How close will you get to empty?

I have 7.5 hours of fuel capacity and have never flown more than 6 hours. Also never have run a tank empty, got down to 1-2 gallons, was having tank patched so needed to empty it, I let the mechanic do the last bit.

@JeffinNV Unlike high wings that are gravity fed, low wings have to monitor both tanks because there’s no “both” position for the fuel selector.
Also when tanks are low you have to be careful not to fly uncoordinated because the fuel can be shifted away from the fuel pickups. So no slips on approach/landing.
 
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JeffinNV said:
How much of the reserve is actually accessible?
Is this information available in the PoH?
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The PoH should list this. For the C172 with gravity-fed tanks, you may not have unusable fule (I can't remember). For my low-wing, I have 2 gallons listed as unusable and they aren't included in any manual or digital flight planning calculations. And the fuel gauge doesn't show them either.

I get anxious with less than an hour, but once landed with 30 minutes. I just don't like that feeling.
 
VFR 1 hour. IFR, which are 90%+ of my flights, 1+15. IFR, if I anticipate that I can descend from my planned cruise altitude in VMC conditions and shoot a visual approach, then I'm willing to reduce my IFR reserves to 1 hour. But I have to be certain of this before I'll reduce it to 1 hour.

I do have a GPS and an accurate fuel totalizer, so if it looks like I'll dip into my 1/1+15 reserve, I'm stopping for fuel. Having said all that, I run LOP and have approx 6+20 endurance. So my personal fuel reserve minimums are easy to meet and I have yet to have to divert for fuel, at least in my personal plane. I regularly fly a route that is 4 hours with no winds. Bladder is good for 4+45.

Edit, having 2 fuel tanks that don't cross feed, makes me even more nervous about dipping into my fuel reserve. Having little remaining fuel potentially divided into 2 separate tanks, no thanks. And no, I won't run a tank dry in flight.
 
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JeffinNV said:
Soon to be student pilot here with a question.

How much of the reserve is actually accessible?
Is this information available in the PoH?

I'm looking at the specs for a C172, 8 gph burn means a 1 hour reserve leaves you 4 gallons in each wing tank.
In a wide flat tank that doesn't seem like much to me, at what point is the suction uncovered?

Is this more critical in a low wing? Or is every manufacturer different?
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It's not like a motorcycle where you have to flip a switch to access the reserve.. the reserve exists in the pilots head. That's the problem, if the pilot does the math wrong, he may not have a reserve. Also, winds not as forecast, closed airports, animals on the runway, traffic... lots of things can cause you to need that "reserve" of extra gas.

Yes, 4 gallons isn't much in a flat tank. Remember though that the dihedral of the wing will keep the fuel at the pickup, which is usually at the inboard bottom corner. As mentioned, in a low wing where you're only feeding from one side at a time, it's possible to "unport" a tank if you're low on fuel and get uncoordinated. If the ball isn't centered, everything in the plane is getting flung to one side, including the fuel.
 
For me it partly depends on how far I am going. If I am just flying nearby I am not as worried as if I am on a long XC. I plan for 1 hour of fuel remaining in the tanks when I land. In my Mooney I usually land with much more. In my old Cherokee on a long XC fuel management was more critical. We used to go 400nm to XHD to visit family. I could go non stop if there was no headwind, but I had to stop if the wind was uncooperative. I would check my fuel progress at 1/2 and 3/4 distance to my destination. If it looked good I'd keep flying, if it looked tight I'd stop for fuel. I always sticked my tanks before filling them.

Once I lost compression on one cylinder on my trip. I didn't notice it during cruise. When I landed there was oil on the belly of the plane and I had cut into my fuel reserve. I didn't have a fuel totalizer then, and time/speed/distance was used to determine fuel burn. I am guessing the cylinder failed later in the flight. I was lucky. We were staying there with family over the Christmas holiday. I got my bird repaired on the field by the local AI. My home AI helped me get the parts to him. Everything worked out well, and we traveled home as initially planned. Sometimes it is good to own a bird that everyone is familiar with and can work on.
 
JeffinNV said:
Soon to be student pilot here with a question.

How much of the reserve is actually accessible?
Is this information available in the PoH?

