Vance Harral

Opinions vary by airplane and operation, of course. I'm guessing an international 787 captain wouldn't call it "hard IFR" until cat III autoland is required. For me, in piston singles, the distinction is generally whether one actually needs to fly a standard instrument approach to land, vs. simply descending through an overcast on an airway or vector, and being cleared for a visual approach below. If I have to navigate IMC to the FAF, and especially if I'm still in the soup when I get there, I call that "hard IFR". My rationale for this isn't so much how close the conditions are to minimums for the approach. I think of it more in terms of how much VMC time I have to deal with a problem. Imagine you're in the clouds, the engine fails, and you glide down to visual conditions. If you have a couple of minutes to decide where to put it down once you can see, that's not hard IFR. If you only have a couple of seconds, it is.

It will most certainly bug me if mine stops doing that! I actually think of the love tap on my butt as an extra "gear down and locked" indicator.

That's a good point. I guess it's not clear to me from the OP whether the movement is occurring at the end of extension and beginning of retraction (which I would consider normal), or at the end of retraction and beginning of extension (which I agree is more disconcerting). Per the service manual, the mains should not actually touch the bumper pad in the retracted position, so significant witness marks on the bumper pads might indicate a problem. Other things could hang up too, including the gear doors, though I'd think the gear doors themselves would flex before any significant flex in the belly pan as retraction completes.

20:1 gearing causes more force between the individual gears, subjecting them to greater wear over time. Eventually they wear to the point of jamming, and if they do, the emergency extension system isn't going to help you. This is discussed in a Mooney Service Bulletin, https://www.mooney.com/wp-content/uploads/2020/12/SBM20-190B.pdf Later model Mooneys with higher gear speeds and more weight/drag (due to additional gear doors) used actuators with 40:1 gears. The idea is that retrofitting these higher ratio gears to older actuators reduces the inter-gear force, allowing them to last much longer.

Well, hang on a minute... We've had this debate before in another thread, I guess it's not resolved. But I maintain that it's completely normal for the seat pan to flex a little when the gear locks into place on extension, and to correspondingly un-flex when it's raised. Our airplane has been doing this for the entire 20 years we've owned it, both with 20:1 and 40:1 gears in the actuator. The gear is correctly rigged per the service manual, and the belly pan is not cracked. Other Mooneys I've flown in exhibit this behavior as well. If you look at the attached photo of the actuator installed in the belly, it makes sense why this is true. In the photo, the motor is on the right, and the jackscrew assembly is on the left (red anodized structure). In the orientation of this photo, the rod that drives the nose gear is at the top of the jackscrew assembly, and the rod that drives the mains is at the bottom (both rod ends are out of the frame). When the gear are extended, the jackscrew assembly experiences compression, due to the springs on the nose and main gears. Look at how the jackscrew assembly mounts to the airframe to hold it in place. It is riveted to the belly pan directly under the pilot's seat. Accordingly, when the assembly is put in compression by the gear springs on extension, that force is translated to some degree to the belly pan. Unless the belly pan is perfectly rigid - which it's not even when new - the pilot will feel some degree of "push" in the seat. Obviously there are reasonable limits. It's one thing for the belly pan to gently flex a small amount and give the pilot a love tap, when the gear is extended due to the springs compressing. Quite another for the pilot to get a huge kick in the a** if the springs are bottoming out and the compression to flex the belly pan to the point of cracking. I can also believe that the specific geometries of individual airframes are such that some exhibit less butt-push than others. But bottom line, I don't think the mere presence of seat pan flex is unquestionable evidence something is wrong.

We have a UBG-16 in our M20F (IO-360-A1A). We have high temp CHT limits set on all four cylinders at 390. We originally set them at 380, but found that was causing us to get an alarm during essentially every climbout in the summer. That was in turn training us to ignore the alarm, which is not a good thing, so we upped the limit. Turns out a 10 degree increase was all it took to almost entirely eliminate the nuisance alarms. In general, I expect CHTs to be in the high 300s on climbouts, and in the low 300s in cruise with the cowl flaps closed. We don't set low CHT limits. First, they'd go off on every engine start, and again that just trains you to ignore the alarm. Second, if a cylinder actually quit in flight, the resulting significant roughness would indicate what was happening way before any temperature alarm. We don't have any limits at all set for EGT. Absolute EGT values are generally uninteresting, particularly on a normally aspirated engine. We also don't enable any alarms for EGT or CHT differentials, or rates (We are unconcerned about "shock cooling"). This thread reminds me that I should probably set an alarm for high oil temp limit. The oil temp probe is a recent addition, and I haven't gotten around to re-programming the UBG since it was installed. The factory gauge redline is 245, but I'm inclined to set the alarm at 225, which is the top of the green arc.

