Ask the A&Ps

How do you fix a fix? Mike, Paul, and Colleen explore STC challenges, including parts, wrong installations, and ADS-B that isn't working. Email [email protected] for a chance to get on the show. Join the world's largest aviation community at aopa.org Full notes below: Barat has a Cirrus SR22 with an STC air conditioner. The driveshaft recently broke and he’s wondering how to fix it. Some mechanics he’s spoken to won’t use alternative parts, but others will. Mike said it’s not unlike altering the original type certificate. The question is whether your alternative to the supplemental type certificate is major or minor. Mike and Paul agree that it sounds like a minor alteration because the parts are now available from Cirrus, based on the STC that Barat had it installed previously.   Kevin has an LX7 with advanced avionics. A month or so after a trip through the Southwest, he got a letter from the FAA saying his ADS-B wasn’t functioning properly. He’s wondering how to know whether or not it’s working. Mike said he thinks this problem is similar to the transponder question. Even though there’s a reg that requires that an installed transponder be on and functioning, there’s no way to know if that’s the case, other than an ATC report or during a 24-month check. The hosts suggest you could do the same with ADS-B, requesting a report from the FAA on a periodic basis.   Byron has a Cessna 170 that he purchased three years ago. The airplane came with vortex generators that were installed incorrectly. Byron is wondering what he should do next in terms of holding the original installer accountable. The hosts caution him on going to the FAA because they can’t investigate halfway. Mike wonders whether the FAA would actually go after the mechanic, since it’s not a safety of flight issue. Paul thinks making an honest mistake is usually let off from the FAA with minor infractions.

Mike, Paul, and Colleen are in the hot seat as they answer live audience questions from Airventure 2025. We'll be back with our regular show next time. Email [email protected] for a chance to get on the show. Join the world's largest aviation community at aopa.org/join

How to tell the difference between greases? Mike, Paul, and Collen break it down, plus high lean of peak temps, breaking in an engine on an experimental, and composite airframe cracks. Email [email protected] for a chance to be on the show. Join the world's largest aviation community at aopa.org/join Full episode notes below: Mark wants to make sure he’s clear on which grease to use for which application. The manuals call for specific greases, but there are allowances for those with equivalent specs. But Mark wonders how to determine whether another grease is equivalent. Paul said you need to find the spec sheet for the grease the manufacturer recommends, and the spec sheet for the grease you’re thinking of using to make sure they more or less match. He also mentions Hartzell’s guidance that you can move up in grease numbers, but not down. Paul also cautions Cessna owners not to grease their flap tracks. They’re not meant to be greased, although the rollers are supposed to be lubricated. Grease Options March 24 2022, David Prizio, Kitplanes:  https://www.kitplanes.com/grease-options/#:~:text=If%20your%20plane%20lives%20on,05%20and%20GN%2015%2C%20respectively   For a full grease cross reference chart: EMTC https://emtc.aero/wp-content/uploads/2021/01/Mappe2.GREASE-XREF-1.pdf From the LPS product application guide: https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://pdf.directindustry.com/pdf/lps-laboratories/application-guide/11942-89226.html&ved=2ahUKEwjYgbmQiIiOAxVHHTQIHS21OzQQFnoECB4QAQ&usg=AOvVaw0KD4UOmbKMMo-0_4cGPymS Todd has a 2008 Cessna 400 that he just took delivery of. The airframe around the windscreen has a few little cracks that look like spider cracks. He’s read that there’s been an issue with this area and he’s wondering how much it matters. Paul said Todd is seeing cracks in the filler, and the expansion and contraction rate of it is different than the structure, which causes the cracks. Cessna apparently said back when it was built that they were working on a warranty repair for this area, but never did so.   David is wondering how to break in a new engine on a new experimental airplane he’s building. He has the engine now pickled, waiting for the airplane to be finished. Colleen did some research and on the Van’s forum someone posted a poll asking how people balanced engine break in. Some mentioned not doing the stalls on the initial flight, and they decided to prioritize the engine break in. Mike said high power ground runs are fine during break in. Low power or long idling can glaze the cylinders.   Jason is worried about his lean of peak temps on his B55 Baron. With the cowl flaps closed and a relatively warm day outside, he can’t keep one of his cylinders below 400 degrees. He’s done the Savvy flight test profile, and Savvy told him that the GAMI spread is acceptable and suggested checking the baffling. The first thing the hosts tell Jason to do is not compare the two engines. It’s irrelevant data. They focus on the baffling, even though Jason’s mechanic said it looks good. Paul said he’s seen cases where the baffling is wavy, which requires a slit be cut so that it lays flat and incoming air flow pushes it against the surface next to it (usually the cowling). After taking a deeper look, the hosts also suggest swapping probes to see what happens.

