Vance Harral

Got curious about this thing: Turns out it's presumably connected to an old-school air data computer for winds aloft info: http://www.insightavionics.com/tas1000.htm. Seems like the Aspen would make this obsolete, curious why it's still there. Maybe just a "it ain't broke and I like it" item?

4 hours to completely change the pan gasket? Heck, it took me and my ham-fisted meat hooks about that long just to remove the lower cowl bowl last time we changed an alternator! OK, not really quite that long just for the lower cowl. But let's think about this, and I'm just going off the top of my head: all the intake tubes have to come off because they connect to the manifold that passes through the pan. The entire exhaust has to come off because it runs underneath the area where the pan would come off. That means disconnecting all the EGT probes in addition to the exhaust itself. You absolutely have to remove the lower cowl to do this job, which requires disconnecting the oil cooler, the air intake boot, the ram air door cable, the cowl flap linkages, and the landing light connection. I think you're probably correct that the fuel injection servo has to come off, my recollection is that's one of the things that gets in the way of tightening some of the bolts. Did I forget to mention that the throttle and mixture control cables pass through a bracket that's hung off the pan? Gotta deal with that too. All that is just the stuff I can remember, I'm sure there are other complications. If I were doing all the work myself, I'd bank on at least a week, if I didn't screw anything up. A pro with experience could do it much faster, of course, but I think it's a big job no matter who's holding the wrenches.

Especially when the gut is a little rounder than it probably should be. We call it, "trim for egress!"

The answer depends on the exact devices you choose. For the G5, seems like you already answered your own question: the terms of the STC allow it to serve as a primary attitude indicator, and/or primary DG/HSI, and/or primary turn coordinator. The terms of the STC do not allow it to serve as a primary altimeter or airspeed indicator, even though the instrument is connected to the pitot static system and can display altitude and airspeed. If you actually saw a Mooney panel with two G5s and no ASI or altimeter, it is either illegal in terms of required instrumentation, or it has some sort of very special one-off field approval.

Over the course of 17 years, five complex endorsements, three instrument ratings, one commercial certificate, one CFI, and one CFII, I'm sure our airplane has accumulated "several" collective hours in the red RPM arc. Neither the prop nor the engine has fallen off the airplane yet, though admittedly that's just one data point.

We can't afford an engine overhaul! Too busy wasting money on foolish panel toys...

Sounds like we're kindred spirits. We have also R&R'd the prop governor (twice), and replaced oil lines, in addition to the other stuff I mentioned, over the last 17 years, all primarily to deal with oil leaks. I've come to the conclusion that chasing oil leaks is just regular maintenance on airplanes that only fly 100-ish hours a year. I know it's de-rigueur to pooh-pooh the calender-time-based component of TBO recommendations, and I concur with Mike Busch on that sort of thing. But it's not as if the concept is simply made up out of thin air. Gaskets and seals and their ilk really do wear just with the passage of time, to some degree. So those of us that take decades to reach 2000, or 2500, or 3000 hours, are going to have more of these sorts of problems than the flight school 172 that gets its 3K in 6 years. When I call our oil leaks a "mess", that may reflect my personality as much as any objective measure. Let me try to be a little more scientific about describing it. If I completely wash the airplane, then we run it for three, one-ish hour flights, without cleaning, here's what we'll see: 2-3 definitive black streaks of dirty oil running back from places like the aft edge of the port side cowl cheek, a stop-drilled crack in the front nose bowl, etc. 2-3 more streaks running back down the nose gear doors, which I think is being blown out the cowl flaps enough oil pooled at the bottom of the cowl flaps to be noticeable, though not enough to actually drip a thin film of oil around the cowl mouth, and a smattering of oil on the windshield (we have the old "guppy mouth" cowl, which actually has a net outward airflow at cruise speed) an irritatingly dirty belly for having only flown 3 flights, though some of that is just ordinary combustion residue out the exhaust rather than un-burned oil Looking around the airport, I've seen worse, so I don't think any of the above is really that big a deal. But it's objectively worse now than it was a decade ago. Used to be the airplane would stay looking pretty decent for a dozen flights between cleanups.

