What happens when a tank empties on a fuel injected engine

N

N1783M

Filing Flight Plan
Joined
Oct 20, 2015
Messages
26
Display Name
Display name:
1783M
Last week, I flew from DVT to OKM, duration 6.3 hours, fuel selector on both on an IO470 engine. Just before the flight, I filled the tanks all the way to the top. The left tank drains more quickly than the right side. 2 miles from the destination, a partial power loss occurred. Full rich mixture and advancing the throttle had no impact on power. I switched from both to right tank only. I landed without incident, taxied to the ramp, and applied full power to the engine successfully.

My JPI EDM830 showed 66 gallons burned with 9 gallons remaining. The fuel used function has been very accurate, usually within 1 gallon on long flights. The tanks took 63 gallons after the flight though I could not fill all the way to the top due to wind at the time of refueling. However, the tanks were filled almost to the top.

I think this is what happened: The left tank ran dry and air was sucked into the fuel lines, fuel pressure was lost (I did not think to look at the gauge during the emergency), and finally the air cleared the lines and fuel pressure was restored a few minutes later when on the ground.

LESSON LEARNED: DURING LONG FLIGHTS, DRAIN GAS FROM ONE TANK ONLY AND SWITCH REGULARLY AND EVENLY!

Any other thoughts on why exactly the partial power loss occurred?
 
I'm more inclined to go side to side, rather than both, even if the flt manual says you can do both.

In the Cherokee line I would run one side dry at times, to keep a known quantity on the other side for landing. The engine never really quits, I also took precautions as to where & when I was running a side dry.

There is discussion on each side of the issues. In your instance, yeah, maybe some air was sucked in.
 
A quick net search suggests fuel burn with that engine can average over 10 GPH??

Maybe a fuel stop next time??
 
I've never seen a "both" system suck one tank dry and the engine quit with fuel in the other tank.
 
Why the engine stopped is air in the lines, as you determined. Fuel management is why the tank was empty and allowed air to get in the fuel line.

Tim
 
Stewartb said:
I've never seen a "both" system suck one tank dry and the engine quit with fuel in the other tank.
Click to expand...

I have not, but I have seen this stated with some Cessna planes.

Tim
 
Not having a zero fuel power out is the purpose of the both fuel selector. If you have a flame out with fuel in one tank while on both you have a vent problem.
 
"What happens when a tank empties on a fuel injected engine"

I got this guys. Stand down.
Being the only person here with 7 tiny tanks, scattered hither and yon throughout their airframe, you can imagine I have some experience with a....fuel-challenged tank.

Here is what happens.
You are 'flying along fd&h' (you know that acronym, no need to insult you by writing it out)
You may be even nodding off at this point in the flight. All is well, that is certain. You could be anywhere...even low over the lights of Detroit at night, for example.
If you happen to be watching (ha - you aren't watching) you might be lucky enough to notice the fuel pressure needle bobble slightly.
Then, as if in synchrony with some grand symphony conductor's commands, all of these happen at once:
-the roar of the engine slows and all you hear is wind on airframe.
-the MP needle falls
-the fuel flow needle plummets
-your airspeed indicator seems to fail.
-you feel deceleration against your seat belt.
-your sweet and innocent wife, who before this moment in 25 years of marriage, has never uttered - or even thought - a curse word, suddenly 'goes all sailor' on you.
-she also grips the 4130 cabin tubing until it is whimpering. (you are thinking through all this, how will I replace that section of tubing?)
-panel lights flash, the airplane starts its death dive, and you hear that TV movie sound where an airplane is pointed nose to ground, accelerating to its doom.
-well, maybe not the last one.
-you awaken from your stupor/slumber, and without even thinking - you 'fullest main, boost pump on' it.

The airplane forgives, you continue.
Your wife does not forgive but you continue.
 
Agree with stewartb. If there was power loss for an extended time in flight due to air in the lines, something's awry in the system, because it doesn't meet certification guidelines.

FAR 23.955(e) Multiple fuel tanks. For reciprocating engines that are supplied with fuel from more than one tank, if engine power loss becomes apparent due to fuel depletion from the tank selected, it must be possible after switching to any full tank, in level flight, to obtain 75 percent maximum continuous power on that engine in not more than
(1) 10 seconds for naturally aspirated single engine airplanes;
(2) 20 seconds for turbocharged single engine airplanes, provided that 75 percent maximum continuous naturally aspirated power is regained within 10 seconds; or
(3) 20 seconds for multiengine airplanes.


