Approximately 47% of general aviation accidents in the Houston area are the result of a fuel related issue. Starvation, exhaustion, contamination... what are they and how can they be prevented? What are the differences when flying a low wing vs. a high wing airplane? What about a fuel injected aircraft? This week the guys are talking about this incredibly important aspect of flying. The fuel system!
You can't fly every day to stay current and proficient. But you can listen to your favorite aviation podcast and keep aviation on the brain! This week we're talking about fuel and your airplane's fuel system.
Clear prop! Number two following twin traffic on 3 mile final. JB using runway 25 on a 4-mile final.
This is Behind the Prop with United Flight Systems owner and licensed pilot, Bobby Doss. and it's co-host: major airline captain Designated Pilot Examiner, Wally Mulhearn. Now let's go behind the prop!
What's up Wally. Hey bobby how are you. I'm great another week. Another show this one. We've talked about it a couple of times but I'll ask you a question that you've answered before what's the three most important things you should be thinking about as an aviator when you're in flight well There's there's yeah there's three things and there's actually Sometimes we can say there's five things but the first of number one is fuel and number two is fuel and number three is fuel and if we go the the five version of this number four is fuel go and number five is fuel. We need fuel and this week. All we're going to talk about as fuel systems and again talking about GA aircraft and what we train in what we normally take flight tests or examinations in our warriors and Cessna’s and archers in those sorts of things. So we're going to we're going to focus primarily on the piper low wing fuel system and the Cessna high wing fuel system and how they work in these GA aircraft man. I think if you if I was really honest again early on in my in my private days and probably up to my private check ride. I knew there was a a left right. Both switch on and off and there was a lever to turn the fuel system off. And I I. I knew there was a fuel vent. But I don't think I really knew what the fuel vent did and I flew strictly Cessna’s from start to to check ride day And I look back in house. I on the fiscal see private pilots and solo students walking around him. I'm sitting here anxiously thinking. Well how well do they know. The fuel system. They know better than I did. When I took the plane yeah, It's a pretty important system as you as you highlight and we joke about. It's a really really important system. Yeah, I And I don't know where I saw the statistic. I know it was at a safety seminar in Houston many many years ago but There is a a slide that was put up in it said that forty seven percent of the general aviation accidents in the Houston region Had a fuel element to them. Whether whether it be fuel starvation or fuel exhaustion and their different Because in a in a piper piper airplane or a Beechcraft airplane where you we have to actually switch the tanks. We could make that engine quit due to fuel starvation and still have fuel in the other tank. So and that's that's that's just really tragic if you know. An airplane crashes due to fuel starvation. But there's still plenty of fuel that we just didn't access. Yeah, and as I sit here and think about it a number of the incidents that I’ve heard over the last decade Around here at hobby Twin landed and fifty-nine because fuel contamination. another topic. That right wasn't in your shortlist. There that you know really can cause problems in an aircraft. I think they got jet fuel in there right Twin and it contaminated the fuel and it ran for a while but then then obviously didn't And he can't run on the wrong fuel so very very important subject. And I think if you we've talked talked, I guess it was last week about the the the the books for check rides the POH. Oh will tell you how that feels works. I think you really should understand how the fuel system does work for sure right right and you know one thing that that I will bring up Sometimes on check rides is if if we're talking about the fuel system you know we're required to cover three systems On a check ride so If you'll system is is one. That occasionally or. I don't I don't know what the percentages are but Sometimes we get into that. And that's one of the systems that I pick for a check. ride I think more so on Cessna’s Most of the Cessna pilots think. Well you just leave it on both. And and that's it. That's all we need to do with it. you know. Are there ever occasions where we would put that. That fuel selector on left or on right In the air there could be You you could have a A fuel leak And I’m not going to go down the rabbit hole of how we would manage a fuel leak but There could be a situation where you wanted to just Burn the fuel from from one given tank In Cessna rather than just leaving it on both Now obviously the system is a little bit a little bit simpler because in a perfect world, I think most of the Cessna’s.
