Fuel System Management

[Morne]

Continuing in the vein of accident causes...

Fuel starvation is one of the more common causes. Here, fuel is onboard but not making it to the engine. I suppose that has something to do with proper pilot management of the fuel system, yes?

The complexity of fuel systems can vary greatly. My 182 has "left, right, both, off" as the only options. Climbing and descending is "both", during flight I change to "right" at 0:30, "left" at 1:30 and back to "right" at 2:30 (at 3 hours I start descending to land, period - no LR tanks in my bird). To me, this is pretty simple.

On the other hand, aircraft with auxiliary tanks can be a real twister to manage. I have read that the 337's fuel system is very complex. I imagine some of the longer-legged twins, and maybe even singles with tip tanks, can be a bit confusing as well.

Anyone care to relate fuel management headaches/tips/tricks/common-goofs?

 

[tonycondon]

when i have to worry about fuel it is either in the 182 towplane (both) or a club 172 or 182RG (both). i used to fly a 421 somewhat regularly which required some thought but once you understood the system it was not too hard.

 

[Fearless Tower]

The fuel system I am not a fan of is the earlier PA32s. They made them with 4 separate tanks (each selected seperately) and the capacities of those tanks are what make it a pain. For example, the tips are 17 gallons each and cruise fuel burn is around 13gph. Mains were 25 each with tabs at 17. The capacity just seemed awkward - If you burned an hour from a tip, you only had 4 gallons left which was kind of useless. Problem is that if you were on a long trip and trying to max out the range, you could easily end up with 4 tanks with 4 gallons each - that is over an hour's worth of fuel, BUT you would be switching tanks every 10-15 minutes to get it.

My rule of thumb in that airplane was to plan flights no more than 4 hrs between fueling and considered the extra fuel to be strictly for an emergency.

Piper fixed this problem in the later models by interconnecting the outer tanks with the inner so you only have to select right or left.

 

[Ted]

Anyone care to relate fuel management headaches/tips/tricks/common-goofs?

It comes down to understanding how your system works and what its limitations are. Once you do that, you just have to keep on top of it. This becomes easy once you understand the hows and whys of the system.

A lot of aircraft have to take off and land on particular tanks. So as part of your landing checklist, you need to make sure you're on those tanks. You should also make sure that you manage your fuel in-flight so that those tanks aren't almost empty. The biggest tool for that is a stopwatch. Writing down when you take off, switch tanks, etc. is a good tool to help you remember the times for each.

I fly a Twin Cessna regularly. I take off on the mains (tips). Fly about an hour, switch to the aux tanks. Wait until those are about empty, switch back to tips (which are now about full, since some fuel was returned to them). Fly until it's time to land. It gets slightly more complex with the wing locker tanks, but still not bad.

 

[wabower]

Most of the fuel management issues relate to two over-lapping design issues with one or more additional side issues:

1. The location of the supply pick-ups that route fuel to the engine.
2. The configuration of the fuel return lines that allow unused (excess)fuel supplied to the engine to be returned to the tanks.
3. Some tanks have neither fuel supply pickups or return lines. Fuel contained in those tanks must be transferred to other tanks that have the necessary plumbing to move fuel to and from the engine.
4. The transfer pumps from these isloated storage tanks may not equally distribute the fuel to operating tanks as desired by the pilot, so use of some other mechanism (usually cross-feed plumbing) may be necessary to accomplish the desired result.

Neither of these situations are particularly difficult, if:
1. The pilot is properly trained
2. The pilot pays attention to business
3. The system works normally.

Guess which two of the three items on the list are the most problematic insofar as accidents are concerned?

Tip-tank twin Cessna fuel systems are not difficult, but contain all four elements in the list. Their undeserved "difficult-to-manage" reputation among pilots who don't understand them stems largely from poor training, often rendered by other pilots with similar lack of knowledge.

A competent twin-cessna instructor can teach a new pilot all the tricks in about 10 minutes, but retention of the various steps and necessary timing can be problematic and should be reduced to check-list format in order to do it right at some indeterminable future date when the memory cells have dimmed.