You'd think the fact that the name of the company was Nukem mighta given it away?

For better or worse, our arrangement has a somewhat "generic" LLC Operating Agreement, which explicitly allows the partners to draft a set of Operating Policies for individual assets of the LLC, and incorporate them as LLC rules by reference. We put all the airplane-specific stuff in an Aircraft Operating Policy document that was drafted at the same time as the LLC Operating Agreement. The AOP covers fueling preferences, where you can land, who can provide flight instruction, etc. It also lays out voting policies in accordance with the LLC Operating Agreement, for certain minor things that we felt should be majority vote rather than unanimous consent. There are a couple of reasons for splitting things up this way. One is that it provides a path for the LLC to own additional assets in the future: another airplane, a boat, or whatever. We've never acted on that idea, though, mostly for all the good reasons Bob E notes about large LLCs with many members and assets. The other reason to split the Airplane Operating Policies out from the base LLC Operating Agreement, however, is that it makes the latter simpler, stronger, and easier to maintain in compliance with state law. You really don't want the LLC Operating Agreement which details financial policies and required meeting notices, to be co-mingled with things like how often the airplane gets washed.

glbtrottr asks excellent questions. I'm going to detail how the partnership in which I participate answers these questions, but not because our answers are necessarily best practice. The point is that we all had to sit down and come up with answers to these questions, and it's that process of coming up with the answers that tells you whether or not you've found compatible partners. Those of you considering a partnership may or may not find this helpful, but I've got some time on my hands today. We have various avenues for exits, including a vote to sell the airplane via broker. But ultimately, if a partner becomes completely unsatisfied with the pace of their effort to exit, they may invoke a definitive exit clause in our partnership agreement, along with providing a "final offer" price. When this clause is invoked, the remaining owners must either purchase the exiting owner's share of the LLC at the final offer price, or all sell their LLC shares to the exiting owner at that same price. The idea here is that if the exiting owner provides an genuinely attractive owner to the remaining partners, and the remaining partners are just being jerks, the exiting partner has the option to immediately buy out the whole LLC at the attractive rate, then turn around and sell it (possibly at a profit), free of the irritation and encumbrances of the other partners. This isn't necessarily easy or convenient, but at least it's a definitive way out. In our partnership, upgrades require a unanimous vote. Individuals are permitted to "sweeten the pot" to obtain this unanimous agreement, by offering to pay for most or all of the upgrade themselves. But - and we believe this is key - such unequal funding is considered a gift to the other partners, and no change is made in equity shares. This provides a natural balance between reasonable people. Anyone can pitch an upgrade, others are free to decline it. If it's declined, but the person pitching the upgrade really, really wants it, they have an avenue to make it happen; but without gaining any future financial and/or voting leverage over other partners. For what it's worth, I've done this twice in the last 20 years, because I just really wanted a basic engine monitor, and an electronic HSI. To the extent this increased the value of the airplane, I only got back 25% of that increase, even though I paid for everything. I decided I was OK with that. We charge all partners an hourly rate to fly the airplane, in addition to the fixed costs which are divided equally. Accordingly, partners who fly more pay more, in proportion to their flying. This is a deal killer for some people, because it makes the whole thing feel too much like renting from a flight school. But the rate is a lot less than a flight school would charge, and you're not going to find a flight school with a Mooney anyway. The hourly rate is enough that it prevents one partner from taking advantage of the others, and the funds go into three logical accounts: one for direct hourly operating expenses fuel/oil/incidentals, one for components that wear/break with use (cables, instruments, tires), and one for depreciation of major components (engine, paint, etc.) As the airplane depreciates, the total value of the LLC remains roughly the same, because the depreciation fund grows in accordance with deposits from the hourly charge. If we dissolve the partnership before putting major money into the airplane on engine overhaul, paint, etc, that cash comes back to the partners in equal shares (not in proportion to hours flown) at the time of sale. So that's how less frequent fliers are treated fairly with respect to more frequent fliers. The depreciation fund we're keeping isn't designed to have enough money to actually pay for an engine overhaul, or shiny new GTN 750Xi when the primary navigator gives up. If/when the partnership decides we want those things, the depreciation funds may be used, but it will be necessary for the partners to pony up cash out of pocket to fund the project. The resultant airplane will - one presumes - be worth a little more than before. Accordingly, the partnership is worth more than before, so at least some of the out-of-pocket cost to the partners is returned to them via an increase in the value of their equity. This strategy does expose us to the possibility that the airplane could need something big, and one or more of the partners doesn't have the out-of-pocket cash to cover it. But that's an essentially unsolvable problem, because major airplane components can need an overhaul or replacement at literally any time - you can't actually estimate when you'll need the funds. So barring the extreme and impractical approach of requiring partners to pony up approximately double the value of the airplane at buy-in, you're going to have to face this one way or the other. Mostly we do so by trying to suss out the financial state of prospective partners, though I concede that's dubious. Our partnership buy-in agreement does permit asking the incoming partner for a credit check, but all of us feel that's not especially useful. Again, though, it's essentially impossible to avoid this in any kind of real-life partnership agreement, so we choose to accept the risk. It's a pretty reasonable risk in a vintage Mooney worth less than $100K. It might not work out so well for a brand new G650. Up to you whether it's reasonable for, say, a late-model Acclaim. That's a depreciation item, see above. This is probably the most interesting question. We have a clause in our operating policies that deals with this sort of thing - assigning responsibility for maintenance that is clearly pilot-induced, to the operating pilot - but it's not foolproof. In the end it boils down to whether the people in your partnership are inclined to embrace responsibility, or avoid it. Across the partnerships I'm familiar with, this generally hasn't been a problem, but perhaps only because it hasn't really come up. Most partnership pilots are not incompetent or deliberately abusive. I think the idea that you'll get stuck with a rogue pilot who is always breaking stuff is a bit of a bogeyman. Our agreement explicitly prohibits any member from expecting recompense in exchange for any kind of maintenance: 43.13 Appendix A stuff, or even just washing and waxing. These things are "allowed", but not required. That doesn't necessarily prevent hard feelings, though, so you do need to seek out partners who are either like-minded, or who are content with nothing other than self-satisfaction for this sort of thing. Mostly this comes up during our annuals, which have always involved a large degree of owner-assist work. That work isn't equal, primarily because some of the partners have the kind of flexible work schedule that permits doing so, and others don't. We just live with it. As one of the guys who does a fair amount of the work, I have no ill will toward other partners that don't, in part because their non-flexible-work-hour schedule is a noble profession that benefits the community.