I'm looking at the specs for a C172, 8 gph burn means a 1 hour reserve leaves you 4 gallons in each wing tank.
In a wide flat tank that doesn't seem like much to me, at what point is the suction uncovered?

Is this more critical in a low wing? Or is every manufacturer different?
Click to expand...

>>How much of the reserve is actually accessible?>>
That depends on your aircraft, but you are asking the question wrong. The "reserve" is not a separate section of the tank, it is an arbitrary restriction you place on yourself. If 1 tank holds 25 gallons, and both tanks hold 50, you decide how much of the tank to hold in reserve and not use. Many low wing airplanes have the pickup tube at the lowest inside corner of the tank, and they can usually be run completely dry, but you could assume the last 1/2 gallon is not usable. So 24.5 gallons usable fuel per tank, or 49 total in both tanks. Out of that you then subtract the fuel burn at cruise for 30, or 45 or 60 minutes. The FAA requires to you plan 30 minutes fuel reserve for daylight VFR, and 45 minutes at night, but AOPA and EAA safety discussions recommended a full hour to be sure. You can use more if you like, it is up to you. Once airborne it is legal to use every drop of fuel you have, but is that a good idea? Probably not.

>>Is this information available in the PoH?>> sometimes.

>>In a wide flat tank that doesn't seem like much to me, at what point is the suction uncovered?>> That partly depends on how the tank is installed and the attitude of the airplane. Nose up and climbing is more likely to uncover the port than straight and level, unless the designers placed the pickup in a specific way for maneuvers. The best answer for you is to keep enough fuel in the tank so you never find out. An experienced pilot can intentionally run one tank dry in the air while flying, then land on the tank with fuel and fill the empty tank to see how much it holds. I've never done that in an airplane, but I have done it in a truck.

>>Is this more critical in a low wing? Or is every manufacturer different?>> low wing vs high wing are different. Low wings have dihedral to help move the fuel to the inboard corner of the tank, but require fuel pumps to the engine. High wings are usually flat, but can gravity feed to a carburetor and some airplanes don't have fuel pumps at all. It all depends.
 
My desire is to land with 1hr of fuel left.
The beauty of having more than one fuel tank and no "Both" position on the selector valve is that it makes me a lot more aware if the fuel state.
Before installing the fuel totalizer, I'd get nervous whenever the gauges indicated less than 1hr of fuel or so.

Let me preface my fuel management plan by stating that I regularly cross-check the totalizer against the fuel gauges (and time flown) to ensure things are adding up. If they don't add up it's a land as soon as practical situation to investigate.

When getting close to the 1hr mark (let's say 1.5 hrs or so) I use the fuel in one tank until I'm left with about 40 minutes of fuel in it. Then I switch to the other tank and plan to use it until it's exhausted or until 5-10 minutes away from destination airport. Then I switch to the tank that has plenty of fuel for a potential go-around and the nose high attitude that could come with it.
I've never run a tank dry. While I am prepared to switch tanks if that happened, I would consider running a tank dry to be a case of suboptimal planning.
 
My POH states minimum fuel for take-off is 13 gallons per side, so I try to never land with less than that in case I can't get fuel for some reason. With 3 gallons unusable on each side that gives me 20 usable, or about an hour and a half reserve. I only broke that rule one time when I was headed home and I knew I'd be able to get fuel before needing to take off again.
 
Ed Haywood said:
Let's say you have a fuel computer and GPS. You launch day VFR with at least a 30 minute reserve. The winds are a bit worse than predicted, or you have to maneuver more than expected.

What is your personal threshold to divert enroute?
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I do not personally go below 1/4 of a tank-ever.
 
I landed once VFR with my 30 minute reserve. Felt strange. So much so that I promised myself to never do that again. I like an hour ...
 
I'm not less than 1-hour reserve, period. But if the gauges show emptier than the totalizer, I believe the gauges.

Simple reason: Totalizers are highly accurate calculators based on fuel actually used by the engine. That's means it's subject to at least two issues. (1) GIGO - the ending numbers are only as good as the starting numbers I gave it. (2) It does not account for the possibility of leaks.
 
I have my digital fuel gauges set to turn red when they have 5 gallons left, yellow when they have 9 gallons left. I try not to ever get them down to red. That’s probably too conservative for a lot of people but not for me
 
I'm still learning in my plane. I like the hour minimum but that's an HOUR minimum in the left main tank to me.

