Ask the A&Ps

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 [email protected] 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. 

Rough idle, electronic ignition basics, airplanes to avoid (or not), and the difference between detonation and pre-ignition are on tap for this episode. Email us at [email protected] for a chance to get on the show.

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Full notes below:

Stephen wants to get the engine on his Cessna 206 purring. At idle the engine stumbles down to 600 rpm. It never quits, but doesn’t run smoothly either. Mike asks if they’ve done an rpm rise test at 600 rpm. Paul explains it’s part of the installation process of a new engine. You set the engine at a set rpm, then pull the mixture back slowly to get a 25 rpm rise. More than 25 rpm means it’s running rich. Less than 25 rpm means it’s running lean. Engines don’t come out of a crate ready to go. They need to be set up properly. Mike also said that landing with full mixture rich is an issue as well. He said there are only two times you should have full mixture. One is when starting cold, and the other is when applying 100 percent power (at lower density altitudes).

Mark is interested in electronic ignition for his 210, particularly the Surefly. Paul loves the Surefly on his airplane. He doesn’t love the advanced variable timing. He thinks a bit aggressive. But it is selectable, so you can turn it off if you like. Mike said he would try it with the variable timing on, and only turn it off if the CHTs are too high. Colleen said her husband has done the dual Surefly on his Legacy. He has higher CHTs, but not unacceptably high. The fuel burn is also lower, but the biggest benefit is easier starting.

Erick is looking for any angle to justify buying his first love, a Cessna 337. He would prefer a turbocharged Skymaster. He’s wondering if there’s any hope for the future of these engines being affordable. You must go and buy a turbocharged Skymaster, Mike said. The engines that Mike has previously been worried about are on the pressurized Skymaster. The turbocharged engines are rated at 210 horsepower, and the pressurized ones are rated at 225 horsepower, which he thinks impacts longevity. He thinks engine longevity is related to horsepower per cubic inch. An O-470 is about .5 horsepower pre cubic inch. The TSIO-360 is around .625 horsepower per cubic inch.

Warren is wondering if detonation caused a power failure in an accident he’s studied. The NTSB data shows that the cylinder reached about 700 degrees, and it went up by about 1.3 F degrees per second. Mike said CHT increases greater than 1 degree per second can only be caused by a pre-ignition event. It means that something in the cylinder was either acting like a glow plug, or if there’s a magneto failure. A cracked spark plug insulator can act like a glow plug, for example.

How do you know when to replace certain parts? They begin to talk to you. Find out what, why, how, and when when Mike, Paul, and Colleen tackle this and other questions. Email [email protected] for a chance to be on the show.

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John is part of a club that owns a Cessna 172. Another member told him he shouldn’t move the rudder by hand when he preflights. Mike said to make sure he pushes it at a rivet line to ensure he doesn’t bend the sheet metal, but otherwise it’s ok. Paul describes how the system is built. He said in a Skyhawk the rudder pedal tension is created by springs that pull them toward the firewall. There’s not a cable tension spec. The steering bungees are between the rudder pedals and the nose gear. If you get in and push the pedals when stationary, you are putting stress on the bungees.

Jarek wants to know if the FAA has lost its mind. He is wondering about the FAA’s AC 20-105, which says that engines that run past TBO have a higher rate of failure, and that engine overhauls at TBO are usually cheaper than those that are run beyond. Mike said Lycoming had previously issued a white paper that said that the typical lifespan of a crankshaft was 14,000 hours. Camshafts have corrosion issues, and don’t cause failures, and sometimes gears need to be replaced. But rarely does time impact safety. There are people inside the FAA who disagree with the policy, Mike says. On one hand they require manufacturers to set a TBO. On the other hand, they tell Part 91 operators that they can ignore it. Typically engines that fail that have run beyond TBO tend to be not related to age, but because of maintenance resulting from the fact that the engine is older. In fact, it’s usually the opposite, Mike says. Lower time engines typically fail because of infant mortality.

Aaron and a partner recently purchased a Seneca with turbo Continental TSIO-360-KBs. They installed new intercoolers and the manual revision suggests new power settings. He’s ignored the chart and is flying around 30 inches lean of peak. Mike said the chart is interesting if you are operating rich of peak, but irrelevant lean of peak. The power output of the engine is determined by whichever component is in shortest supply. Rich of peak, you have more fuel than you need, so power is controlled by air through the throttle and the prop. Lean of peak, fuel is in shortest supply, so power is controlled through the mixture. He would run a slightly reduced throttle, just to avoid overworking the turbos.

