This month Mike, Paul, and Colleen delve into must versus should. Must you open all those inspection ports, is the prop and governor overhaul mandatory, and should one owner retorque his cylinder after a re-installation mistake? Send your questions to podcasts@aopa.org

'We just saved your engine'

Experts Mike Busch, Paul New, and Colleen Sterling answer your toughest aviation maintenance questions. Submit questions to podcasts@aopa.org. New episodes are released the first and fifteenth of every month.

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This episode a perspective owner wonders about the cost of tying down outside. Plus fuel pump problems, major versus minor, and more. Email podcasts@aopa.org for a chance to be on the show.
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Full notes below:
Steve’s primer in his Saratoga sat for a long time and was pumping air when he came back to fly it. He had to track a fitting to get it to pump fuel again. Paul thought that since the pump is lower than the level of the fuel tank, then it should have probably been ok with the long break from flying. He suggested that air had gotten in the system somewhere other than the pump. Although the problem hasn’t re-occurred, he wants to be sure there aren’t underlying problems. The hosts think since there aren’t any stains from leaking fuel that he probably doesn’t have an issue. 

Dennis is looking to buy an airplane and he’s trying to establish the maintenance costs difference between having a hangar and being on a tie-down. They recommended a cabin cover to try and keep the water and UV out of the interior. Dennis is worried about the freeze-thaw cycle during his cold winters, but the hosts aren’t concerned. Paul said not to worry about all the snow that sits on airplanes during the winter either. Dennis asks about glass versus steam, and they suggest that maybe glass would fare better in cold weather. 

Mark wants to install an air conditioner as a minor alteration in an Aerostar. He and the hosts talk in detail about the challenging issue of minor versus major alterations and what’s involved in that decision. Mark’s concern is that the air conditioner should have a few operating recommendations about usage, recharge, and so on, and he is worried about pushing into the major category. Adding limitations and a flight manual supplement would do that, but the hosts think he could legally offer operating suggestions that don’t cross into limitations. 

Andrew works at a flight school with some airplanes have that airspeed in knots and some in miles per hour, and he is looking for a way to make life easier for his students. They discuss the issues involved with glass displays that are incorrectly labeled, and what that does to the legality of the airplane. Mike thinks so long as the original backup instrument is still legal that is probably ok.

"I have permission to get an airplane."

Is there a limit to how much oil consumption is too much? This episode, Mike, Paul, and Colleen answer this important question. Email podcasts@aopa.org for a chance to get on the show.
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Full notes below:
Jim has a Cardinal with 3,000 hours on the engine. Everything looks good, except that the oil consumption has increased substantially. They tried the ring flush procedure, and saw the fluid coming out of the carb intake and exhaust manifold. The second cylinder took an immense amount of effort to pull the prop through. They took that cylinder off, and found that the oil control ring had a lot of crud. Mike said he wouldn’t get too invasive in order to solve the problem. It’s not a safety of flight issue. They suggest replacing the cylinders only if the oil consumption bothers Jim and his partner. Jim’s partner suggested also overhauling the bottom end with cylinder changes. They advise against it, instead looking at the cam when the cylinders are off. Mike wonders if the ring flush was done wrong. None of the fluid should come out of the exhaust or carb. He and Paul said they’ve never seen fluid come out of the valves. They recommend trying again.
Nicolas and his partner disagree on how often they should change the oil on their Grumman Tiger. His partner wants to change the oil before the winter, when they usually only fly a few hours, and then again in the spring, when they fly around 30 hours. Mike said the oil change intervals are inexact. As the airplane is flown, the oil gets increasingly corrosive. He suggests not letting the airplane sit with old oil throughout the winter. So that’s when he would change it. He’s wondering if he can avoid changing the oil in the spring after only flying for seven hours over the winter. The hosts agree that it’s probably fine not to change the oil at that point. They recommend also getting a dehydrator to keep the inside of the engine dry.
John has a twin Cessna with one engine that quits when it’s cold. Mike said the fuel pressure at low rpm isn’t high enough. Or the idle mixture isn’t rich enough, or there’s something wrong with the flow divider. The easiest and cheapest thing to do is to adjust the fuel pressure or the idle mixture on the fuel control unit. Paul said his Cirrus does the same thing in winter. He thinks it’s the fuel divider.
Cheryl has a Skycatcher with a window tint and she is concerned about its legality, and whether it should be noted in the airframe logbook. So long as it doesn’t inhibit the view, the hosts think it’s fine.

"I'm against throwing a part at something"

Can you fly a turbocharged airplane lean of peak? Absolutely! This episode, Mike, Paul, and Colleen describe how to do it. Email podcasts@aopa.org for a chance to get on the show.
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Full notes below.

Mike flies a turbo 206 and a 421 and is trying to fly lean of peak but the airplanes are running a bit rough. He wonders if there are tricks on turbocharged engines. The GAMI spread is half a gallon, so that’s not an issue. Paul said to start by getting the magneto timing really close and gap the spark plugs very tight. Mike said he might be trying to keep the cylinders too cool, which would make it run rougher. He recommends targeting 400 or 410 degrees on the Lycoming engines.

Adam read Mike’s column in AOPA PILOT about LSA viability when the manufacturer goes out of business. He’s been interested in buying an LSA, but the story gave him pause. The FAA wants nothing to do with LSAs, Mike said. The hosts then discuss the differences between certification and ASTM acceptance, and what it means to potential owners.