 

[tonycondon]

yea the counterintuitive part about the twin cessnas is you always want to keep the mains full until the end of the trip since you have to takeoff and land on them. if you burn the mains down first and don't have enough time on the auxes or have the wing locker to fill them back up you'll end up in a corner where you are supposed to switch over to fumes to land and will perhaps be forced into buying gas you don't want/need in order to be comfortable taking off.

 

[Ted]

yea the counterintuitive part about the twin cessnas is you always want to keep the mains full until the end of the trip since you have to takeoff and land on them. if you burn the mains down first and don't have enough time on the auxes or have the wing locker to fill them back up you'll end up in a corner where you are supposed to switch over to fumes to land and will perhaps be forced into buying gas you don't want/need in order to be comfortable taking off.

I wouldn't call it counter-intuitive, just an aspect of the system. The part that's a bit more counteriintuitive is that you can't just switch to your aux tanks after takeoff with full fuel, since you'll then end up spitting fuel out the fuel vents on the mains.

I'm with Wayne, though. The system really isn't complicated, and doesn't require much extra brain power to manage. Although the Commander 690 is the simplest fuel system I've flown. All tanks drain into one sump that either works or doesn't. When you run out, you're out.

Complex fuel management to me gets into various turbines that burn significantly more fuel down low, where a stepped climb or descent can have a significant impact on your range and options.

 

[spinfire]

The complexity of fuel systems can vary greatly. My 182 has "left, right, both, off" as the only options. Climbing and descending is "both", during flight I change to "right" at 0:30, "left" at 1:30 and back to "right" at 2:30 (at 3 hours I start descending to land, period - no LR tanks in my bird). To me, this is pretty simple.

I haven't flown a 182. Why not use "both" for cruise? Is this a limitation of the 182? In the 172 or 172RG I'll leave it in both unless I feel one of the wings is heavy and then I'll just burn from the heavy side until it flies hands off again and switch back to both. For the full length of my primary training I don't think I ever moved the 172 fuel selector out of both. Still checked it every time before takeoff and landing though!

 

[tonycondon]

I wouldn't call it counter-intuitive, just an aspect of the system. The part that's a bit more counteriintuitive is that you can't just switch to your aux tanks after takeoff with full fuel, since you'll then end up spitting fuel out the fuel vents on the mains.

I'm with Wayne, though. The system really isn't complicated, and doesn't require much extra brain power to manage. Although the Commander 690 is the simplest fuel system I've flown. All tanks drain into one sump that either works or doesn't. When you run out, you're out.

Complex fuel management to me gets into various turbines that burn significantly more fuel down low, where a stepped climb or descent can have a significant impact on your range and options.

agree its not that complicated.

counter-intuitive in that with no prior knowledge a pilot would assume you burn off your "main" tanks first and your "auxiliary" tanks second. not necessarily the case

 

[Morne]

I haven't flown a 182. Why not use "both" for cruise? Is this a limitation of the 182? In the 172 or 172RG I'll leave it in both unless I feel one of the wings is heavy and then I'll just burn from the heavy side until it flies hands off again and switch back to both. For the full length of my primary training I don't think I ever moved the 172 fuel selector out of both. Still checked it every time before takeoff and landing though!

When on "both" it seems to primarily feed out of the left tank (where the vent is). There's a fair bit of writing about this phenomenon, actually. So, in order to ensure I'll end up at landing with fairly equal weight wings I need to ensure that the right tank drains some in cruise. By leaving it on "right" for 1:30 of a 3:00 flight I get to be pretty even at landing.

I agree about 172s - I only ever put it to "left" or "right" while adding fuel.

 

[Fearless Tower]

I haven't flown a 182. Why not use "both" for cruise? Is this a limitation of the 182? In the 172 or 172RG I'll leave it in both unless I feel one of the wings is heavy and then I'll just burn from the heavy side until it flies hands off again and switch back to both.

Some 182s from the 70's (and Cardinals too) have the tanks set up where both tanks are connected to the same vent and consequently the fuel system in flight can get itself into a situation where one tank is literally being siphoned to the other in flight when the selector is on both, so some folks just automatically use the separate right and left selection.

 

[Morne]

agree its not that complicated.

...and yet people screw it up time and again.

