Ask the A&Ps

What happens when you shut off the mags in flight? Mike, Paul, and Colleen answer this question, plus Cirrus cylinder woes, lapping technique, and more. 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: Jeff is questioning the part of his checklist that calls for turning off the mags just before shutting down. He remembers doing this accidentially in flight training and his instructor becoming somewhat panicked. The hosts explain that turning off the mags before shutting down is safe and determines if the P-lead is intact. Accidentally turning them off in flight is a different story. Unburned fuel in the exhaust will ignite rapidly and probably ruin the exhaust if you were to immediately turn them back on. If this happens, Paul recommends leaning the mixture completely, counting a few seconds, turning the mags back to both and then slowly brining up the mixture again. By doing this you'll hopefully allow the collected fuel to dissipate. Brian asks about Cirrus cylinder problems after a recently failure caused his partner to execute an emergency landing. The hosts explain that Continental has been having issues with cylinders on certain big bore Continentals. There's an AD that requires the cylinder exhaust ports to be filed, and while they've seen many cracks where the AD had supposedly complied with, Mike said the issue is that most mechanics aren't filing away enough material. However, Paul has also seen cases where the AD was properly complied with and the cylinder still cracked, and even new cylinders that aren't covered by the AD are cracking. He recommends doing a careful visual inspection for cracking near the exhaust port anytime the cowling is off. Yuriy wonders how much exhaust valve sidestepping is too much. Mike said he's had big sidestepping in many of his valves with no adverse effects. They recommend continuing to borsescope a few times a year to ensure the valve isn't burning. As Yuriy's compressions continue to come down the hosts recommend being proactive with lapping. Otherwise they recommend to keep flying as much as possible. Randall wonders how much lapping is enough lapping. He's looking for clarity on when the job is done. Paul invokes the TLAR method (That Looks About Right) while Mike additionally says to invoke the TFAR method (That Feels About Right). They say 4 times with new compound is often enough, but that it's about feel and look of the valve. Mike does recommend a compression check before putting everything back together as a gut check, and that most people new to the procedure often don't go far enough.

A caller wants to know what they don't teach you in A&P school. Plus AD compliance, a scary engine failure, and putting the lean in lean of peak. Email [email protected] for a chance to get on the show. Join the world's largest aviation community at aopa.org/join KC wonders why ADs appear on some logbook entries as having been complied with with a terminating action, and in future entries the AD reappears. He discovered this was a common occurrence when he was looking through logbooks as he and a partner were purchasing an airplane. Mike said you can't tell from an AD compliance summary whether something has been permanently complied with. That is found in the logbook through some sort of permanent change, like a kit or STC. If some other IA signs off the AD compliance again it could be because the IA simply missed that the AD was permanently complied with. Paul said he always assumes an airplane he sees for the first time has errors in AD records compliance and he verifies everything himself. Paul said this often happens because the part was changed somewhere in the airplane's history to make it no longer permanently complied with. Jeff is looking to fine-tune his lean of peak performance. He flies an RV-10 with an IO-540. He has a small window in lean of peak where he is running a bit rough, but if he runs more rich the CHTs will climb into the 360-degree range. Mike said Jeff is trying to run too cool. A Lycoming typically runs 20 degrees hotter than a Continental, so he said flying at 400 degrees CHT is perfect and nothing to worry about. Keeping it cooler won't necessarily matter.  Mark is going to A&P school on the side for additional enjoyment and greater involvement in his airplane maintenance. He is at a Part 147 school, and he feels like the education is good, but he's wondering what else he needs to know about GA maintenance. Paul explains that school is a great intro to the various topics, but it's not long enough to be detailed in all facets of aviation maintenance. Most specific learning is on the job training. Mike suggests Savvy's new IA renewal program, which anyone can take for free.  Frank has a turbocharged Rockwell Commander. The engine sputtered and stopped at 1,200 feet. He turned back to the runway and made it safely. His first thought was water, but none was found. The mechanic sent his magneto out but didn't find anything. Paul said it wouldn't be an ignition problem because both would have to fail or one would have to go badly mis-timed. A key piece of evidence is that the engine did end up restarting again on his approach to the runway. The hosts think it's fuel delivery. The electric boost pump was on. Mike suggests it was a stuck carb float. Paul said the engine will run on a similar engine for about 23 seconds with fuel just in the bowl. 