Mike, Paul, and Colleen explain why they almost never set their parking brakes. Plus, valve guide concerns and gotchas on preflight. 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: William wants to know how Mike, Paul, and Colleen do preflight inspections as A&Ps, and if they look at something that most pilots don’t. Colleen said she always checks the last thing she worked on. She suggests to look really carefully at any work that’s recently been completed. Paul mentions the nut and cotter pin on the trim tabs on Cessnas, especially after maintenance. Mike said he worries if the airplane has been moved while on the ground for things like tow limits. Paul also said to check nests, pitot covers, and fuel vent covers for bugs, dirt daubers, etc.   Michael is wondering what’s wrong with his parking brake. When he first bought the airplane, the parking break worked to hold the airplane, but wouldn’t release without touching the brakes again. Now, after some work during annual, if it’s anything more than an idle, it won’t hold. Paul said he only ever sets the parking brake to get out and set the chocks. There are only two possibilities, the hosts say. IT’s either mechanically mis-rigged, where the valve isn’t cutting off the line completely, and the other is that the valve is leaking. Paul said the system is simple. You hold the brakes, and the valve pinches off the line.   Joey has a Cessna 150 and he does a lot of his own maintenance. About a year ago he had a stuck exhaust valve. A local mechanic did the rope trick to free the valve. He cleaned the exhaust valve guides, although not thoroughly enough. He had planned to do it every 300 hours. He and his wife were flying a few months later, got another stuck valve, and thankfully were able to make a safe emergency landing. He tries to fly very lean, but it happens so often he’s wondering what else he can do. Paul said to definitely ream all four cylinders. Joey is planning to do it every 300 hours at this point. But it takes a full day and he’d like to do it less. Unfortunately the hosts don’t see a way around it until he can run unleaded fuel. He might try a lead scavenger like TCP, they say.

Oil is everywhere this time, with consumption and temperatures problems for three of our owners. Email [email protected] for a chance to get on the show. Join the world's largest aviation community at aopa.org/join Full notes below: Mark has a Twin Comanche and is loving his new electronic ignition. He has an issue where oil temperature and CHTs are slightly different on one engine than the other. His oil temperature also spiked on one climbout on a hot day, and he’s wondering what’s wrong. He’s using the variable timing. Nothing like this happened prior to the ignition install. Paul suggested that maybe some baffling changed during the install. The hosts narrow in on either airflow or oil flow as the culprit. Colleen said to think of baffling not as trying to direct airflow across the engine, but a system that creates a high pressure, pushing air through the cylinder cooling fins.     Chris is wondering what’s wrong with his new engine. He has a Cessna 206 and he put in a new Continental IO-550. After some initial runs, but found that it was burning about a quart of oil per four hours. On one flight is running a bit rough. It had turned out to be a failed magneto. They added an air/oil separator, which obviously didn’t help. He did some low level, high power runs that didn’t seem to help. At 100 hours he did a ring flush on Savvy’s recommendation. The ring flush seemed beneficial. Then after 10 hours he had only burned a quart. They are now at 150 hours and they are at a quart every 4 or 5 hours, and they’ve done another ring flush and it’s burning less oil again. He’s wondering why the rings are clogging up. Mike immediately zeros in on the problem by asking how long Chris has been running straight weight oil. He admits it was 150 hours on the advice of his mechanic. AD oil helps to prevent sludge build-up.   Willie is wondering if you need an A&P to do an AMOC, or alternative method of compliance with an AD. The hosts describe the process, which can be completed by any “operator” meaning owner. So, one need not hold an A&P to request an AMOC. Most AMOCs apply only to the operator, although Mike said a manufacturer can develop a global AMOC that would apply to everyone.   Steve was flying his Cessna 182RG with a Lycoming O-540 that he recently top overhauled with all new cylinders. He flew low and at high power to break them in, and oil consumption stabilized. He flew another 15 hours on regular oil and Camgard with virtually no oil burn. Then on a flight he was asked to slow rapidly on approach, and on that one flight he lost oil at a rate of three-quarters of a quart per hour. The consumption eventually settled at around a quart every 2.3 hours. He’s wondering if ring flutter is real and whether it caused the increased oil consumption. He didn’t notice excessive oil on the airplane. A ring wash didn’t fix it. He eventually decided to just overhaul the cylinders again. On inspection they didn’t find anything. Mike would have suspected a broken ring or expander spring. Paul wonders if the piston rings were wrong for the nickel cylinders Steve had installed. Unfortunately, he found a broken stud at 20 hours on his new cylinders. They hadn’t properly torqued 4 of the bolts on his cylinders, reinforcing Mike’s point that sometimes it’s better to leave cylinders in order to avoid maintenance induced failures.