Not trying to pick a fight or anything, just that when distracted by other tasks (actual IMC, turbulence, chatty PAX) sometimes things get forgotten.

 

[Morne]

Some 182s from the 70's

...and the 60's...

 

[Fearless Tower]

Although the Commander 690 is the simplest fuel system I've flown. All tanks drain into one sump that either works or doesn't. When you run out, you're out.

Interesting. Haven't flown one yet, but looking into the piston commanders, I have heard the fuel system can create problems for line folks fueling them because of the single point refueling (both sides are filled by a single fuel port on the top of the airplane. Can't remember if it was a fuel balance issue, or a problem with thinking that the airplane was topped off when it actually wasn't.

 

[wabower]

Operational realities can (and should) impact purchase decisions of bigger airplanes. I represent a client in Honduras who is buying an Excel or early XLS to to replace an older Citation II.

One of the "advantages" of the more-expensive XLS--as represented by the selling broker--is the ability to achieve unrestricted climbs to FL 4XX. My response was that in the past 20 years of turbo-prop and jet flying, I can count the number of unrestricted climbs without removing my shoes. In most of the places where we operate, rate of climb is much more a function of ATC permission rather than design capabilities.

I wouldn't call it counter-intuitive, just an aspect of the system. The part that's a bit more counteriintuitive is that you can't just switch to your aux tanks after takeoff with full fuel, since you'll then end up spitting fuel out the fuel vents on the mains.

I'm with Wayne, though. The system really isn't complicated, and doesn't require much extra brain power to manage. Although the Commander 690 is the simplest fuel system I've flown. All tanks drain into one sump that either works or doesn't. When you run out, you're out.

Complex fuel management to me gets into various turbines that burn significantly more fuel down low, where a stepped climb or descent can have a significant impact on your range and options.

 

[spinfire]

That's interesting. I recently did the first XC of any length in the 172RG (1980) and sure enough the right wing was the heavy wing. So I just switch to right as needed until it evened out then back to both. I'm guessing this is the vent phenomenon mentioned. My instructor didn't mention it, I'll have to ask. I assumed that the slight imbalance was because I had been uncoordinated during the climb out or something. Probably the bulk of the imbalance showed up during climb out because the fuel consumption was much higher then.

 

[flyingron]

Some of the Auxes on the Navion are "level cruise" only type things. A few people have tried to takeoff on the aux and have learned that was a mistake.

The normal Navion fuel valve is an on-off type thing unusual for a low wing. There's a header tank between the two wing tanks that the fuel draws from.

 

[flyingron]

When on "both" it seems to primarily feed out of the left tank (where the vent is). There's a fair bit of writing about this phenomenon, actually. So, in order to ensure I'll end up at landing with fairly equal weight wings I need to ensure that the right tank drains some in cruise. By leaving it on "right" for 1:30 of a 3:00 flight I get to be pretty even at landing.

In the single vent cessnas, the fuel selector doesn't really help much. If you've got that problem, you'll likely find that fuel is crossfeeding from the left to the right through the vent line even if you have the selector on RIGHT.

The operational consideration (at least on a lot of the 172's) is that there is a vapor lock possibility with running on both (running on one side or the other flows more fuel in the line and prevents it from heating up too much).

 

[Morne]

In the single vent cessnas, the fuel selector doesn't really help much. If you've got that problem, you'll likely find that fuel is crossfeeding from the left to the right through the vent line even if you have the selector on RIGHT.

When I select "right" the fuel guage on the panel does show fuel being used from "right". That is, once I've taken off, climbed and established cruise on "both" for the first 30 minutes.

 

[kgruber]

DHC2 Beaver has 3 tanks in the belly. You run them dry from the rear to the front.

Then.........some have tip tanks added. I can remember having my hand on the fuel lever and watching the fuel pressure at the same time. When the FP wavered, I'd switch tanks quickly. Sometimes the engine would.t even burp!

 

[denverpilot]

Some 182s from the 70's (and Cardinals too) have the tanks set up where both tanks are connected to the same vent and consequently the fuel system in flight can get itself into a situation where one tank is literally being siphoned to the other in flight when the selector is on both, so some folks just automatically use the separate right and left selection.

