Ask the A&Ps

• "Keep torturing those airplanes...and students"

  John is a maintenance officer in a club, and he is wondering about tire ply ratings. The manual calls for 4 ply, but they often install 6 ply and he’s wondering if that’s ok. The hosts all agree that they have subbed in higher ply ratings when supply dictates. Paul’s rule of thumb is that he always allows a higher ply, but not lower. That’s because the ply rating relates to the weight of the aircraft. Heavier aircraft need higher ply ratings. They get into a discussion on retreads, which can cause issues. They like retreads, but caution that you must ensure they will fit in the wheel well on a retract. Paul worked on a 210 once that caught the skins when retracted.   Doug instructs in Aerostars, and he has worked with a number of clients lately who want him to omit the engine-out portion of the training in order to avoid stress on the engines. There’s talk in the Aerostar community about heavy and light cases. Mike said not to worry about the case. Rather, cylinders that rapidly cool are the concern and that’s because the piston and cylinder are different metal densities and cool at different rates, which can lead to scuffing. They all agree the training is important, but pulling the power back slowly, rather than cutting the fuel, will help reduce the risk of engine damage. Paul makes the point that flight schools do this in Seminoles all day, and that he doesn’t hear of widespread issues. Failure isn’t a concern, Mike said. Scuffing is a wear issue. If it’s an issue, Paul said his pistons probably look terrible, but he’s not going to worry about it. He already borescopes regularly. And Mike said he will run an aux tank dry on a long flight.   Jason has a Comanche 250 with some electrical issues. Throughout the flight the bus voltage will come down. After landing and taxiing in the voltage climbs back up, and rests around 13.8. Recently after takeoff, the low voltage alarm flashed and went to 10.8 while raising the gear. The hosts think it’s a voltage regulator issue, where it works when cold but not warm. Paul said he thinks of voltage as an indicator of whether the system is working and the amps as an indicator of how hard it’s working. It should be around 13.8 or 14 when working properly. Colleen said she had an electrical issue where her JPI would go offline when she would cycle the gear. Under the panel she found that there was a loose connection on the shunt, causing high resistance. Jason’s issue could be at the circuit breakers, voltage bus, voltage regulator, or any number of places. One way to easily troubleshoot is to see if he can find anything hot by running his hands along the wires. Or look for discoloration, Paul said.   Steve writes in asking about oil coolers. During his recent engine overhaul the shop asked if he wanted a congealing or non-congealing oil cooler. Congealing is bad, he thought, so he elected to go with non-congealing. But he lives in Arizona and he’s found the engine runs a bit hotter with a higher oil temperature in long climbs. He’s wondering if he made a mistake. Non-congealing oil coolers have a solid line running through the middle that passes warm oil through the cooler at all times. Mike thinks it’s possible the non-congealing has less cooling capacity because it has less surface area.

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  54:31
• "Shame on you for even thinking about it"

  Should you trade your aging airplane in anticipation of higher repair costs on your current bird? Mike, Paul, and Colleen have a strong opinion on this. Plus, sticky valves, taking good care of turbos, and engine monitor set-up frustrations. Email [email protected] for a chance to be on the show. Join the world's largest aviation community at aopa.org/join Full notes below: Scott has a Tecnam P2010 with a Lycoming IO-390. He’s had a few instances where cylinders dropped off, the engine ran rough, and then they quickly came back on. It was followed by morning sickness. In essence he had a sticky valve. He found that his CHT temperatures were quite low. At altitude, running the airplane at best cruise power, his CHTs are about 350 degrees. In climb if he leans he can get three cylinders over 350. Mike said he wouldn’t stress about the CHTs, but he would borescope the cylinders to verify that there isn’t too much build-up.   Yuriy has a new-to-him 2010 Cirrus SR22 that’s turbonormalized and he’s looking for some tips on taking care of his turbos. He flies lean of peak at 28 inches. He is limiting turbine inlet temperatures at 1,500 degrees. Mike thinks 1,500 is excessively conservative. The red line is 1,650 degrees, and Mike tries to keep his at or below 1,600 degrees. He also doesn’t subscribe to the one inch per minute reduction of manifold pressure. Lycoming at one time published a document that said not to cool CHT more than 60 degrees a minute. Mike’s engine monitor alarm is at 30 degrees a minute, and he said it doesn’t go off very often. He also doesn’t cool the turbo on the ground before shutting down unless he had high power right before landing for some reason.   Wade has a Cessna 185 with an IO-550. On his last annual he had a few burned exhaust valves. He’s trying to avoid higher maintenance bills in the future. Paul tries to make Wade feel better by telling him that burned valves have nothing to do with how he’s operating the engine and everything to do with the lead in avgas. Going through his operating technique, the only suggestion they have is for Wade to lean much faster, and avoid using the lean find feature. The green arc on his manifold pressure gauge is also wrong. He was worried that he’d have to take off at partial power in order to stay in the green arc on the gauge. The hosts discuss how to reprogram the display.   Matt doesn’t want to throw good money after bad. He’s wondering how long you should hang on to an airplane as it ages. He has a 1977 Cessna T210. Parts are starting to get scarce. It’s hard to find qualified mechanics. He feels like he wants a great airplane that lasts him well into the future. The hosts all agree that it’s better to hold on to the airplane he knows, and not to worry about 210 parts availability, at least when compared to other airplanes.

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  57:33
• "If that doesn't work you've got the flame thrower option"

  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 [email protected] 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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  1:05:24
• "Your airplane is on a full-time IV drip"

  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 [email protected] 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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  1:08:56
• "You don’t know if he’s going to hit you with a wrench or a lawsuit"

  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 [email protected] 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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  1:09:51

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