Zero Fuel Weight in the JetPROP: The Hidden Limit That Can Cost You

Added: 2026-05-31

[00:00:06]All right, welcome to the Malibu Guru podcast and as the old saying goes when the cat's away the mice will play and the cat Mr. Joe Casey the Malibu Guru is away this week and Kenneth and I our director of maintenance have taken over the podcast for for this session. We hope to get it edited and on the air before Joe notices but we'll see how it goes. Um So you've got myself Deanna Casey and Kenneth Hill director of maintenance at Casey Aviation Services and we're here today to talk about structural issues and differences in damage seen between Jetprop and Meridian and what we think might be causing that and this goes a lot if you've watched or listened to recent podcast we've talked a lot about weight and loading and CG and you know observing limitations and parameters and how that affects the aircraft. So today we've got Kenneth who's going to talk to us from a maintenance perspective on what he's seeing with aircraft that are often improperly loaded. So thanks Kenneth.

[00:01:22]Yeah, or at least what we presume are improperly loaded. I was watching that podcast about zero fuel weights and listening to that discussion and it kind of went in line with what we see in the hangar. So I figured it was worthwhile talking about kind of what we see that may correlate with airplanes being too heavy. Yeah, absolutely. So and it's such an easy trap to fall into in the Meridian or the Jetprop you know they're really not those those six seats are a little bit deceiving. You know um people think they can just load it up with fuel and people and baggage and go where they want to go and that's just not the case. Those those models are definitely you get to give somewhere.

[00:02:08]You've got to give up passengers or you've got to give up fuel. It's not going to do it all. If you want a plane that kind of does it all, you got to move into the M600 or M700 in the Piper Piper world. Yep, that's right. I mean, it's deceiving. The airplane's got the power to pull the weight. It's just structurally, it's not there. I mean, we see issues landing gear issues. We see wing cracking issues, especially only in the jet props, not the Malibu's or Mirages that they're derived from.

[00:02:39]Um and that was kind of the the key that we were seeing is it's only the jet props that have this issue. I mean, they share the same it's the exact same wing that a Malibu or Mirage has. Why wouldn't you see it there?

[00:02:52]It's cuz the engine can't pull the airplane through the air with all the weight and you can't load them as heavy and get away with it. You don't have that crutch.

[00:02:59]So, that's what we've been seeing is, you know, seems like the the heavier aircraft are wearing out their main gear components, the torque link bushings and bolts and the actuator bolts are coming untorqued just due to the weight.

[00:03:15]Yeah, it it is it it's always fun to me to walk through the maintenance hangar when you're pulling something off a plane and going, I think I'll keep this as a teaching tool. And I'm not real sure who needs to be taught more, the the mechanics you're training to spot this stuff or the pilots who are creating some of these issues just due to um honestly, it's pro- it's not it's just it's not I mean, it may be a little intentional, but it's mostly just ignorance. And there's a couple things that sometimes we are simply not taught early on in our um as we're getting our licenses and ratings that we should be taught. And one of those things as Joe and I have mentioned on a previous podcast is zero fuel weight. And the reason you're really not taught that as much in your primary training is because it uh while you have one on some of your smaller piston aircraft you don't often see them see it at see it or see it acknowledged when you're learning your weight and balance calculations and all of that when you're training in a 1967 Cessna 172.

[00:04:33]It's probably not even in that manual although Cessna probably started adding it in the later models, you know, so you just don't it's just something that's kind of glossed over but becomes a pretty big factor in structural loading and what the aircraft will take as you move up in performance um and up in aircraft size. Yep. Yeah, that's 100% correct. We see some gaps in primary pilot education that kind of rear their ugly head once you step into the high performance aircraft world.

[00:05:04]There's no change in licensure, there's no change in education. I mean, you could with the license you have step right into one with no training if you had no insurance or didn't care about that and off you go.

[00:05:17]So, it's kind of important that I mean, that's kind of why we're in the education business both of us as a mechanic, that's why we keep those parts as yes to train my mechanics but two to train our owners cuz we want our owners to take care of their planes to reduce the operating costs for them and it makes them safer. Same reason y'all are doing the same thing you do.

[00:05:38]So, it's it's a matter of continuing education as you grow airplanes.

[00:05:42]>> Yeah. So, this morning I was um, down a little bit of a a YouTube rabbit trail, you know, if you've never typed in, um, aircraft wing flex testing. Oh my gosh.

