Bad fuel gauges?

[WingFlaps]

Hi all,
A recurring theme seems to be that one should should not rely in fuel
gauges. I can understand that from a safety point of view (I always
dip the tank before start), but I get the feeling that they are
considered just plain inaccurate. Why is that, every car I've driven
has a fuel gauge that seems accurate. Am I missing something?

A connected point is that I was taught that if you start to worry
about low fuel you switch to the lowest tank (2 tanks) and note the
time. When the engine splutters you know what time/range you have left
to find a good landing spot (after switching tanks). But if a gauge
can't be trusted is that the best thing to do?

Cheers

[Bertie the Bunyip[_24_]]

WingFlaps > wrote in news:63ec40c3-352b-450a-973d-
:

> Hi all,
> A recurring theme seems to be that one should should not rely in fuel
> gauges. I can understand that from a safety point of view (I always
> dip the tank before start), but I get the feeling that they are
> considered just plain inaccurate. Why is that, every car I've driven
> has a fuel gauge that seems accurate. Am I missing something?
>
> A connected point is that I was taught that if you start to worry
> about low fuel you switch to the lowest tank (2 tanks) and note the
> time. When the engine splutters you know what time/range you have left
> to find a good landing spot (after switching tanks). But if a gauge
> can't be trusted is that the best thing to do?
>

It would depend on the type, and I would only do that if I were really
looking for max range and wanted to ascertain I had a decent head of fuel
in the tank I was using for approach. They really are mostly crap, though,
especially the electric ones found in most airplanes. We have a lot of
problems with them in jets too, believe it or not.



Bertie

[TheSmokingGnu]

WingFlaps wrote:
> Why is that, every car I've driven
> has a fuel gauge that seems accurate. Am I missing something?

Ah, grasshopper. But how often do you get to actually look at the fuel
in your car's gas tank? How many cars do you think are on the road that
have bunk gas gauges (I have one, for example; my friend has another)?

Many older aircraft use float-type gauges, and no matter how hard you
try, most floats will develop a slow leak and indicate improperly (or
worse, get stuck or bent and refuse to indicate at all.

Newer electric gauges rely on the fuel to act as a dielectric between
two charged plates (like in a capacitor); except that fuel at different
temperatures, in different climates, from different sources, or
different formulations all have varied dielectric constants, meaning
that the gauge could indicate 22 gallons one day and 18 the next; do you
want to bet your life that there's four extra gallons in the tank?

TheSmokingGnu

[[email protected]]

> We have a lot of
> problems with them in jets too, believe it or not.
>
> Bertie

Doesn't that mean there's a certain fudge factor in landing weight
calculations?

Given the lack of apparent crashes due to inadequate flap settings I
guess that ya'll pretty much have the innacuracies under control.

[[email protected]]

> different formulations all have varied dielectric constants, meaning
> that the gauge could indicate 22 gallons one day and 18 the next; do you
> want to bet your life that there's four extra gallons in the tank?
>
> TheSmokingGnu

Ye Olde E6B and zeroing in on real fuel consumption at cruise gleaned
from actual flight should save the day (older planes not up to chart
performance, usually).

IIRC on similar thread(s) the idea was put forth that the regs only
require the indicator to indicate properly when full and when
empty ... don't know where that would be in the regs (if in fact it
is); maybe part 23?

[[email protected]]

On Feb 23, 9:49*am, wrote:
> IIRC on similar thread(s) the idea was put forth that the regs only
> require the indicator to indicate properly when full and when
> empty ... don't know where that would be in the regs (if in fact it
> is); maybe part 23?

That's an unfortunate myth. (The usual form of the myth is to say that
the gauges only have to be correct when the tanks are empty.) Pilots
who belive it are likely to underestimate the importance of the fuel-
gauge airworthiness requirement. The myth was just debunked on the
other fuel-gauge thread:

There's an urban legend that the fuel gauge is only required to be
correct for an empty tank. The legend apparently arises from a
bizarre
misreading of 23.1337b1. What 23.1337b1 actually says is just
clarifying that the 'empty' reading must correspond to zero USABLE
fuel, as opposed to zero TOTAL fuel. There is nothing whatsoever to
suggest that non-empty readings needn't be correct--that would be
absurd. (If it were true, a gauge that ALWAYS says 'empty' would be
legal! You could just write 'empty' on a piece of paper and call that
your fuel gauge!)

The requirement for indications of a tank's fuel level (not just on
empty) is stated in 91.205b9, 23.1305a1, and 23.1337b.

[Bertie the Bunyip[_24_]]

wrote in news:38ce9894-6517-473f-b36e-602d70fa1a94
@z17g2000hsg.googlegroups.com:

>> We have a lot of
>> problems with them in jets too, believe it or not.
>>
>> Bertie
>
> Doesn't that mean there's a certain fudge factor in landing weight
> calculations?
>


Not really. We have procedures to know what the actual fuel on board is
before departure ( we compare the indicated against the arrival and the
uplift) and we have fuel used based on FF as we go to cross check. When the
gauges work, they work well, problem is when there is any moisture in the
tank they go nuts, though. The senders are capicitor type and just a drop
renders then next to useless. That's th ebiggest bugaboo with them, but the
computers can also give difficulites. If things don;'t add up we "drip" the
tanks. There are little tubes on the bottom of the wing we can pull down
and get an accurate reading of the fuel in the tank.

> Given the lack of apparent crashes due to inadequate flap settings I
> guess that ya'll pretty much have the innacuracies under control.

We pretty much always land at the same flap setting. Just the approach
speed varies. A ton of weight would only mean about a knot in the
difference.


Bertie

[C J Campbell[_1_]]

On 2008-02-22 20:24:47 -0800, WingFlaps > said:

> Hi all,
> A recurring theme seems to be that one should should not rely in fuel
> gauges. I can understand that from a safety point of view (I always
> dip the tank before start), but I get the feeling that they are
> considered just plain inaccurate.

If an airplane does not have accurate fuel gauges then it is not
airworthy. Knowingly climbing into an aircraft that you know has
inaccurate fuel gauges is both dangerous and illegal. That is why you
check them during preflight. From FAR 91.205:

(a) General. Except as provided in paragraphs (c)(3) and (e) of this
section, no person may operate a powered civil aircraft with a standard
category U.S. airworthiness certificate in any operation described in
paragraphs (b) through (f) of this section unless that aircraft
contains the instruments and equipment specified in those paragraphs
(or FAA-approved equivalents) for that type of operation, and those
instruments and items of equipment are in operable condition.
(b) Visual-flight rules (day). For VFR flight during the day, the
following instruments and equipment are required:
(1) Airspeed indicator.
....
(9) Fuel gauge indicating the quantity of fuel in each tank.
--
Waddling Eagle
World Famous Flight Instructor

[C J Campbell[_1_]]

On 2008-02-23 07:57:38 -0800, said:

> On Feb 23, 9:49*am, wrote:
>> IIRC on similar thread(s) the idea was put forth that the regs only
>> require the indicator to indicate properly when full and when
>> empty ... don't know where that would be in the regs (if in fact it
>> is); maybe part 23?
>
> That's an unfortunate myth. (The usual form of the myth is to say that
> the gauges only have to be correct when the tanks are empty.) Pilots
> who belive it are likely to underestimate the importance of the fuel-
> gauge airworthiness requirement. The myth was just debunked on the
> other fuel-gauge thread:
>
> There's an urban legend that the fuel gauge is only required to be
> correct for an empty tank. The legend apparently arises from a
> bizarre
> misreading of 23.1337b1. What 23.1337b1 actually says is just
> clarifying that the 'empty' reading must correspond to zero USABLE
> fuel, as opposed to zero TOTAL fuel. There is nothing whatsoever to
> suggest that non-empty readings needn't be correct--that would be
> absurd. (If it were true, a gauge that ALWAYS says 'empty' would be
> legal! You could just write 'empty' on a piece of paper and call that
> your fuel gauge!)
>
> The requirement for indications of a tank's fuel level (not just on
> empty) is stated in 91.205b9, 23.1305a1, and 23.1337b.

Despite my years of fighting ignorance, many pilots still seem to
believe that the fuel gauge only has to be accurate when it reads 0. In
fact, I have seen both Rod Machado and the Kings assert this. We have
an uphill fight, my brother.
--
Waddling Eagle
World Famous Flight Instructor

[[email protected]]

> There's an urban legend that the fuel gauge is only required to be
> correct for an empty tank. The legend apparently arises from a
> bizarre
> misreading of 23.1337b1. What 23.1337b1 actually says is just
> clarifying that the 'empty' reading must correspond to zero USABLE
> fuel, as opposed to zero TOTAL fuel. There is nothing whatsoever to
> suggest that non-empty readings needn't be correct--that would be
> absurd. (If it were true, a gauge that ALWAYS says 'empty' would be
> legal! You could just write 'empty' on a piece of paper and call that
> your fuel gauge!)
>
> The requirement for indications of a tank's fuel level (not just on
> empty) is stated in 91.205b9, 23.1305a1, and 23.1337b.

Thank you!

What you say makes perfect sense. I'll go look at the regs too.

[[email protected]]

> Despite my years of fighting ignorance, many pilots still seem to
> believe that the fuel gauge only has to be accurate when it reads 0. In
> fact, I have seen both Rod Machado and the Kings assert this. We have
> an uphill fight, my brother.
> --
> Waddling Eagle
> World Famous Flight Instructor- Hide quoted text -
>
> - Show quoted text -

Rod Machado. I have his audio CD book and it may well be that this is
where I heard the idea of being accurate only when full or empty. I
can't remember at the moment but I'll find out.