One possibility is that your alternator field breaker is old and weak, and trips at less than rated current. This is the usual failure mode of circuit breakers, by design. If you're confident the alternator field breaker is only tripping at rated current, things get more interesting. I do not have schematics for a '92 J model. But in general, the amount of current that flows through an alternator field circuit is controlled by the voltage regulator. If you turn off the alternator field switch with the master on, the voltage regulator will "observe" transients in the system, and it's possible it is very momentarily commanding enough current to flow through the field circuit to trip the breaker. If that's what's happening, it might mean your regulator is beginning to misbehave. It's also possible this is a "doctor, it hurts when I do this" problem - maybe you're just not supposed to do that. Why, exactly, are you regularly turning off the alternator field with the master on? The Lycoming IO-360 in our M20F has been "burbling" when hot like this, for 20 years. We've had no other problems with it. Every once in a while, someone will hear it and say something like, "you ought to get that induction leak looked at". But the engine has no other symptoms of an induction leak, or other bad symptoms of any kind. I also have a friend with a Mooney who is irritated by a similar problem, and who has spent considerable time and energy checking the fuel system and intake system, to no avail. His engine also continues to burble on the ground when hot. The conclusion I've drawn, right or wrong, is that this is simply normal behavior for IO-360-powered Mooneys: that on the ground, when sufficiently hot, enough heat rises from the cylinders to disrupt ("boil") the fuel in the injector lines, even while the engine is running and fuel is flowing. Hence the distinctive burbling/spitting/whatever you want to call it. I'm open to contrary opinions, but I guess I feel like it if were indicative of a real problem, surely something worse would have happened in the 20 years and thousand-plus hours since the first time I heard it.

For that equipment, the appropriate ICAO equipment codes would be "B, G, R, S, Y". In addition, your Surveillance code would be "B2, C, U2", and your PBN information would be "B2, C2, D2, O2, S1". Yes, this is stupid. No, ATC doesn't care. There isn't going to be any difference in safety or operational handling in the United States if you just use "G".

