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"I'm a reformed shock cooling worrier" Jul 01, 2022

Show notes

Is shock cooling myth or reality? Can you run lean of peak with a carbureted engine? These questions and many more come at Mike, Paul, and Colleen in this month's episode. Send your questions to podcasts@aopa.org

Full notes below:

Jerry has an RV-4 with a new battery but the original alternator. When he starts the engine and then turns on the alternator, he sees a big amperage spike. He tested turning on his alternator before starting, and sees the same spike. That piece of information is critical because according to the hosts it means it must be an instrument indication. Without the engine operating and the alternator not turning, it can’t possibly be producing current.

Ken has a Mooney M20 and thinks the inside of the tail section is messy and ugly. He’s looking for a way to clean it out. A vacuum won’t work because the flakes are sticky. Paul suggests that because it’s sticky someone has sprayed a corrosion inhibitor and only hand scrubbing will get it completely clean. Once it’s clean, he suggests spraying in a thin coating of Cor-Ban (https://zipchem.com) or Ardrox AV8.

Dave flies a 1946 Cessna 140 and a Hatz biplane with a carbureted engine. He wants to know how to fly lean of peak. Mike says that Lycoming engines are pretty symmetrical out of the factory, which means they are often ok to run lean of peak from the factory. Continentals are less so. The rear cylinders tend to run leaner and front cylinders tend to run richer. By reducing the droplet size you can better dial it in. Do this by using a little bit of carb heat to better atomize the fuel. The other method is to back the throttle off a little bit to make the airflow through the carb more turbulent. Without instruments to help, the technique is to lean aggressively until the engine stumbles and then enrichen only until the engine runs smoothly again.

Steve is wondering about unleaded fuels in development. He wants to know if the hosts would hesitate to use any of these new fuels in their airplanes. And also if their operating procedures will change as a result. Mike, Paul, and Colleen say they would have no hesitation running one of the fuels once it’s approved. They also don’t expect any operating changes.

Guest Mike wonders why the hosts don’t ever talk about leaning in a descent. Host Mike stresses that although power changes should happen somewhat slowly, it's not as slow as he used to think. Lycoming recommends limiting cooling to no more than 60 degrees per minute, and Mike has an alarm set on his engine monitor for 30 degrees per minute. The only time it ever goes off if he’s doing an “extreme slam dunk.” Colleen makes the point that aerobatic pilots often oscillate between full idle power.

Hannah flies a Super Decathlon and wants to make sure she takes care of it while doing aerobatics. Colleen says to keep it under 6Gs and a close eye on the engine mounts because they are the flexible attach point between the engine and the airframe. Although Hannah was originally asking about general tips, the hosts find out that she has experienced a governor failure that spewed out almost all her oil. Mike asks about rpm overspeed and Hannah said she noticed that used to happen before the governor failed. She’s also seen a drop in oil pressure in the dive. If her inverted system isn’t working well it would starve the governor of oil.

"EGTs are imaginary numbers" Jun 01, 2022

Show notes

Oil all over the nose, cylinders that are too clean, and bush propeller repairs. Mike, Paul, and Colleen handle it all this month. Submit your questions to podcasts@aopa.org for a chance to be on the show.

Adam wonders what to do after a prop overhaul left him with a huge puddle of oil and some shaken nerves. His plan is to remove the newly overhauled prop and send it to the manufacturer. Paul questions whether it was an install error because a seal between the shaft and the prop seal can be broken during the install process. Mike agrees and thinks the manufacturer won’t find anything wrong.

Mike has a Cessna 150 with a 150 horsepower upgrade. He said the seller recommended not running it on Autogas because Lycoming never approved it. Mike says check Lycoming service bulletin 1070AB. It lists which fuels are approved for which engines. Paul correctly makes the point that the whole point of the STC is that it enables you to do things that the manufacturer wouldn’t necessarily have allowed. Mike said so long as there isn’t an operating limitation for specific fuels, you don’t even need the STC. Buying the STC gives you a flight manual supplement and placards.