An earlier post explained the guage can be off by as much as four
gallons. Is that far enough off to not meet regulations?

Well, the important thing to note is they are not accurate. The only
sure-fire method of tracking your fuel, it seems to me, in a GA
aircraft, is to measure starting values, measure your actual
consumption after shutdown, compare to the TDF to climb & cruise
performance charts. Especially if you plan your flight down to the
reserve! (Does anyone really plan to stretch fuel use clear to the
limit of the regs?)

[Denny]

The fuel gauge that goes to zero in flight WILL get my attention....
Other than that, my watch/timer is my fuel gauge...
Being it is my airplane I know how much I takeoff with and what the
burn rate is... From experience I know that engine surging <and tank
switching> is normally within five minutes of what my watch calls
for...
Tips are always burned off first then switched with 30 minutes fuel
remaining... This puts me back on the mains and the timer is reset to
put me back on the ground with 30 minutes, or more, left in the
mains... All told an hour of fuel is always left on board and my
personal check list does not allow eating into that reserve for
anything other than a life or death situation... This iron clad rule
is the result of learning the hard way <no flameout but the tanks took
exactly the usable amount listed in the POH> and has served me well in
the 4 decades since...

[TheSmokingGnu]

wrote:
>> different formulations all have varied dielectric constants, meaning
>> that the gauge could indicate 22 gallons one day and 18 the next; do you
>> want to bet your life that there's four extra gallons in the tank?
>>
>> TheSmokingGnu
>
> Ye Olde E6B and zeroing in on real fuel consumption at cruise gleaned
> from actual flight should save the day (older planes not up to chart
> performance, usually).

Well, even there you have significant challenges; you have to account
for the fuel in takeoff/climb (according to power/leaning), as well as
in descent, and you have to somehow figure out how much you've used in
taxi and runup. There are still large areas where the best you can do is
guesstimate at actual fuel usage.

Even then, unless you have a penchant for wingwalking, it's exceedingly
difficult to measure actual fuel usage in cruise without the fuel
gauges, which we have already established as really "best guess"
instruments anyway.

TheSmokingGnu

[[email protected]]

On Feb 23, 2:11*pm, wrote:
> > Despite my years of fighting ignorance, many pilots still seem to
> > believe that the fuel gauge only has to be accurate when it reads 0. In
> > fact, I have seen both Rod Machado and the Kings assert this. We have
> > an uphill fight, my brother.
> > --
> > Waddling Eagle
> > World Famous Flight Instructor
>
> Rod Machado. I have his audio CD book and it may well be that this is
> where I heard the idea of being accurate only when full or empty. I
> can't remember at the moment but I'll find out.

Maybe the only-accurate-on-empty myth started as one of Rod's jokes
and got out of hand. :)

[Bertie the Bunyip[_24_]]

wrote in
:

> On Feb 23, 2:11*pm, wrote:
>> > Despite my years of fighting ignorance, many pilots still seem to
>> > believe that the fuel gauge only has to be accurate when it reads
>> > 0. In fact, I have seen both Rod Machado and the Kings assert this.
>> > We have an uphill fight, my brother.
>> > --
>> > Waddling Eagle
>> > World Famous Flight Instructor
>>
>> Rod Machado. I have his audio CD book and it may well be that this is
>> where I heard the idea of being accurate only when full or empty. I
>> can't remember at the moment but I'll find out.
>
> Maybe the only-accurate-on-empty myth started as one of Rod's jokes
> and got out of hand. :)
>

I heard it years ago. It doesn't make much difference. They're not reliable
anyway. You wouldn't want to fly around without them, but you woulnd't want
to stake your life on them..


Bertie

[[email protected]]

On Feb 22, 11:24*pm, WingFlaps > wrote:
> A recurring theme seems to be that one should should not rely in fuel
> gauges. I can understand that from a safety point of view (I always
> dip the tank before start), but I get the feeling that they are
> considered just plain inaccurate.

The admonition not to rely on fuel gauges is half-right. The half
that's right is important; the half that's wrong is dangerous.

The half that's right is that you need another way to know how much
fuel there is, because the gauges have limited accuracy, and because a
previously working gauge can always fail suddenly. For the GA planes
I'm familiar with, a visual preflight inspection of the tanks is
required by the POH. From there, you calculate your fuel consumption.
If the gauges say you've got more fuel than you expect, trust your
calculations instead (double-checking if necessary). Aviation safety
is about redundancy.

The half that's wrong is that the admonition ignores a vital
possibility: the gauges may show way LESS fuel than you expect. (Say
you're supposed to have 3/4 of a tank left, but the gauge shows 1/8.)
In that case (if the gauges are working well enough to meet the
airworthiness requirements) you know you've got a problem--perhaps a
fuel leak, which your consumption calculations can't warn you about
without the gauges. A leak may be a very infrequent event, but
aviation safety is about being prepared for unlikely problems, rather
than unnecessarily relying on the gamble that it will never happen to
you.

The Part 91 airworthiness regs (which pilots are required to know
before being allowed to solo) mandate a gauge that indicates the fuel
level in each tank. No specific accuracy is mandated, either in Part
91 or in the aircraft-certification regs in Part 23. So it becomes a
matter of common sense: a working fuel gauge has to be accurate enough
to serve its intended purpose, which (in familiar light GA planes
anyway) is to provide a rough cross-check of the consumption
calculations, to warn of a leak or other problem.

[[email protected]]

On Feb 23, 5:23*pm, Bertie the Bunyip > wrote:
> wrote :
>
>
>
>
>
> > On Feb 23, 2:11*pm, wrote:
> >> > Despite my years of fighting ignorance, many pilots still seem to
> >> > believe that the fuel gauge only has to be accurate when it reads
> >> > 0. In fact, I have seen both Rod Machado and the Kings assert this.
> >> > We have an uphill fight, my brother.
> >> > --
> >> > Waddling Eagle
> >> > World Famous Flight Instructor
>
> >> Rod Machado. I have his audio CD book and it may well be that this is
> >> where I heard the idea of being accurate only when full or empty. I
> >> can't remember at the moment but I'll find out.
>
> > Maybe the only-accurate-on-empty myth started as one of Rod's jokes
> > and got out of hand. :)
>
> I heard it years ago. It doesn't make much difference. They're not reliable
> anyway. You wouldn't want to fly around without them, but you woulnd't want
> to stake your life on them..

Yup, absolutely. They're part of a redundant system--nothing more,
nothing less.

[Bob Gardner]

Look at the Pilot's Handbook of Aeronautical Knowledge, too.

FUEL GAUGES

The fuel quantity gauges indicate the amount of fuel measured by a sensing
unit in each fuel tank and is displayed in gallons or pounds. Aircraft
certification rules only require accuracy in fuel gauges when they read
"empty." Any reading other than "empty" should be verified. Do not depend
solely on the accuracy of the fuel quantity gauges. Always visually check
the fuel level in each tank during the preflight inspection, and then
compare it with the corresponding fuel quantity indication.

Bob Gardner

> wrote in message
...
>> There's an urban legend that the fuel gauge is only required to be
>> correct for an empty tank. The legend apparently arises from a
>> bizarre
>> misreading of 23.1337b1. What 23.1337b1 actually says is just
>> clarifying that the 'empty' reading must correspond to zero USABLE
>> fuel, as opposed to zero TOTAL fuel. There is nothing whatsoever to
>> suggest that non-empty readings needn't be correct--that would be
>> absurd. (If it were true, a gauge that ALWAYS says 'empty' would be
>> legal! You could just write 'empty' on a piece of paper and call that
>> your fuel gauge!)
>>
>> The requirement for indications of a tank's fuel level (not just on
>> empty) is stated in 91.205b9, 23.1305a1, and 23.1337b.
>
> Thank you!
>
> What you say makes perfect sense. I'll go look at the regs too.

[Bob Gardner]

The best fuel gauge is a watch. If the book says that your plane burns 7.4
gallons an hour, subtract 8 gallons from your usable fuel figure and use
that number in all further calculations. Establish a conservative
wheels-on-the-ground time...."Let's see, it's noon now, I have fuel for four
hours on board, I will have the wheels on the ground somewhere (maybe not my
destination), at 3:30."