I'm a fan of partnerships and have been fortunate to be in a successful one for a couple of decades. In addition to reducing costs for the individual pilots, there is much to be said for the fact that partnerships tend to keep the airplane operating a healthy number of hours per year. Sole ownerships often seem to go through periods of inactivity over the years due to life circumstances, and that can wind up creating headaches and devaluing the airplane, due to lack of use. The financials are straightforward: agree on a value for the airplane and other assets (tow bar, cabin cover, tools, whatever) and have the incoming partner give you cash (if they need a loan to come up with the cash, that's their problem, not yours). Determine your fixed costs and split them by equity percentage - typically evenly, e.g. 50/50 for two partners. Then bill each pilot an hourly fee that covers direct (fuel/oil/etc) and indirect (engine overhaul) operating expenses. Since you've owned the airplane a while, you almost certainly already have a decent idea of how these costs break down. You'll need some bookkeeping to track the fixed and operating expenses and payments on a monthly/quarterly/whatever basis, which is a new burden - it's just one of the "costs" of having partners. Most people do this informally and it works out fine. We employ a professional bookkeeper in our partnership, but that's arguably overkill. Having said all that, this statement gives me pause: If you expect a potential partner to care for the airplane exactly the way you do, you probably shouldn't take on a partner. A partnership cannot be successful when one partner feels in their heart that it's really still "their" airplane, where they set the standard for how it's flown and maintained, and the new partner is expected to hew to the original owners' preferences. You have to think of it as if you'd sold your airplane outright, then you and your new partner bought a completely different airplane and started from scratch, together. That doesn't mean you can't look for a partner with similar principles and attitude, of course. Maybe that's all you mean. But having been asked this question by a couple of friends, my usual response is to ask how they'd feel about things that, objectively, are just preferences. How do you think you'll feel if the new partner suggests oil changes every 35 hours instead of every 25? What if they'd like the airplane put away with 3/4 tanks instead of full, or vice versa? What if they ask you to leave the prop horizontal (or vertical) when securing the airplane? If your attitude about these things is, "No big deal, let's try it that way and see how things go", you're well-suited for partnership. If your attitude is, "I've been doing it such-and-such way for the last X years and see no reason to change", you're not well-suited. Similarly, MikeOH's comment about the seats/radios/etc not being the way you left them is a good indicator as well. A partnership works for me, in part because I couldn't care less about those things. But I can understand how they might bother the heck out of other pilots. What I've seen anecdotally is that partnerships where one person has been a sole owner for many years, and later takes on a partner only when the financials start to get tight, tend to not work out. That's what you're proposing. So put yourself in the other person's shoes: would you want to buy into a partnership where, despite carrying half the equity and half the expenses, you are subservient to a "senior" partner who exerts outsized influence on operations and maintenance? I generally advise people to avoid thinking-of-taking-on-a-partner offers unless they're already flying the airplane under some non-equity arrangement that's going well, or - maybe - if they feel they already know the other pilot well despite not actually flying the airplane. Otherwise, better to form an airplane-less partnership with like-minded individuals first, and acquire the airplane second. That's effectively the "market" you're competing against, and you'll do best if you set your mindset accordingly.

Because nobody has new units. We just went through this a few months ago. Not only was overhaul the only choice, but we couldn't even get anyone to do an overhaul exchange, because nobody had overhauled units in inventory. The only choice was to send ours in to be overhauled and returned to us. It's possible the situation has changed, but our experience only dates back to this spring. It's likely the inventory situation remains the same.

Should say so on the data plate, which I've circled in your photo below.

If it's an H&E fuel selector, the part number is 940057-001. You can get them from LASAR: https://lasar.com/seals-gaskets/fuel-bowl-gasket-940057-001 Consider ordering a fresh stat-o-seal as well, https://lasar.com/seals-gaskets/lock-o-seal-600-0101-10. Strongly suggest you verify the exact fuel selector in your airplane, then call LASAR and ask for a seal kit for that unit. Which models have what selectors gets a little complicated. It's not guaranteed you have an H&E selector, you may have a Dukes.

