Ask the A&Ps

• "You have a lot of splaining to do"

  Gotchas and head-scratchers are the theme this episode, as Mike, Paul, and Colleen help an owner with a pitted camshaft, an inop instrument, a faulty vacuum line, and ops procedures. 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: Mike had two airplanes over the past 10 years with crankshaft pitting, despite regularly flying, hangaring, and using an engine dehydrator. He's wondering if there's anything else he can do to keep the rust away. The hosts focus on the timing of the events and consider that maybe Mike was caught up in a period when Continental had manufactured some sub-standard parts. They are confident Mike did the right thing by having his mechanic use the guidance in Continental's Service Information Directive 05-1B, which describes how to inspect and then when to replace the cam if spalding is found. Trevor has a Cessna 152 and he noticed that the vacuum line near the static sump had been bumped and was disconnected. It's a simple assembly that doesn't require tools to replace, only some teflon thread. He's wondering if that would be acceptable to do under the regulations for preventative maintenance. The hosts agree that it fits the definition of preventative maintenance perfectly, but that changing out the line would trigger the requirement for a static system leak-down test, which doesn't meet the definition. So, although a pilot could probably replace the line, he/she would have to hire a mechanic to do the leak-down test anyway. Brian is the manager of a flying club with a Cherokee that has a persistent inop flag on the S-Tec 30 turn coordinator, and he wants to know if you can label only the inop flag as inop. Mike thinks that's sound logic, but Paul and Colleen are a little more skeptical. When Brian says the airplane is used for checkrides, the hosts agree that DPEs are probably not going to allow it, and to placard the entire autopilot inop. Tim is wondering how many times to cycle the propeller during the run-up checks. The hosts all agree that once is sufficient, unless there's a need to do more. That might be because the oil is very cold, the hub is large, or there wasn't a good response on the first try. But all the parameters that need to be checked can be done in one pull, and a second and third pull are unnecessary and cause unneeded strain on the engine.

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• "Mechanics can be ornery sometimes"

  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.

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• Live from Airventure 2025

  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

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• "That'd be like putting grease on the road"

  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.

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• "That's one way to flat spot a tire"

  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.

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