A Cirrus with fluctuating fuel flow, de-injecting an engine, and fear of overhaul are on tap for this episode. Email [email protected] for a chance to get on the show. Join the world's largest aviation community at aopa.org/join Full notes below: Joe has a Maule with a 540 engine in it. The company has a mod to turn the engine to a carbureted version and he’s wondering about the legality of something like that. Paul said it happens in the 210 market. Whether it’s a good idea is another issue, the hosts say. Joe is unable to run autofuel is the injected version, which is why he’s interested in it. Colleen said she’d rather have an injected engine than run mogas.   David wonders how perspective owners are so afraid of TBO. He has a 182 with an engine that’s nearly at TBO, and people who contact him are afraid of the high time. The hosts discuss strategies for buyers who may be looking at airplanes with engines at TBO. Assuming the engine is running well, a new owner can fly it on that “borrowed time” while they learn and enjoy the airplane. Alternatively, if the engine truly needs to be overhauled, the time down is obviously a concern for a new owner. Mike said he thinks it’s best to buy an airplane with a run-out engine. The price has been discounted for the cost of the engine, the seller is motivated, and worst case you have to overhaul it soon. And every hour and year that you don’t have to overhaul it is “free.” And when it does come time to do the overhaul, you get to do it to your spec.   Shalom has a Cirrus that isn’t behaving. If he sets the mixture at lean of peak, the fuel flows start to fluctuate. A few minutes later, it will drop off sharply, and then back quickly. The manifold pressure and rpm stay pretty consistent. He’s changed the fuel pump and the spider. Nothing has helped. Mike said if there’s a constriction in the fuel line between the fuel control unit and the manifold, it can cause oscillating fuel flow and lower flows.

An owner wants to fly his engine after it sat for 7 years. Plus, prop strike at the shop, lean of peak, and break-in trouble. Email [email protected] for a chance to be on the show. Join the world's largest aviation community at aopa.org/join Full episode notes below: Rupert is having trouble breaking in his new cylinders. They have five hours and the temperatures are still trying to go above 420 degrees on departure. They’ve checked fuel flow and baffling. In a twist of irony he is causing his cylinders to run too hot because the break-in is being prolonged because he won’t run the engine hard enough. Paul said Comanche’s have notoriously have poor baffling, which can also compound the problem. They recommend running it hard for a few hours and not to worry about the temps being around 420.   Craig has a Pitts that was damaged on a high-power run-up after his annual. The tail came up and hit the prop. He’s wondering if there’s something else they should inspect since the case is going to be open. His crank is subject to an AD. The associated service bulletin requires replacement if the case is opened, but the AD does not. He said the insurance has agreed to replace the crankshaft anyway. They said other than close cylinder inspections, it sounds like he’s fully covered.   Larry was finding that the lean of peak indication on his Dynon would show that he was lean of peak before the cylinders were actually there. He found a short paragraph in the manual that says if he changes the horsepower percent rating, it works fine. He also describes a procedure in the Dynon that basically recreates the GAMI lean test. Mike describes how Savvy does the AI engine modeling. The amount of air or fuel going into the engine will be the limiting power factor. In rich of peak, fuel is abundant, so air is the limiting factor. In lean of peak, fuel is the limiting factor.   Dave last ran his engine 7 years ago. He mixed oil and camgard, put it into a pressurized tank, and sprayed it under pressure into every place he could. He’s changed desiccant plugs, and had a dehumidifier running as well. If he has pitting he’s wondering if it’s dangerous to fly. Paul said airplanes don’t fall out of the sky because of pitting on the camshaft, and Mike added that they do fall out of the sky after taking off cylinders to look for signs of corrosion. Either the engine will make metal in the filter or it won’t, he said. If the filter is clean for the next 100 hours he dodged a bullet. Nothing that could be wrong corrosion wise is a safety of flight item. It’s a safety of wallet item. Paul said he would recommend changing the oil soon after running it. If the cylinders don’t look corroded the bottom end probably isn’t either, Mike said. Paul suggests he crank the engine with one set of plugs inoperative until he gets an oil pressure indication, and then start it normally.

