If a high percentage of aircraft accidents...

Norman said:
If a high percentage of aircraft accidents... involve fuel starvation, why do so many catch fire right after the crash?
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because a lot of light aircraft have an unused portion still in the tanks which most manuals describe as unusable.
 
I'm not sure I even look at the two fuel gauges in our 172 in-flight. . .maybe on pre-flight, I think I do then? We have a fuel monitor, and it measures fuel flow, and talks to our G-530. It calculates used, remaining, required, fuel flow, etc. We do have to tell it how much is in the tanks to start, but that's usually 38 gals usable, since we almost always top-off.

It won't detect a leak of course, though I don't think massive fuel leaks in 172s are common. I guess if we had a leak, I might/might notice the gauges dropping. Or not.

Anyway, short of a leak or other fuel system malfunction, I don't see much value in hyper-accurate fuel gauges in our aircraft
 
Jimmy: That is my point - you found that you were close to empty when you re-fueld the aircraft. What were your fuel gauges reading? Why didn't your fuel gauges warn you of your fuel state on the Sundowner.
 
I find watching fuel with a known fuel burn and a watch to be pretty accurate. Of course that won't factor in any fuel leak. I usually use my eyes for that.

I never take off with full tanks. I need the extra room for carrying passengers and their rather large bags and still get out of short strips.
 
And some of them have plenty of fuel in one tank and the PIC forgot toswitch
Jimmy cooper said:
because a lot of light aircraft have an unused portion still in the tanks which most manuals describe as unusable.
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Or there was plenty of fuel in one tank and the PIC forgot to switch. A supposedly out of fuel ditched in the lake short of the runway at my home airport. It was found he did indeed have fuel but didn't switch tanks.
 
Scott Philiben said:
Jimmy: That is my point - you found that you were close to empty when you re-fueld the aircraft. What were your fuel gauges reading? Why didn't your fuel gauges warn you of your fuel state on the Sundowner.
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It showed a quarter tank when I left ocean city, maybe just a little more. Later the FBO said" if I could, I'd break every fuel ga. So that every one would have to stick the tank. " It was a stupid thing to do and I told him that. He said it was a miracle it didn't U port in the pattern. I agree.
 
Zeldman said:
I find watching fuel with a known fuel burn and a watch to be pretty accurate. Of course that won't factor in any fuel leak. I usually use my eyes for that.

I never take off with full tanks. I need the extra room for carrying passengers and their rather large bags and still get out of short strips.
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I agree with you. For instance, my 140 cessna ,on a hot day was to be watched carefully if I had my wife along. It was a barking dog on takeoff , climb was lousy and I always made sure I had half tanks . 2000 feet hard surface with trees at both ends. Or if I was local and alone I'd not always fill it up but usually always did when I put it away.
 
Norman said:
If a high percentage of aircraft accidents... involve fuel starvation, why do so many catch fire right after the crash?
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same reason the engine stalls and the plane falls out of the sky.
 
Norman said:
If a high percentage of aircraft accidents... involve fuel starvation, why do so many catch fire right after the crash?
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Because, again, it's not a high percentage.

Ron Wanttaja
 
You keep saying it isn't a high percentage and compared to the other pilot error crashes it isn't. However, my question still stands. Why can't someone come up with a fuel gauge that works all the time, every time?
 
You want me to tell you how much I'll pay for a product that doesn't exist? It doesn't work that way either.
 
Timbeck2 said:
You want me to tell you how much I'll pay for a product that doesn't exist? It doesn't work that way either.
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If there is a demand and a profitable price point.....someone will cultivate the technology and get a design certified.

I doubt there is a profitable price point or demand....
 
Although it won't tell me what's in the left vs right tank (two tank Saratoga) my JPI 830 has been spot on (within a quarter gallon) at telling me how much total fuel I have remaining. I've assessed it's accuracy after several large quantity top-off's and it's amazingly accurate. That's just one of many great features of a good engine monitor.