Sometime circa 2010, Mooney produced searchable PDFs of not only the POH, but also the IPC and service manuals for all the C through G models. I presume they did so using a professional version of Acrobat, or other OCR software. In addition to being searchable, these files contain bookmarks for each section, so they're very user friendly. I know this story sounds too good be true, but not only did Mooney produce these PDFs, they e-mailed all existing owners with whom they had contact at the time, and offered to send them a USB drive containing them, for free, as a promotion/thank-you gift. I took them up on the offer, and I have one of these USB drives (it's got a Mooney logo on it), and I have a copy of its contents on my computer. I just presumed that the various documents in the "Downloads" section here on Mooneyspace contained these searchable PDFs, but I never looked, because I joined Mooneyspace long after I received the USB drive from Mooney. Anyone with a vintage model Mooney, who is suffering with non-searchable PDFs of these documents, should look harder. Given Mooney's hibernating status at this time, I'm not opposed to uploading my copies to the downloads section of Mooneyspace, but I'm not sure how helpful that would really be. There are already 51 different files in the "Pilot Operating Handbook" section there, and it seems likely some of them are from the searchable copies Mooney produced.

Wear on the inside edges of tires is common on Mooneys, I think due to the geometry of the gear. Our birds always look to me like the gear leg isn't actually vertical, though I think it looks worse than it really is due to wing dihedral. As for uneven wear on the right vs. left, I see this a fair amount on piston singles, though it's usually the right main that's the problem rather than the left. The best hypothesis I've heard for this - which jives with my experience as a CFI - is not enough right rudder when lifting the nosewheel on takeoff. The collection of left-turning tendencies in a Lycoming/Continental-powered single causes the nose to swing to the left, and instead of fixing this with appropriate rudder, a lot of... uh... "less sophisticated" pilots will apply right aileron instead. This picks the left tire up off the ground while driving the right one into it. I suppose it's possible you've got the opposite problem of too much right rudder on liftoff, which you're correcting with left aileron. But I'm betting anyone who flies an Acclaim isn't prone to these kinds of errors. Might be a misalignment in the gear itself.

There's a correct, but huge caveat in your statement. Used correctly. Every aircraft owner who installs a "safety device" in their aircraft presumes they'll use it correctly, to great benefit, in an emergency. But both the accident rate, and my personal, anecdotal experience as an instructor, belie this assumption. Whether it's backup attitude on an iPad via a Stratus, or the LVL button on the GFC500 autopilot, I find over and over again that when I ask pilots to demonstrate how they'd use these things in an actual emergency, that many of them have either never practiced with it, or they tried it once, a couple of years ago to make sure it worked, haven't done anything with it since, and aren't particularly confident about how it works. In some cases, their lack of skill in using this backup safety equipment creates a situation worse than not having the backup equipment at all. But you don't have to take my anecdotal word for it. Again, the accident rate isn't changing, despite a widespread proliferation of technology. Seems like every week here on Mooneyspace someone else is installing a GFC500 and/or a full glass panel. My understanding is Garmin has sold many thousands of these units in the last 5 years. But why pick on Garmin? Brittain had a wing leveler 50+ years ago, and many of our Mooneys are/were equipped with them. So why isn't this stuff helping? If you've got a theory, I'm all ears. I know this seems slam-dunk obvious to you. But it's not to me, based on actual experience with actual pilots who have actual instrument ratings, fumbling around with their advanced equipment. What makes you think the gentleman in question wasn't trying to use an autopilot to save himself? We don't actually have any idea what caused the accident, but let's "go there" and assume it was spatial disorientation. Your position is that a modern autopilot could have saved the man, at an installation cost of $10K or $20K or whatever. Maybe it could have. But my position is that a tenth of that cost spent on instrument training would have been much more likely to save him, if the cause was indeed spatial disorientation. I'm sorry for being grumpy about it. But I just can't believe the number of people who will put their airplane in the shop for months and drop five figures on "enhanced safety", but can't be bothered to find a couple of hours on a weekend and spend $50 of avgas on an IPC. As my kids were taught about gear when learning to play sports, "It's the wizard, not the wand."

That's not correct. Your run-of-the mill "deep learning" neural net that people are now ubiquitously calling "AI", does indeed need a set of old training data to produce a trained model. But then new data is mapped against that trained model - that's the whole point of it. If the nature of the new data is essentially the same as the data used to train the model, you most certainly can make real time predictions. The nature of weather today isn't meaningfully different than it was a couple of years ago, ergo weather data from a couple of years ago can be used to produce a model of what the weather will be tomorrow. This is, in fact, how pretty much all modern weather prediction models work. The technology just wasn't ubiquitously known to the public as "AI" until recently. It would indeed be cool to train a machine learning model specifically against aviation go/no-go criteria, rather than just general weather parameters. But I'm not sure that would produce any kind of revolutionary change in flight planning or go/no-go decisions.