Lyle has concerns about his oil analysis and how it relates to the way he operates his Cessna 182. After an engine reman his chrome levels were going up, but are now coming down. His mechanic was concerned he was flying too lean because everything on the borescope looked too good. The hosts describe the ideal leaning procedure as this: Don’t look at any gauges. Lean it until it starts running a little rough, and enrichen it only until it smooths out, and no more. He also has high silicon levels, which Mike attributes to a carb heat door that isn’t sealing fully. Lyle further wonders about his exhaust gas temperatures, which Paul and Colleen remind him are irrelevant. EGTs are only useful for looking at trends, according to Colleen. Mike said it’s not a measure of stress on the engine—only a measure of how much energy is being thrown out the exhaust.

Dewayne has an exhaust leak in his Tripacer. The two pieces of exhaust come together with a clamp, and a test shows it to be blowing more than bubbling. Paul said you can generally ignore leaks that only bubble, by blowing leaks need to be fixed. He recommends an expander and working very slowly to try and get the two pieces to better match. You can only push it about a thousandth of a inch, Paul said.

Rowan asks how to know when a knick or dent in a propeller becomes unsafe to fly. We all check our props before we depart, but few of us have a guide to know whether prop damage is normal or unsafe. Paul said a good rule of thumb is that if you run your fingernail along it and it catches you need to address it. But if it just runs along roughly, but doesn’t catch, it’s ok to continue. But, that’s not an owner-approved repair. Mike said the problem is that they create a stress point. A sharp point at its apex is more worrisome than a rounded dent. Advisory Circular 43-13 Chapter 8 Section 4 gives details for mechanics on how to deal with knicks, and it’s actually a pretty generous standard.

Chris can’t fly as much he’d like, and he wants to know if he should risk a ground run if the airplane has been sitting but he doesn’t have time to fly. Water being a byproduct of combustion, a short flight can be more detrimental to a flight than letting it sit. If the moisture doesn’t boil off it only adds more moisture to the engine. Mike said where Chris lives on the Gulf Coast, he would buy a dehydrator. There’s no hard and fast rule on how long is too long to go between flights, but the hosts say once every few weeks is fine, and try to keep it to less than a month.

"Use the TLAR system. That looks about right" May 01, 2022

Show notes

From the seemingly benign--what tire ply to use--to the extreme--hitting 500 degrees on a cylinder--Mike, Paul, and Colleen face it all this month. And we mean all, like Ron's 172 that produces a loud bang exactly two minutes after shutting down. Submit your questions to podcasts@aopa.org

Full notes below:

Larry has a turbonormalized Beechcraft Bonanza. When it came time to replace his tires he decided to go to with 8 ply, but he later researched and found the type certificate specified 6 ply. The Goodyear spec sheet seemed to indicate he would be over the weight limit on 6 ply. Paul said the older lighter Cessna 210s were 6 ply, but were upped to 8 ply later on. He suggests it’s ok to go up in ply if the dimensions are the same. Colleen also admitted she went from 4 to 6 ply on her Cardinal at the last tire change. Mike says if Larry is in violation by using a higher play, then he is as well. He mentioned a recent tire supply problem that prompted him to go up in ply.

Randy bought an engine without logbooks that was intended for a Cirrus SR20 in Guatemala City. He’s wondering if he can put it in a Cessna 175 or Skymaster. Colleen brings up the lack of AD compliance data. Some ADs are for internal engine parts that can only be verified with paperwork or by opening up the engine. Ultimately Paul said it’s up to the mechanic who has to hang the engine and whether he or she is comfortable with its AD compliance status. Mike said from a safety standpoint he would want to pull the lifters and look at the camshaft. And he would pre-lubricate everything, including the cam while the lifters are out. If it’s not making metal within 100 hours, you’ve dodged a bullet.

Tom is wondering how to tell if his engine with a constant speed propeller is producing full power. At sea level he has 29 inches of manifold pressure with an ambient pressure of around 30 inches. All the hosts agree that this sounds about right, given that you’ll lose some pressure through the intake and other areas.