Rory has a Cardinal that he bought 12 years ago, and he hadn’t ever changed the ignition wires. So he started to wonder about when and why to change them. The hosts agree that if a wire fails it feels like a stumble or mis-fire because it just takes one spark plug offline. They say to run them on condition, and only change them when they start talking to you through mis-firing.

Metal in the filter, starting problems, and mechanics who don't understand the definition of installed are on tap this episode. Email [email protected] for a chance to be on the show.

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Full episode notes below:

Roger has a Mooney M20J that has developed an odd starting problem. Over the past few years he’s had to increase the time the boost pump runs before the engine will start, and even then it sometimes doesn’t fully catch. Paul suggested that the bellows inside the flow divider could be bad, which would cause it to perform poorly. Mike also suggested that the idle mixture could be set incorrectly as well. An rpm rise test can verify if it’s correct.

Craig has a 182 that he uses to go back and forth to his fishing cabin. He took the back seat out and he wants to add in some plywood in the back to protect the structure. He isn’t planning to affix it in any way other than Velcro. His A&P told him to avoid doing this because the wood isn't burn certified. But without installing the plywood with a structural fastener, it’s not technically installed and he can carry it however he likes.

Malcolm has an 182 with the Texas Skyways conversion, and it hangs up during the starting sequence. They’ve replaced the starter, bought a battery tender to check the battery, and more. It’s so obvious what the problem is, Mike says. This is a classic and common problem among Continentals. The starter drive adapter is bad, the hosts say. He can have the part repaired and it should no longer be a problem.

Aaron found a significant amount of metal in the oil filter on his Piper Cherokee 140. There was aluminum in every pleat of his filter after only about 15 hours. They were thin, but large flakes. The pieces were too big to even show up in an analysis. No other metals were elevated in the analysis. Colleen suggests that it could be from the oil pump impeller, but since he only found oil in the filter, and not in the sump itself, he thinks it’s coming from the pistons. Mike said piston pins migrate back the other direction, which often means it’s self-resolving. As it turns out Aaron knew the answer. He removed all four cydlinders, and two of the piston pins were severely worn. They also found ring chatter. Mike said Superior has had issues with ring chatter and they’ve tracked down the manufacturing problem and replacing the cylinders under warranty. 

An airplane that hasn't flown in 8 years quits when going to full power. A turbocharged Mooney meters out less fuel as it climbs. Mike, Paul, and Colleen tackle these questions and many more in this episode. Email [email protected] for a chance to get on the show.

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Full notes below

Eric is having trouble with his Aero Commander. The engine has only 150 hours but sat for 8 years. After an extensive annual, they test flew it. One of the engines dies at full power, but runs fine at partial power. The flow dividers were checked, the fuel lines were blown out, and the fuel servos were bench tested. Colleen suggests that it could be a blockage of the exhaust, especially given the long sitting time. Paul thinks it’s possible that a lack of air supply could be a problem. They suggest opening the alternate air to see if that fixes it. Paul said he would go through the entire induction system to verify it’s clear and open.

Will is struggling to get the fuel system set up in his turbo Mooney. As he climbs he says the fuel pump is decreasing fuel pressure. The manifold pressure starts to decrease when fuel pressure gets low in the upper teens. Mike said there’s nothing wrong with the manifold pressure or upper deck pressure. The line from the upper deck pressure to the fuel pump aneroid is bad. The aneroid thinks it’s seeing lower pressure as he climbs, even though it shouldn’t. He thinks there’s a leak in that line, the aneroid, or the upper deck pressure. He suggests pulling the b-nuts and replacing the seals first.

Jim is wondering about how to lean when flying low in a formation fly-over. With 10 airplanes and lots of throttle changes back and forth, it’s hard to know how to lean. Colleen suggests doing some tests at the same altitudes not in formation to see what sort of power settings he’s at and apply it based on those tests. Mike said he would lean to around best power.

Jason is a partner in a 182 and a potential new partner went for a test flight and found a potential issue. The rpm dropped 150 to 170 during the mag check, and he refused to fly the airplane. So he’s wondering if the pilot was overreacting or if he was right not to fly it. Paul said EGT rise is a better indicator than rpm drop. Very little drop or no drop could mean the P leads weren’t connected. Mike said bigger drops, like 300 rpm, should prompt a timing check. Switching to one plug has the effect of artificially retarding the mag timing. If it’s already retarded, that can make a large drop

Live from Airventure 2024, we present the first of two sessions. Listen as the audience tries to stump Mike, Paul, and Colleen with its toughest maintenance questions.