Cessna Pilots Association has a good write up on this and how to work on it to minimize it with the help of your mechanic, but...

They also point out that if you look at all of the fuel diagrams from the start of the 182 line of aircraft up to the modern ones, Cessna kept adding cross-over vents and lines in an attempt to fix what ultimately is a vent/pressure issue between the tanks, and in the process of doing that they created some almost unstoppable fuel paths between the wings until fuel is really really low.

So basically, putting the fuel selector on left or right *sometimes* isolates the tanks from each other but the later in model year you go, it becomes worthless.

You either fix the vent positions and make sure the lines are free of obstructions/kinks while also testing the "emergency" vents in both fuel caps (there in case the main vent isn't working, the little "rubber" part gets pulled open by too much "suction" in the tank to keep the bladders from collapsing inside the wing -- until you get to the wet wing models) -- or you just live with whatever you get on the "both" setting.

I tend to just leave mine on both, unless there's a huge imbalance during a long XC or I want to stop *some* of the cross feeding on an uneven ramp.

We had to move the only vent on the left side a bit up and twist it inward to properly "hide" it behind the strut -- CPA calls out the Cessna document on the issue and that's the number one thing I see on other Cessnas that contributes the most to the problem. Cessna's doc gives measurements for how much of that vent tube should be in the airflow down to one-hundredths of an inch, which gives a clue as to how touchy it is, and just hammering around in slow-flight versus cruise is going to change the pressure and flow of air into that vent tube anyway... You'll only ever get it "just right" for a particular cruise airspeed.

After a long high-speed descent and jump out quick, you can often hear that the system got a bit pressurized and there will be gurgling and bubbling noises at the vent if you listen closely. Especially a bladder system. Too much of this flexes the bladders a bit each time you fly so getting that vent behind the strut at the level flight attitude and cruise speed is critical -- if you're nitpicky about things.

If you ever have a serious in-flight pressure buildup from the vent, you can "blow out" the vents in the fuel caps and sometimes send amazing amounts of fuel overboard. Hard to see in a high-wing too. Might even just not see it and wonder where all the fuel went after a flight. That scenario should be a big red flag anytime (way higher than normal fuel burn) but some folks can't/won't track it. (When was the last time you saw a real fuel burn chart over time for a rental for example?)

Due to a safety discussion with my co-owners and because our home hangar is generally level, we also don't bother with left/right when parked on the ground as long as we're not fully topped off and concerned about the typical small leak from the vent -- which can turn into a siphon and drop an impressive amount of fuel on the hangar floor if it gets a little stuck open.

The reason? Leave it in a position where if the next guy to go flying forgets a checklist item he's not sucking fuel from an empty tank for takeoff.

Short-circuit that accident chain, basically.

Same reason we leave the cowl flaps open in the hangar. Outside I close 'em to avoid the nesting birds and critters from being too tempted. Still have to look in every orifice, but it's just another "courtesy" thing we do.

So, even within the same type, you'll find little differences like the bejillion cross-feed paths in the mid-year and beyond Skylanes.

Bottom line is: Know your particular aircraft's fuel system.

 

[Morne]

So basically, putting the fuel selector on left or right *sometimes* isolates the tanks from each other but the later in model year you go, it becomes worthless.

Yeah - any earlier and my bird would be a narrowbody. Back in 1961/1962 ("E" variant) they had yet to start worrying enough about this to really screw it up.

 

[tonycondon]

but if there are a whole bunch of crossfeed lines how would taking off on left or right lead to taking off on an empty tank?

 

[ronnieh]

Tony, I think you would find the opposite true. In most planes you want to get rid of aux fuel first because of restrictions on landing or taking off on aux tanks. The one fly in the ointment as Ted pointed out on the 310 is you have to burn enough fuel from the mains for the return fuel not to over fill the mains. On the Cessna twin the unused fuel goes back to the mains. On the 310 I am familiar with even with locker tanks this fuel has to be pumped into the tips to be used. On the Navajo I always climbed to altitude and leveled off then switched to outboard. Ran 1:45 then switched back to mains.
On the IIIA it is almost idiot proof. A short story: I ordered 30 gallons per side for courtesy fuel, I always specify in the narcelles. Well it appears one of the new linemen did not know what a narcelle was. He squirts 30 gallons in one tip and another lineman who knew the plane caught it. I was loading luggage and he comes up to me all tore up about his mistake wanting to know what to do. I acted like I was giving this serious thought then told him just make the same mistake on the opther side. Should have seen the look on his face. Yes I explained to him later that all tanks are interconnected. On, off, or cross feed truly KISS. The tips are rarely used but if you do put fuel in the tips after topping off the narcelle tanks do not open the narcelle fuel caps!