[00:05:56]>> It's terrifying. It is absolutely terrifying. And, you know, in all the examples that are well documented and out on you The ones you'll find the most are the big Boeing aircraft and Airbus aircraft. And you watch these wings flex like 25 ft. I don't I I know the Pipers aren't flexing 25 ft on their wings. You know, it's going to be commensurate with the size of the aircraft and the type of aircraft. Um, but what those wings are tested to and what they will do in to in turbulence and to create a smoother ride in the fuselage is absolutely amazing. It it's the coolest testing process, you know, you can see yourself.

[00:06:36]>> It's destruct- It is destructive testing to the max. I mean, it is definitely destructive by the end of the test. But, that's how you find out what it can do.

[00:06:45]That's how you find out what it can do.

[00:06:46]And And so, the forces acting on that wing that it's simulating, um, is basically lift and turbulence and fuselage loads. And so, the the fuselage is pulling on that wing at the at the root or the base. And the tips, of course, are flexing up much higher with the turbulence and whatnot. And we count on a fuel load to kind of counter that with with weight and dampen it a little bit on the flexing. And so, there we end up with our zero fuel weight on how much we how much loading can that wing take with no fuel dampening those oscillations. And if you repeatedly over, uh, go over that weight inside the fuselage with passengers and cargo and whatnot, then where are we damaging our wing? Well, in the jet props, it's consistently the first rib outboard in the fuel tank. Cuz in a jet prop, you've only got one wing tank, and it starts at the wing break, and it goes all the way to the tip where your extended range fuel caps are.

[00:07:57]Um and that's been very consistent. Um there's a stringer that runs from the base of the wing to the tip of the wing.

[00:08:06]It's almost a continuous extrusion from the beginning of the tank to the tip.

[00:08:10]And the ribs have to uh cut out over that stringer. And on either side of that stringer, there's rows of rivets that go down the rib, and they tend to crack at the stringer and then to the next set of rivets to the next set of rivets and so on and so forth till someone says, "Oh, wow, there's fuel coming out of the wing. We should probably get this fixed."

[00:08:30]>> Right. Um Piper's got a very good service bulletin about wing fuel leaks and when you should do things if you have fuel leaks and where they're located. One of the big ones is if you have a fuel leak coming from a rivet, you must determine the source of the leak. If it's a crack or a structural crack, in a 100% of the time, we defuel a jet prop, pull panel off, get the sealant out of it, and then the first thing you're looking at is a pair of cracks extending away from that stringer.

[00:08:57]Uh I'm not an engineer. I I know what I see every day though, and my best guess my my best educated guess is that the stringer is flexing in an op- opposite direction of what that rib is wanting to do. So, you've got a stringer running towards the wing tip, and you've got a rib perpendicular to that, and the stringer's flexing up, and the rib wants to stay still, and it's basically taking that rivet row and trying to stretch it out of its holes.

[00:09:24]That's been consistent on every jet prop that we've had to fix these fuel leaks on. And I think I've fixed probably eight or nine of them now. Yeah. And just ballpark, if you have if you have cracked uh that particular area and that has to be repaired.

[00:09:41]What are you about to pay to have this repaired? Between 8 and 12,000 dollars depending on how many cracks and how severe the cracking is and how severe the engineering work's going to be to fix it. Yeah. And it's not an easy repair. I mean you're working through an access panel that's you know, 4 inches wide by 10 inches long.

[00:10:00]And you've got one arm in each one and that means you can't see what you're doing now. Right.

[00:10:04]>> So you're kind of working blind off of a borescope or a mirror or another assistant holding a mirror in the other access panel for you. It is difficult.

[00:10:13]Yeah.

[00:10:14]>> risky for the airplane cuz if your mechanic botches it which I've seen plenty of botched ones where mechanics use the wrong hardware or they you know, double drill holes or I've seen it done wrong a hundred times now.

[00:10:28]It's it makes the repair process even more complicated because now you're left trying to repair the original problem plus whatever the last guy created. It's it's messy. Yeah. So why do you think you're seeing this in the Jet Prop specifically and not the Meridian?

[00:10:46]They're both turbines.

[00:10:48]Owners are probably overloading both of them a little bit to a certain extent knowingly or unknowingly. Why why are we seeing the damage primarily in the Jet Props? Because of the way that Piper redesigned the wing in the Meridian where the weight of the fuel is held. In the Meridian they basically split up the fuel loading into three tanks. You have an outboard wing tank. You have a center section wing tank that's another 12 gallons of fuel and then an inboard header tank that is another 8 and a half gallons of fuel.