If you have dollars to spend on "safety", the best use of that money is not avionics. Not even an autopilot with envelope protection. The best use of safety dollars is training, training, training: dual instruction, simulator training, training for additional certificates and ratings... anything you can do to increase your basic muscle memory and decision making in unexpected situations. Spend your safety money on instruction and avgas, not on transistors. This is in no way a criticism of modern autopilots - there are lots of great reasons to have them. They make non-emergency flying more comfortable and more fun. But don't kid yourself that you're buying down your risk by installing them. Digital autopilots first reached the GA market about two decades ago, and a substantial portion of the fixed wing, non-commercial fleet is now equipped with them. But there has been no meaningful change in the accident rate, and I'm not aware of any insurers adjusting rates based on what autopilot you run. This makes sense when you look at where and why the accidents occur. The vast majority of accidents involve scenarios in which fancy autopilots don't offer any help, e.g. basic aircraft control during takeoff and landing, fuel mismanagement, etc. There is a pretty good summary at https://www.redbirdflight.com/landing/ga-safety-trends-what-should-we-worry-about I think the community is best served by thinking about modern autopilots the same way you think of having a killer sound system in your car. It's cool, and fun, and adds a lot to the enjoyment of trips both short and long. But it's not a safety tool. I know the manufacturers and the community tell you it's safer, but there's just no evidence to back this up.

Thanks for the clarification. Yes, the C307PS is what you want. It is specifically called out by name in the G5 installation manual. The D307PS has an integrated A/D converter somewhat like the GAD13. But it converts the current produced by the AD590 to 1-wire digital protocol, rather than the CANBUS protocol needed by the G5. Other Davtron products can receive this 1-wire protocol, e.g. their M303 display. I don't know if any avionics manufacturer other than Davtron supports 1-wire. It's interesting that the D307PS is less expensive than the C307PS, given that by definition it must contain more "stuff" inside. Maybe the D307PS uses an IC which integrates the A/D converter, and is manufactured in greater bulk such that the component is cheaper despite being more sophisticated. Or it might just be a certification or "what the market will bear" thing. Might also be a loss leader to try to get you buy the M303 or other Davtron products.