Bob Gardner

"WingFlaps" > wrote in message
...
> Hi all,
> A recurring theme seems to be that one should should not rely in fuel
> gauges. I can understand that from a safety point of view (I always
> dip the tank before start), but I get the feeling that they are
> considered just plain inaccurate. Why is that, every car I've driven
> has a fuel gauge that seems accurate. Am I missing something?
>
> A connected point is that I was taught that if you start to worry
> about low fuel you switch to the lowest tank (2 tanks) and note the
> time. When the engine splutters you know what time/range you have left
> to find a good landing spot (after switching tanks). But if a gauge
> can't be trusted is that the best thing to do?
>
> Cheers

[William Hung]

On Feb 23, 7:10*pm, "Bob Gardner" > wrote:
> The best fuel gauge is a watch. If the book says that your plane burns 7.4
> gallons an hour, subtract 8 gallons from your usable fuel figure and use
> that number in all further calculations. Establish a conservative
> wheels-on-the-ground time...."Let's see, it's noon now, I have fuel for four
> hours on board, I will have the wheels on the ground somewhere (maybe not my
> destination), at 3:30."
>
> Bob Gardner
>
> "WingFlaps" > wrote in message
>
> ...
>
>
>
> > Hi all,
> > A recurring theme seems to be that one should should not rely in fuel
> > gauges. I can understand that from a safety point of view (I always
> > dip the tank before start), but I get the feeling that they are
> > considered just plain inaccurate. Why is that, every car I've driven
> > has a fuel gauge that seems accurate. Am I missing something?
>
> > A connected point is that I was taught that if you start to worry
> > about low fuel you switch to the lowest tank (2 tanks) and note the
> > time. When the engine splutters you know what time/range you have left
> > to find a good landing spot (after switching tanks). But if a gauge
> > can't be trusted is that the best thing to do?
>
> > Cheers- Hide quoted text -
>
> - Show quoted text -

That's how I'm being taught.

Wil

[Andy Hawkins]

Hi,

In article >,
William > wrote:

> That's how I'm being taught.

And if you've left the fuel cap off in your pre flight, and your fuel has
gradually been ****ing all over the wing, how will you know?

Andy

[[email protected]]

On Feb 23, 7:10*pm, "Bob Gardner" > wrote:
> The best fuel gauge is a watch.

The best fuel gauge is a watch IN CONJUNCTION with an actual fuel
gauge. Neither suffices by itself.

[[email protected]]

On Feb 23, 7:03*pm, "Bob Gardner" > wrote:
> Look at the Pilot's Handbook of Aeronautical Knowledge, too.

Wow, that's depressing. Whoever wrote the handbook apparently couldn't
be bothered to read the regulations before writing about them.

CJ, have you tried to get the FAA to correct their handbook? It's hard
to overcome this nonsense while the FAA is actively recycling it.


> FUEL GAUGES
>
> The fuel quantity gauges indicate the amount of fuel measured by a sensing
> unit in each fuel tank and is displayed in gallons or pounds. Aircraft
> certification rules only require accuracy in fuel gauges when they read
> "empty." Any reading other than "empty" should be verified. Do not depend
> solely on the accuracy of the fuel quantity gauges. Always visually check
> the fuel level in each tank during the preflight inspection, and then
> compare it with the corresponding fuel quantity indication.
>
> Bob Gardner
>
> > wrote in message
>
> ...
>
>
>
> >> There's an urban legend that the fuel gauge is only required to be
> >> correct for an empty tank. The legend apparently arises from a
> >> bizarre
> >> misreading of 23.1337b1. What 23.1337b1 actually says is just
> >> clarifying that the 'empty' reading must correspond to zero USABLE
> >> fuel, as opposed to zero TOTAL fuel. There is nothing whatsoever to
> >> suggest that non-empty readings needn't be correct--that would be
> >> absurd. (If it were true, a gauge that ALWAYS says 'empty' would be
> >> legal! You could just write 'empty' on a piece of paper and call that
> >> your fuel gauge!)
>
> >> The requirement for indications of a tank's fuel level (not just on
> >> empty) is stated in 91.205b9, 23.1305a1, and 23.1337b.
>
> > Thank you!
>
> > What you say makes perfect sense. I'll go look at the regs too.- Hide quoted text -
>
> - Show quoted text -

[William Hung]

On Feb 23, 7:49*pm, Andy Hawkins > wrote:
> Hi,
>
> In article >,
> * * * * * *William > wrote:
>
> > That's how I'm being taught.
>
> And if you've left the fuel cap off in your pre flight, and your fuel has
> gradually been ****ing all over the wing, how will you know?
>
> Andy

I was taught to use that method to cross check with the gauge.

Wil

[[email protected]]

On Feb 23, 8:23*pm, William Hung > wrote:
> On Feb 23, 7:49*pm, Andy Hawkins > wrote:
> > In article >,
> > * * * * * *William > wrote:
> > And if you've left the fuel cap off in your pre flight, and your fuel has
> > gradually been ****ing all over the wing, how will you know?
>
> I was taught to use that method to cross check with the gauge.
>
> Wil

Yup, that's absolutely the way to do it.

[[email protected]]

> The half that's wrong is that the admonition ignores a vital
> possibility: the gauges may show way LESS fuel than you expect. (Say
> you're supposed to have 3/4 of a tank left, but the gauge shows 1/8.)
> In that case (if the gauges are working well enough to meet the
> airworthiness requirements) you know you've got a problem--perhaps a
> fuel leak, which your consumption calculations can't warn you about
> without the gauges. A leak may be a very infrequent event, but
> aviation safety is about being prepared for unlikely problems, rather
> than unnecessarily relying on the gamble that it will never happen to
> you.

Very good point.

A fuel guage rapidly dropping toward E would cause me to go for the
closest airport (hopefully with gas -- but I wouldn't insist on that!).

[RST Engineering]

>
> If an airplane does not have accurate fuel gauges then it is not
> airworthy. Knowingly climbing into an aircraft that you know has
> inaccurate fuel gauges is both dangerous and illegal. That is why you
> check them during preflight. From FAR 91.205:

Horse****.



>
> (a) General. Except as provided in paragraphs (c)(3) and (e) of this
> section, no person may operate a powered civil aircraft with a standard
> category U.S. airworthiness certificate

> ...
> (9) Fuel gauge indicating the quantity of fuel in each tank.


To what precision and accuracy and where defined? More than half but less
than full? More than empty but less than a gallon? More than ten gallons
and less than 11? Cite accuracy regs, please.

Jim

[RST Engineering]

Gee, the world famous aviator is now telling us that the FAA doesn't know
what it is talking about when it writes documents.

Idiot. Get a little real world sense. Whoever wrote the handbook has
dozens of years, thousands of hours, and an understanding of how the world
works.

Rod Machado has not made an error of fact or interpretation as long as I've
known him, and that was probably while you were still in liquid form.

Jim


> Look at the Pilot's Handbook of Aeronautical Knowledge, too.

Wow, that's depressing. Whoever wrote the handbook apparently couldn't
be bothered to read the regulations before writing about them.

CJ, have you tried to get the FAA to correct their handbook? It's hard
to overcome this nonsense while the FAA is actively recycling it.

[RST Engineering]

There is this big blue cloud coming off your flaps and the gas gauge,
admittedly a piece of crap, will SUDDENLY go from full to empty.

Jim

>
> And if you've left the fuel cap off in your pre flight, and your fuel has
> gradually been ****ing all over the wing, how will you know?
>
> Andy

[[email protected]]

On Feb 23, 9:47*pm, "RST Engineering" > wrote:
> Gee, the world famous aviator is now telling us that the FAA doesn't know
> what it is talking about when it writes documents.
>
> Idiot. *Get a little real world sense. *Whoever wrote the handbook has
> dozens of years, thousands of hours, and an understanding of how the world
> works.
>
> Rod Machado has not made an error of fact or interpretation as long as I've
> known him, and that was probably while you were still in liquid form.

People who have truth on their side don't need to resort to insults,
name-calling, bullying, and appeals to authority. They explain their
reasoning instead.

Until you came along, this was an interesting, civil discussion in
which people who disagreed were genuinely trying to understand the
reasons for the differences in their points of view.

But you just want to have a brawl. Sorry, not interested.

>
> Jim
>
> > Look at the Pilot's Handbook of Aeronautical Knowledge, too.
>
> Wow, that's depressing. Whoever wrote the handbook apparently couldn't
> be bothered to read the regulations before writing about them.
>
> CJ, have you tried to get the FAA to correct their handbook? It's hard
> to overcome this nonsense while the FAA is actively recycling it.

[Jay Maynard]

On 2008-02-24, Andy Hawkins > wrote:
> And if you've left the fuel cap off in your pre flight, and your fuel has
> gradually been ****ing all over the wing, how will you know?

By the blue streaks back from the cap along the top of the wing?

Yeah, this kinda leaves 172 drivers out in the cold...
--
Jay Maynard, K5ZC http://www.conmicro.com
http://jmaynard.livejournal.com http://www.tronguy.net
http://www.hercules-390.org (Yes, that's me!)
Buy Hercules stuff at http://www.cafepress.com/hercules-390

[Jay Maynard]

On 2008-02-24, > wrote:
> Until you came along, this was an interesting, civil discussion in
> which people who disagreed were genuinely trying to understand the
> reasons for the differences in their points of view.

Pot, kettle, black. Not once in this discussion have you shown the slightest
interest in dealing with the reality of the large number of aircraft in the
GA fleet having gauges that are unusable in flight beyond "they'r all
illegal!".
--
Jay Maynard, K5ZC http://www.conmicro.com
http://jmaynard.livejournal.com http://www.tronguy.net
http://www.hercules-390.org (Yes, that's me!)
Buy Hercules stuff at http://www.cafepress.com/hercules-390

[[email protected]]

On Feb 23, 10:19*pm, Jay Maynard >
wrote:
> On 2008-02-24, > wrote:
> Pot, kettle, black. Not once in this discussion have you shown the slightest
> interest in dealing with the reality of the large number of aircraft in the
> GA fleet having gauges that are unusable in flight beyond "they'r all
> illegal!".

