Vance Harral
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Posts posted by Vance Harral
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On 1/27/2021 at 11:43 AM, RobertGary1 said:
I’m also unconvinced about the hard landing theory
Me too, primarily because flying in anything other than glass smooth air generates a ton of flex cycles on the wing, some of which are on par with the loads of a hard landing. If rough landings impact sealant life, then so does turbulence.
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23 hours ago, Yetti said:
Since we are not cutting airframes should be a simple sign off of an IA.
I believe you're talking about the difference between a "minor modification" which requires only an IA signoff, and a "major alteration" which requires either an STC/337 or field approval.
I'm not sure if you're talking about course error or heading error at this point. For course error, yes the installation manual defines acceptable inputs in terms of signal levels, which I understand to be the key that lets you e.g. wire up to a GI-106 indicator.
If you're talking about building a heading interface out of a GAD29B with transformer connects based on the Brittain being similar to a Cessna 400-series autopilot, that kind of interface work is specifically defined as a type of major modification in the "Major Repair and Alteration Job Aid" document which accompanies FAA Order 8300.16. This is not a fuzzy, arguable thing; the Feds have taken a specific position that changes to autopilot interfaces constitute a major alteration. I'm sure if you looked hard enough you could find a seasoned IA on the brink of retirement who would sign off such a thing as a minor mod anyway. But there's no way it would hold up when push came to shove. And if your argument is that push is unlikely to come to shove, then why bother with the sign off in the first place?
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On 2/7/2021 at 9:54 AM, Yetti said:
it makes you marvel at the couple of resistors on a board of the Brittian system.
This is an interesting lesson in expectations. If the altitude hold on our Brittain maintained the selected altitude within 20' using climb rates of 50-200 fpm as shown in the OP's video, I'd consider it to be doing a fantastic job - much better than expected. For us, it's a pretty good day when it holds altitude within 100' or so, which is all it promises.
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29 minutes ago, Bob - S50 said:
But before you lose a GI275 you have to lose the alternator, then run the ships battery dead, then run the GI275 battery dead. Hopefully you be on the ground by then, or at least VMC.
Sure, but we're talking about certification standards, not practical strategy. The original conversational offshoot was about when a certified rate-of-turn indicator is legally required, and whether or not various electronic displays are certified as primary rate-of-turn indicators for this purpose.
A bit of searching around suggests to me that a pair of GI-275s are legally certified to replace the entire steam gauge 6-pack. But I couldn't actually find the installation manual, so don't quote me on it. Those same searches turn up posts that say actually getting rid of your steam gauge ASI, ALT, etc. may not necessarily be a good idea. Setting aside questions of redundancy, some people feel the size of the instrument isn't kind enough to aging eyes to be a practical replacement for every individual steam gauge. Probably not an issue if you can quickly and easily read 14pt type at 2-3 ft, but not everyone can.
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5 hours ago, gsxrpilot said:
@Vance Harral it sounds like the student version is more of a "To Do List" and the owner version is a "checklist"?
Yeah... sorta.
A student-oriented check list does have items that aren't necessary for an experienced pilot. For example, "TAIL - INSPECT" is adequate for an owner's preflight checklist, but a student checklist typically breaks out the individual surfaces and/or linkages.
That said, the preflight checklists I write just say "INSPECT" for these items, regardless of how they're broken out, so a student is going to have to ask me what exactly they're supposed to look for, until they absorb how the system they're inspecting actually works. Similarly, I write "MIXTURE - SET FOR TAKEOFF" for students (and myself), rather than spelling out how to set the mixture. To me, that's one important difference between a "Check" list and a "Do" list. A pilot using a checklist should know how to check/do things based on their systems knowledge. The checklist is just a safeguard against tactical mental lapses.
Fortunately, this philosophy is synergistic with multiple goals. Avoiding prescriptive details keeps checklists short and tidy, which in turn reduces the risk of skipping items. And as a CFI, the way a student works through such a checklist gives me a pretty good idea of their level of understanding of the systems they're checking/operating.
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1 hour ago, Ragsf15e said:
There’s only 1 continuously displayed attitude.
Not only that, but both GI 275s are powered by the same source (the alternator), so one could argue the terms of AC 91-75 aren't met.
It's unclear to me if/how the backup batteries in these devices play into the AC.
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16 hours ago, Pasturepilot said:
I had forgotten about that AC, thanks for the reminder.
Note, however, that the absence of a TC still requires two certified attitude sources. Not one primary AI and a Stratus, or GTX-345 with ADHARS, or Dynon pocket panel, or whatever.
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5 hours ago, Yetti said:
Here is a question for the "must use checklist" crowd. How many times have you missed a step on the check list?
Setting aside my own mistakes (which are many), let me give a CFI perspective on this.