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An owner wants his engine perfect for flying around the world, how to start an airplane with electronic ignition, when to fire your mechanic, and defining approved data are on tap for this episode.

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Full show notes below:

Ethan is flying a 182 around the world, and he is worried about a CHT imbalance. He’s added an electronic ignition, changed some baffling, changed cylinders, and even got a new engine. It also gets worse as he levels off. Paul said Ethan still has a baffling issue, and the first step is to cut slits in the material to make sure it’s laying flat. The temperature imbalance changing when leveling off makes sense to Paul because the airflow over the engine changes as the pitch of the airplane changes. Mike said it can be inter-cylinder baffling as well. Even CHTs are impossible, he says. A 50-degree spread is good. Colleen suggests pushing the baffling off the back cylinder by wedging in a spacer between the cylinder and the baffling to create a small gap.

Frank just installed an electronic ignition for his 182 and is wondering how to properly start the airplane with a split switch. He has been starting it on battery only, as per the airplane handbook. Paul made the point that older Cessnas didn’t have a split switch. Theoretically with the alternator on during the start, you avoid an electrical jolt, although he said he can’t say the battery only start is always better. He recommends starting on both mags. Mike said the only time you wouldn’t want to turn the alternator on during a start is if you have an almost dead battery. It’s more important to avoid the jolt on a gear-driven alternator.

Benny is headed for a bread-up with his mechanic. He likes the work the mechanic has done, but in talking to the mechanic about his approach to maintenance, he is concerned they don’t agree on tactics. The mechanic doesn’t believe in lapping valves, for example, and may have a hard adherence to TBO. Benny wants to know whether to switch now or try to work through the disagreements. Mike thinks it’s worth a conversation given how difficult it can be to switch mechanics. Colleen said it’s not going to work, and that the mechanic is most likely set in his ways. Paul agrees that getting a mechanic to change his mind is incredibly difficult.

 Dwayne is restoring an antique airplane is wondering what constitutes approved data. Xerox copies are acceptable, despite what others have told him. He also wants to know if reverse engineering a part is considered approved data. Dwayne and the hosts discuss the difference between acceptable and approved data. 

An owner wants to know if he should tear down his engine after harvesting some corn with his prop. Plus, the benefits of flying oversquare, why you should use the boost pump at higher altitudes, and pre-flight procedures.

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Full notes below:

John wants to know if he can manipulate the rudder on his club’s 172 during a preflight. Another club member told him he would stress the nosewheel steering by doing that, but the hosts agree that John that was right. Paul explains that the tension on the rudder pedals is created by springs that pull the pedals to the firewall. The steering bungees are between the rudder pedals and the nosegear, not the rudder. The rudder may move the pedals a little. Bigger stress is when you move the pedals from the cockpit without the nosewheel moving, but even so, Paul said the system is made to do that and is unhurt by those checks.

Jeff had a botched landing in his Super Cruiser and hit some corn at full power, and he is wondering whether or not he had a prop strike. The engine didn’t seem to have an rpm drop, and the prop was undamaged. Mike said there’s two possible outcomes. The first is that he didn’t have a prop strike because there wasn’t a reduction in rpm. If Jeff thinks he had an rpm reduction, the AD requires the accessory case to be removed, but not torn down. In all the prop strike events Paul has been involved with, he’s never seen rotational damage due to a prop strike. Magnetos are usually the first thing to be damaged. He said he thinks it’s also unlikely there wasn’t an rpm reduction as it slashed through the corn, and he thinks Jeff is subject to the AD.

Tyler is looking at buying a turbo Piper Arrow and he has questions about turbocharging. He wonders about the diminishing returns of oversquare or overboost as it relates to reduced longevity. He’s also worried about boot strapping, which Paul said is self-limiting. Mike said the highest amount of oversquare allowable within the operating envelope is the most efficient place to operate. It’s important to remember that the chart is rich of peak, and lean of peak provides more of a detonation margin. Mike said the abuse to worry about is horsepower per cubic inch.

Fred’s engine on his Cirrus had a hiccup and he’s wondering why. He was at 10,000 feet climbing in the clouds. One cylinder was getting hotter, and one had passed 400, so he leveled off, things cooled off, and he started climbing again. Just as he leveled off he tried to do the big mixture pull, it stumbled, so he pushed it forward and it still stumbled. The hosts quickly figure out he had vapor lock. Paul said a lot of Cirrus pilots run the boost pump on low all the time. Mike does that on his 310. With a hot engine and high altitude, the fuel is vaporized, so the boost pump helps move things along a bit. 