No, I haven't just proclaimed that. Rather, I've explained in detail
why I think the gauges ARE useful, in a particular way, if they're
anything like the dozens of planes I've rented in various places. And
I've explained in detail why I think they're illegal otherwise, citing
specific regulations. (There may or may not be a "reality" that
illegal planes are common--but that doesn't change whether they're
illegal.) And CJ and I and others have given reasons that fuel gauges
are desirable for safety as well as legality.

You may disagree with the reasons we've put forth, and that's fine.
But we have in fact been explaining ourselves, and responding
constructively and politely to opposing explanations.

[Airbus[_4_]]

In article
>,
says...
>
>
>Hi all,
>A recurring theme seems to be that one should should not rely in fuel
>gauges. I can understand that from a safety point of view (I always
>dip the tank before start), but I get the feeling that they are
>considered just plain inaccurate. Why is that, every car I've driven
>has a fuel gauge that seems accurate. Am I missing something?
>

What kind of car do you drive?
I've never yet driven a car with an accurate fuel gauge. Usually they go
down very slowly for the first half, then much more quickly - exactly the
opposite of the response you would want if your life were to depend on
it.

Fuel gauges in small airplanes often have problems, and should not be
relied upon. There are better methods for soiuynd fuel management.

This said, thje later-generation (post GARA) airplanes have made huge
strides in this respect, and I definitely have a much higher level of
copnfidence in the gauges of a 172-R or a 182-S than the older models.

[Bob Noel]

In article >,
wrote:

> A leak may be a very infrequent event, but
> aviation safety is about being prepared for unlikely problems, rather
> than unnecessarily relying on the gamble that it will never happen to
> you.

But aviation safety is not about being prepared for every single problem
no matter how unlikely. Aviation safety is about reducing the residual
risk to an acceptable level. These levels are defined in AC 23.1309
and AC 25.1309.

>
> The Part 91 airworthiness regs (which pilots are required to know
> before being allowed to solo) mandate a gauge that indicates the fuel
> level in each tank. No specific accuracy is mandated, either in Part
> 91 or in the aircraft-certification regs in Part 23. So it becomes a
> matter of common sense: a working fuel gauge has to be accurate enough
> to serve its intended purpose, which (in familiar light GA planes
> anyway) is to provide a rough cross-check of the consumption
> calculations, to warn of a leak or other problem.

You've just added an "intended purpose" with the claim that the gauge
is there to warn of a leak, etc. The reg states the intended purpose,
that is, to indicate the fuel level. If a aircraft manufacturer wants to
add another intended purpose, then it is allowed to do that. In that
case, it would also be obligated to include that in the Failure Hazard Analysis.

--
Bob Noel
(goodness, please trim replies!!!)

[Bob Noel]

In article >,
Andy Hawkins > wrote:

> And if you've left the fuel cap off in your pre flight, and your fuel has
> gradually been ****ing all over the wing, how will you know?

In a low wing Piper, you look over and see the fuel flowing out of the hole.
You don't need a gauge to detect that hazard. (Perhaps this is another
advantage of flying a cherokee)

--
Bob Noel
(goodness, please trim replies!!!)

[Peter Clark]

On Sun, 24 Feb 2008 07:18:25 -0500, Bob Noel
> wrote:

>In article >,
> Andy Hawkins > wrote:
>
>> And if you've left the fuel cap off in your pre flight, and your fuel has
>> gradually been ****ing all over the wing, how will you know?
>
>In a low wing Piper, you look over and see the fuel flowing out of the hole.
>You don't need a gauge to detect that hazard. (Perhaps this is another
>advantage of flying a cherokee)

And at night?

[Allen[_1_]]

--

"Peter Clark" > wrote in message
...
> On Sun, 24 Feb 2008 07:18:25 -0500, Bob Noel
> > wrote:
>
> >In article >,
> > Andy Hawkins > wrote:
> >
> >> And if you've left the fuel cap off in your pre flight, and your fuel
has
> >> gradually been ****ing all over the wing, how will you know?
> >
> >In a low wing Piper, you look over and see the fuel flowing out of the
hole.
> >You don't need a gauge to detect that hazard. (Perhaps this is another
> >advantage of flying a cherokee)
>
> And at night?

Your 2 D-cell or equivalent flashlight?

--
*H. Allen Smith*
WACO - We are all here, because we are not all there.

[C J Campbell[_1_]]

On 2008-02-23 16:03:52 -0800, "Bob Gardner" > said:

> Look at the Pilot's Handbook of Aeronautical Knowledge, too.
>
> FUEL GAUGES
>
> The fuel quantity gauges indicate the amount of fuel measured by a
> sensing unit in each fuel tank and is displayed in gallons or pounds.
> Aircraft certification rules only require accuracy in fuel gauges when
> they read "empty." Any reading other than "empty" should be verified.
> Do not depend solely on the accuracy of the fuel quantity gauges.
> Always visually check the fuel level in each tank during the preflight
> inspection, and then compare it with the corresponding fuel quantity
> indication.
>
> Bob Gardner

So that is where people keep coming up with that stupid myth! This is a
serious error in the Pilot's Handbook of Aeronautical Knowledge.



--
Waddling Eagle
World Famous Flight Instructor

[C J Campbell[_1_]]

On 2008-02-23 18:41:51 -0800, "RST Engineering" > said:

>>
>> If an airplane does not have accurate fuel gauges then it is not
>> airworthy. Knowingly climbing into an aircraft that you know has
>> inaccurate fuel gauges is both dangerous and illegal. That is why you
>> check them during preflight. From FAR 91.205:
>
> Horse****.
>
>
>
>>
>> (a) General. Except as provided in paragraphs (c)(3) and (e) of this
>> section, no person may operate a powered civil aircraft with a standard
>> category U.S. airworthiness certificate
>
>> ...
>> (9) Fuel gauge indicating the quantity of fuel in each tank.
>
>
> To what precision and accuracy and where defined? More than half but less
> than full? More than empty but less than a gallon? More than ten gallons
> and less than 11? Cite accuracy regs, please.
>
> Jim

I have had this issue come up in a ramp check. The inspector insisted
that the plane was not airworthy because the gauges read half full and
the tanks were full.

If there is a regulation specifying the tolerances for accuracy, I am
unaware of it. However, the regulations do specify that you must have
fuel gauges indicating the quantity of fuel in each tank and that the
gauges must be calibrated so that "0" means 0 usable fuel. I guess it
depends on how far you think you can get away with it if you are ramp
checked.
--
Waddling Eagle
World Famous Flight Instructor

[C J Campbell[_1_]]

On 2008-02-23 18:47:30 -0800, "RST Engineering" > said:

> Gee, the world famous aviator is now telling us that the FAA doesn't know
> what it is talking about when it writes documents.

Are you claiming that there are no errors in those documents? That the
regs, handbooks, advisory circulars and all the rest are more inerrant
than the Bible? I was not aware that the FAA publications were written
by God.

>
> Idiot. Get a little real world sense. Whoever wrote the handbook has
> dozens of years, thousands of hours, and an understanding of how the world
> works.

I have dozens of years, thousands of hours, and a pretty good
understanding of the how the world works, too.

>
> Rod Machado has not made an error of fact or interpretation as long as I've
> known him, and that was probably while you were still in liquid form.
>
> Jim

In fact, when Rod Machado repeated this myth in AOPA Flight Training
Magazine I wrote to him and asked him about it, pointing out the
regulations. He wrote back and admitted that my interpretation was
probably correct.

Unlike you, Rod is capable of admitting he made a mistake and I have a
great deal of respect for him.

I am not sure which of us is older.



--
Waddling Eagle
World Famous Flight Instructor

[Bob Noel]

In article >,
Peter Clark > wrote:

> >In a low wing Piper, you look over and see the fuel flowing out of the hole.
> >
> >You don't need a gauge to detect that hazard. (Perhaps this is another
> >advantage of flying a cherokee)
>
> And at night?

Flashlight

--
Bob Noel
(goodness, please trim replies!!!)

[[email protected]]

On Feb 24, 7:15*am, Bob Noel >
wrote:
> In article >,
>
> wrote:
> > *A leak may be a very infrequent event, but
> > aviation safety is about being prepared for unlikely problems, rather
> > than unnecessarily relying on the gamble that it will never happen to
> > you.
>
> But aviation safety is not about being prepared for every single problem
> no matter how unlikely. *Aviation safety is about reducing the residual
> risk to an acceptable level. *

Agreed. Or more precisely, it's about reducing the risk-to-cost ratio
to an acceptable level. Some particular small risk might be deemed
acceptable if it would cost $100,000 to avoid, but unacceptable if it
would cost $100 to avoid.

> These levels are defined in AC 23.1309 and AC 25.1309.

The levels are implicitly defined throughout the FARs. For instance,
whenever some item of equipment is deemed necessary for airworthiness,
the FAA is thereby stipulating that the risk of not having that
equipment (in operable condition) is unacceptable, compared to the
cost of having and maintaining that equipment.

> > The Part 91 airworthiness regs (which pilots are required to know
> > before being allowed to solo) mandate a gauge that indicates the fuel
> > level in each tank. No specific accuracy is mandated, either in Part
> > 91 or in the aircraft-certification regs in Part 23. So it becomes a
> > matter of common sense: a working fuel gauge has to be accurate enough
> > to serve its intended purpose, which (in familiar light GA planes
> > anyway) is to provide a rough cross-check of the consumption
> > calculations, to warn of a leak or other problem.
>
> You've just added an "intended purpose" with the claim that the gauge
> is there to warn of a leak, etc. *The reg states the intended purpose,
> that is, to indicate the fuel level.