When we first definitively identified the pan gasket as a source of leaks, we did try re-torquing the bolts near the point of the leak. Didn't help, and the mechanic was not surprised. For one thing, you can't get to all the bolts without removing the exhaust and other components, so we only re-torqued "some" bolts and not others. Doing that around a flat surface is always a little sketchy. For another, once a gasket loses enough suppleness to start seeping, squeezing it tighter is a Hail Mary idea anyway. We have not tried the gooping on exterior sealant. I'm not opposed to that trick necessarily, just seems like an Aggie-engineered thing (I can say that cuz I iz one), that's about as likely to cause a new problem as it is to fix an old one. At this point we simply live with the leaks, and have instituted a voluntary program in the partnership of trying to wipe down the cowl after every flight, so we have a better chance of noticing if they suddenly get worse. It is amazing how little oil it takes to create a giant mess. All these leaks have no observable effect on the number of hours we go between adding make-up oil. It's right at one quart every 10 hours today, just like it was in 2004.

Well, yeah, but not literally forever up to infinite time. There is a point on the far right of the "bathtub" curve where the theoretical risk creeps back up to about the same level as a newly overhauled engine. That's the sweet spot we'd all love to get to under benign circumstances. No disagreement from me that the overall fleet statistics show the right side of the bathtub way beyond published TBO, for engines that are run regularly, and ours is. But anyone with a basic understanding of statistics knows that fleet numbers only apply to an entire fleet of machinery. We don't own a fleet, we own one unit. Deciding how to manage a single unit is a lot more like gambling. We'll place our bet at some point, and it likely won't be any time soon, for all the reasons elucidated in this thread. But it's still totally reasonable, as the engine goes past 2000 hours of service, to start thinking more about what triggers feel right to you/me/us. We use all the right tools to guide us: compression, cutting filters, pulling the pickup screen, UOA, periodically checking performance against book, etc. But it's simply undeniable that feel/guess/hope is a component too, unless your philosophy is to keep running until gross failure. The end game I'm hoping for is to see a definitive knee of the curve in some combination of declining compressions, uptick in oil consumption, slightly reduced performance, more than the very occasional sliver/flake of metal in the filter, etc. If several of those things came together over the course of a year, I'd gladly overhaul the engine that winter. I'd also fully understand that doing so exposes us to a whole new set of risks for the next couple hundred hours. But like everyone else, I'll tell myself the lie that I guessed perfectly, and that the risks over those first couple hundred hours are no worse than the risk of having continued to run the old engine. In reality, no one knows the answer to that question for a single unit, so you just tell yourself whatever makes you feel good.

Nah. The manufacturers define TBO numbers because the FAA's engine certification standards require them to do so: CFR 14 Part 33, Apendix A, 33.3(a)(6). Even the lawyers know a single number for all circumstances is bogus, but the companies have to pick something to put in the ICA, otherwise no type certificate. If it were as liability-driven as your tounge-in-cheek comment suggests, there would be all kinds of efforts to get the 2000 hour TBO significantly reduced, or to push everyone much harder to value the calendar time over engine time. But there aren't, even though plenty of engines don't get anywhere near TBO before some sort of catastrophic failure. The number of aircraft operators running piston engines under anything other than Part 91 where it's not meaningful, is so small that there is no value in debating changing the existing recommendations. Whether that's a cause or effect is an interesting debate, though. One wonders if there might be a lot more piston Part 135 operations if TBO numbers were different. The sad tale told in this Mooneyspace post seems relevant.