The MU2 is rather complicated. Restrictions on landing with too much fuel in tip tanks. All fuel has to be pumped to center tank to be used. If the tip tank cap is leaking it will blow out at least 50 gallons if it was full. They use bleed air pressure to push the fuel out of the tips into the main tank. Cap loose or leaking and the fuel just get pushed overboard.

In short, you need to know the systems of the plane you are flying.

 

[Skylane81E]

Yeah - any earlier and my bird would be a narrowbody. Back in 1961/1962 ("E" variant) they had yet to start worrying enough about this to really screw it up.

Then on the Q they finally added a vent on each wing. MUCH better.

 

[wabower]

The Citation 650-series airplanes (III, VI, VII) have similar methodology as the tip-tank twins, in that main tanks must be burned down sufficiently to transfer trunk fuel to mains without pumping it overboard.

Tony, I think you would find the opposite true. In most planes you want to get rid of aux fuel first because of restrictions on landing or taking off on aux tanks. The one fly in the ointment as Ted pointed out on the 310 is you have to burn enough fuel from the mains for the return fuel not to over fill the mains. On the Cessna twin the unused fuel goes back to the mains. On the 310 I am familiar with even with locker tanks this fuel has to be pumped into the tips to be used. On the Navajo I always climbed to altitude and leveled off then switched to outboard. Ran 1:45 then switched back to mains.
On the IIIA it is almost idiot proof. A short story: I ordered 30 gallons per side for courtesy fuel, I always specify in the narcelles. Well it appears one of the new linemen did not know what a narcelle was. He squirts 30 gallons in one tip and another lineman who knew the plane caught it. I was loading luggage and he comes up to me all tore up about his mistake wanting to know what to do. I acted like I was giving this serious thought then told him just make the same mistake on the opther side. Should have seen the look on his face. Yes I explained to him later that all tanks are interconnected. On, off, or cross feed truly KISS. The tips are rarely used but if you do put fuel in the tips after topping off the narcelle tanks do not open the narcelle fuel caps!

The MU2 is rather complicated. Restrictions on landing with too much fuel in tip tanks. All fuel has to be pumped to center tank to be used. If the tip tank cap is leaking it will blow out at least 50 gallons if it was full. They use bleed air pressure to push the fuel out of the tips into the main tank. Cap loose or leaking and the fuel just get pushed overboard.

In short, you need to know the systems of the plane you are flying.

 

[Fearless Tower]

The one fly in the ointment as Ted pointed out on the 310 is you have to burn enough fuel from the mains for the return fuel not to over fill the mains. On the Cessna twin the unused fuel goes back to the mains.

DC-3 is piped the same as well. Fuel return is to the Main's only.

 

[Ted]

agree its not that complicated.

counter-intuitive in that with no prior knowledge a pilot would assume you burn off your "main" tanks first and your "auxiliary" tanks second. not necessarily the case

It might have more to do with the aircraft that I've flown vs. what you've flown. Typically, what I've flown has either had main tanks only (i.e. all tanks are mains) or else they have mains that you need to take off and land on, thus you need to be careful with burning the fuel out of them. So normally you want fuel out of the auxes as fast as possible.

On the twin Cessnas, this is especially true. If I have an engine failure, the aux tank on the dead engine side now contains fuel that I have no means of getting at (at least on the 310). So burning that aux fuel off means that all the fuel I have in the mains is accessible by the one good engine. This is important if I'm flying over the Gulf or in the middle of nowhere, Canada.

