Running out of fuel

[black hole]

In flying in the bush there are many times that the fuel can be tight.--- I had sufficient fuel for the flight but late afternoon TCUs caused some diversions. Yes I read the aircraft POH --the part on cruising for endurance and reduced power. I always got home with safe fuel. Its called fuel management.

BH

[Doc]

In flying in the bush there are many times that the fuel can be tight.--- I had sufficient fuel for the flight but late afternoon TCUs caused some diversions. Yes I read the aircraft POH --the part on cruising for endurance and reduced power. I always got home with safe fuel. Its called fuel management.

BH

It's also called dumb ass luck. Keep this in mind.

[pdw]

One thing that always bothered me was pilots accepting fuel gauges that didn't read correctly. I've heard many King Air pilots explain that the fuel gauges just don't read right. Unless we are talking about a -100 with float senders, there is simply no reason for fuel gauges that don't work. Every time you get an aircraft with fuel gauges that don't read correctly, record the behaviour, talk to the engineers about it, and write it in the book. If it comes back not reading correctly, repeat the process. Keep repeating until you get fuel gauges that work correctly through the entire range. Keep in mind that water and fungi in the tanks can also cause fuel gauge problems, so make sure the tanks are clean and being sumped regularly.

When there's a lot of pilots of the same aircraft design in agreement that gauges aren't reading right, the engineers should be able to explain why. The only way the PIC would know the gauge is incorrectly showing 'fuel level' with some proof is if he/she measures it manually and compares them, .. unless very-obviously far askew in one direction. Might not show up every time either, hit and miss? But unless the concerned pilot comes up with real proof, it's also more difficult to take seriously for those with the ability to troubleshoot where the issue lies. If the gauge is consistantly inaccurate it should be straighforward to find the problem is the gauge.

You're not differentiating "fuel gauges that just don't read correctly" (no matter how small the misrepresentation of the jet fuel ... low-side or highside) from a non-functioning gauge, .. are saying when gauges are "not reading correctly" ... they "don't work".

[Doc]

I kind of prefer gauges don't work at all to ones that read incorrectly. Fill them, dip them or park it. Really pretty simple. If you can't ascertain how much petrol you have.....you just shouldn't go at all. Not rocket science. Really.

[photofly]

I'm reasonably sure that an aircraft that has a malfunctioning fuel gauge is automatically not airworthy. A way to determine the fuel in each main tank from every pilot station is required even for VFR flight. [605.14(j)(i)]

[Doc]

I'm reasonably sure that an aircraft that has a malfunctioning fuel gauge is automatically not airworthy. A way to determine the fuel in each main tank from every pilot station is required even for VFR flight. [605.14(j)(i)]

You could be wrong. But you'd have to start with full tanks and have a functioning time piece. Or you could "dip" the tanks like in the good old days and go with that. Otherwise, most fuel indication problems would be in your MEL....if you have one.

A little common sense would also dictate that if your 172 is FULL, and the mission is 2 hours, you know you'll be alright. But fill it up for the return flight as well.

[pdw]

I will admit to putting more gas in a Baron than the POH claimed it held. Long story. Had the CP, and the company owner on board and we were all crapping bricks! But the puppy kept running!

What time of year ? My guess is early spring. Stratified fuel storage ... the denser fuel layer settles out to the bottom where the sump is ... the ground is also still cold (if the tanks are at least partly underground). Then as the fuel is used up for the flight there's some expansion as it warms so you get lucky there's a bit more than you thought there was ... in such case no problem to have 5% more gas than average in your tanks.

[pelmet]

Almost anybody who has been around in GA for a while has come across fuel gauges that were U/S. And most of us have gone flying in such situations. I certainly have used a dipstick or tank that has "tabs" and eyeballing the level. In fact I have done this quite a lot. One aircraft I currently fly has no fuel gauge in one of its tanks and fuel consumed is based on time and power setting only.

But there are certain gotcha's. Was the aircraft on a level surface when you checked the fuel level. That can make a big difference depending on type. Long range tanks on some Cessna's can have a large area. A little bit below the top of the tank can equal a lot of gallons when the area times the relatively shallow depth are multiplied together.

I used to fly a twin Cessna with long range tanks. 7 hours worth at cruise power. The fillers were far outboard and after about 2.5 hours, you were looking at the bottom of the tank yet had plenty of fuel. It was a bit of a concern if the A/C was left alone at a small airport for a while(as in several hours). People have been known to steal fuel.