I have two 20 gallon wing tanks and one 10 gallon aux tank in the back. I have gauges for all 3.

3GPH returns to the left wing tank regardless of which tank you're using.

I use around 10 GPH depending on settings.

Start on Right tank, run an hour (10 gallons remaining, probably a little less since you did a takeoff and climbout there), then work your way through the others in logical order depending on the flight and W&B.

Land on the LEFT tank with at least 10 gallons in it.

This would mean switching tanks a few times during a 4 hour flight to keep the plane even.

I have not been bold enough to run the aux tank dry. I should do that at 6,500 feet over a quiet but long airport with MX sometime just to make sure i can do it and that no "gunk" in the bottom causes any issues.
 
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Daleandee said:
I landed once VFR with my 30 minute reserve. Felt strange. So much so that I promised myself to never do that again. I like an hour ...
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Yep. 30 minutes in my plane is a couple or three gallons. Landed once, got gas, and watched the pump keep going and going and going...

"Do you feel lucky? Well, do ya?"

ONCE.
 
I like an hour…first hour’s burn in airplanes where it’s different per hour. I’ve planned less than that in airplanes that didn’t have enough capacity, but the only times I’ve burned into whatever my reserve was, I had at least declared minimum fuel.

Well, I should say “knowingly” burned into my reserve. One time I wasn’t paying attention to my fuel, and ended up landing at a nearby farm strip and stealing some gas. (When I told him about it later, he didn’t want me to pay for it, so is it still stealing?)
 
MIFlyer said:
I have not been bold enough to run the aux tank dry. I should do that at 6,500 feet over a quiet but long airport with MX sometime just to make sure i can do it and that no "gunk" in the bottom causes any issues.
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I assume the aux tank has its own drain for sampling, the drain should be below a screened fuel pickup so unless you don’t sample the fuel there should be no gunk.
Running the tank dry means you will have air in the fuel lines, this could cause your restart to be less than enthusiastic if you have a fuel injection system. Carburetor engines don’t have this problem.
If you’re running it dry to maximize the fuel usage, watch your fuel pressure, if it starts fluctuating, switch tanks and you’ll not have to worry about restarting.
 
So we're all talking about how much fuel we'd like to have when we land. Better thing to point out for @Ed Haywood is why... So Ed, ever hear about anyone arriving at an airport and it closes because the guy in front of you just blew a tire and is sitting on the center line? And the other thing we're not discussing, though I'm sure it is why so many people have their limits, is that it's how much are you going to land AT YOUR ALTERNATE even if you are VFR?

USUALLY there are alternates within 30 min or less. But out west that is not always the case. So don't go planning to your destination and then saying you're going to have 30 min. left in the tank. You might be looking for a nice field or straight stretch of highway. :D
 
M20K said:
And the other thing we're not discussing, though I'm sure it is why so many people have their limits, is that it's how much are you going to land AT YOUR ALTERNATE even if you are VFR?
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That was noted in post #2. ;)
 
M20K said:
So we're all talking about how much fuel we'd like to have when we land. Better thing to point out for @Ed Haywood is why... So Ed, ever hear about anyone arriving at an airport and it closes because the guy in front of you just blew a tire and is sitting on the center line? And the other thing we're not discussing, though I'm sure it is why so many people have their limits, is that it's how much are you going to land AT YOUR ALTERNATE even if you are VFR?

USUALLY there are alternates within 30 min or less. But out west that is not always the case. So don't go planning to your destination and then saying you're going to have 30 min. left in the tank. You might be looking for a nice field or straight stretch of highway. :D
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Or a taxiway or the grass next to the runway if they can't get the disabled plane off the runway in 30 minutes. VFR reserves don't have anything to do with alternates.
 
M20K said:
ever hear about anyone arriving at an airport and it closes because the guy in front of you just blew a tire and is sitting on the center line?
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Yep. Had that happen once when flying a C-414. As @Lindberg suggested, I landed on the taxiway. One hour later I took off from the taxiway.

There were a few times in Alaska where I would land on the road going to the landing strip. Mostly because of the wind, though.
 
