How much do you trust sight gauges?

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asicer

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asicer
You are on your way home VFR on a CAVU day in an airplane (single engine land) equipped with marked sight gauges. 15 minutes out, your timer expires indicating that you hit your fuel reserves. However, your sight gauges are showing about 20 minutes of fuel remaining plus reserves. You tip the wings/nose and verify the readings against the AI. There is an airport directly below you, another halfway home and a straight non-busy freeway connecting them all.

Do you press on? Or do you divert?

EDIT: My answer is in post #63
https://www.pilotsofamerica.com/com...trust-sight-gauges.116775/page-2#post-2679962
 
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Divert! I trust my watch far more than I would the fuel gauges. Especially with an airport directly below. What's the old joke, the only time you can have too much fuel is when you're on fire? I'm a BIG fan of having more than necessary.
 
I go by time elapsed and nothing else.

36 gals useable @ 8 gals/hr

I theoretically have 4.5hrs endurance, but I’ll throw on my own conservatism and say 4hrs and I’m finding an airport to refuel. In this case, I’d divert.
 
I think to answer your question you need to tell us what our AGL altitude is...
 
Dave Arata said:
I trust my watch far more than I would the fuel gauges.
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Ryanb said:
I go by time elapsed and nothing else.
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Isn't your timer ultimately based on a reading you got from when you sticked the tanks? How is a graduated sight gauge different from a pipette? (Assuming smooth air and unaccelerated straight and level flight)
 
asicer said:
Isn't your timer ultimately based on a reading you got from when you sticked the tanks? How is a graduated sight gauge different from a pipette? (Assuming smooth air and unaccelerated straight and level flight)
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I can’t answer that because I don’t fly anything with sight gauges, but I suppose it would be the same readout bearing you have smooth air.
 
I will believe whichever one gives me the worst case scenario. I am not sure exactly how the sight glass works, but I'd hate to run my tanks dry while a plugged up sight glass still has some fuel in it.
 
Sight gauges are the most accurate form of fuel gauge (assuming they were installed and marked properly) so I would go with the sight gauge. That said, my plane has Cessna gauges so I dip the tanks, write down what is in each tank on my knee board and calculate when I will have 10 gal in my tank flying at 7.5 gal/hr. I start the clock at engine start and keep an eye on the time in my tanks. When I have 10 gal I will land at an airport with fuel.
 
15 vs 20 minutes?
I’d assume it’s 15 or less. But I always flight plan for 90 minutes of fuel reserves.
I don’t trust any fuel gauges to that accuracy.

Tom
 
In order of decreasing reliability:

1) most reliable: stick the tanks before takeoff and start the timer on takeoff.
2) sight gauge - glass tube with fuel visible in a calibrated tube.
3) mechanical float type gauge such as used on the PA-32-301.
4) 40 year old POS factory electric gauges.

-Skip
 
What’s your reserve? If you planned an IFR reserve but everything turned out VFR, then you have plenty of reserve.
 
a safe bet is to always go with whatever is giving you the lower indication, if that's the sight gauge then go with that, or if that's your calculation then go with that

With fuel exhaustion being one of the main causes of forced landings and such an easy thing to fix this is the safest bet
 
On a plane that I don't know and haven't been flying in much, I take the most conservative measure.

If I know the plane and have learned how accurate the sight gauges are vs. my (conservative) time estimates, then I might trust the sight gauges. After a while you can develop pretty accurate time estimate of fuel burn on a piston, though.
 
Heftiger said:
What’s your reserve? If you planned an IFR reserve but everything turned out VFR, then you have plenty of reserve.
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VFR pilot here. Reserve time varies based on location, hard minimum 45 minutes. I just don't push it. -Skip
 
Who's sight gauges? I have some in my Cub that I don't trust at all when they get low. I use sight gauges to validate other indicators, like what my expected burn is based on time. Sight gauges aren't perfect.
 
When you are worried about fuel levels stop and get more. ( it doesn't matter which type of gauge you have) That's a lot easier than dealing with the State police, FAA, NTSB. and another group that will have questions
 
If you are within five minutes of your estimated fuel range and you still have a 30 minute reserve, why would you not continue?