I should have included emojis or elaborated. I am not seriously suggesting that fixing an oil pan gasket leak is not much different from an overhaul. But it is very invasive, expensive, and won't make the engine "dry" anyway - as I said, we have evidence of other minor leaks too. The more of those that occur and the greater the rate at which they leak, the greater the risk of having a more serious problem masked. So we're unlikely to replace the oil pan gasket, much more likely to keep living with it until "someday", when a collection of those leaks and/or other symptoms push us over the threshold. I'm all for running these engines long, and I don't have any serious concerns about our 2200 hour/25 year engine today. At the same time, my ideal endgame is accumulating enough small, compound, symptoms of wear, to the point we decide to pull the overhaul trigger under benign circumstances. The alternative is to run it until gross malfunction. Maybe that's cool if the gross malfunction is just a surprise bunch of unexpected metal in the filter at the next oil change, from parts we're going to replace during the overhaul anyway. But if it's from a ruined crankshaft, or worse yet the engine throws a rod in flight, I won't be too proud of the extra hours of runtime we got in exchange. The good news in our case is, we've already gotten everything we could ask from the engine, and everyone in the partnership is mentally and financially prepared for the overhaul. The complex question in our case is simply estimating the point at which the relative risk of continuing to run the old engine crosses the risk of infant mortality in a new one. There is no definitive answer for that, only speculation and gut feel.

This may be what eventually triggers us, and I'm watching this thread with interest since our engine is about the same age as the OP. We're currently at about 2175 tach hours and 25 calendar years () since overhaul on our airplane. Oil analysis, borescope, and compressions all reasonable, takeoff and cruise performance right at book numbers, no metal in oil filter or pickup screen, oil consumption has been steady at about 1 quart every 10 hours since we bought the airplane in 2004. Basically no indication whatsoever that it'll need an overhaul any time soon. But... it leaks enough oil to make a giant mess inside/around the cowl and down the belly, even just a couple of hours after cleaning everything up. We've addressed the easy stuff: valve cover gaskets, drainback tubes, etc. But the main leak source is the gasket between the oil pan/intake manifold and the crankcase, which seems difficult to address (would have to disassemble so much to drop the pan that it feels like you may as well do an overhaul). There's also some evidence it's seeping a little at the cylinder bases and/or case split, though it's just a drop or two if at all. None of those leaks are individually concerning or reason to overhaul by themselves. But collectively they indicate all the "soft seals" that are designed to last the life of the engine are timing out; and what bothers me about it is they could mask something more serious that you'd otherwise know about right away in a dry engine: crack in the case, loose accessory seal, etc.

My airplane partner tried reaching out to Cici via e-mail just last week, but no response. Hopefully she is well, and I continue to root for Brittain. But the longer they stay in this state of "deep hibernation" - where they can't even supply parts, much less service - the less optimistic I am about Brittain ever again being a viable concern. It's possible to keep the Brittain system going as long as the only thing that fails are the simple mechanical components. But if our control head unit with its printed circuit board and big multi-plane control switch goes south, I don't know of any viable path - either legal or gray market - to repair it.

Couple of ways this can be done. First, the terms of the STC for various Brittain autopilots allow them to be driven from various CDI indicators, several of which are compatible with Garmin navigators (either by name or by interface). In this setup, the CDI outputs an analog DC voltage to the autopilot giving it left/right deviation info, and the autopilot converts that to steer left/right signals. So the autopilot is not really being "driven" by the navigator in this case, at least not directly. Rather, the navigator drives the CDI, and the CDI drives the autopilot. This works OK for basic course tracking, but it won't correctly do anything" fancy" like flying around a hold. It's also unclear to me whether it is actually legal - strictly speaking - to engage the autopilot when the CDI is in GPS mode. So I have never done this, of course! Second, Brittain did have drawings to interface their autopilots to at least one GPSS roll steering unit (I think it was the DAC GDC31). So there are a few people flying around with a 430W or other Garmin navigator driving a roll steering unit, and the roll steering unit in turn feeding heading data to the Brittain system. You make this work by putting the autopilot in heading mode, and flipping a switch that muxes the autopilot heading input between the roll steering unit and the conventional heading interface for the Brittain. Again, Brittain made drawing for this back when Jerry was still alive. This is the slicker setup, as roll steering will follow more complicated GPS courses, and it is completely on the up-and-up to fly GPS courses this way. The problem we're facing in the time of the Garmin G5/GI-275 is, we'd like to connect the DG/HSI to a Garmin GAD29B adapter, which can produce the analog signals the Brittain needs; then interface the GAD29B to the Brittain autopilot. That's different enough that no existing approved STC or drawing from Brittain addresses it. Jerry was working on these drawings around the time he passed away, and there are copies floating around showing the connections. But from a legal perspective it doesn't matter, because they were never approved by the FAA.