Indicating the fuel level is WHAT the gauge is required to do. We need
to consider WHY it's required to do that if we want to draw a common
sense conclusion about what kind of accuracy is required (since the
regs don't specify it quantitatively). If we can infer the gauge's
intended purpose, then common sense tells us the gauge is supposed to
be at least accurate enough to be usable for that purpose.

We all agree that fuel gauges are typically much less accurate than
flow calculations or flow measurements. Yet the FAA requires the
gauges, not just the calculations and flow measurements. And one
obvious reason is that the calculations and flow measurements don't
take into account the possibility of a leak. That's not a
controversial explanation, is it?

[Andrew Sarangan]

On Feb 24, 7:18 am, Bob Noel >
wrote:
> In article >,
> Andy Hawkins > wrote:
>
> > And if you've left the fuel cap off in your pre flight, and your fuel has
> > gradually been ****ing all over the wing, how will you know?
>
> In a low wing Piper, you look over and see the fuel flowing out of the hole.
> You don't need a gauge to detect that hazard. (Perhaps this is another
> advantage of flying a cherokee)
>
> --
> Bob Noel
> (goodness, please trim replies!!!)

I have flown airplanes with a fuel sump drain that would not close
properly. This always happened when I took a fuel sample from the
sump, so it was was easy to notice it and fix it. But if it can happen
on the ground, it could also happen during flight.

An accurate fuel gauge is long overdue in aviation. It doesn't have to
be fancy gadgetry, fuel flow integrators or capacitive sensors. One of
the experimental guys had installed a simple pressure sensor under the
fuel tank which measured the total weight of the fuel tank. While not
perfect, it was far better than anything else I have seen, including
sight gauges.

[RST Engineering]

I wonder if a pressure sensor placed inside the bottom of the tank could be
made sensitive enough to "weigh" a column of fuel inside the tank above the
sensor. That would only work for regular sized tanks (no triangles) but
could be integrated over a long enough time to take care of any slosh.

Just a random thought, mindya...and I haven't run the numbers.

Another thought is a string of LEDs separated from photosensors with, say,
10 or 15 of them inside the tank mounted vertically.

Hmmm...any other thoughts for liquid level measurements? Sonar a la
Polaroid?

Jim




> An accurate fuel gauge is long overdue in aviation. It doesn't have to
> be fancy gadgetry, fuel flow integrators or capacitive sensors. One of
> the experimental guys had installed a simple pressure sensor under the
> fuel tank which measured the total weight of the fuel tank. While not
> perfect, it was far better than anything else I have seen, including
> sight gauges.
>

[Bob Noel]

In article >,
wrote:

> > But aviation safety is not about being prepared for every single problem
> > no matter how unlikely. *Aviation safety is about reducing the residual
> > risk to an acceptable level. *
>
> Agreed. Or more precisely, it's about reducing the risk-to-cost ratio
> to an acceptable level.

No. Cost is not part of the equation wrt reducing risk, at least as far
as the FAA is concerned. If you were an applicant and tried to get
an aircraft certified that didn't meet the standards in AC 23.1309 or
AC 25.1309 because it would cost too much, the FAA would deny
the application.



> Some particular small risk might be deemed
> acceptable if it would cost $100,000 to avoid, but unacceptable if it
> would cost $100 to avoid.

More important is the hazard, not the risk.



>
> > These levels are defined in AC 23.1309 and AC 25.1309.
>
> The levels are implicitly defined throughout the FARs. For instance,
> whenever some item of equipment is deemed necessary for airworthiness,
> the FAA is thereby stipulating that the risk of not having that
> equipment (in operable condition) is unacceptable, compared to the
> cost of having and maintaining that equipment.

Have you read AC 23.1309 or AC 25.1309?

--
Bob Noel
(goodness, please trim replies!!!)

[Larry Dighera]

On Sun, 24 Feb 2008 12:50:38 -0800, "RST Engineering"
> wrote in
>:

>I wonder if a pressure sensor placed inside the bottom of the tank could be
>made sensitive enough to "weigh" a column of fuel inside the tank above the
>sensor.

It should be pretty easy to test by connecting the pressure sensor to
the tank drain. I don't see why such a system would be any worse than
a float-based system.

>That would only work for regular sized tanks (no triangles)

I don't know what makes you say that. The pressure sensing system
just needs to be calibrated like one would do with a dip stick, or am
I overlooking something?

>but could be integrated over a long enough time to take care of any slosh.
>
>Just a random thought, mindya...and I haven't run the numbers.
>
>Another thought is a string of LEDs separated from photosensors with, say,
>10 or 15 of them inside the tank mounted vertically.

Placing electrical conductors within fuel tanks always makes me
nervous. I know Boeing does it, but there have been problems.

>Hmmm...any other thoughts for liquid level measurements? Sonar a la
>Polaroid?
>

I'll bet you can get some ideas here:
http://www.sparkfun.com/commerce/categories.php


http://www.sparkfun.com/commerce/product_info.php?products_id=7918
Breakout board for the Analog Devices 7746 capacitance sensor.

http://www.sparkfun.com/commerce/product_info.php?products_id=8257
This is a simple breakout board for the SHT15 humidity sensor from
Sensirion. The SHT15 digital humidity and temperature sensor is
fully calibrated and offers high precision and excellent long-term
stability at low cost.

http://www.sparkfun.com/commerce/product_info.php?products_id=8161
The SCP1000 is the very first absolute pressure sensor on the
market to use MEMs technology to grant 17-bit resolution. Under
ideal conditions, this sensor can detect the pressure difference
within a 9cm column of air.

http://www.sparkfun.com/commerce/categories.php?cPath=23_84
http://www.sparkfun.com/commerce/product_info.php?products_id=8502
Ultrasonic Range Finder - Maxbotix LV-EZ0

If you're not already familiar with this vendor, I think you'll find
the breadth of their products surprising.

>
>> An accurate fuel gauge is long overdue in aviation. It doesn't have to
>> be fancy gadgetry, fuel flow integrators or capacitive sensors. One of
>> the experimental guys had installed a simple pressure sensor under the
>> fuel tank which measured the total weight of the fuel tank. While not
>> perfect, it was far better than anything else I have seen, including
>> sight gauges.
>>
>

[B A R R Y]

On Sun, 24 Feb 2008 12:15:07 -0800 (PST), Andrew Sarangan
> wrote:

>
>I have flown airplanes with a fuel sump drain that would not close
>properly. This always happened when I took a fuel sample from the
>sump, so it was was easy to notice it and fix it. But if it can happen
>on the ground, it could also happen during flight.

Your sump re-opened itself?

There's a difference between not closed, as in you just removed the
jar, and a sump opening by itself.

I'm not saying it can't happen, but the two conditions are very
different.

[Andrew Sarangan]

The reason for the weight sensor was because he did not want to
penetrate the fuel tank to add his sensors. Once inside the fuel tank,
I do not see the benefit of an optical sensor vs a float sensor. In
fact, I don't quite understand why float sensors are so inaccurate in
the first place. It is just a variable resistor. The shape of the fuel
tank can be easily calibrated out. Averaging the sloshing is equally
easy to do. Anyone know what makes them so notoriously inaccurate?



On Feb 24, 3:50 pm, "RST Engineering" > wrote:
> I wonder if a pressure sensor placed inside the bottom of the tank could be
> made sensitive enough to "weigh" a column of fuel inside the tank above the
> sensor. That would only work for regular sized tanks (no triangles) but
> could be integrated over a long enough time to take care of any slosh.
>
> Just a random thought, mindya...and I haven't run the numbers.
>
> Another thought is a string of LEDs separated from photosensors with, say,
> 10 or 15 of them inside the tank mounted vertically.
>
> Hmmm...any other thoughts for liquid level measurements? Sonar a la
> Polaroid?
>
> Jim
>
> > An accurate fuel gauge is long overdue in aviation. It doesn't have to
> > be fancy gadgetry, fuel flow integrators or capacitive sensors. One of
> > the experimental guys had installed a simple pressure sensor under the
> > fuel tank which measured the total weight of the fuel tank. While not
> > perfect, it was far better than anything else I have seen, including
> > sight gauges.

[Larry Dighera]

On Sun, 24 Feb 2008 14:45:58 -0800 (PST), Andrew Sarangan
> wrote in
>:

>Anyone know what makes them so notoriously inaccurate?

A lack of federal regulations mandating their accuracy throughout
their range? :-)

Perhaps inaccuracy is induced over time, because of drift of the
resistance element. But I'd sooner believe, it's because there is no
regulation for accuracy.

[Bertie the Bunyip[_24_]]

Andrew Sarangan > wrote in
:

> The reason for the weight sensor was because he did not want to
> penetrate the fuel tank to add his sensors. Once inside the fuel tank,
> I do not see the benefit of an optical sensor vs a float sensor. In
> fact, I don't quite understand why float sensors are so inaccurate in
> the first place. It is just a variable resistor. The shape of the fuel
> tank can be easily calibrated out. Averaging the sloshing is equally
> easy to do. Anyone know what makes them so notoriously inaccurate?


The mechanical ones, like the wire in a cub or T-craft, was very reliable.
The mechanicla dial gauges you see in the Luscombe, Citabria and some older
Cessnas are also pretty good, though you have to undertand what the
airplane's attitude can do to some indications. It's when there is an
electrical connection that it seems to go wrong.

