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
  • "If that doesn't work you've got the flame thrower option"

    "If that doesn't work you've got the flame thrower option"
    Mar 1 2025
    Ever wonder how the flap system in a Cessna works? This episode Mike, Paul, and Colleen take a deep dive on the system, plus engine vibrations, leaning for high altitude takeoffs and go arounds, and getting bees out of a restoration. 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: Ken is experiencing vibrations in his Cherokee at certain throttle settings. After installing an engine monitor he discovered that with the throttle at roughly 90 percent full he could induce the vibration, but then quell it by using the mixture. He could see that a cylinder was going offline at full rich, but came back online when leaned. Mike suggests that he needs to lean in the climb to compensate for the overly rich mixture, but Ken said he’s also able to stop the vibration by reducing the throttle setting but keeping the mixture full rich. The hosts still think he’s too rich. They recommend leaning in the climb and keeping the EGT constant as he climbs. Ken also noticed that the cylinder that goes offline is also an outlier on the engine monitor. They tell him to do a GAMI lean test and an induction leak test to try and isolate whether he has a problem or just a poor mixture distribution. Find the test Mike described on Youtube: https://youtu.be/_VfiPuheeGw For more on the induction leak test Paul described: https://www.savvyaviation.com/wp-content/uploads/savvy_pdf/Savvy-Flight-Test-Profile-Expanded.pdf Marcus has a first generation Cirrus and he wants to ensure he is leaning properly for high-altitude takeoffs. Paul said to put his EGT around 1,300 or 1,350 degrees, which will put him close to the Cirrus chart, but is more accurate. For high altitude go arounds, Paul knows his fuel flow at around 1,300 degrees EGT, so he just sets the fuel flow to the expected amount. Luke has been having an issue with the flaps coming down in his 182. What follows is a loooooonnng and detailed description of the Cessna flap system. Blythe was restoring his family’s Cessna 150 and found a bunch of mud daubers. The inspection panels allowed him to clean out some, but he assumes there are more that he couldn’t reach. Paul said the potential corrosion is a key to the solution. He said the bees don’t like to build nests on corrosion inhibitors. He also said to make sure to check up the vertical stabilizer, which is a popular spot. Mike said he’s had luck with moth balls in other machinery.
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    1 hr and 5 mins
  • "Your airplane is on a full-time IV drip"

    "Your airplane is on a full-time IV drip"
    Feb 15 2025
    Can one high oil pressure reading forever alter your engine? Mike, Paul, and Colleen answer this question, plus the quirks of the O-470, compression test redemption, and repairman certificates. 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: Everett is wondering if his oil pressure is forever altered. He has a Piper Colt with an O-235. The pressure used to be 75 psi, and on a flight the oil temp spiked and the pressured went up to 85 psi. Even after cylinder work, the temperature and pressure have remained high. Paul starts by asking if he’s sure the indications are correct. They suspect a blockage somewhere, although there’s no oil cooler on the O-235. They suggest getting a manual to check for the engine’s entire oil pathway and follow it to see if he can find a blockage. Randall wants to know if the hosts are too hard on compression tests. He asks whether they hold any value. Mike said there’s no harm in doing compression tests, but that one should never change or overhaul a cylinder with compression numbers alone. Knowing where the air is escaping does offer some value, they say. There’s not much you can discover on a compression test that you wouldn’t discover on a borescope inspection that impacts safety of flight, Paul said. Manuel asks how EGT and fuel flow relate on his Cessna 180. He’s seeing a spike in EGTs before they come down again on takeoff. The low compression O-470 will have higher EGTs, especially on takeoff. Mike said Manuel's engine monitor is configured for a carbureted engine, and thus puts a big time delay and smoothing function on the fuel flow. Without the smoothing, the fuel flow would wobble up and down often, making it hard to read. That’s why fuel flow indications rise so slowly after adding takeoff power. And bu slowly adding power, Manuel is delaying the addition of the enrichment function of the carb, which is why he’s seeing a delay for the EGTs coming down. Marty is trying to understand repairman certification limitations. He’s done some work on his prop, magnetos, and so on, and he wants to make sure it’s all been legal. Mike said as he understands it, you basically have unlimited authority to do what you want on your airplane. The common sense rule applies, which is to get a demo or some instruction before you do it for the first time.
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    1 hr and 9 mins
  • "You don’t know if he’s going to hit you with a wrench or a lawsuit"

    "You don’t know if he’s going to hit you with a wrench or a lawsuit"
    Feb 1 2025
    Should you overhaul an engine based on oil analysis? The hosts answer this question, plus fuel pumps, valve grinding, and a pesky hot cylinder. 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: David is worried about the relatively new IO-470 in his Bonanza. His oil analysis history shows a lot of aluminum, and recently, high on all metals. The narrative said to check for crankcase fretting. Paul said he would check the torque on the through bolts for piece of mind. Mike said he’s not particularly concerned about any of the numbers on the report. He said oil analysis is only a trend monitoring system. Once you establish a baseline you look for major diversions from the report. Colleen disagrees and said they aren’t stable, but have been increasing. There’s nothing that would cause all numbers to go up unless there’s dirt or a bad sample. Paul then details how David can use his borescope to look at the cam, a few lobes, lifters, and so on. It might not give him any information, but it could give him some reassurance that things are ok. Colleen suggests inspecting the pick-up screen if he can. Mike said he would never tear down an engine based on an oil report. Maurice wants to know about the fuel pump on his Mooney M20J with a Continental IO-550. He has an altitude compensating fuel pump, and he wants to know how to use it. Mike explains that it automatically leans for you in the climb. Once he’s ready to lean in cruise, it’s time to lean manually. Jared is ready to start grinding some valves. As he gets deeper into lapping valves in place, he’s wondering what sort of threats there are. Is it maintenance to the extent of being subjected to potential maintenance induced failures? Is it better to wait until a valve needs it, or could it be done pre-emptively? Mike said he wouldn’t necessarily do it pre-emptively, but if he sees any sort of potential deposits then it can be worth doing it. Paul said they go through an inspection process afterwards, including making sure the grinding compound is cleaned up as well as possible, that the valve keeper is properly in place, and that the bolts holding the rocker shaft holds are torqued properly. Paul said it’s critical to get another set of eyes and not check yourself. The hosts haven’t heard of any failures from lapping. Chris has an O-540 in his Cherokee 6 that was recently overhauled. His number 6 cylinder spikes up to 450 degrees CHT on takeoff and he can’t figure out why. Mike looked at his data going back before the current engine and found that even the old engine had high temps on number 6. Chris finds that the cylinder also run the leanest. Paul suggests it could be an induction leak.
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    1 hr and 10 mins

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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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