Have you actually put it on left or right When you shut down. And that's that's just to basically exercise the fuel valve and make sure all the all the seals and everything stay You know lubricated a little bit But You know there are some other things to think about on a Cessna. That fuel vent is usually over on the left The left tank which causes pressure differential in the two fuel tanks. And typically. When you when you fill up a Cessna on the left tank will usually take a little bit more fuel in the right tank. And that's that's that's normal. I mean it's not going to be noticeably but if you may put You know ten gallons in the left tank and nine point two on the right tank. Something like that I have. We've had that squawked many times that there's a there's a problem with the fuel system because they're they're going at different rates when in fact it's it's just as simple as that or maybe. The fuel vents got moved a little bit and the pressures is immensely Stronger than expected in and the fuel drains quite a bit differently. I think from a learning perspective for me again. Learning these systems early on. I remembered I couldn't fly these fancy s models. They were more expensive in nicer and they were fuel injected and I knew they were fuel injected and I. I didn't want to spend the money. I am trained in those. And so I stayed in these other planes. That were carbureted And I I. They were cheaper inside. Liked it more. I thought I thought the s models had a fuel pump in that the N and p models didn't have a fuel pump. I've gone smarter. And I know that all plants have a fuel pump but maybe we could talk a little bit still high wings fuel systems the difference in a Cessna that has an electronic fuel pump and A Cessna. That doesn't have an electron a fuel pump. Well you can go back in and we can look at The the engine Most of these airplanes Have Lycoming engines and The they're usually oh three twenties. Or oh three sixties And that “O” has a meaning in it. What it means is opposed means that the cylinders are horizontally opposed. We're not this isn't about that but sometimes you'll find airplane has an IO three sixty and the I stand for injected means fuel injected. You may flying airplane. That has a TIO. Maybe TIO five forty on that t. stands for turbocharged charged. So the the the the designation of the engine tells you something right there so if you're flying an airplane that's an IO three twenty on IO three sixty for instance It's fuel injected. So it's not going to have a carburetor so a couple things that you're going to know right right off the bat it's it's You know there's obviously there's not going to be any carburetor heat So it does simplify something right there and this can go back to the reason. We use checklists Maybe we're in a carburetor airplane today that we're not really used to flying it so we're not used to using the carburetor heat but guess what it's going to be on the landing checklist so just just use the checklist and follow the prescribed procedure From from the manufacturer but IO three sixty or or three twenty Doesn't really matter is is a fuel injected engine and it will have an external an electric fuel pump and as an in addition to the engine driven fuel pump. The engine driven fuel. Pump is something that we don't really have control over if it fails. There's nothing we can do about it and in fact We may not even know that it failed. So there's nothing we can really do about it but on an IO An airplane will have a fuel pump and that is basically how we prime the airplane. How we get the fuel to get the airplanes started. Yeah, and some. I think in the piper. We'll get to them. Maybe but we use that indifferent critical phases where we're maybe changing the fuel system because of gravity is not driving some of that as well But I, I think. I've I’ve now looking back feel pretty stupid.