Interesting. Haven't flown one yet, but looking into the piston commanders, I have heard the fuel system can create problems for line folks fueling them because of the single point refueling (both sides are filled by a single fuel port on the top of the airplane. Can't remember if it was a fuel balance issue, or a problem with thinking that the airplane was topped off when it actually wasn't.

We've got three fueling ports. I don't know how the piston Commanders work (never flown one). I've also never had to fuel this one, so I don't know how much line people like or dislike it.

What I do know is that, from the pilot's perspective, it's pretty nice.

Operational realities can (and should) impact purchase decisions of bigger airplanes. I represent a client in Honduras who is buying an Excel or early XLS to to replace an older Citation II.

One of the "advantages" of the more-expensive XLS--as represented by the selling broker--is the ability to achieve unrestricted climbs to FL 4XX. My response was that in the past 20 years of turbo-prop and jet flying, I can count the number of unrestricted climbs without removing my shoes. In most of the places where we operate, rate of climb is much more a function of ATC permission rather than design capabilities.

Obviously, you have much more experience than I do in this realm since I was still small enough that I thought my mom was pretty tall back then. And I agree fully that operational considerations can and should impact purchase decisions.

Around here, we'll get climb restrictions, but will typically have what amounts to a virtually unrestricted climb up to our cruising altitude, as they'll keep on giving us new altitudes by the time we reach whatever we were assigned. We also are flying out in the middle of nowhere, not in and out of a Bravo, and not in the way of any big arrival corridors. On these planes, getting up near the flight levels happens pretty quickly, so even if we do get a restriction going up to FL200-260 (since I'm still only flying turboprops), by the time we get there we're out of the "Holy **** this thing burns a lot of fuel" altitudes.

 

[Fearless Tower]

We've got three fueling ports. I don't know how the piston Commanders work (never flown one). I've also never had to fuel this one, so I don't know how much line people like or dislike it.

Okay, sounds like the turbine ones are a little different. The pistons have several inter-connected bladder tanks, but only one single fueling port on the top of the fuselage. I believe there were some issues with fuel caps not being fully seated and siphoning fuel out the cap which also collapsed the bladders resulting in the pilot believing there was alot more fuel onboard than reality.

 

[Ted]

Okay, sounds like the turbine ones are a little different. The pistons have several inter-connected bladder tanks, but only one single fueling port on the top of the fuselage. I believe there were some issues with fuel caps not being fully seated and siphoning fuel out the cap which also collapsed the bladders resulting in the pilot believing there was alot more fuel onboard than reality.

The 690A has 22 inter-connected bladders that all feed into a main sump. However, there are multiple places where one can fuel the plane, probably in response to issues with previous models that only had a single fueling port.

 

[Fearless Tower]

The 690A has 22 inter-connected bladders that all feed into a main sump. However, there are multiple places where one can fuel the plane, probably in response to issues with previous models that only had a single fueling port.

Is there any other way to check the fuel level in the 690A besides the cockpit gauges?

 

[wabower]

The altitude restrictions are governed by LOA's between and among the various facilities, so even if I'm flying a lightly-loaded and powerful King Air, I'm restricted by the same turbo-prop restrictions as all the others in the fleet. Departing north or east from KADS is relatively painless insofar as climbs are concerned, but a westerly departure through the DFW maze can approximate water torture when "looking for higher." I've found myself restricted to 8,000' when I was pretty sure that I was within a few miles of ABQ.

It might have more to do with the aircraft that I've flown vs. what you've flown. Typically, what I've flown has either had main tanks only (i.e. all tanks are mains) or else they have mains that you need to take off and land on, thus you need to be careful with burning the fuel out of them. So normally you want fuel out of the auxes as fast as possible.

On the twin Cessnas, this is especially true. If I have an engine failure, the aux tank on the dead engine side now contains fuel that I have no means of getting at (at least on the 310). So burning that aux fuel off means that all the fuel I have in the mains is accessible by the one good engine. This is important if I'm flying over the Gulf or in the middle of nowhere, Canada.



We've got three fueling ports. I don't know how the piston Commanders work (never flown one). I've also never had to fuel this one, so I don't know how much line people like or dislike it.

What I do know is that, from the pilot's perspective, it's pretty nice.