There is one system I have seen in an old car that was extremely accurate
and reliable. It had a tube that ran from the panel to the fuel tank and
inside th etank it branched out to a a number of tubes, about eight, I
think. Each tube had a little pan shaped dish on it. In the panel there was
a small liquid barometer type device theat sensd the pressure from the
tank. The liquid in the gauge was a red substance, supposedly metal, that
showed the level in eights of a tank. I can't remember what the stuff was
but it was extremely dangerous to handle and you had to send the gauge to a
specialist to have it filled.
It worked really well, bu tI doubt it would be much use in an airplane.


Bertie

[Bertie the Bunyip[_24_]]

Larry Dighera > wrote in
:

> On Sun, 24 Feb 2008 14:45:58 -0800 (PST), Andrew Sarangan
> > wrote in
> >:
>
>>Anyone know what makes them so notoriously inaccurate?
>
> A lack of federal regulations mandating their accuracy throughout
> their range? :-)
>
> Perhaps inaccuracy is induced over time, because of drift of the
> resistance element. But I'd sooner believe, it's because there is no
> regulation for accuracy.
>
Of course you would.


Bertie

[Jim Logajan]

"RST Engineering" > wrote:
> I wonder if a pressure sensor placed inside the bottom of the tank
> could be made sensitive enough to "weigh" a column of fuel inside the
> tank above the sensor. That would only work for regular sized tanks
> (no triangles) but could be integrated over a long enough time to take
> care of any slosh.
>
> Just a random thought, mindya...and I haven't run the numbers.
>
> Another thought is a string of LEDs separated from photosensors with,
> say, 10 or 15 of them inside the tank mounted vertically.
>
> Hmmm...any other thoughts for liquid level measurements? Sonar a la
> Polaroid?

Just looked through my copy of "AIP Handbook of Modern Sensors" by Jacob
Fraden for existing ideas and inspiration. Here's what I got:

It shows one fiber-optic sensor that relies on the change in refractive
index between air and the liquid being measured. If you can find a copy,
check under section 5.8.2 "Fiber-optic sensors". But since it mentions
the company Gem Sensors as already having a product built on the
concept, you can go to their web site for technical details:

http://www.gemssensors.com/content.aspx?id=382

Unfortunately it is a "point level" detector. Gen Sensors also has level
sensors that use ultrasonics in a different way: impedance changes (see
for example):

http://www.gemssensors.com/uploadedFiles/Literature/Spec_Sheets/exosense_specsheetPRINT.pdf

Another idea with respect to refractive index change: use a laser diode
at the top of the tank angled down to a mirror at the bottom of the tank
and a line of receiving photodiodes or phototransistors at the top of
the tank, like so:

Laser
Diode P1 P2 P3 P4 P5 (Line of photosensors)
\ /
\ /
------------------------ liquid level
\ /
\/ (Trying to show change in angle)
-----==========--------- Bottom of tank
(mirror)

As the liquid level changes, the photosensors(s) that receive most of
the light also change. Obviously vibration will make the reception dance
around but time averaging should probably work to resolve that.

Ironically I think vibration noise can actually be used to yield a
higher resolution than that given by the number of receptors. That is,
if you had only 10 sensors but did 100 readings and got 70 hits at P7
and 30 hits at P8 you could reasonably say the average is near (70*7 +
30*8)/100 = 7.3 within (I think) an RMS of +/- 0.1 (That is, 1/sqrt(N)
where N is the number of measurements. But my statistics is very rusty.)
By contrast, if there were no noise the resolution would be limited
to +/- 1.

[Andrew Sarangan]

On Feb 24, 5:40 pm, B A R R Y > wrote:
> On Sun, 24 Feb 2008 12:15:07 -0800 (PST), Andrew Sarangan
>
> > wrote:
>
> >I have flown airplanes with a fuel sump drain that would not close
> >properly. This always happened when I took a fuel sample from the
> >sump, so it was was easy to notice it and fix it. But if it can happen
> >on the ground, it could also happen during flight.
>
> Your sump re-opened itself?
>
> There's a difference between not closed, as in you just removed the
> jar, and a sump opening by itself.
>
> I'm not saying it can't happen, but the two conditions are very
> different.

No it did not re-open by itself, just refused to close. I ended up
with a big puddle of fuel on the floor by the time I forced it in. I
realize it is spring loaded and is not the same thing as coming lose
on its own. However, whats to say that a sudden upward acceleration
can't pop the valve open? Being on the underside of the fuselage/wing
there will be no way of knowing if there is a small leak.

[Jim Logajan]

Andrew Sarangan > wrote:
> The reason for the weight sensor was because he did not want to
> penetrate the fuel tank to add his sensors.

An ultrasonic transducer mounted outside a tank might work - it would get
one reflection off the surface of the liquid in addition to reflections off
the tank walls. The tank wall reflections would remain constant and could
be ignored (or even used for calibration) but the reflection off the liquid
surface should be detected and time-of-flight or sonic interferometry could
be used to compute its location.

[Bertie the Bunyip[_24_]]

Andrew Sarangan > wrote in news:ec390484-a14f-475c-
:

> On Feb 24, 5:40 pm, B A R R Y > wrote:
>> On Sun, 24 Feb 2008 12:15:07 -0800 (PST), Andrew Sarangan
>>
>> > wrote:
>>
>> >I have flown airplanes with a fuel sump drain that would not close
>> >properly. This always happened when I took a fuel sample from the
>> >sump, so it was was easy to notice it and fix it. But if it can
happen
>> >on the ground, it could also happen during flight.
>>
>> Your sump re-opened itself?
>>
>> There's a difference between not closed, as in you just removed the
>> jar, and a sump opening by itself.
>>
>> I'm not saying it can't happen, but the two conditions are very
>> different.
>
> No it did not re-open by itself, just refused to close. I ended up
> with a big puddle of fuel on the floor by the time I forced it in. I
> realize it is spring loaded and is not the same thing as coming lose
> on its own. However, whats to say that a sudden upward acceleration
> can't pop the valve open?


That doesn't happen. it's usually grit in the seat that keps them from
closing properly or a badly gummed up drain.

Being on the underside of the fuselage/wing
> there will be no way of knowing if there is a small leak.

Well, if you check it carefully after you drain it, it's extremely
unlikely.


Bertie

[Andrew Sarangan]

On Feb 24, 6:17 pm, Jim Logajan > wrote:
> "RST Engineering" > wrote:
> > I wonder if a pressure sensor placed inside the bottom of the tank
> > could be made sensitive enough to "weigh" a column of fuel inside the
> > tank above the sensor. That would only work for regular sized tanks
> > (no triangles) but could be integrated over a long enough time to take
> > care of any slosh.
>
> > Just a random thought, mindya...and I haven't run the numbers.
>
> > Another thought is a string of LEDs separated from photosensors with,
> > say, 10 or 15 of them inside the tank mounted vertically.
>
> > Hmmm...any other thoughts for liquid level measurements? Sonar a la
> > Polaroid?
>
> Just looked through my copy of "AIP Handbook of Modern Sensors" by Jacob
> Fraden for existing ideas and inspiration. Here's what I got:
>
> It shows one fiber-optic sensor that relies on the change in refractive
> index between air and the liquid being measured. If you can find a copy,
> check under section 5.8.2 "Fiber-optic sensors". But since it mentions
> the company Gem Sensors as already having a product built on the
> concept, you can go to their web site for technical details:
>
> http://www.gemssensors.com/content.aspx?id=382
>
> Unfortunately it is a "point level" detector. Gen Sensors also has level
> sensors that use ultrasonics in a different way: impedance changes (see
> for example):
>
> http://www.gemssensors.com/uploadedFiles/Literature/Spec_Sheets/exose...
>
> Another idea with respect to refractive index change: use a laser diode
> at the top of the tank angled down to a mirror at the bottom of the tank
> and a line of receiving photodiodes or phototransistors at the top of
> the tank, like so:
>
> Laser
> Diode P1 P2 P3 P4 P5 (Line of photosensors)
> \ /
> \ /
> ------------------------ liquid level
> \ /
> \/ (Trying to show change in angle)
> -----==========--------- Bottom of tank
> (mirror)
>
> As the liquid level changes, the photosensors(s) that receive most of
> the light also change. Obviously vibration will make the reception dance
> around but time averaging should probably work to resolve that.
>
> Ironically I think vibration noise can actually be used to yield a
> higher resolution than that given by the number of receptors. That is,
> if you had only 10 sensors but did 100 readings and got 70 hits at P7
> and 30 hits at P8 you could reasonably say the average is near (70*7 +
> 30*8)/100 = 7.3 within (I think) an RMS of +/- 0.1 (That is, 1/sqrt(N)
> where N is the number of measurements. But my statistics is very rusty.)
> By contrast, if there were no noise the resolution would be limited
> to +/- 1.

All of them good ideas, but why are they likely to be more accurate
than the float level sensor?

[RST Engineering]

Because

a) floats inherently leak over time unless they are some light solid, and
then they have a tendency over decades to break down and saturate.

b) the "state of the art" for float sensors use a wiper against a nichrome
wirewound resistor and the wiper tends to wear a hole and the nichrome tends
to redistribute itself across the form somewhat nonlinearily.

c) just because it was good enough for Henry Ford, it's good enough for us
{;-)


Jim



> All of them good ideas, but why are they likely to be more accurate
> than the float level sensor?