[00:11:23]So instead of your Jet Prop where you have 70 gallons of fuel all in the outboard wing plus the extend well, 60 plus the 10 gallons of the extended range that I've also seen abused and people put more than 10 gallons. You can squeeze 15 in there if you're really trying.

[00:11:39]>> Right. Uh all of that weight is in the outboard wing. So, all of the weight is concentrated in probably the the weakest part of the structure because the further you get away from the base of the wing, the less structure there is to carry that wing loading and weight.

[00:11:56]Piper fixed that and split it up.

[00:11:59]Yeah.

[00:12:00]So, it So, it's important It's important to note, although they're both turbine engines, they're both going to haul the weight.

[00:12:08]The wings are different. The JetProp is a conversion from the piston model.

[00:12:13]And in the pistons, of course, you know, you overload them to the extent that some of the turbine owners overload them, you're not climbing off that runway very well, and you'll only do it [laughter] if at all. And you'll only do it once or twice before you decide that's not such a good idea, and you start minding those margins a little bit more. But like you said, the turbine operator that turbine's got a lot of horsepower, and it just you take off.

[00:12:39]So, what happens um What happens if you take off and you you're at max gross or let's let's say you're at max gross um gross weight. So, you you did your basic weight and balance calculation, but you've ignored the zero fuel weight, and more of your weight is in that fuselage than out in those wings.

[00:13:03]We have an immediate return to the airport for whatever problem cropped up after after takeoff.

[00:13:11]What kind of What kind of um What kind of damage is that possibly causing to Is that where the damage is happening?

[00:13:20]To the landing gear? To the spar?

[00:13:22]>> that's got a lot of a lot to do with it as far as the landing gear wear and tear is concerned. you know, the main gear actuators are the locking device and they're the retraction extension. So, they're doing all of it. It's not like a King Air where you've got a, you know, mechanical actuator with a secondary down lock or anything like that. It's not that sturdy. Now, I will give credit where credit's due. It's a pretty robust gear system. I've seen them survive some things that they probably ought not should have. But, you know, whenever we're talking about continued abuse, that's where we're seeing the problem. It's the constant over gross weight taxis or overloaded fuselages like you said. I mean, the the gear's having to brunt the force of that weight during taxi, take off, and landing whenever you're past that zero fuel weight. So, it's just eating bearings, bushings, bolts, actuators. You're just opening yourself up for the risk of wearing those components out. You know, your main gear actuators, you know, 12, 13,000 dollars on a good day if you if your parts are bad inside, it's even more than that.

[00:14:28]It's wearing the end seals out, which cause them to leak.

[00:14:32]Um so, it's just really hard on the gear. The other big one is if you're over gross or over your zero fuel weight to start with and then you add fuel.

[00:14:43]Uh there's a factor called wing loading.

[00:14:45]So, how many pounds per square foot of force are exerted on the wing in flight to carry that weight through the air?

[00:14:53]Right. Because the wing's what generates the lift, right? You you can cheat that with horsepower a little bit, but the higher you load the wing, the higher the stresses are on that wing.

[00:15:03]The more it flexes, the more it moves, the more the fuselage moves with the wing. So, you start seeing those um those fillet seal panel rivets wear out.

[00:15:13]And because you've got more movement at the base of the wing as the wing's trying to flex. And it's a pretty stiff wing. It's made to flex a a bit, but not a lot. You say You see what starts to wear out? Say that again. There's uh filler panels between the wing and the fuselage.

[00:15:28]Filler panels. Yeah, it's um they're just aerodynamic panels CherryMax to the wing, which is just a blind structural rivet. Yeah. But basically, over time as that wing is stress cycling, it is taking those rivets and trying to pull them out of the fairing.

[00:15:44]So, we spend a lot of time fixing that and it's just it's Nitinol, but it wears the holes out, wears the holes out in the wing and we're having to fix it all the time. It It is so important so important for jet prop owners, especially I'll say for all all aircraft owners, everyone, please observe your limitations. But this one little thing that gets glossed over in private pilot training or not touched at all, you know, that zero fuel weight would make such a difference, I believe, in the end maintenance state of these aircraft with the with the wing damage, the structural cracks, the pulling rivets. I never like the thought of anything screws, rivets, anything pulling off trying to remove itself from the aircraft. Um but yeah, I mean the the more times and and most of these owners aren't the first owners. You have no idea how previous owner treated that aircraft repeatedly. You know, you don't know how many overloaded landings that aircraft already has on its airframe.

[00:16:55]>> You'd like to think none. You'd like to think none. But it's impossible to know.