Jeff has a Cessna Cardinal with a recently installed electronic engine monitor. He saw on climb-out near El Paso that the cylinder head temperature on the third cylinder topped out around 500 degrees. Now he’s wondering what to do. Compressions are excellent and the oil analysis is good. He also fixed the baffles, which fixed the problem. Mike suggests borescoping the piston. Failure points would be corner melting or the pockmarked appearance of detonation. If the piston looks ok, you’re probably fine, he says.

Ron has a 172 that has an unusual problem. Every time the fuel level is below half, and two minutes after engine shut-down, there’s a loud bang. It sounds like someone hit the top of the wing with a bat, he said. Paul thinks it’s possible the tank is being overpressurized, and the reason it takes two minutes is because the weep hole is so small that it takes that long for the tank to equalize. He suggests quickly depressurizing after landing by taking off a fuel cap and seeing if air rushes by. If the tank vent tube is in the wrong position it can cause the overpressurization.

Robert has a Cherokee 140 that is burning about a quart of oil per hour. Mike said oil consumption is always a cylinder problem, but not always a problem with all cylinders. Borescoping the cylinders may help identify oil pooled in one particular cylinder. Oil consumption comes from three sources--crankcase compression, which will show as oil out the breather tube. Burning oil will show as soot on the airplane. Or there could be a leak. Paul suggests a ring wash to further identify the problem cylinder, and potentially solve the issue. A detailed explanation is available at bit.ly/solventflush

"Your airplane may look like the molting hide of an animal" Apr 01, 2022

Show notes

This month Mike, Paul, and Colleen tackle questions about inexpensively improving aircraft paint, cylinders that are too cool, low compression readings, and a magic floatplane that burns less fuel with its floats fitted. Plus, the ultimate stumper, an airplane that can't turn left. Submit your questions to podcasts@aopa.org

Full notes below:

Eric has a Pitts with an unusual problem. When he turns left the engine starts to sputter, and when he turns right the rpm increases. They initially suspected the flop tube in the header tank. Although it looked to be in good shape they replaced it anyway. They also overhauled the wobble pump, and carefully inspected all the fuel lines. There were no obvious problems. Colleen reached out to Pitts experts. They suggested making sure the fuel divider was properly bled. Eric is pretty sure it’s not vapor lock. “It has to be the flop tube,” Mike and Colleen say. Another theory Eric and his mechanics came up with is the fuel controller. They sent it for service, and the shop found that the throttle body mounting hole had a little rounding from vibration damage. They thought that maybe turning opened it to allow in more air, leaning the mixture. Once he gets it back, Eric is planning to do a test flight.

Doug is looking at his paint job, and while he knows that paint is an important protector, he’s trying to avoid a costly and invasive full repaint. Paul said you can absolutely go in and touch it up yourself. You can use a touch-up brush, sprayer, or anything you like. Colleen said that the vast majority of the work is in prep, and that the paint color will never match because the original paint will have faded. “Be careful and measured,” she said. Mike said to make sure the aluminum is clean and corrosion-free prior to applying the paint. Paul suggests Scotch Brite and Alumiprep (https://www.aircraftspruce.com/catalog/cspages/alumiprep.php) and Alodine (https://www.aircraftspruce.com/catalog/cspages/alodine1201.php) to make the primer stick. Get an automotive paint person to help blend the colors, he said. And Mike says to make sure you don’t sand through the thin layer of Alclad.

Andy wonders if his IO-540 is running too cool. His cylinder head temperatures only top out at 310 degrees, which he's reading on an Electronics International engine monitor. Mike said EI makes two probes for their engine monitors, and the P-100 always reads low because there’s an air gap at the cylinder head probe that makes it artificially low. The only downside of running too cool is potential lead scavenging. Mike said to pull the spark plug and use a borescope to look at the exhaust valve stem. If there isn’t deposit build-up, then there’s nothing to worry about. But lots of lead means you have to somehow increase the temperature.