[Jay Maynard]

On 2008-02-24, > wrote:
> No, I haven't just proclaimed that. Rather, I've explained in detail
> why I think the gauges ARE useful, in a particular way, if they're
> anything like the dozens of planes I've rented in various places. And
> I've explained in detail why I think they're illegal otherwise, citing
> specific regulations. (There may or may not be a "reality" that
> illegal planes are common--but that doesn't change whether they're
> illegal.) And CJ and I and others have given reasons that fuel gauges
> are desirable for safety as well as legality.

You have not, however, explained why, since fuel gauge accuracy is
notoriously unreliable for good and sufficient reason, half the GA fleet or
more isn't grounded.

Your responses are all straight out of the book, with no grounding in the
real world.
--
Jay Maynard, K5ZC http://www.conmicro.com
http://jmaynard.livejournal.com http://www.tronguy.net
http://www.hercules-390.org (Yes, that's me!)
Buy Hercules stuff at http://www.cafepress.com/hercules-390

[GeorgeB]

On Sun, 24 Feb 2008 12:50:38 -0800, "RST Engineering"
> wrote:

>I wonder if a pressure sensor placed inside the bottom of the tank could be
>made sensitive enough to "weigh" a column of fuel inside the tank above the
>sensor. That would only work for regular sized tanks (no triangles) but
>could be integrated over a long enough time to take care of any slosh.

Pressure transducers have sufficient resolution and range to do that.
The problem is that you need to "dial out" the G forces as the fuel
weight will vary with that. For straight and level flight it would be
pretty good.

You are not looking at a garden variety transducer, however; with
avgas at 6#/gal, it takes about 3 feet to generate 1 psi. Depending
on tank geometry and size, I doubt a piston single would exceed that 1
psi. (3 ft tall tank)

[C J Campbell[_1_]]

On 2008-02-24 17:29:14 -0800, Jay Maynard
> said:

> On 2008-02-24, > wrote:
>> No, I haven't just proclaimed that. Rather, I've explained in detail
>> why I think the gauges ARE useful, in a particular way, if they're
>> anything like the dozens of planes I've rented in various places. And
>> I've explained in detail why I think they're illegal otherwise, citing
>> specific regulations. (There may or may not be a "reality" that
>> illegal planes are common--but that doesn't change whether they're
>> illegal.) And CJ and I and others have given reasons that fuel gauges
>> are desirable for safety as well as legality.
>
> You have not, however, explained why, since fuel gauge accuracy is
> notoriously unreliable for good and sufficient reason, half the GA fleet or
> more isn't grounded.
>
> Your responses are all straight out of the book, with no grounding in the
> real world.

I would have to see some actual evidence that half the GA fleet should
be grounded for inaccurate fuel gauges. In fact, I doubt if they are
nearly as inaccurate as you claim them to be. Blind belief in an
aviation legend is not real world experience.

Yes, I know fuel gauges can be inaccurate. But that does not mean that
they are always inaccurate, that they are totally unusable, or that
they only have to be accurate when they are empty. Assertions like that
are simply nonsense.

Airplane fuel gauges are generally accurate. Yes, they can be thrown
off by lack of maintenance, unusual attitudes, turbulence, and
malfunction. But those are the exceptions, not the rule. Flying with
malfunctioning fuel gauges can get your ticket pulled, whether you
think that is fair or not. Flying with a malfunctioning fuel gauge
simply because you think that is normal or that it is inaccurate anyway
is simply an excuse for poor piloting, poor maintenance, and general
laziness.
--
Waddling Eagle
World Famous Flight Instructor

[Bertie the Bunyip[_24_]]

C J Campbell > wrote in
news:2008022418524316807-christophercampbell@hotmailcom:

> On 2008-02-24 17:29:14 -0800, Jay Maynard
> > said:
>

> I would have to see some actual evidence that half the GA fleet should
> be grounded for inaccurate fuel gauges. In fact, I doubt if they are
> nearly as inaccurate as you claim them to be. Blind belief in an
> aviation legend is not real world experience.
>
> Yes, I know fuel gauges can be inaccurate. But that does not mean that
> they are always inaccurate, that they are totally unusable, or that
> they only have to be accurate when they are empty. Assertions like
> that are simply nonsense.
>
> Airplane fuel gauges are generally accurate. Yes, they can be thrown
> off by lack of maintenance, unusual attitudes, turbulence, and
> malfunction. But those are the exceptions, not the rule. Flying with
> malfunctioning fuel gauges can get your ticket pulled, whether you
> think that is fair or not. Flying with a malfunctioning fuel gauge
> simply because you think that is normal or that it is inaccurate
> anyway is simply an excuse for poor piloting, poor maintenance, and
> general laziness.

I'd agree with al of this except the part that says they're generally
reliable. I've seen lots of them that aren't. Lots and lots!

Bertie

[[email protected]]

> The requirement for indications of a tank's fuel level (not just on
> empty) is stated in 91.205b9, 23.1305a1, and 23.1337b.

Let me just quote these.

91.205, b9:
"(a) General. Except as provided in paragraphs (c)(3) and (e) of this
section, no person may operate a powered civil aircraft with a
standard category U.S. airworthiness certificate in any operation
described in paragraphs (b) through (f) of this section unless that
aircraft contains the
instruments and equipment specified in those paragraphs (or FAA-
approved equivalents) for that type of operation, and those
instruments and items of equipment are in operable condition."
....
(9) Fuel gauge indicating the quantity of fuel in each tank.

I did my primary training in a plane that had a right wing tank fuel
gauge that always showed less than "F" when the tank was completely
full. If the interpretation of the FAR is STRICT, I guess that means
my training was done illegally, because the gauge DID NOT indicate the
quantity of fuel in the right wing tank (ie, FULL). Rather, it
indicated less than full.

But the writing of the reg is not explicit (they get explicit in
1337b). To me it comes down to ramp checks, FAA enforcement, and case
law. I have never flown that aircraft to the end of its usable fuel,
so I don't if the aircraft I did my primary training in adheres to
1337b:

"(b) Fuel quantity indicator. There must be a means to indicate to the
flightcrew members the quantity of usable fuel in each tank during
flight. An indicator calibrated in appropriate units and clearly
marked to indicate those units must be used. In addition--
(1) Each fuel quantity indicator must be calibrated to read "zero"
during level flight when the quantity of fuel remaining in the tank is
equal to the unusable fuel supply determined under [Sec. 23.959(a);]"

So, what's the case history? How many pilots / mechanics have been
fined, had their certification suspended or even revoked because a
fuel gauge was shown to not indicate "the quantity of fuel in each
tank."

The FAA regs listed only speak to calibration when talking about zero
useable fuel. Nothing else.

If that's the only unambiguous calibration statement in the FARs then
I think that's because the FAA realizes fuel gauge accuracy is subject
to reasonable limitations. Why would they otherwise have us spend so
much time understanding calculated vs real fuel usage, especially
during cross country training for the private certificate? If gas
gauges were really accurate then the FAA wouldn't bug us so much about
learning to calculate and cross-check, and cruise charts wouldn't be
such a critical part of the POH. The recommended way and the way we
train is to KNOW YOUR AIRCRAFT through repeated measurement and cross-
checking the perf charts.

No FAA or other training manual says "Just check you gas gauge real
quick to see if you need to pull over for gas -- and make sure you
land and refuel when the idiot light comes on!"

Gas gauges provide solid value as indicators of possible leak
situations and when you are almost out (again, calibration is mandated
to be correct only at zero).

Lawyers specialize in writing that is crystal clear when they want it
to be, and subject to court judgement otherwise. I think the fuzzy
language the government lawyers used in crafting the regs around fuel
gauges was done on purpose.

[WJRFlyBoy]

On Sun, 24 Feb 2008 17:26:53 -0800, RST Engineering wrote:

> a) floats inherently leak over time unless they are some light solid, and
> then they have a tendency over decades to break down and saturate.

Kevlar?
--
Remove numbers for gmail and for God's sake it ain't "gee" either!

[[email protected]]

On Feb 24, 8:29*pm, Jay Maynard >
wrote:
> On 2008-02-24, > wrote:
> You have not, however, explained why, since fuel gauge accuracy is
> notoriously unreliable for good and sufficient reason, half the GA fleet or
> more isn't grounded.

Yes I've repeatedly explained that. What I keep pointing out is that
the gauges are typically at least accurate enough to alert you to a
large leak, which is a warning that your flow calculations cannot give
you. That makes the gauges useful (and operable), in a limited but
important way, and explains why they're required for airworthiness.

But as I have acknowledged, the flow calculations are typically much
more reliable than the gauges under NORMAL circumstances. That's fine--
the guages are just one part of how you're supposed to keep track of
your fuel.

[[email protected]]

On Feb 24, 8:06*pm, Clark > wrote:
> That said, how on Earth can fuel gauges be considered accurate? At the very
> least one would have to specify attitude (which some gauges do but most
> don't). Maybe there could be a calibration card for airspeed, weight, and
> CG? Wouldn't that be fun?

The gauges are typically at least accurate enough to alert you to a
large leak, which is a warning that your flow calculations cannot give
you. That makes the gauges useful (and operable), in a limited but
important way, and explains why they're required for airworthiness.