That I didn't even think my plane had a fuel pump. But it does its engine driven. And it's mechanical in nature not electronic in nature other highlights about fuel system. I guess the shutoff valve is obviously a pretty important one. You would need to check and obviously follow checklists again and you'll be fine with that one. We talked about the switch going from off left. Both right What do you feel about moving switch during flight. While do you like to move that switch during flight. Well talk about both systems here. I guess this is yeah. This is a pretty critical lever right right now in a in a Cessna you know. It's going to stay on both and you're not not really going to move unless you're in some sort of a An abnormal situation However piper you are going to move from from tank to tank When I was taught, I was. It was a big deal. It was a big deal to move that that fuel valve To go from one tank to the other and You know you're going to do what the POH prescribes In in most airplanes it will have you turn the fuel pump on and then move the vow from one side to the other and then my eyes are always on the fuel pressure gauge. Making sure that fuel pressure gauge doesn't go anywhere and then I will turn the fuel pump up off. I actually Flew Friends bonanza Probably about a year ago and When I switched the fuel from one tank to the other, I got a bump in the fuel pressure. I just went right back to the other and just left it there and landed that way and then when when I landed, I called him and I I mentioned it to him he said oh yeah. That's that's that's pretty normal. Should be fine but it sure. Got my attention. The other thing I do and this is probably over. The top in this may be considered paranoid but before I switched the fuel from one to another, I'm looking for an airport or hard surface airport to land at in just in case that I shut it off of course if it if I if I flip the valve and the engine shuts down. I'm going to go right back to the other side and hopefully the engines going to start right back up and then I’m going to get the airplane on the ground but what I see on on check. Rides is is most of the flight schools. Have some sort of a timer set up on their Again the standard around here is Garmin 430. Four thirty or five thirty s in these airplanes. And you can set timers and most of the schools have thirty-minute timer. So every thirty minutes were flipping the valve from one side to the other. And I see some. A lot of people are pretty casual about moving that valve and again. I've never. I've never had an engine quit From moving that bell but they are pretty casual and You know I would say just just pick your time. I mean that that when that message comes up. That's a switch tank. It's really a suggestion. It's not a mandate you know six hundred feet on final approach when we're coming in. The probably isn't a good time to switch the valve. Do you think do you think that. Unfortunately we've taught or students in general where we become robotic to the to the buzzer the like the beep beep. Now we got to change it. Yeah, I think we have. I think we lose some of that professionalism of like does this make sense. Am I using my using all my good decision-making processes to do the right thing. Yeah, and I have a Saratoga which is a low wing piper Holds a lot of fuel hundred. Two gallons In what I do. Is I run it. If I’m going on a long cross-country flight. I run it one hour on one side and then I switched to the other side and I stay on the other side for two hours and then Then go back to the original side for the last hour and quite honestly. I don't know if I’ve ever made that second Switch because. I don't think I’ve ever flown by airplane longer than three hours My bladder doesn't last that. So I’m I’m usually stopping now if there's a flight You know a distance that's Four hour and five minutes. Flight would I might I might but I think I would. Just leave it on that that other that other tank and just just come in and land Just to minimize the number of times it on switching the valves now you know.
The other side of that is well. Jeez I’m in a Cessna. I'm just going to leave it on both and I’m never going to. I'm never going to move the valve. Well that's not good either. You need to exercise valve and make sure everything stays lubricated and and so forth in there so You know and that that's just out of the POH on most of these airplanes as you switch it to one side when you shut down and I don't I probably could be completely urban legend but I when I was a student, I had heard that we did some of that. In case we got the wrong gas pumped in would only and they caught it. It only contaminates one tank. Not both thanks and that might save some money if we only had to clean one tank out or if we put water bad gas or whatever else were were causing half the damage instead of the whole damage but I like the cycling to keep it in working order. Because we've all seen things brakemen. The I can't imagine what my heart would do if I reached down and turn that and it popped out. Yeah, and like. I couldn't turn it. Yeah, and it might be got stuck to the off position or in-between positions. And who knows what's going on with the fuel system at that point so I fly more than I do. Pipers but the twins low wing plane has four tanks. We use like axillary fuel tanks. We're doing a lot with that fuel system as well and different times different stages of flight you're using main versus auxiliary tanks and you may be changed that more in the twin but let's talk through the lower wing aircraft. We've got two tanks right and left. We have an electric fuel pump. That helps the non-gravity system. Get it to the electric or the engine driven fuel pump. Let's talk through a little bit about what we're thinking there on that system Wally as it relates to. How do we prime the engine. Same sort of stuff there right. Yeah, yeah and You know even in a piper if it's non you know fuel injected airplane You will have a primer again. Fuel injected airplane. You're not going to have a primer. So it's it's prime using the fuel pump essentially and I say not having a primer it. It essentially does. The fuel pump is the primer but not the the Little piston Little thing that we pump in in just an “O” three twenty say so. Even carbonated piper warrior archer may have a primer and it has an electric fuel pump. But it’s just not fuel injected. So I would use that fuel pump in different stages of flight whereas