Obviously, you have much more experience than I do in this realm since I was still small enough that I thought my mom was pretty tall back then. And I agree fully that operational considerations can and should impact purchase decisions.

Around here, we'll get climb restrictions, but will typically have what amounts to a virtually unrestricted climb up to our cruising altitude, as they'll keep on giving us new altitudes by the time we reach whatever we were assigned. We also are flying out in the middle of nowhere, not in and out of a Bravo, and not in the way of any big arrival corridors. On these planes, getting up near the flight levels happens pretty quickly, so even if we do get a restriction going up to FL200-260 (since I'm still only flying turboprops), by the time we get there we're out of the "Holy **** this thing burns a lot of fuel" altitudes.

 

[Ted]

Is there any other way to check the fuel level in the 690A besides the cockpit gauges?

You can look in the fuel tanks through the fillers. However, the cockpit gauge on the 690A is remarkably accurate. Moreso than probably any other I've used.

The altitude restrictions are governed by LOA's between and among the various facilities, so even if I'm flying a lightly-loaded and powerful King Air, I'm restricted by the same turbo-prop restrictions as all the others in the fleet. Departing north or east from KADS is relatively painless insofar as climbs are concerned, but a westerly departure through the DFW maze can approximate water torture when "looking for higher." I've found myself restricted to 8,000' when I was pretty sure that I was within a few miles of ABQ.

Where I am, the LOAs are pretty non-restrictive. One of the advantages of living someplace that nobody else wants to, and primarily flying places that nobody else wants to. Maybe I'm on to something. I best keep it to myself.

 

[ronnieh]

Wabower, I feel your pain. Most of the time I can get to the high teens unrestricted. It may take one level off before I get the 270 or 280 (no RVSM). There is one direction over here where you can get hung up under a MOA but, I think areas where an urestricted climb to RVSM altitudes is available is getting harder to find. If they had to pay for the fuel I suspect they might try a little harder.

 

[Dan Thomas]

Uneven fuel flow in Cessna singles has to do with the venting system and the fuel caps. The whole system is vented from the single drop tube aft of the left strut and if the vent inlet is sitting a bit low it might not only ice over or get a bug banged into it but it can elevate the pressure in the tanks. As fuel is drawn, the full left tank will send fuel across the vent crossover from the top front of the LH tank to the top front of the RH tank, keeping that RH tank full until the LH tank drops down enough to expose the vent outlet to air. Because of dihedral, this can be significant fuel.

If the tanks still drain unevenly (usually the RH is slower) it is caused by a leaking fuel cap gasket or aux vent check valve. The low pressure atop the wing will extract air from the tanks through even a small cap leak and imbalance the tank pressures and upset the fuel flow rates. If the caps and their vents are tight and there are no other leaks, the pressures inside the tanks MUST be the same, as the air is not moving between them at any significant rate.

FAR 23 demands that any fuel system that has multiple interconnected tanks (meaning those that have a "Both" position on the selector) must have a common vent system to keep pressure equal between tanks to prevent wildly different flow rates between tanks. Some homebuilts, with vent systems designed by naive amateurs (and some by folks who should have known better) have crashed due to fuel starvation with lots of fuel on board just because the action of vents in flight had not been considered. The earlier Glastars were an example: a fuel valve that was either on or off (like a 150's) that fed fuel from both tanks but had a separate vent for each tank that generated slightly different tank pressures and could conceivably empty one tank while keeping the other full, or actually forcing fuel from a high-pressure tank through the system tee to the other (lower pressure) tank and overboard out its vent. Such a flaw could at least stop fuel flowing to the engine once the higher pressure tank ran dry.

I ran into that and installed a vent crossover to stop it. It makes one realize that FAR 23 was written by guys who saw some folks learn things the hard way.

Dan

 

[timwinters]

The complexity of fuel systems can vary greatly. My 182 has "left, right, both, off" as the only options. Climbing and descending is "both", during flight I change to "right" at 0:30, "left" at 1:30 and back to "right" at 2:30 (at 3 hours I start descending to land, period - no LR tanks in my bird).

Yeah, we're fortunate that our 182s are relatively simple. Mine has 65 gal w/ 55 usable and the simple, both/r/l/off selector.