As well, a fuel leak can go undetected. I ferried a Citabria one time which only had one fuel guage and it was for the right tank. I suppose it was built that way, I don't know. That right side fuel guage was decreasing faster than normal and I diverted. I discovered the leak was at the left fuel cap. Fuel from the right side was being sucked over to the left side via a cross-tube resulting in the greater than normal decrease in quantity. I had experienced this many years earlier in the same type by leaving the cap off after refuelling one time so it was a familiar experience but if the right tank had been leaking, I would not have had the same indications and instead would have had full for a long time, then a quicker than normal drop and maybe just disregarded the funny indications. Who knows.

[photofly]

I'm fascinated by people who should know better practically boasting about violating the CAR that forbids takeoff in an aircraft without a working fuel gauge.

It seems to me that the "fuel gauges are optional" theme is the first hole in the cheese that leads to a "too much air in the tanks" scenario.

Are there any other "optional" mandatory items?

[photofly]

Otherwise, most fuel indication problems would be in your MEL

Does anyone know of an aircraft where completely inoperative fuel gauges are MEL-able?

In the case of the Gimli Glider one of the issues was that the Captain thought he was authorized to fly without fuel gauges when in fact he wasn't.

[Prairiefire]

Twin otter, you have to run around with full bellies

[pelmet]

I'm fascinated by people who should know better practically boasting about violating the CAR that forbids takeoff in an aircraft without a working fuel gauge.

It seems to me that the "fuel gauges are optional" theme is the first hole in the cheese that leads to a "too much air in the tanks" scenario.

Are there any other "optional" mandatory items?

Well, maybe that Citabria with only one fuel guage installed was not legal. Not sure butit was not an empty spot with a guage missing, it looks like it came from the factory that way. Another aircraft I fly has two fuel tanks but only one has a fuel guage installed. Mind you...it does not have a type certificate. A lot of pilots with working gauges have run out of fuel.

Maybe having no operating guage makes you less likely to run out as you are on top of the burn rate and a bit paranoid about it.

Fascinating isn't it.

[teh1pilot]

I'd like to mention that personally, I've always thought the fuel gauge conversation was brought about from some instructor at a FTU.....a "FTUism" as it has been called in the past here. Really, think about it. A fuel gauge is in a plane for a reason...if the needle just arbitrarily moved around for no reason, there would be no purpose of having one. While some could argue that the gauge typically isn't very "reliable", it would at the very least provide a pilot as a cross check to his calculations. For example, if after "X" amount of time a pilot calculates that half of the fuel remains, if he glances up and notices both gauges are indicating more or less 1/8 remaining, for example, some bells should be ringing in the back of the pilots mind.

Now the idea of not relying on the fuel gauge sprouting up in an FTU, to me, actually makes a lot of sense. Really, an instructor telling a student not to use a fuel gauge as a primary indication of fuel remaining serves 2 purposes. It causes a student to do the calculations to be certain of the fuel remaining, while stressing the number 1 priority of an instructor....Safety. The instructor simply just put the student in a scenario that forced him to learn another skill that he can just throw into his large list of "toolbox" items. Other instructors caught wind of this, liked it, and was simply just blown out of proportion. But this is just me speculating.

So at the end of the day, I believe this is why a lot of pilots have it in their minds not to rely on the fuel gauge. Personally, I don't completely dismiss the idea of using the fuel gauge. It's there for a reason, so use it. If you are doing your walk around and notice your 172 gauge isn't functioning properly, note it, talk to the AME. That way if you have full tanks and the gauge is indicating 0, the mechanic can take a look at it right there on the ground and rectify the situation.

[Doc]

Otherwise, most fuel indication problems would be in your MEL

Does anyone know of an aircraft where completely inoperative fuel gauges are MEL-able?

.

Without scampering off to the airport and looking it up, I'm pretty sure one has to work, but are we talking "legal" or "safe"? It IS safe to fly your 172 (for example) on a two hour mission if you've filled the tanks. Legal? Look it up.

[Doc]

Twin otter, you have to run around with full bellies

Lets hear it for common sense! Perfectly safe.

[photofly]

Personally, I don't completely dismiss the idea of using the fuel gauge.

Just... almost completely?

[Big Pistons Forever]

One fact that does not seem to be well known is that fuel gauges have to be checked by maintenance annually. The check is to ensure that when the tank is empty the gauge shows zero or "E". One of the issues with small aircraft, especially Cessna's is the gauges tend to be not that accurate at higher values, but my experince is once they get to a third or lower you will get a very accurate measure of fuel quantity and of course if you see the gauge at zero then there had better be an airport under you.

Note 1 There is an exception. The gauges in GA aircraft are DC electrically powered. If there is a power failure to the gauge then it will fail but it will indicate less than zero. A operating fuel gauge will never go below the zero mark.