Mike, Paul, and Colleen dig deep for some detailed troubleshooting on digital fuel indicators, oil temperature, gear problems, and more this episode. Send your questions to [email protected] for a chance to get on the show. Join the world's largest aviation community at aopa.org/join Full notes below: Will's fuel indicators are giving off infrequent red Xs on his Garmin G1000, and it started happening right after maintenance. Paul is suspect that a mechanic caused it, especially because you have to take the wings off to get at the sensors. But he's pleased at Will's level of troubleshooting, which includes info about what happens when the tanks is full, half full, and while turning on the ground. Based on the information, Paul is sure it's a sensor issue. On computer-based fuel indications, a mismatch between multiple sensors can often result in the EFD showing red Xs, he says. It turns out Will's mechanic was able to fix the problem by checking the connectors in the same inspection panel he had opened for the annual. Brad has a Cessna 182 that he keeps in a dry climate but is now flying to the Texas Gulf Coast a few times a month, where it sits for three days. He's wondering how to hold back corrosion. Paul suggests he wash the airplane when he gets home each time, and make sure the inside is fogged with Corrosion-X. Mike said not to worry too much about the engine because his single-weight oil and CamGuard will help protect it for those three days. Carl has a Cessna 210 and twice the landing gear motor didn't stop running when he cycled the gear. Paul then spends a few minutes describing the 210 gear system in great detail, including all the safety of wallet issues. The oil temp is high (235 degrees) on one of the engines on Ben's Twin Comanche. The hosts go through a slew of troubleshooting steps, most of which Ben has already performed. The hosts settle on this being an airflow issue, and not a fuel issue. Mike said the oil temp limit is an oil longevity concern, not an engine damage concern.

What's in our oil, how to keep cool (and warm), and lean of peak 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 episode notes below: Mark flies a 182 and he read on a forum that the reason we've had so much spalling of lifters is because they took zinc out of the oil. Mike said this rumor has been going around for years, but doesn't make sense considering zinc was never in aviation oil. It's in STP, which is used as a thread lube. He cautioned not to put that in the engine because it's not ashless. The problem with lifters has been poor manufacturing, Paul said. Bob has an RV-10 and he's been trying to run lean of peak with wide open throttle. His technique has been to reduce rpm to get to 55 or 60% power and then lean. But doing so puts him at around 2,000 rpm. He's worried that running it too low might result in problems. Mike gives Bob a better technique. He said the mixture controls power while lean of peak, although running at a lower rpm is generally better since the combustion event takes longer. By running a lower rpm you're giving the engine more time to burn through the available fuel/air mixture. The low rpm prohibition that Bob is worried about in other airplanes is usually the result of propeller resonance issues, they say. Jeremy wants to know when to plug in the pre-heater. Other pilots have told him he needs to plug it in 10 to 12 hours before flying, but he's checked the temperatures with his engine monitor and found they rise about 35 degrees above ambient in two hours. Paul cautions that the oil won't be that warm, only the metal at the CHT probe, but because Jeremy is running multi-weight oil it doesn't matter. Mike said his rule of thumb is generally to preheat when it gets below 32 degrees F, and that when the rocker covers no longer feel cold to the touch that you're done. In Jeremy's case they agree that two hours seems fine. Johann has a Cessna 210 that has a hot cylinder. He's gone over the baffling, which helped, but he's wondering what else to do. Paul tells Johann to throw fuel at the problem. He sets the fuel flow a half-gallon to one gallon over the book number, advising that you'll know you've done too much if it runs rough at takeoff. With Johann's intercooler, he recommends even more. Because intercoolers bring more dense air into the engine, you have to adjust the fuel flow, although the manufacturer doesn't say how much. So it takes some trial and error. Paul also advised Johann to look at his engine mounts and considering installing an aftermarket prop. On the 210 a tight tolerance between the spinner and the cowling can greatly reduce temperatures. If the spinner is low you can raise it with new mounts or spacers under the front mounts.