Garhett has had a bunch of maintenance-related failures, and it has prompted him to be more involved in his airplane’s maintenance. He’s now wondering the best way to obtain his A&P certificate. Paul suggests he should start by reading the FAA manuals. It took Mike 10 years to amass the required hours by working on his own airplanes under supervision. Short of going to school or getting a job as an apprentice, this is the best route. They then discuss creative ways to build experience.

Victoria wonders how to keep the family airplane clean when the airport doesn’t allow water to be used. Mike and Paul suggest flying somewhere else and washing it. Colleen said she would use water or cleaner wax from a spray bottle. Paul really likes Crazy Clean, but cautions against using anything other than water during pollen season. For windshields, Paul said Cessna recommends a lot of water, Dawn, and your hand. Definitely don’t use power tools, they say.

"You become the supervisor of your maintenance"

A light oil mist on his windscreen has one caller concerned he needs to split the case. Plus, Mike, Paul, and Colleen tackle cold cabins, tire changes, and horsepower calculations. Email podcasts@aopa.org for a chance to get on the show.
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Full notes below:
Grant has a Mooney M20F and he’s seeing a light mist of oil on the windscreen after flying. His mechanic thought it was coming from a case bolt, which he re-torqued. That didn’t solve the problem, and the mechanic said the proper way to fix it would be to split the case, which Grant doesn’t want to do. Paul said that’s not the problem anyway. He said misting oil on the windscreen is almost always the crankshaft seal or the prop o-ring, both which should be fixed together. The parts are cheap, and the job is relatively easy. Colleen just did this on her airplane and describes the process.

Joe’s kids are freezing in the back seat of the family Cherokee. They’ve put tape around some gaps, and while it’s helped a little, it’s still very drafty. Paul mentions the spar carry-through gap between the cabin and the wing. There’s supposed to be a piece of foam in the gap, but often when the wings are removed the foam isn’t replaced. The floor is lifted up, and you can look in the gap with a flashlight and mirror to see if the foam is there. The rear spar also has a gap where there should be rubber discs glued onto the box where the flight controls pass through.

Todd is curious how JPI derives the horsepower number. Mike said JPI keeps the math as a closely held secret. But he said there’s a right way to do it, and it's how Savvy does it. Power is regulated by air or fuel, whichever is in shortest supply. Rich of peak, you have more fuel than the engine can combust, so air is in short supply. Mass airflow is therefore the power determinate, which can be calculated with manifold pressure and rpm. MP is how much air goes into the cylinder, and rpm is how often that happens. Multiplying the two gives the mass airflow number. Power when lean of peak is a function of fuel flow. Fuel flow times a set number based on the compression ratio gives horsepower. He thinks the engine monitor doesn’t know whether it is rich or lean of peak, so it probably computes it both ways, and the lower number is the right one.

Seth has some dry rot on his tires and he’s wondering if that means he needs to change thems. Desser says they need to be replaced when the cord is showing, and his mechanic says the dry rot means it should be changed. The hosts agree with the manufacturer that there’s no minimum tread depth, and to keep going.

"Don't split the case halves"

A Vans customer wonders what to do next, and a 172 pilot asks if carb heat is really necessary all the way to the ground. Plus, the best spark plugs, and a vexing gear issue are on tap for Mike, Paul, and Collen this time. Email podcasts@aopa.org to be on the show.

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Full notes below:
Greg has a kit from Vans on order and he’s wondering what to do next. He can replace his quick build wing kit with the small cracks installed, but he wants to know if he should order replacements. Paul said when sheet metal work is done on certified aircraft in the field, a lot of cracks naturally come up. Greg said a customer has to agree to accept the modified terms of the new contract, and you have to either accept what they send you, or spend money on a second kit. Paul said to deburr as little as possible. The goal is clean, sharp corners, not a knife edge that can cut the rivet. Just barely touch the hole, he said.

Travis has an unusual gear problem. He was tasked with ferrying a Wheeler Express RG, an unusual experimental. On the ground the gear works perfectly, but when flying it won’t reliably retract. The system is based on a Glasair 3, and Colleen said the Glasair racers have a similar experience with their airplanes at Reno. On a ferry flight the hydraulic fluid built pressure over a few hours, and Travis had to select the gear down lever in order to release the pressure. Paul said not to spend any more time on the system, and replace it with something from Cessna.

Brian wants to get to the bottom of the fine wire and massive plug choice. His shop said he had to replace all 12 fine wire plugs at the last annual, all with around 800 hours on them. The shop recommended Temptest massives, which is what he did. He’s wondering if there’s really a difference in performance. Paul said fine wires tend to idle a little better and smoother. Corrosion was an issue on older Champion fine wires, which is what Brian had. And the ceramic is thicker on Tempest. Fine wires also last longer, usually long enough to cover the additional cost. Mike said they cost about four times as much, but last four times as long. He said some people also report smoother operation at very lean mixtures and small fuel economy improvements. Colleen has fine wire Tempests in her Cardinal but massives in her Skybolt. Her fine wires run a bit cleaner and don’t need to be gapped. Brian has seen a larger EGT differential when flying lean of peak with the massives.

Dennis has a 172 and he wants to know if it’s really necessary to keep carb heat on all the way to the ground. Mike said a newer Lycoming Skyhawk is less susceptible to carb ice, but his Continental O-300 is much more likely to produce ice. He recommends installing a carb heat gauge if he really wants to avoid having the carb heat on longer than necessary.

'We just saved your engine'

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