That's the purpose of fuel reserves. You may land with very little fuel in your tanks with no drama as long as you planned for contingency and carried that extra fuel to ensure an arrival with a safe margin.

Some pilots have been trained to never use their planning reserve. Plans don't always work out, though...
 
IK04 said:
If you are within five minutes of your estimated fuel range and you still have a 30 minute reserve, why would you not continue?

That's the purpose of fuel reserves. You may land with very little fuel in your tanks with no drama as long as you planned for contingency and carried that extra fuel to ensure an arrival with a safe margin.

Some pilots have been trained to never use their planning reserve. Plans don't always work out, though...
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And when you get to your destination and the runway is closed, then what?
 
Airport below me? Land... Whats the time penalty in landing? You'll need gas at home so you can't count the fill up time. Just the extra time to do the pattern, land, taxi and reverse it. That is a small small time penalty to pay vs being in a field or short final or anywhere but terra firma when they run dry. I don't want to be a statistic. If there wasn't an aiport right below me, then that is what your reserve is for. But I would never use my reserve a single drop if I have another option, those reserves are there if you don't have another option... Just my theology of it...
 
asicer said:
At what altitude would you choose not to divert? :)
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I re-read your question and I misinterpreted it the first time. With the scenario given I would stop and get fuel because something isn't right. Better to figure it out on the ground...
 
I try to be an optimist in all of my life, but when I get to the airport I try to become a pessimist...
 
IK04 said:
That would be an example of inadequate preflight planning.
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Runway close in a moments notice.. that aircraft 2 minutes ahead of you blew a tire/crashed, and you can't land.

Now what?
 
Oh how I wish I could tell what's 5 minutes ahead of me.
 
Land, get fuel, continue your day. I consider my reserves emergency fuel. I would NEVER use reserves for convenience. Besides, that wouldn't make the news. Land 100' short with dry tanks and you'll be on the cover of every newspaper and the lead story at 6:00 and 10:00. "Local firefighters called to the scene to save inept pilot that refused to purchase fuel! Life threatening flight completed without a flight plan!"
 
Tom-D said:
Runway close in a moments notice.. that aircraft 2 minutes ahead of you blew a tire/crashed, and you can't land.

Now what?
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If I have a Cirrus, put the chute and land as normal ;-)


Tom
 
The sight gauge on my airplane is a metal rod sticking up through the fuel cap with a cork at the bottom.
It actually tends to stick; the slipstream will pin the rod to the tube until the gas level goes down low enough that the weight overcomes the friction.
cork1.jpg

So I tend to go more by the clock.....

Ron Wanttaja
 
MooneyDriver78 said:
If I have a Cirrus, put the chute and land as normal ;-)
Tom
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then it becomes a question is it cheaper to gas up or re-pack a chute? reposition an aircraft from some field. :)
 
Tom-D said:
When you are worried about fuel levels stop and get more. ( it doesn't matter which type of gauge you have) That's a lot easier than dealing with the State police, FAA, NTSB. and another group that will have questions
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This.
 
Tom-D said:
Runway close in a moments notice.. that aircraft 2 minutes ahead of you blew a tire/crashed, and you can't land.

Now what?
Click to expand...
land anyway. Never done a spot landing 1500' down ghe runway?
 
Wheels said:
So based on this scenario I have 15-20 minutes of fuel plus reserves. What the scenario doesn’t tell me is how far I am from my destination and how long I expect it to take to get there. Without that piece of information I can’t answer the question.
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No. You are 15 minutes from your destination and you have 20 minutes of fuel plus reserves if you go by the sight gauges and 0 plus reserves if you go by the timer. It boils down to the question in the thread title.
 
asicer said:
No. You are 15 minutes from your destination and you have 20 minutes of fuel plus reserves if you go by the sight gauges and 0 plus reserves if you go by the timer. It boils down to the question in the thread title.
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Ok, I misread the original post.
 
Skip Miller said:
In order of decreasing reliability:

1) most reliable: stick the tanks before takeoff and start the timer on takeoff.
2) sight gauge - glass tube with fuel visible in a calibrated tube.
3) mechanical float type gauge such as used on the PA-32-301.
4) 40 year old POS factory electric gauges.

-Skip
Click to expand...
1) Most reliable: when the engine quits, the fuel is all gone.
 
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