Lots of leaks this episode, as Mike, Paul, and Colleen diagnose a leaky strut, a defroster that's not working, a leaking brake system, and more. Send your questions to [email protected] for a chance to get on the show.

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Full notes below:

Greg has a Cherokee with a leaky strut. His mechanic suggested pressurizing it with shop air instead of nitrogen. He asks about Granville Strut Seal. Mike said he has a big success rate with Granville, and that he should definitely use it on all the struts. He disagrees with Greg’s mechanic that shop air is ok to use to fill a strut. The reason to use nitrogen is to avoid corrosion inside the strut because shop air has moisture in it. The air valve in the top of the strut is probably where his air is leaking from.

Jim has a Mooney M20C and the defroster ducting is falling apart. He’s wondering how to replace it. They recommend taking out the glareshieild, grabbing out the tubing, and buying a new one from Lasar or the factory. The existing one might be repairable with epoxy or new fiberglass pieces. Paul cautions that it’s possible something won’t work after he gets it all back together. Mike thinks it’s almost not worth fixing because of the complications in that tight of a space.

Andy is trying to understand the carb ice potential of the Cessna with an O-300 that he’s flying. He’s heard it’s very prone to icing, and the carb temperature gauge shows it’s almost always in the yellow. To stay out of the yellow he would need to fly with the carb heat on almost all the time. Mike said the extreme dryness in a Minnesota winter would make carb ice unlikely.

Nick has a few questions about his 182. He’s first wondering when to replace the battery. Mike said that the way to check is an annual capacity check, and there’s an official and unofficial way to do it. The official way is to buy a capacity checking instrument, but that’s expensive. First fully charge the battery, then time how long it takes to go down to a certain level. If it gets below a certain ampere-hour rating, it’s time to replace it. Unofficially you can draw current in the airplane and see how long it takes to draw down. But the act of the capacity check seems hard on the battery, according to Mike. Paul said Concorde has told him it’s not an issue, and that checking them doesn’t damage anything. Nick's second question deals with the brakes. When he bought the airplane he saw in the logbooks that they were being rebuilt once a year. He changed out the master cylinder, the flexible line, the o-rings, and he blew out the line. It’s better, but he still has to occasionally fill the reservoir. Paul suggests checking the line near the calipers. If it’s a solid tube, he said it’s possible that fluid can work it’s way back up the system. He suggests leaving a rag wrapped around the top of the reservoir and fly to check if that’s where the fluid is coming from.

This month Mike, Paul, and Colleen cover the basics. An owner wants to know if he should pull the throttle or propeller first in a climb, another wonders what the ideal power setting is for the run-up. Plus, mis-fueling and tired turbos. Email [email protected] for a chance to be on the show.

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Full show notes below:

John has a 210 and wants the definitive answer on whether to pull back the power or prop first. Paul said he has a 5-minute restriction on full power. He suggests after 1,000 feet, reduce the rpm only to 2600 rpm. Then reduce the mixture in the climb to maintain the exhaust gas temperature that was roughly at takeoff. Then when he gets to cruise he can set the rpm where he wants. But leave the throttle wide open all the time. Paul sets the rpm where the engine runs smoothest. After the mixture and prop are set, then he can go lean of peak. Mike said lean of peak is usually most effective at lower rpm.

Ingram bought a Diamond DA-40 with the Austro engine and he’s worried about mis-fueling. The POH isn’t helpful because it only says to drain and flush the tanks if mis-fueling is suspected. The hosts aren’t aware of a test kit that ensures he gets jet fuel, so they recommend smelling the fuel sample because avgas and jet fuel smell much different.

Justin wants to know whether to believe his instructor and general guidance, or the manual. He said he was taught to do the run-up at 1,800 rpm, but the engine manual for his airplane said to run it up at 50 to 65 percent power. Mike said it’s better to run the engine up lean, and that 1,800 is perfectly fine. Without proper cooling, he worries about engine wear with regular high-power run-ups.

Royal is wondering if the turbo in his TR182 is losing it’s oomph flying higher. Paul said the fact that it’s turbonormalized means it lasts longer. The waste gate on his system is open until he gets much higher than most. Mike said turbochargers generally don’t lose power. It’s more likely the throttle linkage has changed over the many years that he’s owned the airplane. Paul said cam lobe wear can also be an issue.