I've watched dozens of students miss dozens of items on checklists. In every single case, I'm able to identify something about the checklist itself which contributes to the error. So one possible snarky reply to "How many times have you missed a step on the check list?" is, "Never, with a well-designed checklist". That's not really a true statement, of course. But if you're going to pooh-pooh checklists, pointing out the foibles of a poorly-designed one is kind of a strawman argument.
I actually wrote a short treatise on checklist design for a CFI candidate recently, pasted below for your consideration.
First, good checklists are audience-specific: e.g. items that are helpful to a renter student pilot are distracting to an experienced owner, and vice-versa. One-size-fits-all would be simpler, and I used to think I could teach new student pilots to just grow into the kind of lightweight, streamlined checklist owners prefer. But experience has taught me differently, and given me an appreciation for the compromises made by people who write factory POH checklists. So... the checklist I give to a pre-solo student for a Cessna will work well for them, but be totally bloated for a Cessna owner; but that's fine - there isn't going to be a single checklist that works best for everyone. As an example, my normal procedures checklist for students has an item for "Taxi to Departure Runway". This is a stupidly obvious action for anyone with even a few flights under their belt, and I didn't have it there initially. But I've had no less than three different greenhorn students try to start performing pre-takeoff and runup checks while idling on the ramp, because they lack the context and experience to understand/remember that those checks are done from the run-up area. Adding an item for taxi provides an obvious, helpful separator.Second, while my student checklist is geared toward students, it still avoids detailed, prescriptive actions. e.g. it says, "Prime as needed", rather than, "Prime 3 strokes in cold weather, 1-2 strokes in warm weather, not at all if engine was recently shut down". This makes the checklist more compact, which helps avoid skipping things (see below). But it also forces students to learn the nuances of and purposes behind various actions, rather than performing them mindlessly. To put it in FAA terms, I am trying to ensure they quickly move from the rote level of learning, through understanding, to application. The end goal is for them to use checklists as actual *check* lists, rather than *do* lists. Failing to understand this is a mistake I made when I first started creating custom checklists, and that I see repeated by others - especially mid-time pilots transitioning to new aircraft. It's tempting to fill your custom checklists full of prescriptive details, but doing so winds up creating more problems than it solves.Finally, the most serious and most common checklist mistake I see students (and experienced pilots) make, is simply skipping an item outright, without realizing they've done so. Sometimes it's just an inexplicable brain fart (myself included). But I've observed a couple of specific issues caused by the design of the checklist itself, and my checklists try to avoid those:1) Adjacent items that look almost the same are prone to getting skipped. Consider a checklist that says:Lighting - ONHeadsets - ONAvionics - ON... vs. one that says:Lights - AS DESIREDHeadsets - ONAvionics - ALL ONAt first glance it seems like there's no meaningful difference between these, but each line of the lower one is distinctly, visually different. Whether you're using your finger or your eyeballs or both to track to the next item, you're more likely to skip an item in the first case. This is analogous to how some old airplanes have switches that all look alike, while newer ones have distinctive shapes for landing gear, flaps, etc. Some of the wording in my checklists is designed to provide this sort of visual distinction.2) You can teach students to use a finger or thumb as a checklist place holder to avoid skipping items, but only if the checklist mechanically supports doing so. A few checklist operations require both hands, so there is no perfect solution. But you can't thumb-track the checklist at all, if it's a big, multi-page and/or multi-column monstrosity. So within bounds of reason regarding eyesight, smaller is better, and that's why my checklists use a "long and skinny" format.3) The more pages a checklist has, the longer it takes to find the section you care about (especially in an emergency); and the cardinal sin is a checklist that requires you to turn pages in the middle of a single sequence. For example, a lot of flight school 172s have laminated copies of the POH procedures pages in the map pocket, bound with a ring. The POH checklists themselves are fine, but the ring-bound "flip book" is unwieldy, and I've lost track of how many times I've seen a student skip items in the BEFORE TAKEOFF list because it spans two pages. For whatever reason, turning the page causes them to blow past items at the end of the preceding page and/or the beginning of the next page; and they'll often keep making that mistake even after multiple corrections. So again within bounds of reason regarding eyesight, smaller/fewer pages is better, and this is another reason for my "long and skinny" format.In summary, the whole point of having a checklist is to ensure every item on it gets checked, so anything you can do to minimize the chance of skipping items is valuable. The ergonomics of the checklist are at least as important - and maybe moreso - than what items you actually put on the list.-
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3 hours ago, carusoam said:
TCs aren’t making a comeback...
If you mean "traditional", standalone turn coordinators, sure. But to be clear, IFR flight requires a rate-of-turn indicator per 91.205 (except for a few exotic corner cases with three attitude indicators, one of which works through 360 degrees of pitch and roll). So you can't legally fly IFR unless something in your panel is certified as a primary rate-of-turn indicator. The G5 is certified as a primary rate-of-turn indicator, I'd bet at least a dollar that the GI-275 is too.
