Ask the A&Ps

By: AOPA
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  • Summary

  • 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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Episodes
  • "There's a serious brain drain in aviation maintenance"

    "There's a serious brain drain in aviation maintenance"
    Jan 15 2025
    A 182 mysteriously losses power and the hosts struggle to explain why. Plus, basic engine temperature theory, confusing ADs, and why it's so hard to find good help these days. 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: Andrey was flying low and slow on autopilot for a mission when he noticed the airspeed dropping. He saw a drop in rpm, and an increase in manifold pressure. He also saw very low oil pressure. He added power, climbed, and returned to the airport. After landing, he checked the oil level and everything was fine. On a run-up check after talking to his mechanic, the engine stumbled. A new oil pressure sensor seemed to have fixed the issue, but he’s wondering if that’s really what was wrong. The hosts agree that it sounds like Andrey was having two issues because a drop in oil pressure shouldn’t impact engine performance. A big drop, or complete loss, will impact the prop governor, but not in the way Andrey experienced. After looking at the data they wonder if there was also something working through the oil pressure relief valve. Willie has a Cessna 310T and is confused about the exhaust AD. He’s getting conflicting information from mechanics and 310 experts. Mike was involved in the fight surrounding this AD, which is so confusing that the FAA had to issue an SAIB after the AD to explain it further. Yet the community is still confused, with the top Twin Cessna shops divided on when the AD should be complied with. Mike said it’s his opinion that it happen at overhaul. Others believe it’s 12 years. Andy is a maintenance manager and wants to know how to teach troubleshooting skills. Paul said in his experience techs can troubleshoot in their heads, do it via manuals and diagrams, or not do it at all. The process should not be, let’s go change this part and see what happens, he said. It should be, let’s go test something and see what we learn from the result. Relatively few mechanics are talented diagnosticians, Mike says. It requires a different skill set. Mike discusses Savvy Aviation’s new mechanic troubleshooting service they are working on. Royce wants to know if power equals risk. For example, if you have a higher compression engine or a turbo engine that produces more heat, will that impact EGT? Are peaks different based on the engine? Mike said CHT is basically measuring how much heat is present during the power stroke, while the EGT is measuring how much energy is being wasted out the back door. Paul said you can see this with an in-flight mag check when EGT goes up and CHT goes down. Running on only one plug shows how it’s more wasteful. Compression ratio is the big determining factor in the level of peak EGT. A higher compression engine will waste less heat, and thus have lower EGTs.
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    1 hr and 4 mins
  • "Check it, log it, and then relax"

    "Check it, log it, and then relax"
    Jan 1 2025
    Can you have a prop strike without a prop? This is one of the more unusual questions the hosts have faced. They also track down a carbon monoxide leak, advise on Continental rpm settings, and help an owner who likely had a pre-ignition event. Email podcasts@aopa.org for a chance to be on the show. Join the world's largest aviation community at aopa.org/join Full notes below: Robert is an A&P who is trying to help a flight school track down a carbon monoxide leak in a Cherokee. An instructor had a carbon monoxide event, took up a monitor, and found that it was reading at least 300 ppm. The exhaust and heater shroud were replaced, but the cabin was still getting more than 10 ppm. He’s wondering if there is a maximum level allowed in aircraft. Mike said Car 3 didn’t have a maximum, but that Part 23 says 50 ppm is the allowed maximum under current regulations. Hypoxia and carbon monoxide are cumulative, and he said his current comfort is below 20 ppm. He also said leaning impacts CO levels. Peak or lean of peak EGT lowers CO. How it gets in is a bit of a mystery sometimes. He said there was a case where Mooneys with air conditioning were drawing in air from the intake on the side of the airplane. Paul said in a Cherokee it comes in via the forward wing attach point. There is supposed to be insulation to stop it from coming into this area, but over time they are taken out or lost. It’s often not from the engine compartment. It’s through the belly or downstream from the exhaust pipe. John wonders if you can have a prop strike without a prop on the engine. He bought an RV9 with the engine on, but no propeller. He loaded it into the back of a box truck. Stopping partway to check on it, he found the tie-down straps had slipped and the airplane had be banging around in the truck. He’s wondering if he should be concerned, and what he should be checking for. Paul said to put a dial indicator on it and check to make sure it’s less than .005. Some of the bolts on the Van’s prop simulator were lose, and one was hard to screw back in. Paul said he would be surprised if there was any damage. Jesse has a 310 with Continental engines and he’s wondering about the service bulletin that recommends maintaining 2300 RPM in cruise. Previously the hosts said it’s probably good advice when rich of peak, but you could ignore it lean of peak. He wonders if he should go lean of peak first, and then pull the prop back, or is going to a lower rpm first ok? Mike thinks it’s sufficiently brief that it won’t make a difference. Rick had an infant mortality issue with his Mooney. His A&P found valve wear, oil though the rings, and corrosion on the engine, which only had a few hundred hours. He did a top overhaul, flew for 27 hours with the propre break-in procedure. About 30 hours later he got a high CHT indication on a descent, followed by dropping oil pressure. The belly was coated with oil and only 2.5 quarts were left. They found broken rings on 3 of the cylinders. They took off the electronic ignition, but are looking for ideas as to what may have happened. Mike found Rick’s data, which showed the CHT event was in cylinder #1, and the temperature rose at around .7 degrees per second. That approaches Savvy’s rule of thumb that anything at a rate of a degree per second or higher is a pre-ignition event. The hosts think it's possible the electronic ignition was the culprit. He thinks the broken rings may be an unrelated event. Colleen said improper ring installation could have caused the new ones to break She also suggests checking to make sure he doesn’t have a cracked plug.
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    1 hr and 17 mins
  • "There’s a reason they call these amateur built"