FAR 25.951(a) Each fuel system must be constructed and arranged to ensure a flow of fuel at a rate and pressure established for proper engine and auxiliary power unit functioning under each likely operating condition, including any maneuver for which certification is requested and during which the engine or auxiliary power unit is permitted to be in operation.
(b) Each fuel system must be arranged so that any air which is introduced into the system will not result in
(1) Power interruption for more than 20 seconds for reciprocating engines; or
(2) Flameout for turbine engines. ​

The earlier CAR 3 3.4221(d), in effect when the C-182 was certified, had an even stronger requirement for single-engine airplanes:

If an engine can be supplied with fuel from more than one tank, it shall be possible to regain the full power and fuel pressure of that engine in not more than 10 seconds (for single-engine airplanes) or 20 seconds (for multiengine airplanes) after switching to any full tank after engine malfunction becomes apparent due to the depletion of the fuel supply in any tank from which the engine can be fed. Compliance with this provision shall be demonstrated in level flight.​
 
Stewartb said:
I've never seen a "both" system suck one tank dry and the engine quit with fuel in the other tank.
Click to expand...

Flying a little uncoordinated can cause more gas to be taken out of one tank over the other and run that tank dry. No idea if that is what happened here.
 
TCM injection usually has a header tank in the system. What airplane are we talking about? I assume a high wing gravity fed Cessna?
 
tspear said:
I have not, but I have seen this stated with some Cessna planes.

Tim
Click to expand...
Some Cessnas will siphon fuel from one tank to another which leads to a fuel imbalance when the fuel selector is on both, but I've never heard of an engine quitting because of it.
 
I can't see unporting one tank causing an engine stoppage if the other tank has fuel.....at least on a gravity feed high wing system. I've been flying Cessnas for years and occasionally have drained one side or the other and never had the engine quit if there was still fuel on one side. The only way I can see it happening is if you have one wing way low and run the high tank empty. On the other hand if you're running on one tank and it goes dry it can get really quiet. The Cruismaster Bellance could get a little scary when you didn't lean right and the aux tank emptied quicker than expected.....starts right back up when you switch to either wing and hit the pump.
Frank
 
If the O-rings in the fuel caps are bad, the suction from the reduced air pressure on the top of the wing in flight (and a big hello to you, Dr. Bernoulli) can actually impede or stop fuel in the tank from feeding into the line. That happened on one of the aux tanks on my Bonanza -- the last four gallons of the ten-gallon tank would simply not feed in flight. Replacing the O-ring in the fuel cap fixed it immediately.
 
Pilawt said:
If the O-rings in the fuel caps are bad, the suction from the reduced air pressure on the top of the wing in flight (and a big hello to you, Dr. Bernoulli) can actually impede or stop fuel in the tank from feeding into the line. That happened on one of the aux tanks on my Bonanza -- the last four gallons of the ten-gallon tank would simply not feed in flight. Replacing the O-ring in the fuel cap fixed it immediately.
Click to expand...
.

I dont think a leaking O-ring would impede fuel flow on a high wing airplane (cessna) because the fuel is gravity fed?
 
Stewartb said:
TCM injection usually has a header tank in the system. What airplane are we talking about? I assume a high wing gravity fed Cessna?
Click to expand...
.

Yes there is a header tank. What is the purpose of a header tank?
 
I need to check my computer for a Cessna fuel system diagram. The header in a Cessna may not be important in this discussion. Cubs use header tanks to maintain fuel supply in case a wing tank is momentrily unported while maneuvering. They didn't have a both position on the selector so unporting a tank is easy to imagine. Lots of Cub guys switch to a L-R-Both selector and eliminate headers during rebuild. Cessna calls their header an accumulator tank since Cessnas have a fuel return line from the fuel servo.

edit: I checked my Skywagon manual for the 185 fuel system. The main tanks feed the accumulator tank and the outlet from that tank feeds the engine so the accumulator does work like a header to buffer momentary unporting of a wing tank. In any case the both selection SHOULD have prevented a power loss from fuel starvation while there was fuel in one tank, assuming you were flying in a normal attitude.
 
Last edited:
This was a worry of mine on long-ish cross countries in the 172, the left tank drains much faster. I've heard theories why this is, but with the vents being connected I'm not really exactly sure why it happens

BUT, looking at the diagram at least for the 172N it seems like there is no realistic way to actually lose the engine even if the left tank runs dry first, this is because the tops of the tanks are connected so you shouldn't have a blocked vent issue, and because as long as one of the tanks has fuel in it the gravity will keep the fuel line filled.. I suppose any air bubbles that may sneak in would work themselves out in the carb float tank

On a fuel injected engine I suppose there is a mild possibility of this happening (air bubbles getting in and causing some power loss), and in the case of the OP it sounds like fuel was low enough that perhaps both tanks unported during maneuvering?

P.S. - some people gave the OP a hard time for running tanks dry, but technically if it was day VFR then with 9 gallons remaining he should have been within legal limits (not saying that's a good practice, but it doesn't sound like he blatantly did something wrong)

upload_2017-6-26_10-43-1.png
 
N1783M said:
.

I dont think a leaking O-ring would impede fuel flow on a high wing airplane (cessna) because the fuel is gravity fed?
Click to expand...

It can. It causes a lower pressure in one tank, which will draw fuel across, through the system, from the other tank when the selector is on both. Empty that second tank and you have air in the system. There is far more than enough suction atop the wing to do that. We're only talking a few inches of head pressure here.