4 hours ago, 81X said:After reading more, are they certified primary for the TC and VSI?
VSI instrumentation is not required for any kind of flight, VFR or IFR.
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On 2/4/2021 at 5:29 PM, Hank said:
I don't get it. My trim wheel is well out of the ingress / egress path, and spinning it either way doesn't affect how the plane sits on the ground . . . .
In older Mooneys with the spring bungee system on the elevator, the position of the trim wheel affects the neutral position of the yoke on the ground. Trimming full down moves the elevator down and the yoke close to the panel, making entry/egress a little easier. Newer Mooneys with bobweights naturally "fall" to full down elevator and yoke close to the panel regardless of trim setting.
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One possibility on the vacuum regulator is that the tab or safety wire which is supposed to hold the adjusting nut in place has come loose, and the nut has spun all the way in/out/off/whatever to the "unregulated" position.
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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?
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19 minutes ago, 201Steve said:
Stupid question, but what’s so invasive about changing pan gasket? 4 hours labor?
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.
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1 hour ago, RobertGary1 said:
Also makes it easier to climb out of the plane.
Especially when the gut is a little rounder than it probably should be. We call it, "trim for egress!"
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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.
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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.
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4 hours ago, gsxrpilot said:
Whatever you do @Vance Harral don't pull that engine until I get mine back. We can't be completely without a Mooney around here.
We can't afford an engine overhaul! Too busy wasting money on foolish panel toys...
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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.
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22 minutes ago, Immelman said:
We haven't touched the oil pan yet. That seems like the last one. Just curious, have you tried anything? Re-torquing, exterior sealants (I'm assuming nothing along that gasket is pressurized)??
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.
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1 hour ago, MBDiagMan said:
Exactly correct. Statistically you are much safer in a high time properly operating engine than flying behind an engine within about the first 250 hours.
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.
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3 hours ago, MikeOH said:
I swear TBOs are set by Lycoming's LAWYERS not the engineers
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.
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5 hours ago, cctsurf said:
An overhaul is MUCH more than you would have to have done to drop the pan.
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.
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2 minutes ago, 1964-M20E said:
I'm doing an engine now because the one on my plane is leaking oil and not getting any better
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.
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9 hours ago, carusoam said:
We should invite the Brittain guy/gal.... to the conversation.... @CSmith (Cecilia)
Best regards,
-a-
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.
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Britain AP with G5 HSI
in Avionics/Panel Discussion
Posted
No, a garmin 430 cannot legally drive any arbitrary heading indicator. It can only interface with units for which a specific drawing exists in the installation manual.
Given all the thrash in this thread, I actually dug into the installation manual for the "Brittain Flight Control Installation Instructions 402-731-504 for B-5 System, Nav Flight II System, LSA-4 System, LSA-5 System, LSA-6 System". This is the governing document for the autopilots in question. Let's see what it has to say:
First, from section 1.2: All phases of this installation can be accomplished by a qualified A&P mechanic with the exception of the connections to the existing omni system. These connections and associated checkout must be accomplished by qualified radio technicians.
So the OEM's installation manual specifically requires a radio technician for omni connections, not just any old A&P/IA.
Next, from the "Electrical Schematic", Note 1: Hook-up to omni indicator is across left-right meter terminals for compatibility with specified VOR/ILS makes see sht 21
Sheet 21 turns out to list a bunch of specific CDIs the Brittain units are compatible with. So no, the installation manual doesn't actually allow interfacing to "any" CDI on the basis of an electrical interface spec; it allows interfacing to a specific list of CDIs. In other words, I think I was wrong to state that the Brittain can be legally interfaced to any CDI that provides a certain millivolt-level output. I think legally interfacing to a CDI other than those on sheet 21, requires an additional manufacturer's drawing to do so. My understanding is that Jerry provided FAA_approved drawings of this sort on request from time to time, for CDIs beyond those in the installation manual. I don't claim to understand the machinations of how the FAA was involved with these drawings, nor do I claim to understand the certification basis on which the shop that installed our GI-106 indicator connected it to the Brittain. But they signed it off on their authority as a certified repair shop.
The installation manual for the autopilot doesn't provide any information at all about interfacing it to a DG with heading bug. Again, this requires a separate OEM drawing to do so. There are such drawings for specific DGs, I have one that calls out the Century G502A.
Bottom line, an interface spec isn't what makes an installation legal, you need a specific drawing that references the parts in question. Jerry was working on one for the G5/GAD29B when he passed, but he did not complete it. If such a drawing is not required, he wouldn't have been going through the effort in the first place.