.

  1. Fill the plane to completely full.

  2. Monitor gallons used on the furl totalizer.

  3. Switch tanks when each two to three gallons is burned.

  4. When the amount gets down to total remaining depicted on the the fuel caps (add both sides), then look in the tanks and see where the fuel level is in relation to the tabs. Then you know!

Unless you fill the plane yourself, even using the above method will never guarantee you are right at the tabs unless you agin look at gallons used and ask to fill only with the number of gallons adding up to the tab level.