in a Cessna that's fuel injected that has an electronic fuel pump. If I were to switch tanks. I don't turn that fuel pump on. I don't need that boost pump to be on while I throw that lever but it's pretty important a low in plane that we engaged again. Follow the checklist. Ninety-nine out of one hundred of them say engage that boost pump fuel pump while you're switching tank. What is that doing for the system or for the aircraft while they're switching things just giving a little extra boost to the fuel pressure just in case there's I don't know. Maybe I think there's a little air on the line or so It should help you with that. I've always thought of it as like a a backup for you for whatever's going on since this is so freaking critical that we're going to flip the switch. We'd better get the fuel moving as best we can no matter what because even if there was some hesitation, we'd want some pressure to be in that line to be getting that fuel to the cylinder so that we get get an explosion of course And I think for me as I fly more sustenance with the one eighty-two versus the pipers always. I normally think of the thirty minutes or whatever system. I'm on from switching tanks but it's those other critical phases on takeoff. You normally have the fuel pump on and on landing. I think most planes will say have the fuel pump on in the warrior archer flavors but again it's more about critical phases of flight. Where you want to make sure you've got as much redundancy as you can because if that if that engine driven fuel pump for whatever reason failed and we didn't know it we definitely wouldn't want there to be some hesitation at one hundred feet on the go and that electronic fuel pump would provide us a little bit more say a backup right that that critical phase a flat and and something else to think about. Is you know if if it's just like when you when you pull the mixture on the airplane it takes just a few seconds for that fuel to Stop in the engine. The quit When we're switching tanks if weird us take the the fuel selector go to off the engines. Going to run for a little while one thing I would be in this technique I think it's a good technique.
But if you're taking the runway and you realize that your fuel selector is not on the tank you want it to be on Right before the takeoff roll is probably not a good time. Make that switch because you could You know push the power and get the power and just about the time you lift off as who the fuel actually all goes away and that means the engine goes away Of course that may be a horrible place to lose an engine just as you lift off because you probably have plenty of ahead of you usually but anyway Just just be careful and make sure it. Just make sure that that it makes sense to switch the tank You know when when you thinking that you should do it. In other words. I going back to the Six hundred feet on final approach. Probably not the most ideal time to switch To move that field off. Yeah, I like. I like the thought of just make good decisions like. That's not a good decision. So if I’m going to make the decision to move this don't be doing it. Just because a buzzer went off buzzer might have gone off to say. Hey you might want to start thinking about. Is this the right time to switch the tank and go through that decision process to make it so we talk a lot about it around here Fuel gauges they're they're A very important tool we don't nobody should trust the field gazes early. We want to visually inspect and go. Look at those those tanks and our tanks as well. let's talk about a little bit about the fuel gauges for a second one. I'll tell you as a fly. School owner fuel. senders are very expensive so as a fuel sender goes bad from a tank to get it. Fixed is a very expensive proposition but one this required so they get fixed but if you'll sender is nothing more than a float and a device that then sends the information to a mechanical electronic fuel gauge to give the pilot an indication of where that fuel tank is. And if you fly much at all you've probably seen one that's a little out of out of calibration, we'll call it but They should be working. Some planes have A panel that might say low fuel or some other Indication that you're having a fuel system problem but a pretty important part of the fuel system all up is the fuel sender and the fuel gauges And not one. That I think many student pilots learn about. It's you know. We live in an iPad world while they were. It's either on or off or works or doesn't work but it can give you some good information if I if I want. My one. eighty-two to be half full. But the gauges are showing three-fourths. Even dipstick that. I might want to think about this a little bit like I could be way overweight here right right not get off the ground. So I should do some investigating. You might not trust them. But I would validate the information that they were sharing with me for sure and one thing I would caution on the very cautious about is airplanes. That have Engine analyzers they're becoming more and more common. I've I’ve got them in in both my airplanes and We you have the ability to tell the engine monitor. How much fuel is on board the airplane so You know I. I have JPI is mine and every time we start up at asks if we feel the airplane and you either say yes or no and if you say no it assumes that it has the same amount of fuel in it that It thought it had when we put the airplane to bed the last time, we flew it and if we we say yes, we filled it up. It will ask you. How much are do you full. Tanks did you. Just add twenty gallons. Whatever just know that that that unit is now taking the amount of fuel that you said was onboard the airplane and it's measuring the the amount of fuel. That's going to the engine and it's giving you a number now again in my airplanes the number is we've got dialed in where it's I can almost tell to the tenth of a gallon. How much fuel. I'm going to need when I when I go. Top the airplane off. But the one thing that that Those engine analyzers will not know they will not know about a fuel leak so If we've got fuel leaking out of the left side or or say someone comes and has taken fuel out of the left side again. Just a leak It doesn't know that because it's not actually a fuel gauge. So you're looking at your engine. Analyzer it's a nice digital display at says you've got seventeen point six gallons and because it's it's so much easier to read. It's tempting to not pay attention to the fuel.