Tom is worried about his compression readings. His O-320-D2G had a cylinder of 38/80 only 18 hours after overhaul. Two more cylinders are reading a little low now at 100 hours. He thinks all of them are leaking a bit, and have gotten slightly worse. He expects them to get to the low 60s, and he’s worried that when he wants to sell, buyers will baulk at the numbers. So he’s wondering if he should just replace the cylinders now so he never has to worry about it. The hosts all agree he is overanalyzing and should monitor as normal, keep flying, and work on the cylinders only when it’s required.

Jeff has a Cessna 180 floatplane and a new fuel flow meter has him thinking. He’s wondering if the performance charts are based on tach time or clock time. Paul assumes that because the tach was the only instrument they had when they certified the airplane, it has to be tach based. “They had clocks when that airplane was built,” Colleen says. She and Mike are sure it’s clock time. Jeff also wonders why his float supplement shows fuel flow lower than the original handbook. With a difference of only .2 gallons per hour, Mike says they are effectively the same number, and not to worry about it.

"We don't check the accuracy of your fuel gauges" Mar 01, 2022

Show notes

You may think an annual inspection includes a verification of the accuracy of your fuel gauges, but you'd be wrong. Nor does the IA check the accuracy of your tach or any other number of instruments. This information comes to a pilot undergoing a first annual. Mike, Paul, and Colleen also tackle oil loss and temperature issues, why we stop our engines with the mixture, and the difference between a major and minor alteration. Submit your questions to podcasts@aopa.org for a chance to be on the show.

Full notes below:

Chuck flies a 1941 Interstate Cadet with a Continental 85-8F engine. He had a prop strike four years ago, was inspected and got some new rings, gaskets, and a few other parts. He’s noticed he goes through a quart every four or five hours, compared to 15 hours prior to the overhaul. Mike suggests there may have been a problem when honing the cylinders, and Colleen suggests borescoping to see what the honing looks like now. Paul said a normal honing crosshatch is about 30 degrees, but that on a teardown they use a ball hone that doesn’t make a regular pattern. If it’s at all shiny it means they’re glazed. But ultimately they all agree it doesn’t matter and that it’s an acceptable amount of oil loss.

Tom is a new mechanic who is looking for advice. A friend asked him to install a new stall warning horn to augment the stall warning light in his Cherokee. Paul suggests looking at a newer version of the airplane with a horn and a light, and submitting that information as approved data to the FAA. FAR 1.1 defines a major versus minor alteration. Advisory Circular 43-2B is acceptable methods for aircraft alterations, which Collen calls the bible of alterations. Mike makes the point that it’s a mechanic’s decision as to whether an alteration is major or minor. A major requires someone else’s signature, such as a field approval or FAA sign-off, while minor is only the mechanic’s signature.

Jay flies a Mooney with M20F with an IO-360 with a JPI engine monitor. The oil temp probe is located near the first cylinder. On climb it hits 230F and trips the over-temp alarm. In cruise it stabilizes at 195F. The analog probe shows 30 degrees cooler. The hosts aren’t at all surprised that the probes are different. Colleen mentioned that when she changed engine monitors they moved the probe and her oil temps have gone down. Mike said our goal is to usually measure the oil temp at the coolest location.

Peter has a Cardinal and is going through his first annual. He is wondering where the accountability is for previous mechanic oversights. His IA has found things like airworthiness directives that haven’t been complied with, a bucking bar left in the airplane, and so on. Mike makes the point that there is a difference between airworthiness discrepancies and things that are more discretional in nature. And all three hosts caution that each annual and pre-buy inspection are unique, and that it’s impossible to snag every discrepancy.

Walter asks why we don’t just turn off the key when stopping a traditional piston airplane engine. The hosts agree that it is solely a safety consideration, and meant to get gas out of the system. That way an ungrounded mag can’t refire the engine and create a safety issue with the propeller.

Rolf has a TB-20 with an IO-540 engine that’s never been overhauled and is trouble-free. Last year he noticed on the engine monitor traces that the number 1 and number 2 EGTs were very low at low fuel flow. His shop measured the dry tappet clearance and found the intake valves were well in excess of the limit. They were able to bring them within limits, but the EGTs are still bottoming out. Mike makes the point that the valve clearance limit is only to ensure that the amount of play in the system so that the hydraulic lifter can “take it up.” The hosts agree his engine is in fine shape, and not a safety issue. They do recommend he prepare for an overhaul in the future based on the symptoms.

