Ask the A&Ps

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Ask the A&Ps

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.

  1. قبل يوم واحد

    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 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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  2. ٢ شعبان

    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 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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  3. ١٥ رجب

    There's a serious brain drain in aviation maintenance

    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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  4. ١ رجب

    Check it, log it, and then relax

    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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  5. ١٤‏/٠٦‏/١٤٤٦ هـ

    There's a reason they call these amateur built

    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.

    ١ من الساعات

  6. ٢٩‏/٠٥‏/١٤٤٦ هـ

    Don't open up the fuel system if you don't have to

    Clogged injectors, how to care for an engine while training, avoiding costly altimeter checks, and engine design considerations are on tap for this episode. Email podcasts@aopa.org for a chance to be on the show. Join AOPA to become a member of the world's largest aviation community at aopa.org/join Full notes below: Marko’s engine had a strong revving sound on takeoff. He saw that he had an EGT above 1,800 degrees and one that was below baseline. A run-up after landing made it seem like it one cylinder wasn’t firing. A borescope inspection revealed nothing unusual. A subsequent check of the injectors found that there was debris in one. His mechanic suggested it was a blocked injector. He’s wondering what would cause that. It turns out this event was soon after the annual when the injectors were cleaned. The hosts agree that the maintenance is clearly what caused the clogged injector. Mike said this is such a delicate operation that he thinks it’s almost as if the fuel system should only be cleaned under sterile conditions. Colleen said she used to clean hers, but now doesn’t because she knows the risks. Paul colorfully describes the problem of cross-contamination. Dylan teaches in a carbureted Seminole and he wants to treat the engines well, and is looking for best practices. He mentions shock cooling, which the hosts quickly debunk. The school’s engines are over TBO and they’ve never had to replace a cylinder. Obviously whatever the school is doing is working. He’s also wondering about failing the engines. Lycoming recommends failing the engine with mixture, but many people like to shut off the fuel. Mike said he wouldn’t worry about shutting the engine down from the fuel selector, and that it shouldn’t introduce air or other issues. Mike worked in the auto industry for many years, and he works on his own airplanes as much as possible. He’s wondering why aircraft engines don’t have ventilated crankcases. Mike said crankcase ventilation is primarily for environmental reasons. And piston aircraft engines have significantly more blowby. You don’t want to keep it in the crankcase. He said air/oil separators return a lot of junk back with the oil. You want the filth to leave as much as possible. Doug has three altimeters in his airplane, and he’s wondering how to save money on the checks. Mike thinks he shouldn’t be charged three times for three checks because you hook up the equipment once, and adding on a second or third altimeter doesn’t take too much additional time. Each check includes about five tests, according to Paul, and each has to be separately documented.