As I have acknowledged, the flow calculations are typically much more
reliable than the gauges under NORMAL circumstances. That's fine--the
gauges are just one part of how you're supposed to keep track of your
fuel.

[[email protected]]

On Feb 24, 4:10 pm, Bob Noel >
wrote:
> In article >,
> No. Cost is not part of the equation wrt reducing risk, at least as far
> as the FAA is concerned. If you were an applicant and tried to get
> an aircraft certified that didn't meet the standards in AC 23.1309 or
> AC 25.1309 because it would cost too much, the FAA would deny
> the application.

I see what you're getting at. Those ACs indeed specify a maximum
acceptable probability for e.g. a catastrophic failure, regardless of
the cost of keeping the probability within that bound. But that's
still consistent with my point about cost, for three reasons.

First, the decision where to set the acceptability threshold is
already informed by the FAA's knowledge of what threshold is
affordable. The ACs' acceptable probability of catastrophic failure,
especially for the less expensive classes of GA aircraft, is high
enough to allow many fatalities per year across the fleet. If much
higher safety were achievable at a reasonable cost, the FAA would
presumably have set the probability threshold lower.

Second, for the more expensive classes of GA aircraft, that threshold
IS set lower, by two or three orders of magnitude! Presumably, that's
in part because the bigger planes can afford to meet higher safety
standards--standards that would swamp the cost of the smaller planes.

Third, those ACs set a CEILING for acceptable failure probabilities.
Unless I've missed something, there's nothing in the ACs to prevent
the FAA from deciding that a particular item of safety equipment is
required for airworthiness, even if the absence of that equipment
would still leave the catastrophe probabilities within the standards
set by the ACs. And cost is surely a factor in making THOSE decisions.
(For example, if ADS-B technology cost $500,000 per plane, the FAA
would not be proposing to require it.)

[Maxwell]

> wrote in message
...

<The gauges are typically at least accurate enough to alert you to a
<large leak, which is a warning that your flow calculations cannot give
<you. That makes the gauges useful (and operable), in a limited but
<important way, and explains why they're required for airworthiness.

Fuel gauges fail a lot more often than we develop significant leaks, and
fuel gauges will never be able to reassure you that you don't have small
leak causing an extreme fire hazard.

Hence, experience has taught all of us (including the FAA), that there are
much better ways to manage your fuel 99 and 44/100% of the time, than the
fuel gauges made possible by current technology.

Get over it!!

I can assure you:
if you get caught on a ramp check,
and they even notice a failed fuel gauge,
and are anal enough to stick you for it,
and they can prove that it didn't just happen,

It just wasn't your day to be flying, and you are probably damn lucky you
didn't actually get in the air.

These are the kind of days you get run over by an F-16, loose both mags over
water, stroke out, your dog leaves you, etc. You should actually be glad
you only got stuck with 90 day suspension for a bad fuel gauge.

[Maxwell]

> wrote in message
...
> On Feb 24, 4:10 pm, Bob Noel >
> wrote:
>> In article
>> >,
>> No. Cost is not part of the equation wrt reducing risk, at least as far
>> as the FAA is concerned. If you were an applicant and tried to get
>> an aircraft certified that didn't meet the standards in AC 23.1309 or
>> AC 25.1309 because it would cost too much, the FAA would deny
>> the application.
>
> I see what you're getting at. Those ACs indeed specify a maximum
> acceptable probability for e.g. a catastrophic failure, regardless of
> the cost of keeping the probability within that bound. But that's
> still consistent with my point about cost, for three reasons.
>
> First, the decision where to set the acceptability threshold is
> already informed by the FAA's knowledge of what threshold is
> affordable. The ACs' acceptable probability of catastrophic failure,
> especially for the less expensive classes of GA aircraft, is high
> enough to allow many fatalities per year across the fleet. If much
> higher safety were achievable at a reasonable cost, the FAA would
> presumably have set the probability threshold lower.
>
> Second, for the more expensive classes of GA aircraft, that threshold
> IS set lower, by two or three orders of magnitude! Presumably, that's
> in part because the bigger planes can afford to meet higher safety
> standards--standards that would swamp the cost of the smaller planes.
>
> Third, those ACs set a CEILING for acceptable failure probabilities.
> Unless I've missed something, there's nothing in the ACs to prevent
> the FAA from deciding that a particular item of safety equipment is
> required for airworthiness, even if the absence of that equipment
> would still leave the catastrophe probabilities within the standards
> set by the ACs. And cost is surely a factor in making THOSE decisions.
> (For example, if ADS-B technology cost $500,000 per plane, the FAA
> would not be proposing to require it.)

Your going to "fit right in" around here!

[Andrew Sarangan]

On Feb 24, 8:26 pm, "RST Engineering" > wrote:
> Because
>
> a) floats inherently leak over time unless they are some light solid, and
> then they have a tendency over decades to break down and saturate.
>
> b) the "state of the art" for float sensors use a wiper against a nichrome
> wirewound resistor and the wiper tends to wear a hole and the nichrome tends
> to redistribute itself across the form somewhat nonlinearily.
>
> c) just because it was good enough for Henry Ford, it's good enough for us
> {;-)
>


Good point. I never thought about the leaking float.

[[email protected]]

On Feb 25, 1:40*pm, "Maxwell" > wrote:
> > wrote in message
>
> ...
>
> <The gauges are typically at least accurate enough to alert you to a
> <large leak, which is a warning that your flow calculations cannot give
> <you. That makes the gauges useful (and operable), in a limited but
> <important way, and explains why they're required for airworthiness.
>
> Fuel gauges fail a lot more often than we develop significant leaks,

No one here has claimed otherwise. But the point of redundant systems--
in this case, the gauges plus your flow calculation--is that if
there's a problem with one system, the other probably still works. And
that's true regardless of which of the two systems fails more often
than the other.

> and fuel gauges will never be able to reassure you that you don't
> have small leak causing an extreme fire hazard.

Of course not. No one has suggested that the gauges are useful for
reassuring you that you DON'T have a leak.

The point is just that if the gauges are screaming that you DO have a
leak, then they've conveyed a useful warning that you should notice
and react to.

> Hence, experience has taught all of us (including the FAA), that there are
> much better ways to manage your fuel *99 and 44/100% of the time, than the
> fuel gauges made possible by current technology.

Of course. As I've said repeatedly, your flow calculation is normally
a much more accurate way to keep track of your fuel, and should never
be neglected.

But IN ADDITION, you should be monitoring your gauges for signs that
your situation ISN'T normal. The FAA requires working gauges so you
can do that. That's all I've been saying.

[Maxwell]

> wrote in message
...
On Feb 25, 1:40 pm, "Maxwell" > wrote:
> > wrote in message
>
> ...
>
> <The gauges are typically at least accurate enough to alert you to a
> <large leak, which is a warning that your flow calculations cannot give
> <you. That makes the gauges useful (and operable), in a limited but
> <important way, and explains why they're required for airworthiness.
>
> Fuel gauges fail a lot more often than we develop significant leaks,

No one here has claimed otherwise. But the point of redundant systems--
in this case, the gauges plus your flow calculation--is that if
there's a problem with one system, the other probably still works. And
that's true regardless of which of the two systems fails more often
than the other.

> and fuel gauges will never be able to reassure you that you don't
> have small leak causing an extreme fire hazard.

Of course not. No one has suggested that the gauges are useful for
reassuring you that you DON'T have a leak.

The point is just that if the gauges are screaming that you DO have a
leak, then they've conveyed a useful warning that you should notice
and react to.

> Hence, experience has taught all of us (including the FAA), that there are
> much better ways to manage your fuel 99 and 44/100% of the time, than the
> fuel gauges made possible by current technology.

Of course. As I've said repeatedly, your flow calculation is normally
a much more accurate way to keep track of your fuel, and should never
be neglected.

But IN ADDITION, you should be monitoring your gauges for signs that
your situation ISN'T normal. The FAA requires working gauges so you
can do that. That's all I've been saying.

[Maxwell]

> wrote in message
...
On Feb 25, 1:40 pm, "Maxwell" > wrote:
> > wrote in message
>
> ...
>
> <The gauges are typically at least accurate enough to alert you to a
> <large leak, which is a warning that your flow calculations cannot give
> <you. That makes the gauges useful (and operable), in a limited but
> <important way, and explains why they're required for airworthiness.
>
> Fuel gauges fail a lot more often than we develop significant leaks,

No one here has claimed otherwise. But the point of redundant systems--
in this case, the gauges plus your flow calculation--is that if
there's a problem with one system, the other probably still works. And
that's true regardless of which of the two systems fails more often
than the other.

> and fuel gauges will never be able to reassure you that you don't
> have small leak causing an extreme fire hazard.

Of course not. No one has suggested that the gauges are useful for
reassuring you that you DON'T have a leak.

The point is just that if the gauges are screaming that you DO have a
leak, then they've conveyed a useful warning that you should notice
and react to.

> Hence, experience has taught all of us (including the FAA), that there are
> much better ways to manage your fuel 99 and 44/100% of the time, than the
> fuel gauges made possible by current technology.

Of course. As I've said repeatedly, your flow calculation is normally
a much more accurate way to keep track of your fuel, and should never
be neglected.

But IN ADDITION, you should be monitoring your gauges for signs that
your situation ISN'T normal. The FAA requires working gauges so you
can do that. That's all I've been saying.

Ya just don't get it, do ya?