Valves are sticking all over as the hosts give advice on how to avoid pulling cylinders. Send your questions to [email protected] for a chance to be on the show. Join the world's largest aviation community at aopa.org/join Full notes below: Rick has a 182 with a new Pponk engine and he’s burning lots of exhaust valves. He’s wondering what he should change operationally. Paul said to borescope more frequently to find the asymmetric burn patterns before they need to be replaced, and if they start to have asymmetric patterns to lap them immediately. He recommends borescoping every 100 hours. Mike gives some initial results of Savvy Aviation’s borescope initiative, which after 100,000 images found that 7 or 8 percent of valves showed signs of heat distress. Twenty five percent of the engines had at least one valve that was heat distressed. About 85 percent of those valves were in the early stage of distress and could be lapped. Only about 15 percent were considered late stage.   Brad has an SR22 with an IO-550 that had high oil usage. They pulled a cylinder, rehoned it and put on new rings. Later he started asking questions about torquing the through bolts, and the shop told him they held a wrench on the other side, but didn’t torque both sides. He’s wondering if he should go back and retorque the bolts. Mike and Paul think he’s probably ok.   Bruce is sick of sniffing gas fumes. They installed new fuel senders and a digital fuel gauge in their 172. They followed the procedure to calibrate the fuel senders, but he’s having trouble getting it correct. He’s as much as two gallons off from what it should be. Paul starts by asking what bucket Bruce is using because the utility buckets from the home stores are unreliable as calibrated containers, he said. The other issue is the wet wing construction, which can lead to dams that make it difficult to fully defuel or refuel. Bruce has even accounted for temperature. He’s within half a gallon on one side, which Paul said is usually as close as you can get it. Ed is stirring the pot. He read that in an article in the American Bonanza Society publication that operating lean of peak is bad for engines. Obviously the hosts disagree, and a discussion of the merits of rich of peak and lean of peak ensues.