I don't know what constitutes "limited authority", and as you note, our opinion doesn't matter - only the opinion of the decision makers at the FSDO. To be fair to those guys, it's not difficult to construct a sound argument either way. You've constructed the pro- argument, which I agree with. The con- argument goes like this: "The autopilot has three pairs of servos that connect to aileron/rudder/elevator, and it can hold a heading, intercept and fly a course, and not only hold altitude, but also pitch attitude. That's neither 'single axis' nor 'limited control authority'". Maybe I shouldn't say that out loud...

I'm in the middle of trying to get this question answered for a Brittain B5 (very similar to the B6), through the Denver FSDO. Here's what I know so far: The DER I'm working with says feasibility hinges on whether the FSDO personnel who would grant the field approval consider the B5 to be a, "simple, single-axis autopilot system with limited control authority", as defined in table row D.13h(1) of the "Major Repair and Alteration Job Aid" document which accompanies FAA Order 8300.16. That's the governing document for autopilot system modifications, and whether they can be field approved. This is a tough sell for the B5, because (1) it includes a pitch control and altitude hold system, albeit one that operates completely independent of the lateral control system involving the DG/HSI; and (2) even ignoring the pitch control system, there are servo boots connected to the rudders as well as the ailerons, which arguably makes it at least a 2-axis system. Frankly, I'd be in better shape if we had an older AccuFlite rig, but even that might not be viewed as "simple". If my DER can convince the FSDO to consider the B5 a "simple, single-axis autopilot system with limited control authority", he is willing to help me pursue a field approval for a G5/Brittain connection. His estimate is that it would cost between $5000 and $10,000 to do so, i.e about half the cost of throwing away the B5 and installing a Garmin GFC500 in its place. It's unclear to me if all that money would go in his pocket for consulting, or if the FAA actually bills applicants for their time (you'd think it would be "free" being a federal government organization, but who knows). But it's extremely unlikely I could do this without going through a paid DER consultant anyway: I lack detailed knowledge of the rules and process, I lack any direct connections to the FAA, and I lack the patience to develop these things. If the FSDO decides the Brittain B5 is not a "simple, single-axis autopilot system with limited control authority", the only path to certification is a one-time STC. My DER says certification and flight test for such a thing runs about $50K, so obviously a non-starter. Net result of all this is that I'm unlikely to pursue a field approval, but I did agree to pay the DER for a couple of hours consulting time to get an answer to the "simple, single-axis autopilot system with limited control authority" question. I'll report back here when he gets back to me. The frustration, of course, is that none of this has anything to do with whether a B5/G5 interface would work. Everyone agrees it would. But if you want your certified airplane to continue being legally certified, the paperwork rules are what they are.

Sound recommendation. That said, if you're on a budget, a pair of G5s is a considerably cheaper option that achieves most of the same functionality. The hardware and installation costs for GI-275s are not just slightly higher than the prior-generation G5, they are dramatically higher. I have no quarrel with people who think the touchscreen interface, higher resolution, and additional functionality of the GI-275 is worth it (particularly when it comes to autopilot integration). But a pair of G5s is a really sound ADI/HSI solution for considerably less money. If you keep your eye out, you just might find a pair of pre-owned G5s in good shape, say from someone upgrading to the GI-275.

I'm still flying with a mechanical AI and DG, I think that puts me in the grave.