Sure it would be nice to know specifically left vs right... and that actually would be possible if I took notes regarding "remaining fuel" each time I switched tanks. Personally, I find it's perfectly fine for me to compare my Remaining fuel on the 830 to the tractor gauge quantities. They generally agree pretty well, and are good enough considering I have no intention of ever getting less than 1.5 hours of fuel remaining.
 
arkvet said:
Although it won't tell me what's in the left vs right tank (two tank Saratoga) my JPI 830 has been spot on (within a quarter gallon) at telling me how much total fuel I have remaining. I've assessed it's accuracy after several large quantity top-off's and it's amazingly accurate. That's just one of many great features of a good engine monitor.

Sure it would be nice to know specifically left vs right... and that actually would be possible if I took notes regarding "remaining fuel" each time I switched tanks. Personally, I find it's perfectly fine for me to compare my Remaining fuel on the 830 to the tractor gauge quantities. They generally agree pretty well, and are good enough considering I have no intention of ever getting less than 1.5 hours of fuel remaining.
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Just dry tank all but your last tank and you know exactly where all the fuel is. :D
 
Scott Philiben said:
ircphoenix - I use the Wing Monkey - He crawls out of the baggage area and opens the door climbs out on the wing and sticks the tanks
if the fuel quantity is not to plan - he gets back into the aircraft beats me with a stick - grabs a parachute and leaves.

Capacitance is not the answer for Avgas and GA - ask Piper on the new Digital Mirage and Matrix system

There are new fuel quantity designs - and they predominate in new delivered aircraft. Over 75% of new delivered aircraft have fuel quantity systems that are not resistive or capacitive.
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Not resistive or capacitive? Are they inductive or optical or what?
 
It's possible with good equipment. Our JPI EDM 960 keeps of course a perfect calculation of total fuel on board, but the gauges for each tank are also very accurate, barring a couple of issues with a bad sensor that showed zero all the time.
 
From my looking at Fuel Exhaustion accidents, most cases are due to excessive optimism. What's needed is to COMPLETELY remove the human from the equation.

What's needed is not (just) a highly-accurate fuel gauge, but a highly accurate "Time Before Silence" clock. Said clock would have to merge the physical fuel level, throttle setting, fuel tank and system geometry, aircraft attitude, etc. to be able to generate a accurate prediction as to when the go-juice will be gone. Ideally, control of the fuel tank selection will be removed from the pilot's control to make connectivity more reliable and support predictions better. Connect to the CAPS as well; run out of gas in the chute's envelope, it automatically deploys.

Fuel exhaustion is the #2 cause of aircraft accidents...but it's #2 by nearly an order of magnitude. If you want to save lives, develop an adaptive system to help maintain control of the aircraft, not a fancy fuel gauge.

Ron Wanttaja
 
Like I said in my an earlier post, the problem isn't inaccurate fuel gauges, it's poor planning and stretching the limits of aircraft. You can have the best fuel totalizer in the world but you'll always have the pilot who will think he can fly for 7 hours without getting fuel and make it out alive.
 
I *can* do over 7 hours if I lean....forward :)
9 if I throttle back and lean it out.
 
You can have all the fuel in the world In the other tank....but, selecting an empty tank helps nothing. No super duper high tech gauge gonna fix that.:no:
 
@Dan

Time Domain Reflectometry is one and Magnetic field is the other
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@wanttaja

I was looking at this from a NY City crime viewpoint - A few years back NYC put in a policy as follows

Many attribute New York's crime reduction to specific "get-tough" policies carried out by former Mayor Rudolph Giuliani's administration. The most prominent of his policy changes was the aggressive policing of lower-level crimes, a policy which has been dubbed the "broken windows" approach to law enforcement. In this view, small disorders lead to larger ones and perhaps even to crime. As Mr. Guiliani told the press in 1998, "Obviously murder and graffiti are two vastly different crimes. But they are part of the same continuum, and a climate that tolerates one is more likely to tolerate the other."