"You'll ruin a set of clothes for sure" Feb 01, 2022

Show notes

This month Mike, Paul, and Colleen talk fluids. Danny has an oil leak, Steve has a fuel leak, and Jeff is puzzled by guidance on which oil to use. Plus, a question from a maintenance newbie, looking ahead to overhaul, seeing double on batteries, and a pesky propeller governor problem. Submit your question to podcast@aopa.org for a chance to be on the show.

Full notes below:

Dash has a T-34 and is wondering about the implications of having two 12-volt batteries in series, rather than one 24-volt battery. Paul says one battery is simpler and less costly to maintain, but two 12-volt batteries in series can generally push out more current. You can treat them as one 24-volt batteries and use the applicable trickle charger, Mike says. To do this you would take a 24-volt charger and treat them like one battery, Colleen says. Take the cables and hook up the positive from one battery and the negative from the other battery. They all cautioned to make sure not to hook anything to the short, stout cable connecting the two batteries. Dash also says a mechanic at his airport told him not to continuously charge the battery because it will reduce capacity, but the hosts say that’s bad advice and that a trickle charger can be on the batteries all the time.

Danny has a continuously oily windshield on his Bonanza, which he thinks might be coming from the top of the case. The engine has 2,200 hours and looks great on the borescope, and he’s hoping an overhaul won't be necessary. Paul said he definitely wouldn’t pull an engine for this. He goes straight to the crankshaft seal as the offender. Mike thinks the o-ring that seals the prop to the flange is another good culprit to check. Mike said oil coming from the top of the case would go on the back baffles and other spots inside the baffles, not on the windshield.

Chris has an O-540 on a Cherokee 6, and although the engine is still running strong, he’s planning ahead and wondering if a rebuilt or overhauled engine is better. Mike said this is the worst time he’s ever seen to do anything to an engine. Colleen said she thinks people are risk averse and she’s always overhauled engines and has been very happy. Mike said the only reason to go rebuilt is if you know you have to replace a major component or if you want to minimize downtime.

Mahesh is looking for resources to become better acquainted with managing the maintenance on his Cirrus. The hosts recommend the Cirrus Owners and Pilots Association seminars, owner-assisted annuals, and Mike’s books https://www.amazon.com/dp/B08KHDPPWG?binding=kindle_edition&qid=1643661371&sr=8-4&ref=dbs_dp_rwt_sb_pc_tukn

Sebastien and Tim have a Murphy Super Rebel with a governor problem. The propeller wanders 35 rpm up and down, and they’re wondering if it’s a problem and how to fix it. Colleen suggests checking the integrity of the rod end to the bell crank.

Jeff has a Lancair and wants to switch oils, but Continental Service Information Letter 19-04 that says operators shouldn’t change oil until the engine is overhauled. The hosts all agree that this was a misguided document, and that switching oils will have no determinantal impact to the operation of the engine.

Steve’s Piper Lance is weeping fuel and he is wondering how critical the problem is. His A&P said he could take the tanks out to have them resealed, but all agree that this isn’t necessary. Paul said the Piper maintenance manual and FAA maintenance advisory circular have a good chart to show the various fuel leaks and what to do about them. If it’s not leaking bad enough to pull the tanks he said it’s probably not worth doing anything.

"It's not our job to be the safety police" Jan 01, 2022

Show notes

Mysterious metal in the filter, reporting an owner to the FAA, when to change ELT batteries, and the elusive perfect hot start. This month Mike, Paul, and Colleen handle some of the toughest questions in aircraft ownership. Submit yours to podcasts@aopa.org for a chance to be on the show.

Full episode notes:

Brian asks how one is to know when the ELT battery runs for more than an hour or has reached 50 percent of its life. FAR 91.207 requires replacement on these conditions. Short answer: you don’t. The hosts point out that the batteries can’t be load tested and there’s no outside monitor to know how long they may have been active. So, if in doubt, replace them.

