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Ask the A&Ps

Ask the A&Ps

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 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.
Épisodes
  • "If you lose a cylinder in your Cessna 150 you are down on a road somewhere"

    "If you lose a cylinder in your Cessna 150 you are down on a road somewhere"
    May 1 2026
    Sticky valves, sleepy valves, and valves destined for the trash are on tap this episode. Email podcasts@aopa.org for a chance to get on the show. Join the world's largest aviation community at aopa.org/join Full episode notes below: Mac is trying to get a cylinder to wake up on his Piper Lance. The engine ran rough, and a magneto clearing procedure didn't help. The number 5 cylinder was dropping off according to the engine monitor. It's also next to the turbocharging exhaust. His A&P thought maybe the injector line being next to the pipe might be causing a problem. It only happens after landing, not while flying. Paul thinks it would be a more widespread issue if the plumbing engineering were the issue. The aux fuel pump stops it from happening. Mike suggests a mixture that's too lean could cause this. They suggest checking the idle mixture rise on shutdown. The rpm should rise 25-50 when pulling the mixture at idle. If it doesn't rise as much it's too lean, and if it rises too much it's too rich. They also suggest running a GAMI lean test to determine if the cylinder is a lean outlier. Conor has a Cessna 150. On the way back from Oshkosh last year he experienced a stuck valve. There was discoloration from being hot when the cylinder was pulled. He leans aggressively. He's wondering if he's leaning too aggressively and is getting the engine too hot. He leans to roughness and enrichens only until it gets smooth. The hosts think the engine has to be in detonation for it to get too hot. The piston tops are fine under borescope, so the hosts think it's fine. Andrew wants to knock the rust off his A&P certificate. The hosts suggest the new Savvy Aviation IA recurrent course. It's a free 8-hour course to help refresh his memory. Beyond that, Paul suggests a 172 course, which is the airplane he plans on buying. There really isn't a hands-on refresher course, according to Colleen. She suggests he could hire an A&P and work alongside him or her to brush up. He could also take an LSA repairman course, which is shorter than a typical A&P course. James is asking about the right time to overhaul an engine. He is in a club with a Diamond that flies about 500 hours a year. When he wrote in there were 1,900 hours on the engine. They were told the turnaround would be three months. They decided to order a reman from Lycoming, which was scheduled to take 15 months. Then they got a notice that it would be an additional 12 months. It ended up only being 17 months. Their club decided that more than three months of downtime wasn't acceptable. If the lead time for engines is more than a year, so how do you listen to the engine when the delay is so long. Paul said you buy consumables, like cylinders. Cylinders can sit on the shelf for a long time.
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    51 min
  • "Am I doing anything evil?"

    "Am I doing anything evil?"
    Apr 15 2026
    Avoiding maintenance can be a good thing when what's recommended is unnecessary. Email podcasts@aopa.org for a chance to get on the show. Join the world's largest aviation community at aopa.org/join Full notes below: Dominick is questioning his mechanic's advice on prop overhauls. He has a Cessna 310 and his left rpm is too low on approach when the control is full forward. It's not an issue on the ground or on takeoff. His mechanic recommends overhauling the propeller, and since he's doing one he should do both. He swapped governors and that didn't change anything. He sent the prop back for IRAN and they didn't find anything significant. Paul suggests it's the low pitch stops. This is a classic twin owner trap, Mike says. The two engines are never the same. Everyone agrees that he can leave it as is. Vas has an RV-10 and the Lycoming IO-540 has been acting up. During some flight training in the airplane, he noticed oil consumption went up, metal was in the filter, and he ended up overhauling the engine. He's wondering if he should have just pulled a cylinder instead. He was flying 140 hours a year, and he's wondering why he would get corrosion. Higher oil consumption isn't a corrosion problem, but the cam and lifter spalding do indicate it. These were unrelated problems, according to Mike. Paul thinks it's possible the damage was already in place when there was a previous IRAN. They settle on it being a lifter hardening issue, meaning poorly manufactured parts. Jim has a Mooney M20K and an instructor showed him a leaning procedure while in cruise at 9,000 feet. They set the manifold pressure to 30 inches, the RPM at 2300, and then pulled the fuel back to 11 gph. That's how he's been leaning ever since. CHTs are in the 360/370-degree range. He trails the cowl flaps to try and cool the CHTs if it's a hot summer day. If the TIT gets too high he'll enrichen it just a touch. Paul said if he adds more fuel and the TIT goes down, he's running rich of peak. Peter found some residue on the top of his intake valves on the engine on his 172N. He typically flies with autogas. He's wondering if can or should get rid of it, and if so, how to do it. Paul said people talk about it, but he's never done it. They suppose it's not carbon, but probably coked oil. They suggest a wobble test if he's really worried, but generally they think he can leave it alone.
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    57 min
  • "That installation is fraught with peril"

    "That installation is fraught with peril"
    Apr 1 2026
    How much should a mechanic tell a client during an annual? Mike, Paul, and Colleen handle this question and more. Email podcasts@aopa.org for a chance to get on the show. Join the world's largest aviation community at aopa.org/join Full notes below: Justin flies a Twin Bonanza and cylinder 5 on his left engine takes as much as a minute to fire up and start running. It comes online fastest if he goes very lean quickly after starting. He's pulled the valve cover and springs off, and it's not a sticky valve, and he's reamed the valve guides. Mike wonders if it could be a primer problem. Justin disconnected the primer line, ran the boost pump, and checked for leakage and couldn't find any. Paul suggests taking the line off, capping off the injector, and then trying it. Jorg is trying to make sense of his data. He has a K35 in Austria and he has GAMI injectors and an engine monitor on his IO-470. He has a low CHT on the number 6 cylinder, and it's the first one to go on the lean side, and it shuts down first if they go very lean. An induction leak test seemed fine, and his GAMI spread is less than a gallon an hour. The valve was also lapped. Mike said a low probability culprit could be if the bleed air holes in the injector nozzle were plugged, since they don't seem to have an impact at wide open throttle, but would at a reduced throttle. Mark saw a Youtube video and is now wondering if there's danger lurking in the alternator. The video mentioned how an alternator elastomer coupler failure could lead to a catastrophic engine failure. Paul said the installation is critical because of some critical components. Mike thinks the video relies on old information. He said Continental used to employ a spring, which would come apart and throw large chunks of metal into the engine. The coupler is meant in part to protect the engine if the alternator seized, but sometimes the coupler would fail and cause its own failure. The newer versions have an elastic or rubber piece instead of a steel spring, which shouldn't cause an engine failure. Chaz is an A&P/IA and he wants the team to weigh in on the debate as to whether the inspector should give pilots a full list of squawks or only the airworthiness issues. He personally thinks he should give the whole list so the owner knows where he stands. The hosts agree that the full list is preferable. The mechanic is giving a full slate of options, and not a required list. Airworthiness items can be listed separately or be flagged.
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    54 min
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