[00:17:00]There it's it's definitely an honor system. There's no way to really determine that in the hangar because most of the damage is in the tanks. It's under sealant. You can't see it. So, you don't know about it until it finally crops up and you've got leaking rivets on the bottom side of the wing and it's like, oh, well, I guess we've got a problem now. Yeah.

[00:17:20]Um yeah, so uh so we've covered the the difference in the Jet Prop and the Meridian and why you see this more in the Jet Prop. Do you ever see it in the Meridian? Never. And I've never seen it in a Malibu or a Mirage, and that was the other important thing.

[00:17:36]I'm sure you'll get some questions on uh the biggest difference between a Jet Prop and a Malibu or Mirage are horsepower and the weight of the fuel and where it's stored. Right, because the Jet Prop allows you to put more fuel in that wing than it was originally designed for.

[00:17:52]And it's heavier, that's right. Six 6 lb per gallon for avgas versus 6.7 lb for jet fuel. Yeah, and whenever you total that up over 140 theoretical gallons in a Jet Prop, that's a big difference.

[00:18:06]The other one is your average Mirage or Malibu owner is not going to have the extended range tanks, and if they are, they know they won't be using the weight in the cabin. You'll either be two people up front with a full load of fuel and a bag or two in the back. You're going to have a cabin full of passengers and not a whole lot of fuel. That's already lighter.

[00:18:25]So, that's been I think the consistent trend. That's why you don't see it in the pistons cuz fuel's lighter and you can't load it as heavy as far as fuel's concerned in the wing. Yeah, you know, the pistons burn so much less fuel per hour than the than the turbines do, so they can get by with less fuel. And again, I know I've said this before, I don't care how much these Malibu guys brag about their plane going 8 hours lean of peak, whatever, >> [snorts] >> you're not going to talk four, five, you're probably not even going to talk your spouse into going that long with you without a stop.

[00:19:01]>> Nope, I'm good at three. Right.

[00:19:02][laughter] We good at three. Three to three to four is about my limit as well.

[00:19:08]Um but yeah, so you've just got different missions, different demands versus the engines. And so, you you take this conversion, and it's a great conversion.

[00:19:18]I I don't want to knock the JetProp. I love the JetProp. I think it meets a very specific mission, um and does a great job at doing that.

[00:19:26]Uh it's a great entry into the turbine market. Um very economical, fast, but it's not going to haul a lot. No, it's a Ferrari, you know, if you're not going to go to Lowe's and put a pallet of concrete in the back of your Ferrari.

[00:19:41]You don't do the same thing with a JetProp. It's not really designed for that. That's not really the use case for it. If you want to load three people in it and get somewhere fast, by all means, that is the airplane. It is going to get you there. It's going to get you there economically, and it's going to get you there fast. Yeah. And they're easy to acquire. Yeah.

[00:19:59]>> But, you know, if if you need an F-150 that can haul people, too, that's probably not the airplane, especially if you're talking long-range missions. Right. Um all right. So, we've covered wing loading and zero fuel weight. Anything else you think we should add to this discussion? I don't think so. Um biggest thing is just make sure your maintenance guys are looking at your landing gear at the annuals. I mean, we see a lot of gear discrepancies, a lot of nose gear discrepancies.

[00:20:26]That's uh you know, I think that ties into just talk at M-Class probably about nose gear failures and steering issues.

[00:20:34]>> Right.

[00:20:35]All of that kind of ties together, especially in the JetProps. Man, I tell you, I don't care what airplane it is, landing gear takes a beating Yep. on every one of them. Um there are some that will mask those beatings better than others. I'm looking at you, trailing link gear. But, uh Yeah, the the M-Class does not uh does not hide bad landings whatsoever. No, it doesn't.

[00:20:59]>> [laughter] >> Um so, how much of this can be called I if I'm an if I'm looking at a JetProp um versus a Meridian. I'm a new buyer, and I'm trying to decide between the two, and how much it you know, I've I've I'm kind of leaning towards the Jet Prop. I sent one for a pre-buy. How much of this can be caught in a in a good pre-buy inspection? I mean, you You already mentioned you can't see the damage that occurs in the tanks. You're just not going to see that until it produces a leak, and it can produce that leak 2 hours after purchase, and I know that's where it It It never fails how many times we do pre-buys, they come back clean, within the first 10 hours of ownership, the new owner calls, and there's a prop governor that failed, or a fuel leak that sprung up, or you know, and they just spent money on, you know, an annual basically for a pre-buy, and I I know the frustration. I can feel their frustration, but there are limits to what can be seen before it's seen, right?