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  7. ١٣‏/٠٥‏/١٤٤٦ هـ

    The engine didn't explode

    Mike, Paul, and Colleen sludge through oil pumps that lose prime, skipping an oil filter change, and using the right oil in this Texas tea-themed episode. Email podcasts@aopa.org for a chance to get on the show. Join the world's largest aviation community at aopa.org Full notes below: Mike has a Cessna Bird Dog with an oil pump that isn’t cooperating. When he lets the airplane sit for a month or more, he doesn’t have oil pressure on the first start up. He’s conceived a workaround of pumping oil by hand into the engine and turning the prop backwards. Paul and Mike both describe having experienced this issue with Continentals. Mike said that Continental told him to prime the pump by removing the top spark plugs and pressurizing the case with shop air while you move the starter. Paul said they will unscrew the oil filter, fill it with oil, and then put it back on. Cameron is trying to protect the Aeronca that’s been in his family for decades. He thinks using thinner oil sounds good because its viscosity helps after not starting for a long time, but the thicker W100 might better protect? He flies mostly in the winter, but he preheats. Mike thinks his strategy to use W100 when it’s warm and multiweight is good for colder temps. Paul likes multiviscocity so he doesn’t have to worry about temperatures. Chuck is an A&P with another job, and he’s considering maintenance side hustles. He’s thinking of offering aircraft weighing services. He can either defuel aircraft or completely fill the tanks prior to going on the scales. Advisory circular 43-13 is unclear about which approach is better. Paul has always thought it strange that proper weighing procedures are in the POH, and not the service manual. That’s the first place to check, and the procedure that should be followed first. If there’s no procedure you go to the AC. He finds that most airplanes must be de-fueled first. Mike says to use FAR 43.13(a), which says that the mechanic must use the procedures in the maintenance manual, or acceptable practices and techniques. The AC has a note at the beginning saying that it’s only to be used if the manufacturer doesn’t have a process. But given that the procedure is in the POH, and not the maintenance manual, Mike suggests Chuck can pick and choose the way he weighs the airplane. Jared is looking for a more permanent oil filter solution. First he wonders if he can skip changing the filter when changing the oil, in part because they were hard to get at one point. Paul said the only time it’s required to change the filter is during annual, when the IA is required to inspect it. Mike said he would like to inspect the filter as often as possible. He considers it the most important thing to do to monitor engine condition. Although people have taken their filters beyond 100 hours, there is oil analysis data showing that it’s a bad idea. The hosts then discuss reusable oil filters. Mike changed to reusable filters prior to Oshkosh, and has been initially pleased with the results. The Challenger filter comes off, the filter element comes out of the can, and the filter then washed. He was astonished by what came out of the filter because it’s easier to see what comes out after washing versus having to see what’s in the pleats of a filter.

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  8. ٢٩‏/٠٤‏/١٤٤٦ هـ

    When they go bad the engine is toast

    Lean of peak is causing odd vibrations in a Commander, and the hosts discuss proper troubleshooting. Plus carb heat on the ground, dehydrators, and parts no longer manufactured. Email podcasts@aopa.org for a chance to get on the show. Full notes below. Chip said his mechanic is concerned about lean of peak because we don’t know the actual temperature at the valve, as the temperature is taken downstream. Colleen makes the point that EGT temperatures are fine because it’s well below the valve limit temperature. Mike said valves burn only when they don’t seat properly. They shed their heat through physical contact with the seat at the cylinder head. They also shed it through the valve stem. Detonation once flying lean of peak isn’t a concern. It’s getting to that point that’s the biggest risk. Paul suggests that once you know the fuel flow at your desired power setting you can lean straight to that fuel flow and not worry about EGT or CHT until it’s set and stable. Chip is also concerned about a vibration in the floor of his Rockwell Commander. Mike suggests he do some testing to help isolate the issue. If it goes away at certain rpms, then it suggests that it’s an engine-based issue. At a constant rpm but with changing pitch, it suggests a potential airflow or airframe source. Frank is questioning the logic of the Luscombe handbook. It says to put the carb heat on for takeoff. It’s also placarded that way on the panel. The hosts can’t figure out why this would be required. The hosts suggest he ignore the handbook and operate as he would in other airplanes, in part because the engine would be breathing unfiltered air while on the ground. Bill has a Cessna 180 on floats with an O-470-50 engine. For the last few months he hasn’t been flying as much and he wants to preserve the longevity of the engine. He is looking for details on engine dehydrators and whether they actually work. Colleen looked through some research and found that those who had done some side-by-side testing had found good results. Mike said Tanis found that people who ran their heaters all the time were causing corrosion, but that if they use engine dehydrators they are fine to run the heater all the time. In other words, they seem to work. Mark is pushing back on airport naysayers that tell him autofuel is dangerous. He flies airplanes with older, small Continentals, and with all the info that has come out on the transition away from 100LL, he’s wondering if he should be worried. Mike said running on autofuel is the best thing he can do for his engine. People tell Mark he has to run at least half low lead. Mike said they’ve never seen issues with low compression engines running on autofuel. Mark flies from an airport a mile high, and locals are also telling him that vapor lock is also an issue.

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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.

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    ١٤٤١ هـ - ١٤٤٦ هـ
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    Ask the A&Ps

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