I'm not sure exactly what you're asking here. Both the Garmin GTP59 and the Davtron C307PS are analog temperature sensors, albeit different technologies. In fact, all temperature sensors are analog devices. The whole point of the GAD13 is to convert that analog information from the probe, to digital information transmitted over CANBUS to the G5. Since I'm feeling nerdy this morning... An OAT probe is just a metal shell wrapped around an integrated circuit. In the case of the Davtron C307PS and similar products, the IC is an Analog Devices AD590. When supplied with a voltage differential across its two pins, this device produces a current that is proportional to absolute (Kelvin) temperature. Data sheet is available at https://www.analog.com/media/en/technical-documentation/data-sheets/AD590.pdf. The data sheet shows that the AD590 comes in two flavors, with two different accuracy specs. Garmin techs like to point out that the "cheap" flavor has a potential accuracy error of +/- 5C (with no external temperature compensation circuit). They imply their competitors use this cheap configuration, while Garmin uses more accurate hardware. These claims are probably true, but I argue they're not meaningful - more on that shortly. In the case of the GTP59, Garmin doesn't publish what IC is inside their probe, but based on the way the GAD13 connects to it, it's almost certainly a 3-wire resistive sensor. These sensors present a resistance which varies with temperature, across 2 of their leads. The 3rd lead is just a short to one of the two other leads. It exists so the controller can measure the resistance of the connecting wires themselves, and effectively subtract that resistance out of the calculation. I'm sure there are high quality/accuracy versions of these sensors. But if I were building an experimental, I might try a ten-dollar, hot tub probe, e.g. https://www.amazon.com/Waterproof-RTD-PT100-Temperature-Sensor/dp/B07DP3LYPX/. At that price, I could buy several units, use the one that tests with the best accuracy in an ice bath, and throw away the others. Garmin probably doesn't buy hot-tub quality sensors, but they almost certainly qualify incoming units from their suppliers, and reject those outside Garmin's own tolerance limits. Anyone else can do this too, though. Again, more on that shortly. So let's examine the worst case scenario on "cheaping out" with the Davtron probe: if Davtron purchases the cheapest version of the AD590, and you are unlucky enough that the particular unit you get has the worst possible error, and neither you nor Davtron performs any QC testing on the probe, you could get a C307PS that is off by +/- 5C. At piston airplane speeds and altitudes (including turbocharged airplanes up to the flight levels), a 5C inaccuracy results in a true airspeed error of 1-2 knots, which is not meaningful. Accuracy is more of a concern if you're talking about whether you'll get airframe icing. But since it's foolish to assume you're completely safe at +1C and completely in peril at 0C with any temperature probe installation, it's hard to argue this has much operational meaning. In practice, we start looking outside for airframe icing any time OAT dips within a few degrees of 0C. So even a 5C inaccuracy is relatively meaningless, other than bragging rights. In reality, though, I think it's extremely unlikely you'll get a Davtron probe that's off by 5C. I presume here that Davtron doesn't have a completely stupid manufacturing process. If my assumption is correct, they assemble the units, then perform some sort of "smoke test" to guard against assembly errors, as well as bad parts received from their IC supplier, just like Garmin. Such a test would catch, and allow Davtron to reject, the very small number of parts at the worst of the accuracy range. You'll have to decide for yourself what you think about Davtron QC. But if you're a cynic about that - and have some patience - you can be your own QC. Buy the cheap Davtron probe, hook it up on a bench, drop the probe in an ice bath, and return it for another if the temperature it reports is off by more than your personal tolerance. Lather/rinse/repeat until you get what you want, and proudly proclaim your CB status. In summary, temperature probes are just a wrapper around an IC supplied from an outside source. Those ICs have accuracy specs on paper, but in reality the accuracy of the probe you get depends on the QC process used by the manufacturer, which potentially rejects outlying units. Garmin's process might be better than Davtron, and it makes sense to pay their price if you're manufacturing a $40M bizjet. For the rest of us, a less expensive solution makes sense; and to Garmin's credit, they support this by supplying an AD590-compatible input to the GAD13. I think that's an entirely reasonable position for Garmin to take, and I happily supported them in buying their GAD13. But I also supported Davtron by using their "cheap" probe.

Another +1 on the Davtron C307PS probe. Many, many G5 installations in the field are using this less expensive probe rather than the GTP59. Garmin will tell you the GTP59 is TSO'd, used in certified installations up to business jets, and achieves better accuracy than the C307PS. All that is probably true, but it's not meaningful in a GA piston single, and not worth the extra cost.

Yep, I missed that one. ... and that one too. I don't know much about it either, but as with "minor modifications" and "standard parts", I expect it will boil down to the interpretation of individual mechanics. I deliberately prefixed my list of methods for approval with "at least" because I was sure I'd miss some. The point is simply that there are many different avenues of approval, so the question asked in the OP isn't really meaningful. It's like asking what regulation prohibits a person from getting a pilot certificate in a certain scenario. There aren't any such regulations. There only regulations that define a variety of methods for various people to obtain various pilot certificates, and you can get one via any of them: traditional experience/check ride, military equivalency, foreign certificate equivalent, etc.

This is, IMO, the most difficult thing to understand about parts on certified airplanes. Everything installed on a certified airplane must have a "basis for approval". But there are many, many such approval mechanisms, including at least: part listed on original type certificate replacement part provided by a manufacturer with PMA aftermarket modification with STC aftermarket component which meets a TSO aftermarket component meets NORSEE standards replacement or add-on is an "industry standard part", see https://www.faa.gov/sites/faa.gov/files/aircraft/safety/programs/sups/standard_parts.pdf replacement or add-on is judged in the opinion of an appropriately certified mechanic to be a "minor modification" aircraft is a "vintage" aircraft and part falls under new VARMA regulations Anyone who tells you that you can't install a non-original part on a certified aircraft without an STC is ill-informed. But that doesn't mean you can install anything you want regardless of STC. If there is no STC which permits installation of the component on your certified aircraft, then there must be some other basis for approval: TSO, NORSEE, signoff as "minor modification", etc. The "minor modification" sign-off is the one that generates the most argument. Appendix A of 43.13 explicitly lists items that count as major repairs/alterations, such that a mechanic cannot really claim those specific items are "minor modifications". Beyond that, though, the definition of what constitutes a minor modification is - best as I can tell - just up to the judgement of the individual mechanic. Some mechanics are a lot more liberal than others with this interpretation.