[00:22:08]>> Yeah, I mean, it's pre-purchases and annuals are great inspection tools, especially for your new aircraft owner.

[00:22:15]Um we like to think that we'll find everything we can find, but there will always be those things you can't. Um most of the time it's going to be like what you were just speaking of, components that have aged, but they're not standard inspection items.

[00:22:32]Uh there's no way to detect that the performance is degraded because one, either you've got a pilot that didn't report it, or it wasn't discovered in the test flight because you couldn't discover it.

[00:22:44]Um Just, you know, weird things like that that shake out. Yeah, it was going to fail in 10 hours no matter what, but there's just no way of knowing that. In terms of inspecting for an aircraft that's been ran overweight, typically the gear system's going to show it the most cuz I like I said, it's taken the beating.

[00:23:01]Um but that's about all you will be able to find. Um, the the fuel tank issue, I wouldn't go looking for that problem. It is a problem eventually, but it's not what I would go looking for early. It It It's not It's not as bad as an engine replacement or having to replace cylinders and a piston, you know, it it uh in terms of cost scale, you know, you're going to spend more money trying to find the problem before you know that it's a problem than you will just fixing it when you have it.

[00:23:32]>> Yeah. It's just easier to prevent having that problem in the first place.

[00:23:36]>> Right. And, you know, gosh, fuel leaks as seem to pop up on every airplane off line some shape, form, or fashion. Yep.

[00:23:46]You know, uh whatever the manufacturer.

[00:23:48]So, yeah, and and I've been told over and over we're you're troubleshooting one for me right now on a King Air that needs a bladder replace. It's got bladders multiple bladders inside each wing to hold the fuel and those bladders are interconnected.

[00:24:04]And I've been told for you know, we've replaced three or four of them and I've been told every time it goes down we're like, "Should we just replace them all?"

[00:24:13]And the mechanics are always like, "No, don't touch it until it fails." You know, cuz you can you can create your own problem sometimes by looking for those problems and then uncovering stuff and maybe not putting it back in safely.

[00:24:25]>> Yeah, I've said that multiple times on here. I think that um Some preventative maintenance is great and some preventative maintenance can cause more problems than it's worth.

[00:24:36]Yeah. You got to weigh your options. Uh you kind of got to know what you what else you may be buying into, you know, manufacturing defects on parts, making mistakes as a mechanic, which is human factors 101. We're all capable of making a mistake. We all like to think we don't, but it does happen. Well, in that you've introduced more opportunities for those mistakes to occur. The more you do what you don't have to do, the more risks there is.

[00:25:03]So, you kind of have to weigh your options, and that all comes from time and experience. Yeah. So, I've kind of gone off a rabbit trail here into pre-buy inspections and away from our original thing, but you know, in in exploring whether that original uh rib cracking and stuff should whether you should go looking for that in advance or if it just presents itself. But, um if we haven't done a broadcast on pre-buy inspections, we need to get that one in the lineup. I think there's a lot to do there, a lot to talk about.

[00:25:33]>> that's a broad topic. Yeah. Um but anyway, thanks for chiming in and talking about all the nuances of this and what you're seeing out in the field because what you're seeing in the field just it can't adequately be I hate to say it, people just in general feel it in their wallet before they'll get it in their head. I can tell them all day long, but till they get hit with that, you know, bill from that crack repair, you know, sometimes it just doesn't sink home. But, >> Well, and there's not a lot of data paths for that information to make it from the mechanic back to the owner community, either.

[00:26:16]Uh that information typically goes from me to the customer, and then it dies after they pay for it, and they take the airplane home, and they stop doing what they were doing, but it's it's hard to get that information past that stage. Yeah, so if you're listening or watching this podcast, don't go don't exceed that zero fuel weight. Don't overload your jet prop. Don't overload any of your aircraft.

[00:26:38]>> Yeah, don't don't do that. It's bad for them. Yeah, you're you're you're doing damage you're not seeing, and you can do it over and over and over until something gives. And when it gives, it's always at the wrong moment, and then we get to talk about it at convention and Manny's accident briefing for the for the year. And hopefully they're with us to talk about it. That's not always the case, but you know, it does happen.

[00:27:04]Well, uh thanks for joining. Thanks for chiming in. Thanks for everyone who held in while Joe wasn't here to moderate. I know he's yeah, I know he misses being here. He's all in search of cooler weather. I think he's in Colorado this week. And yeah, while we're here in muggy rainy East Texas. But anyway, thanks for joining and Joe will be back with you next week.