    "There’s a reason they call these amateur built"
    Dec 15 2024
    How to identify CamGuard in an oil analysis, erratic idles, how to check the oil, and what the wrong prop does to an engine are on tap for the latest episode. Email podcasts@aopa.org for a chance to be on the show. Join the world's largest aviation community at aopa.org/join Full notes below: Tan has a 1968 Piper Arrow 180. He has an erratic idle as the engine warms. Mike and Paul said it sounds like maybe sticky valves. He and his mechanic haven’t done the wobble test. It almost can’t be a spark plug, Mike said. Colleen said it could be an ignition harness. Paul suggest he could do an in-flight mag check to help verify. Even though it should start with morning sickness, Paul said it’s not unlikely that it’s a sticky valve. Fuel could also be an issue, as they’ve cleaned the injectors, which Mike, Paul, and Colleen think they induces more problems than it solves. Dicky is concerned about his last oil analysis report. Some of his wear metals are much higher since he’s been using CamGuard, and he’s wondering whether that’s normal. High calcium and high phosphorus are CamGuard’s signatures on an oil analysis, according to Mike. One thing Mike noticed that Dicky didn’t ask about was high silica, indicating dirt in the engine. High silica usually brings high wear metals because the dirt acts to scrub the cylinders. Dicky said he had a problem with his air filter box, and had replaced a part. Enock is trying to settle a flight school debate. He checked the oil and the instructor asked if he screwed the dipstick back in when checking it, or if he just tapped the stick to the top of the tube. Everyone he asked at the school had a different answer. Paul said he screws it back in to check. Colleen agrees. Mike said all the readings should be taken with a grain of salt. He recommends running about two-thirds full. Many type certificate data sheets have a minimum level. And the only somewhat accurate reading is the first one of the day when the oil has time to fully drain back into the sump. Rex is doing his best to follow the hosts’ leaning guidance. He has an RV-8 with an IO-360 engine with high compression pistons and e-mags and a fixed pitch propeller. He isn’t able to lean full throttle, but he can at cruise power. Mike clarifies that the guidance to leave the throttle full forward was for constant-speed propellers. Operating lean of peak slows the combustion event. The flame front takes longer to propagate. Engines don’t like lean of peak if the rpm is too high because the faster speed of the engine doesn’t like the disparity. Mike said he lowers rpm while keeping the throttle full before he leans. Then Rex makes an off-handed comment about his prop pitch, which the hosts quickly pick up on. They are convinced he has the wrong prop. He’s only getting 2400 rpm at full power in cruise. He also had a denotation event, and is trying to determine what the normal timing is supposed to be.
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    1 hr

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Profile Image for Coffey

Great Information

I enjoy the varied questions and the discussions regarding the issues. I have learned a lot.

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Profile Image for Andrea

Highly appreciate your show!

Excellent information since I am just a brand new power plant and soon to be airframe mechanic there’s so much to learn what is not being taught at schools and some very good information has been gained from your show thank you.

I look forward to your next podcast.

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Profile Image for T. V. Mackey

Binged and listened to the whole series

I binged through the whole series. I am a gearhead and the family fixit guy. I love car shows, and this aviation themed podcast definitely has appealed to me. Even if you don't normally indulge in aviation activities, I suggest giving this podcast a listen. I think it will have cross appeal for many with other interests. please

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Profile Image for Garhett Langer

Wonderful podcast. Learned so much in just the first few episodes!

Wonderful podcast. Learned so much in just the first few episodes! Highly recommend it to anyone!

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