I'll refrain from recommending any specific hardware. Just don't buy so much hardware that it eats into your budget for actually flying the airplane. I'd much rather ride along on a "bicycle" flown by a pilot with 100 hours in the last year, than a "Cadillac" with 10. Heck, I'd rather fly IMC with certain pilots in a non-GPS, steam gauge-only airplane, than others with a $100K panel, based completely on how often and how carefully they train. Due respect to Don, but he's an outlier. His (well-deserved) financial status allows him to make avionics spending decisions completely independent of hours flown. I admire and aspire to that, but most of us are more constrained.

Yes this initially confused me. But then I understood you were talking about the CDI *indicator* (and the waypoint sequence right above it) as opposed to the CDI *button*. This is one area where the extra screen real-estate of the 750 is an advantage. The Default Nav page you get by pressing and holding HOME on the 750 shows the CDI indicator and flight plan sequence, soft keys for Menu/CDI/OBS/Zoom/etc, and also a map. That means you're only one click away from the Flight Plan page using the "click the CDI" trick. On the 650, however, the Default Nav page doesn't have enough screen real-estate to show the map. So instead, Garmin gives you a soft key on the Default Nav page that takes you to the map, and a "Back" key on that map page that takes you back to the Default Nav page. Unfortunately, the CDI indicator and flight plan sequence isn't shown on the map page, so you can't use the trick. If you're looking at the moving map on a 650, the flight plan page is always at least two clicks away.

That is a great tip, thanks!

I think Paul has his pictures confused. That's some old, gray-bearded dude in the left seat. Couldn't possibly be me.

Because the GTX-327 can be configured to auto-switch between ALT and STANDBY based on GPS ground speed.

A lot of the discussion above centers around how to avoid reloading the approach, when you get a late clearance change you weren't expecting. The commonly-discussed case is when you thought you were getting vectors to final, then you get cleared to an IAF or IF instead. Hence the "Never load VTF" strategy to avoid that particular case. I have a contrarian position about this. I teach students to practice reloading approaches to select a different transition, until they can do it quickly and correctly with little anxiety or stress. Then the guidance on loading approaches becomes simply, "Load your best guess at a transition/VTF, change as needed". Using myself and my own airplane as an example, I don't consider it some kind of workload crisis if I've loaded one transition (VTF or otherwise), and then get cleared to a fix not in my flight plan. The HOME -> PROC -> Approach -> Transition -> Activate sequence on a GTN navigator is pretty ingrained, so just a few seconds and no big deal to change the plan. If I'm being cleared to an IF rather than an IAF, then the extra steps are HOME -> Flight Plan -> select fix -> Activate Leg. It's a little more involved on an "etch-a-sketch" GNS navigator, but I teach in some airplanes with those, and I still don't think it's too bad: reload with PROC -> big knob to Select Approach -> Enter -> Enter -> Big knob to select transition -> Enter -> Enter. If being cleared to an IF instead of an IAF, add FPL -> big knob to select fix -> Direct -> Enter -> Enter. My main problem with the "Always load this, never load that" strategy, is it primes the student to think switching to a different transition is somehow "scary" and/or an unfair request by ATC. That doesn't bode well for fairly common situations that require deft button-ology even without ever loading VTF. e.g. training/proficiency flights with multiple approaches in compressed time and space, and/or ATC reroutes to a different IAF/IF late in the sequence for legitimate operational reasons. I have a lot less instruction given than Mark, Gary Reeves, etc. You should weight their opinions more than mine. But I think it's fair to say that "Never load VTF" doesn't guarantee you'll never have to reload an approach late in the game. So just like you're expected to be able to hand-fly an approach without an autopilot, fly partial panel if an instrument fails, etc; so should you also be reasonably proficient at reloading approaches to select a different transition. As Don says above, it's just not that hard to change on-the-fly (literally in this case ).

Sure, but that's all part of the power equation. Everyone quotes max cruise numbers at the optimum altitude, and it takes a lot of power to get way up in the flight levels.