Gauges that over somewhere else on the on the panel and they're hard to read but they're actually accurate in that seventeen point six is not because you may have had a fuel leak again. We don't see fuel leaks a whole lot but it is something to definitely be thinking about. Well I’ve heard. I've actually heard a few stories of fuel caps not being back on you know you fly and then my that's a fuel leak but not one that's going to leave a residue when you come back on the ground and see that there's nothing dripping but you might have lost a number of gallons Because that cap wasn't seated correctly or was gone. All the way right I guess the last thing that jumps to my mind and if you have others. Let's talk about him but the sumps Some are on every aircraft nowadays. I think that We fly at this fly school and other fly schools. We something that fuel. There's the POH would tell you how many there are but on N and P model I believe there's one on each wing and one or two on the belly or something this for what reason Wally why. Why are we something. The fuel tanks Right there underneath the wings. Well basically were. We’re trying to see. If there's water in the fuel or any contaminant. In the fuel. I I shouldn't just say water but could be any any Contaminant anything other than in these airplanes. We usually run. One hundred low lead But everything but a blue tint to the to the fuel if if we don’t, We got some sort of a problem And I I would. I would suggest that as a student pilot. If you've never seen what water in the fuel looks like Tested out there and and get your little fuel test or get a little bit. One hundred low lead in there. And if you've got a little water bottle with you just pour some water in there so you can actually see what it looks like. It's very distinct. You can tell right away that that that something You know that that it's it. It doesn't look like the other the is going to sink to the bottom. Water is heavier than hundred low lead. And you'll notice it right away no doubt and it and it's an interesting thing where people should look at it and know what that's going to look like before. Maybe they accidentally run into later on in the future and jet fuel is heavier than hundred low lead. So if if by chance there happen to be jet fuel pumped in your airplane You You You would see it right there and and you you know most of the time. In a little Cessna one seventy twos or warriors not going to be a big thing but Sometimes in in bigger airplanes the the line personnel are confused. is that a turbo prop or or not. Yeah, I think that's the one that scares me is the twin four tanks and you know a fuel or might just make a bad assumption and that would be very expensive. that sump for sure bright. So hopefully you've learned a whole lot about fuel systems today. Both the Cessna of the flavor of Cessna and piper There's there's obviously a whole lot more to learn but hopefully we shared. We shared a lot of insights with you to make you more aware of what's going on in your fuel system always reference back to that. POH and if you have questions call and ask for more information as always fly safe and stay behind the prop.
Thanks for listening. Thanks for checking out the Behind The Prop podcast. be sure to click subscribe and check us out online at BehindTheProp.com behind the prop is recorded in Houston, Texas. Show creator and host is Bobby Doss. Co-host is Wally Mulhearn. This show is for entertainment purposes Only. and not meant to replace actual flight instruction. Thanks for listening and remember: fly safe!