Some of the older systems had an underwing vent for each tank. They both face forward, and Cessna has specific instructions as to where they are located behind the strut. Get them wrong and you get uneven fuel flow, sometimes drastically uneven. If the tank pressures are differentiated badly enough, the tank with the higher pressure shoves its fuel over to the lower tank, and sometimes even causes overflow out of that tank's vent and/or leaking fuel cap. That drives air into the lines once the first tank has lost all its fuel, and the engine quits.

There should be a placard next to the fuel selector telling the pilot to turn on the boost pump momentarily if you run a tank dry. Is it there in the OP's airplane?
 
I'd think this 172N fuel system schematic is misleading in that the elevation distance on the down lines to the selector valve and its contribution to possible unporting isn't obvious.
upload_2017-6-26_10-43-1-png.54483
 
A few years ago I did a test on a 1966 182 (O-470), because I wasn't entirely confident the Usable fuel was as published. So on a Cross country flight I planned it such that if ran on the Right tank, IIRC, so that it was nearly empty at my destination (my home airport). Then at about 4000 feet I orbited the airport until I ran the right tank dry. I have ran a number of tanks dry before both inadvertently, just knowing it was possible (burning more fuel than planned), and inadvertently. Most airplane will just lose power, just like you moved throttle to idle, until fuel is restored to the engine.

The 182 however started surging and continued to surge for a couple minutes before I had enough and switched to the other tank. On filling the tank as I recall it still was a couple gallons below the rated usable fuel for the tank. My theory is that you need to be careful with bladder style fuel tanks as it may be possible for them to fold or not fully fill the fuel cavity and may not carry as much fuel as the say they should. Depending on the filler neck it can be challenging to actually fully fill some tanks. I also suspect the bottom of the fuel bladders may not be completely flat causing that last bit of fuel to not flow evenly to the fuel port, this I suspect caused the surging that I don't typically see in airplane with solid fuel tanks.

Brian
 
Fearless Tower said:
Wind could have been causing the wings to rock.
Click to expand...

That bad that it prevented fueling it up? I might have reconsidered flying in such horrible weather if that happened. I haven't been flying that long but even here in FL where it gets rather windy on the tarmac I've never had a situation where I couldn't top off due to wind. Sure I've had some strong gusts blow a little fuel out before I got the cap on, but that would be a loss of a few OZ, not gallons...
 
When I'm low on fuel I check qty by lifting a wing a little and holding it there. Then I do the same for the other side. When the gauges stop responding to that? Time to land. If you need to get all the fuel out of a tank you need to do the same thing. Lift that wing. Fuel runs downhill.
 
Stewartb said:
When I'm low on fuel I check qty by lifting a wing a little and holding it there. Then I do the same for the other side. When the gauges stop responding to that? Time to land. If you need to get all the fuel out of a tank you need to do the same thing. Lift that wing. Fuel runs downhill.
Click to expand...
yup....cept the pickups/drains for each tank are optimized for "level" (coordinated) flight.
 
That makes no sense. If I can manipulate the tanks to have gas cover the outlet that's the best plan to assure continuous fuel flow. Especially if one tank is known to be empty and the other is known to have fuel.
 
What makes no sense? You can't pump out of an empty tank and pumps won't draw fuel if they're sucking air. Basic experiment: get two straws. Stick one in a glass of your favorite beverage. Leave the other out in the air. Try sucking from both at the same time.
 
N1783M said:
.

I dont think a leaking O-ring would impede fuel flow on a high wing airplane (cessna) because the fuel is gravity fed?
Click to expand...
It may or may not impede fuel flow, But it can, (and has happened to a certian person that I know) cause premature fuel depletion,
by siphoning fuel overboard, and when you make an emergency, dead stick landing, at a closed airport, you find that your nice red and white 182 has turned blue.
 
Another thing, Why are Cessna pilots flying long x-country flights below 5000'?

Nevermind, I guess AD 72-07-02 only applies to 172s.
 
Last edited:
bluerooster said:
Another thing, Why are Cessna pilots flying long x-country flights below 5000'?
Click to expand...
Same reasons that Piper and Beech pilots do the same.

Sometimes you just want to go lower to have a better view of the scenery.

Other times you go low to be able to stay VFR or stay low so you can see and avoid t-storms.
 
I suppose so. But the remark was in reference to an AD. But I went back and corrected my post.
But as for myself, On a long trip, I prefer to get high, for a better fuel burn, cooler temps, less turbulence, etc.
 
I can speak from personal experience 52 years ago when the Aeronca Sedan seaplane (S15AC) I was inexperienced in did that exact thing for me. After all, what could be more reliable than a sight glass gage into the tank? Except if the wing tank is a bladder (didn't know about them!), and the various fuel caps (dropped overboard) replaced with everything above corncobs. I recall it went from showing near full to empty and engine quit in 5 minutes. Landed in a slough, drifted to shore, asked the farmer to take me 5 miles for fuel. He was sure surprised...........:eek:
 
You must log in or register to reply here.
Back
Top