Ryland wants to know if he can install a non-certified engine monitor in his certified airplane. Mike breaks down the decision tree that leads to an answer with an extreme example—installing a refrigerator in your airplane. You must show it meets the same certification requirements the aircraft had to meet. As Mike said, you have to jump through the same hoops that the manufacturer would have had to do had it decided to install one at the factory. First you must decide if it’s a major or minor alteration. A major requires approved data, which means getting an FAA field approval. If it’s a minor alteration the technician must make the determination that it meets all the applicable certification standards. Most difficult of which is that it doesn’t interfere with other systems in the airplane. Most mechanics won’t take it upon themselves to do that, he says. Colleen said she has gone through the field approval process and it’s quite difficult.

Richard wonders if he’s damaging his engine by keeping the rpm below 800 on initial startup. He flies a Cessna Skylane with a Continental O-470. The hosts agree that Richard is overthinking this a bit and there’s no risk of damage at operating at such a low rpm. Mike said he would use roughness as the lower limit.

Justin asks about his responsibility to report an unsafe aircraft to the FAA. After an alarming pre-buy inspection of an airplane he decided not to buy, he’s concerned another potential buyer may be at risk. Mike, Paul, and Colleen have strong feelings about this issue. Paul said a pre-buy isn’t an annual inspection, and it’s the owner’s responsibility to ensure airworthiness. This is the only person you should report the findings to, he said. As a follow-up Justin mentions an airplane he was asked to ferry that had a hole in the bottom of the wing. Mike explained the four entities responsible for airworthiness--the factory when the airplane is built, the owner, a mechanic one day a year at the annual, and most critically, the pilot in command.

Tim asks aviation’s most difficult simple question—how do you consistently hot start a big bore fuel-injected engine? As a CFI his normal advice to clients is to use the technique that works best for you in your airplane. In his Cirrus Paul goes throttle and mixture forward, fuel pump on until the fuel pressure stabilizes, then everything back, throttle cracked, and mixture slowly increased while cranking the starter. He uses this for hot or cold starts. Mike suggests priming and cranking simultaneously. Paul mentions a technique of running the boost pump on high for at least 45 seconds while the mixture and throttle are at idle cut off, and then performing a normal start. This circulates cold fuel in from the tank.

Jared is the maintenance officer of a flying club with a Cessna 172M. They’ve been finding metal in the oil filter that doesn’t look like that from normal sources. Lycoming couldn’t find it, and neither could the shop that did the overhaul 600 hours prior. The overhaul shop did warranty work, including replacing the crankshaft. It didn’t work. Jared had sent in photos and Mike didn’t think they looked like crankshaft issues. Paul thinks the oil pump is a strong suspect. But overall the hosts are stumped, and Jared promised to come back later with an update.

"That little cap doesn't hold the wings on" Dec 01, 2021

Show notes

Ever wonder what you're looking for when you preflight a Cessna with those small oil doors? So did our caller this month. Mike, Paul, and Colleen also field questions about a burned valve, winterizing for cold-weather ops, how to do an in-flight magneto check, and whether you'd really run out of fuel before oil with a leak in the gauge line. Submit your questions to podcasts@aopa.org

"Only a CFI would ask a question like that" Nov 01, 2021

Show notes

This month Mike, Paul, and Colleen dive into questions about valve failures, tracking engine times, aging engine accessories, and worrying cylinder head temperatures. Plus, a question that could only come from an instructor.

"Compression readings are garbage" Oct 01, 2021

Show notes

This month Mike, Paul, and Colleen tackle everything from radio gremlins to the big questions of aviation, such as an overall maintenance philosophy and the reliability of our aircraft. Send your questions to podcasts@aopa.org for a chance to get on the show. And please take our survey to tell us how we're doing. You can find it at https://aopa.az1.qualtrics.com/jfe/form/SV_cZSqTKSpaOTVjdI?Referral=APS

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