M20K said:
… ever hear about anyone arriving at an airport and it closes because the guy in front of you just blew a tire and is sitting on the center line?…
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I’ve been the guy with the flat before. Luckily winds were calm and they were able to use the crossing runway for the half hour or so it took to get the plane up on a trolly and towed to the FBO.
 
TCABM said:
I’ve been the guy with the flat before. Luckily winds were calm and they were able to use the crossing runway for the half hour or so it took to get the plane up on a trolly and towed to the FBO.
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This reminds me of being on a jumpseat out of DCA. The CA briefed that in case of an engine failure after V1, the plan is to "head on over to BWI and come to a stop right at the intersection of the runways, just to **** Southwest!" :p
 
GeorgeC said:
Yep. 30 minutes in my plane is a couple or three gallons. Landed once, got gas, and watched the pump keep going and going and going...

"Do you feel lucky? Well, do ya?"

ONCE.
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This right here. In a 172 with fuel on both, I landed back at home base with about 30 minutes of fuel left, right to my calculations. Perfectly legal, but I never thought about how VERY LITTLE is there in each tank until I stuck the tanks and pumped 35-37 gallons (into 42-or-whatever gallon tanks 172k's have).

I've always planned at 1 hour min remaining for me after that.
 
M20K said:
So we're all talking about how much fuel we'd like to have when we land.
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I believe the original question was at what point do you divert due to unforeseen circumstances.
 
Ed Haywood said:
Let's say you have a fuel computer and GPS. You launch day VFR with at least a 30 minute reserve. The winds are a bit worse than predicted, or you have to maneuver more than expected.

What is your personal threshold to divert enroute?
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If I hit an left hour, I'm looking for someplace to land. Better to get gouged pay to twice as much for a few gallons and get home.

I don't have a fuel computer and GPS, so I plan 2.5 hours flight time max in a plane that realistically can go somewhere between 4 and 5. I was taught a long time ago that the #1 reason for fuel exhaustion is that the fuel was never there to begin with.
 
mark.staggs said:
This right here. In a 172 with fuel on both, I landed back at home base with about 30 minutes of fuel left, right to my calculations. Perfectly legal, ...
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hmmm, I seem to recall the fuel reserve requirements applied to departing. Landing with even just 1 minute of fuel is legal, isn't it?

Or did that requirement change when I wasn't looking?
 
Numerous times I have gotten to my destination IFR and spent 20-30 minutes being vectored around.
 
1 hour minimum. Declared minimum fuel once going into KTUS; scared me to the 1 hour minimum policy.
 
Bob Noel said:
hmmm, I seem to recall the fuel reserve requirements applied to departing. Landing with even just 1 minute of fuel is legal, isn't it?

Or did that requirement change when I wasn't looking?
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Correct.

Fuel reserves (VFR and IFR) are based on planning. Once the aircraft is in flight you can burn into your reserves. Nothing illegal about it.

Flight planning should include trip fuel, reserve fuel and contingency fuel.
 
Doc Holliday said:
Correct.

Fuel reserves (VFR and IFR) are based on planning. Once the aircraft is in flight you can burn into your reserves. Nothing illegal about it.

Flight planning should include trip fuel, reserve fuel and contingency fuel.
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The VFR and IFR regulations on fuel reserves are worded differently.

VFR (91.151): No person may begin a flight in an airplane under VFR conditions unless (considering wind and forecast weather conditions) there is enough fuel…

IFR (91.167): No person may operate a civil aircraft in IFR conditions unless it carries enough fuel…

Leaving aside the always-terrible phrases “VFR conditions” and “IFR conditions,” I don’t know if there is an official interpretation of these two sections. I think, though, that the way the IFR version is worded requires you not to burn into your legal reserves. That is also supported by the different wording about weather information you have to consider, with the IFR section referring to “weather conditions” in addition to forecasts, while the VFR section only refers to wind and forecast weather.
 
iamtheari said:
The VFR and IFR regulations on fuel reserves are worded differently.