So let's just concentrate on #1 - why not solve - the easy first -
Or maybe that we tolerate a climate that leads to #1

Jordane :
Yours is a well supported idea - However
  • Commercial Aircraft starting with business aircraft don't as a rule run out of fuel
  • Commercial flight is the most closely related to GA flight in the transportation continuum
  • ATP's run out of fuel in GA aircraft.
  • Nobody has a death wish - unless they do
  • In all other transportation modes - inaccuracy in fuel gauges leads to fuel starvation
The idea that pilots just flat desire to outfly their range isn't supported in the accident records

GM recalls 52,000 vehicles to repair inaccurate fuel gauges - the reason provided was that inaccurate fuel gauges in trucks could lead to fuel starvation

In aviation - inaccuracy has nothing to do with pilots making bad decisions given the information provided right in front of them - they know better or I guess they don't

I do know that what pilots have been told to believe - I just don't believe it to be true

Most of the pilot heresy in this particular arena fails simple logic tests
 

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I put the stick on a stick and do it in flight. I leave the gas caps off before I take off, as they just get in the way.
 
ircphoenix said:
I put the stick on a stick and do it in flight. I leave the gas caps off before I take off, as they just get in the way.
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I rather like the image of a guy wingwalking. Kind of goes with the image of one of my passengers having to sit on the tail to take pictures while his grandson is in the right seat.
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@timbuck2, poor planning leads to fuel outages. In the car, I can monitor the milage driven and calculate about how much fuel I've used. If I run dry, I'll coast to a stop. Since I know the warrior is 7 gallons an hour, I can be pretty sure a full tank should yield 8 hours. For planning, 9 gallons gives me 5 1/2. I'll need a watercloset long before I'll need fuel. If I land, I'll replace what I used for the next leg.
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I never want to be the next news item. But there was that one time.... lesson learned!
 
These inaccurate gauges are how old? 25, 35, 40 years? More? How many cars that age have gauges that still work?

The typical fuel sender is a wirewound rheostat that has a lever with a float. The fuel moves the float up and down and changes the resistance of the rheostat. That changing resistance alters a small current flow through one electromagnet in the gauge, with an opposing electromagent driven directly by the power supply. The idea is a system that doesn't misread too badly with aircraft system voltage changes. The electromagnets drive the gauge needle.

The fine resistance wire in the rheostat wears a little as a tiny carbon button runs across it. The button is driven by the lever. The button eventually wears out and the metal starts riding on the wire, chewing it up and making the gauge do stupid things. There's also a small brass runner that grounds the lever, since the sender is the ground for the variable electromagnet in the gauge. That gets worn and/or oxidized, too. And there's usually a small ground strap from the airframe to the sender flange on the tank, to make sure it's grounded, and it gets oxidized or dirty or contaminated with fuel leakage or whatever. The sender body inside the tank can get corroded if the tanks aren't full.

So the failures and inaccuracies are due to age, wear or lack of maintenance. Or all the above. An airplane tied down outside is always moving a tiny bit as the breezes work on it, and the fuel moves a little and that float moves a little and the sender suffers wear. Besides the senders, control cables are always moving a bit, too, even with column-type control locks, and they wear out against fairleads and seized pulleys and whatnot. We regularly find worn cables in low-time, old airplanes that have been outside a long time. Proper external gustlocks can save you money.
 
I look at the fuel gauges sometimes... one always shows fuller than I think it should be, the other one always shows a little more empty than I think it should be. For all practical purposes I ignore the fuel gauges and estimate quantity based on time. My fuel burn is almost exactly 10gph so the math is easy.
 
as long as they are accurate when empty....."what difference does it make?"....:D
 
FastEddieB said:
$2,950 for a Cirrus:

https://www.ciescorp.net/cirrus-aircraft-retrofit.html
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It still uses the seriously limited float-on-a-stick. They claim it's "digital" but so much of this stuff just uses a potentiometer to obtain a varying current flow that's then converted to a digital signal. The potentiometer/rheostat is the wear point and the single-point float is responsible for plenty of inaccuracies. For instance, in a tank with dihedral, where do you put the float? Near the lower end of the tank where the float hits the top of the tank long before it's full, or near the upper end where it hits the bottom long before it's empty, or in the middle where it's inaccurate at both ends of the scale?

Floats also lose a certain amount of movement just because they can't describe accurately the surface of the fuel. They hit the top and bottom of the tank shortly before the fuel does. The old barrel-shaped floats were worse for that than the newer flat floats.
 
Sometimes we make "improvements" where they're not needed. My 140 has the gauges in the wing-roots. They're a simple float and they're extremely accurate. I guess over the years Cessna decided they wanted everything on the panel in front of the pilot.