It's all engines all the time this episode. Rusty ones, sticky ones, and one that doesn't burn oil. Email [email protected] for a chance to be on the show. Join the world's largest aviation community at aopa.org/join Full episode notes below: Ralph had to throw away his relatively new engine. His flying club has a 1968 Cherokee 180. They overhauled their engine, and the first annual looked good. On the second annual and after only 100 hours of flying, they had a stuck valve. Digging in they found extensive corrosion. Now past a second overhaul, they want to ensure it doesn’t happen again. The hosts focus on how much (or little) the airplane flew with the new engine. 50 hours a year isn’t much, especially if they weren’t regular hours. An hour a week is great, for example, and something like 4 hours once a month is worse. They advise Ralph use camgard, fly more often, hangar it, and use an engine dehydrator.   Adam has a Cirrus SR20 on leaseback to a flight school with only 500 hours on it. A student was taking off, and around 900 feet they heard a bang, and experienced partial power and a loss of oil pressure. Lycoming took the engine back for an inspection. Sticking valves caused it to throw a rod. Mike said Lycomings often stick valves, and it’s something that should be expected. The manufacturer recommends a wobble test per Lycoming Service Bulletin 388C every 400 hours in airplanes and 300 hours in a helicopter. You can go a thousand hours with the new valve guides. Mike stressed that it’s also very important to be trained to detect morning sickness, which is usually the first sign of a valve sticking problem. If a cylinder doesn’t light up with the others on a cold start, or feel rough, it indicates valve sticking and the engine should be shut down right away and examined by a mechanic. Colleen suggests having an eagle eye on the engine monitor during the first startup of the morning. Mike said leaning aggressively, especially on the ground, can also help. Adam asks if Lycoming’s recommendation to run the engine up before shut down in order to clean the valves actually does so. Mike thinks it’s just inconsiderate of those around you, and maybe not terribly helpful.   Jason runs mogas on his Cessna 182. Last year he was climbing through about 8,000 feet and the engine started to stumble. He added carb heat and a few other things, but the engine seemed to come back to life on its own. His Savvy account manager said it was probably vapor lock. Mike agrees with the account manager that the airplane was exhibiting vapor lock symptoms. He thinks it’s possible that a fuel line might be close to the exhaust or something else is warming the fuel before it gets to the carb. Paul suspects it might be the fuel line to the JPI engine monitor transducer. They recommend wrapping it the fuel lines in fire sleeve to see if that improves the problem.   Thad has a 1977 Cessna 182Q. He had the engine rebuilt in 2021 and since then it has been “a rockstar.” He thinks it might burn too little oil. It’s only burning about a quart every 50 hours. It makes more chromium and aluminum than the lab is happy with. He wonders if the lack of fresh oil is somehow concentrating the contaminants. It’s possible he’s not getting enough lubrication on the cylinders, Mike said. The chromium can only come from the rings and the valve stems. Usually the problems with the valve stems come combined with increased nickel because they are made of an alloy. Mike said the aluminum in his report is ok, although slightly high. Thad said they’ve borescoped the cylinders and everything looks good. There’s still cross-hatching on the cylinder walls. The hosts are intrigued, but Mike thinks it’s faulty thinking. They debate how much metal stays in suspension though the process of adding quarts. Mike suggests keeping an eye on the filter, but otherwise to keep flying.

Chris is trying to make sense of his logbooks. He has a Cessna 172 RG and he and his partners had a few electrical issues recently. Some of the logbook entries went in the airframe book and some went in the engine logbook, and he’s wondering about the decision-making process involved in picking the proper logbook. Mike said there’s no requirements around which entry to put in which logbook, and in fact, there’s no requirement to have a logbook in the first place. It’s easier and retains the value of the aircraft, of course, but the need to keep a specific logbook isn’t based on regulation. The reason we use different logbooks, he said, is because if we were ever to sell the engine separately from the airplane, it would be nice to be able to include the record in the sale. If the item would move with the engine, put it in the engine logbook. Paul said his shop only puts the annual inspection in one logbook, and typically that’s in the airframe book. Brandon has a 1977 Cessna 182Q with a low-time engine. Every time he borescopes it he sees lots of lead buildup on the valve stems of the cooler cylinders. He’s wondering if there’s a way to run it hotter, or is there something he can add to the fuel. The hosts agree that it’s actually a mixture distribution issue, something normal and expected in the O-470. Paul had a 182 and he did a bunch of lean testing. When he would lean to roughness and roll it back only enough to smooth out the engine, he would have two cylinders lean of peak, two at peak, and two rich of peak. Mike suggests adding TCP to the fuel. The main downside is that it’s quite toxic, so careful handling is required. Scott is interested in pushing the boundaries of the maintenance regulations. He’s wondering if he is allowed to sign off an AD as an owner because the regs don’t specifically state it has to be a mechanic. Mike thinks it must be an A&P because they are inspections, and only A&Ps can do inspections. There are a few ADs that explicitly allow the owner/operator to perform them. Paul suggests that a lot of ADs require a maintenance action that is outside the scope of owner-performed maintenance as well. Mike is questioning Continental’s guidance that limits extended running below 2,300 rpm. He finds that his airplane runs smoothest at 2,100 rpm. Mike explains that the bulletin came about after an issue with Cape Air and their 402s. After a few in-flight engine failures, they grounded the fleet and started inspecting engines. The failures were caused by counterweight release with accelerated wear in the pins and bushings. Continental couldn’t find anything wrong with the parts, and they guessed that it was due to operation at low rpm. Cape Air was operating at high power, rich of peak. They never tracked down the real problem, and guessed this was the issue. Cape Air had gone from operating at 2,300 rpm to 2,200 rpm. Mike believes that if you are operating at high power and rich of peak, it might be worth observing the limit, but if you are operating at low power, or lean of peak, you can ignore it.