VFR (91.151): No person may begin a flight in an airplane under VFR conditions unless (considering wind and forecast weather conditions) there is enough fuel…

IFR (91.167): No person may operate a civil aircraft in IFR conditions unless it carries enough fuel…

Leaving aside the always-terrible phrases “VFR conditions” and “IFR conditions,” I don’t know if there is an official interpretation of these two sections. I think, though, that the way the IFR version is worded requires you not to burn into your legal reserves. That is also supported by the different wording about weather information you have to consider, with the IFR section referring to “weather conditions” in addition to forecasts, while the VFR section only refers to wind and forecast weather.
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So you are on an IFR flight plan and going into a high density traffic area. The weather is lower than forecast and ATC is holding aircraft to sequence into the approach. So as you are being vectored around to final you realize you will land with 40 minutes fuel.

What do you do? Have you violated the regulations? You did your planning based upon current information and started the flight. However things change, weather deteriorates and ATC backs up.

Take it a step further. With everything that happened, you will land with exactly 45 minutes remaining. On short final approach tells you to go around due to an aircraft on the runway.

Now what?

With that being said, what’s the purpose for reserve fuel?
 
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In a glider it is not fuel, it's altitude. Planning a cross country, one establishes wayponts and determines the altitude required over that point to make the next waypoint or divert. On nice days I have made several 3 hour flights and a couple 5 hour flights without any fuel ever being on board. (Yes, there was a relief tube.)
 
Doc Holliday said:
So you are on an IFR flight plan and going into a high density traffic area. The weather is lower than forecast and ATC is holding aircraft to sequence into the approach. So as you are being vectored around to final you realize you will land with 40 minutes fuel.

What do you do? Have you violated the regulations? You did your planning based upon current information and started the flight. However things change, weather deteriorates and ATC backs up.

Take it a step further. With everything that happened, you will land with exactly 45 minutes remaining. On short final approach tells you to go around due to an aircraft on the runway.

Now what?

With that being said, what’s the purpose for reserve fuel?
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In your opinion, why did the FAA write "operate a civil aircraft" in 91.167 but "begin a flight" in 91.151? If they meant the two rules to have the same meaning, they would presumably have used the same words in both of them. (I continue to couch all of this in the context of "VFR conditions" and "IFR conditions" being nonsensical phrases, the use of which might rebut the presumption about other parts of these regulations having been drafted with a close match between intended and actual meaning.)

Assuming the FAA meant what they wrote, then in your scenarios...

If you realize you are going to land with 40 minutes of fuel and you are either under IFR or in IMC (whatever "IFR conditions" means), you have several options. You could tell ATC that you have minimum fuel, declare an emergency, request priority handling, get out of "IFR conditions" by hook or by crook, and/or exercise your prerogative under 91.3. Same answer if you will land with exactly 45 minutes of fuel remaining and get waved off into the clouds.

As far as the purpose of reserve fuel, I would say that it's to prevent these types of minor emergencies from becoming major catastrophes.
 
For planning, if I'm taking a 2hr flight I'll take a bit over 4 hours fuel. Then I don't have to think much about fuel, just about time. If I'm planning a longer trip, and close margins, I'll do the math more carefully and make sure I have places to land that'll still give me about an hour of fuel left.

If I'm in flight and end up with less than an hour, I'm going to divert for fuel. I treat the 30 min as empty for all planning purposes.

For the math impaired or student pilots in the group, when I would fly a cub, 12 gal tank, about 4 gal/hr, I'd plan on taking my flights into the wind. Fly an hour into the wind, then turn and come back with a potentially significant ground speed increase, and you're way less likely to get stranded far away without fuel.

I just fly for fun. If I'm stressed about fuel it's way less fun. So I plan to have plenty. Plus I love the sound the engine makes when it's running.
 
Doc Holliday said:
So you are on an IFR flight plan and going into a high density traffic area. The weather is lower than forecast and ATC is holding aircraft to sequence into the approach. So as you are being vectored around to final you realize you will land with 40 minutes fuel.

What do you do? Have you violated the regulations? You did your planning based upon current information and started the flight. However things change, weather deteriorates and ATC backs up.

Take it a step further. With everything that happened, you will land with exactly 45 minutes remaining. On short final approach tells you to go around due to an aircraft on the runway.

Now what?

With that being said, what’s the purpose for reserve fuel?
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The purpose of reserve fuel is for unanticipated situations such as vectors and unforcasted headwinds. You can legally land with no reserves. It wouldn’t be smart and the FAA might violate you for careless and reckless operating, especially if you overflew potential fuel stops.
 
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