My fuel mgmt system:

Take off on both, fly 30 minutes.
Switch to R for 1 hour.
Switch to L until engine sputters (or until I catch the fuel flow meter wagging out, which it does a good 30 seconds before the engine sputters).
Switch to R for the duration of the flight and descent. (while occasionally going back to the left tank to ensure that no fuel has crossfed back to it)
Switch to both for landing (only because the POH says to).

By dry tanking the left tank, my bird will burn 32 of the 32.5 gallons in level flight, so I pick up almost a half hour useful fuel (confirmed by countless fill-ups after long flights). But I don't include that fuel in my flight planning; I just keep it in my back pocket for an additional safety margin.

I burn 11 gph so the 55 gal usable gives me 4+15 w/ IFR reserves & 4+30 with VFR reserves (plus an extra 4.5 gallons in both cases from dry tanking).

I don't fly over 4+15 though and before I had my fuel flow meter I wouldn't fly over 3+45 using the same method.

 

[wabower]

My 180 carries 96 gallons. The selector valve is welded in "both" position. Or could be, no more often than it is moved.

Yeah, we're fortunate that our 182s are relatively simple. Mine has 65 gal w/ 55 usable and the simple, both/r/l/off selector.

My fuel mgmt system:

Take off on both, fly 30 minutes.
Switch to R for 1 hour.
Switch to L until engine sputters (or until I catch the fuel flow meter wagging out).
Switch to R for duration of cruise and descent.
Switch to both for landing (only because the POH says to).

By dry tanking the left tank I can burn 32 of the 32.5 gallons in level flight so I pick up almost a half hour useful fuel. But I don't include that fuel in my flight planning; I just keep it in my back pocket for an additional safety margin.

I burn 11 gph so the 55 gal usable gives me 4+15 w/ IFR reserves & 4+30 with VFR reserves (plus an extra 4.5 gallons in both cases from dry tanking).

I don't fly over 4+15 though and before I had my fuel flow meter I wouldn't fly over 3+45 using the same method.

 

[Morne]

Interesting theory about "dry tanking" the left. Might have to try that sometime.

I don't fly over 4+15 though and before I had my fuel flow meter I wouldn't fly over 3+45 using the same method.

Yeah, 3:45 is the absolute longest leg I've flown or will fly in my 182, which does not have a fuel flow meter. Matter of fact, the only reason it went to 3:45 was because the first airport we landed at (about 3:20) had a broken fuel pump. The next airport we had trouble getting the self serve pump to work but we weren't taking off without getting more fuel. Better to sleep in the pilot shack than at the crash site.

I figure that planning on 3 hour legs is just easier. Although if my wife is onboard I plan for roughly 2 hour legs. That's one of the reasons I didn't put any additonal value on LR tanks - can't use 'em hauling the family anyway.

 

[denverpilot]

We've got the 79 gallon tanks in our 182 (75 usable) and our fuel selector is pretty much "welded" to the Both position also.

It's far too much gas on board in the summertime around here if you're going to carry anything, but my recent foray down to Nebraska for a week, it was topped off regularly and the silly plane still pegged the VSI in the climb.

That was cool.

I'd try Tim's technique sometime, but...

a) Engines sputtering in flight don't make me particularly happy.

b) I'd have 168 pounds of fuel on one side, and very little on the other (assuming 11.5 gph and one hour on the dot out of the right wing) which would mean even more left yoke than it already needs... and some of that fuel is quite a ways out there and has a pretty big lever arm.

I could go the other way and make the left wing heavy... but anyway...

I think I'll stick to "Both" with the big tanks.

 

[BillTIZ]

The T-41B I fly was two 23 gallon wing tanks and a 17 gallon baggage area tank. Fuel management can get tricky when using the extra tank. The extra tank can only feed the right wing tank.

So select Both for takeoff. During climb or level off, select Right tank, 10-11 gph fuel flow. 1 hour later select left tank, turn on fuel transfer pump from extra tank to right wing. 30 min later, left tank is down 5-6 gallons, transfer pump has moved about 6 gallons into the right wing. Fuel is close to level in both wing tanks. Turn off transfer pump, re select right tank.

Repeat.

I made a fuel log form to keep track.