Note 2 large aircraft have AC powered fuel quantity indicating systems and these gauges will fail showing what ever value was indicated when the power was interrupted.

[photofly]

The check is to ensure that when the tank is empty the gauge shows zero or "E".

The gauge must show zero when no useable fuel remains, not when the tank is empty.

[iflyforpie]

As well, a fuel leak can go undetected. I ferried a Citabria one time which only had one fuel guage and it was for the right tank. I suppose it was built that way, I don't know. That right side fuel guage was decreasing faster than normal and I diverted. I discovered the leak was at the left fuel cap. Fuel from the right side was being sucked over to the left side via a cross-tube resulting in the greater than normal decrease in quantity. I had experienced this many years earlier in the same type by leaving the cap off after refuelling one time so it was a familiar experience but if the right tank had been leaking, I would not have had the same indications and instead would have had full for a long time, then a quicker than normal drop and maybe just disregarded the funny indications. Who knows.

Know thy aircraft.

All Citabrias are like that... at least all of the one I flew... Two tanks, one gauge. The reasoning behind it is they designed the aircraft fuel tanks to cross-feed that way... so it is essentially one big fuel tank. This is no different than lots of other aircraft out there that have several fuel tanks connected like the Beech Baron or Cessna Skymaster... it's just that they are usually on one side of the aircraft.

Like the 172, the Citabria only has a fuel vent on one side, so one tank will drain much faster than the other. This gives the illusion of a fuel leak. About the time the gauge reads zero, there is enough differential pressure to transfer the fuel from the other tank, and the gauge will actually start to go up again.


Another thing to be cautious of with these types of tanks is the cross-feeding when filling and the time it takes to fill the adjoining tanks. If you fill up a Skymaster like you fill up a 172, you are going to be short anything from minutes to hours of fuel depending on how fast your nozzle is. I always top up each main after filling to give the interconnected tanks time to find their levels.

[teh1pilot]

Personally, I don't completely dismiss the idea of using the fuel gauge.

Just... almost completely?

I should have chosen my words better. I don't use the fuel gauge as a primary indicator of fuel remaining....Ever. If the information at my disposal just doesn't add up, well I need to fix it.

[photofly]

I should have chosen my words better. I don't use the fuel gauge as a primary indicator of fuel remaining....Ever. If the information at my disposal just doesn't add up, well I need to fix it.

I think that's the point I'm making.

Let's consider a scenario where the information at your disposal "just doesn't add up". Suppose you start on a four hour cross country with full tanks. You've calculated that you'd land with an hour of fuel. An hour into the flight the fuel gauges are reading one quarter tank remaining.

Do you

a) terminate the flight because you're uncertain if you have a fuel leak or not

or

b) Assume the gauges are wrong and continue?

There's no doubt in my mind what I'd do.

[Big Pistons Forever]

The check is to ensure that when the tank is empty the gauge shows zero or "E".

The gauge must show zero when no useable fuel remains, not when the tank is empty.

So if the tank has no useable fuel how is it not empty ?

[photofly]

I guess it depends on where the fuel outlet is. Usually the quick drain is at the lowest point, with the fuel line a bit higher, no?

Unusable fuel in a 1973 C172 with long range tanks (from the POH) is 4 US gallons. Some of that is in the fuel lines, fuel bowl etc, but not all 4 gallons. So the rest must be in the bottom of the tanks.

[Beefitarian]

Rats, fast posted!

The check is to ensure that when the tank is empty the gauge shows zero or "E".

The gauge must show zero when no useable fuel remains, not when the tank is empty.

So if the tank has no useable fuel how is it not empty ?

Leaps in to type, "The tanks are designed to draw the fuel above the bottom. Thus leaving some "unusable" fuel even when the rest has been depleted." Therefore even though it could be considered functionally empty, there will be fuel in the tanks.

You knew this and are saying that the gauges should maybe show an empty indication, when the usable fuel is depleted?

[Big Pistons Forever]

I guess it depends on where the fuel outlet is. Usually the quick drain is at the lowest point, with the fuel line a bit higher, no?

And this matters how ?

I suggest you review the definition of "unusable"

The bottom line is that when the gauge is sitting on zero the engine is going to be stopping soon so you should endeavor to never be in that situation.

Or in your case you could get your calculator out and figure out the effective volume of the space remaining between the absolute bottom of the tank and the pick up tube, corrected for every degree of bank and pitch and combination of bank and pitch angles and then subtract the volume held in the lines, gascolator, and carb, divided by every possible fuel flow, including both rich and lean mixtures and get a graph of potential remaining flight time to the nearest second for use when the fuel gauges are indicating zero.....