I really like the sight tube a lot of planes use. Easy and 100% accurate!
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Dan Thomas said:
It still uses the seriously limited float-on-a-stick. They claim it's "digital" but so much of this stuff just uses a potentiometer to obtain a varying current flow that's then converted to a digital signal.
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There is actually no limitation to the float on the stick - It is a perception and not a reality in measuring fuel level. The system described does not use a wiper and is truly digital.

Dan Thomas said:
The potentiometer/rheostat is the wear point and the single-point float is responsible for plenty of inaccuracies. For instance, in a tank with dihedral, where do you put the float?
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You seem to believe the float is the issue. As a matter of practical application it is definitely not. What you are sharing is a common opinion but it is not factually true
Probe placement is a challenge for every fuel sending technology. Capacitive can't measure at the ends of travel either as support and connection issues occur. Ultrasonic is confused by vapor, TDR can't measure full volume either.

Dan Thomas said:
Near the lower end of the tank where the float hits the top of the tank long before it's full, or near the upper end where it hits the bottom long before it's empty, or in the middle where it's inaccurate at both ends of the scale?
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This is definite opinion on your part not supported by any factual information. If you look at all other practical technologies - they suffer similar issues. See above - capacitive probes in certified aircraft do not touch the upper and lower tank wall for various reasons Aircraft have a zero fuel level that is not the botton of the tank and aircraft fuel tanks have to have expansion space above. There is no smoking gun at the top bottom or in the middle.

Dan Thomas said:
Floats also lose a certain amount of movement just because they can't describe accurately the surface of the fuel. They hit the top and bottom of the tank shortly before the fuel does. The old barrel-shaped floats were worse for that than the newer flat floats.
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Dan - it is what you believe - but it is completely not the case. Floats lose zero movement because they ride on the surface of the fuel they actually damp out minor surface motion that would have to be averaged in a capacitance system. While your opinion is common, it has no real basis in actual fuel measurement.

As stated floats but with digital sensor technology is the most popular new technology for new delivered aircraft.
 
Scott Philiben said:
Probe placement is a challenge for every fuel sending technology. Capacitive can't measure at the ends of travel either as support and connection issues occur.
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The capacitive systems on large aircraft, as I said, use multiple strategically-placed probes in each tank, and the outputs are summed. It doesn't matter where the fuel is; if one probe sees a lower level, another will see a higher level, and the net output is the same.

If a light airplane had four senders, one in each corner of the tank, we could get accuracy. Along with more cost, more leak points, more maintenance...
 
Capacitance is "strategically placed" is a misnomer and an indicated bias to a system that has significant issues in modern aircraft. Intrinsic safety being the

largest issue

Capacitance is optimized to reduce probe locations but also provide a completely redundant path because capacitive probes are prone to failure. So in large aircraft it is desired to have a redundant fuel quantity system for every tank.

This was true for the 737 IGW option I was part of and Gulfstream aircraft I was involved in. Capacitance also requires access panels so that failed sensors can be cleaned a source of leakage and replaced.

Despite the supposed supremacy of capacitance - even with a dual redundant capacitive system, commercial and business aircraft can be dispatched with drip sticks (another leakage point) because there is a potential for both redundant capacitive systems to fail. Failure happens quite often

And when professional pilots fly commercial aircraft with non functional fuel indication - (i.e. the two Air Canada events that are well reported) Both examples were commercial aircraft dispatched with non functional dual redundant capacitive systems. The results were news.


Outfitting legacy systems in GA - you are left with traditional locations. Float based probes can be installed to the tank wall - so a smaller opening and the probe can be repaired without tank access. Though that has not proven to be necessary. The probe could be just left inside the tank.

From the data I have a modern float sensor of the type described prior, has a in service history of 350,000 hrs without a single unscheduled removal.

therefore a 99% confidence that it will last multiple lives of a GA aircraft or 70,000 hrs. No capacitive systems even comes close




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Without the constant washing down with JET a a capacitance system is provided in commercial service, failure rate and performance has proven to be un-acceptable in GA (Cessna Pennycap comes to mind). AVGAS has a larger permittivity range (dielectric) and the casual use of GA causes latent corrosion issues. It is these latent corrosion issues that GA pilots fight with traditional resistive wiper systems.

Somebody said it above - If you are flying with the original probes and displays - it is probable and likely that they do not meet the airworthiness requirement of a new system.

Piper Calibration.png
 
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