Ask the A&Ps AOPA

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 podcasts@aopa.org 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 podcasts@aopa.org for a chance to be on the show.
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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. 

This episode Mike, Paul, and Colleen tell a flight school owner not to throw away a perfectly good engine. Plus, the origins of the annual inspection, safety wire, and poor engine monitor guidance. Email podcasts@aopa.org for a chance to get on the show.
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Full notes below:
Mike has a Cessna 150 with a bunch of advanced avionics, including a Garmin GI275 as primary engine instrumentation. The oil temperature setting frustrates him because it’s flashing cautionary at 200 degrees and warning at 210 degrees. The POH says the max is 240 degrees. Paul said the engine monitor should match the original gauge, so if there wasn’t a cautionary range on the original there shouldn’t be one on the electronic instrument.

David is challenging the maintenance norms. He’s wondering how the FAA originally came up with the idea and time frame of the annual inspection. Mike thinks it’s arbitrary because some things should go less than a year, and some can go much longer. Firewall forward and wheels and brakes should probably be less than a year, but things like cable tensions could go less. The phased inspections that turbines go through is more logical, he thinks.

The airplane in Albert’s flight school is difficult to start, and his mechanics can’t figure out why. They’ve looked at spark plugs, adjusted the fuel, fuel servo, magnetos, and more. They recommended replacing the engine next. Don’t do that, the hosts say. Mike asks for the starting procedure. In Albert’s write up he mentioned having to wait some time prior to trying to start again. Mike said the only way that would happen is if the engine is continuously flooded during starts. Paul said if there’s leakage in the flow divider, the engine can become overprimed because its as if it is being continually primed. Colleen said it’s not a bad idea to check the ignition harness and other electrical components. And Paul said to also look at the P-leads.

Slavic is learning to fly helicopters and he was surprised to find that none of the oil filters were safety wired, and he wants to know if it’s safe. The hosts are shocked. However, a safety bulletin from Robinson says that it’s not required. 

This episode a perspective owner wonders about the cost of tying down outside. Plus fuel pump problems, major versus minor, and more. Email podcasts@aopa.org for a chance to be on the show.
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Full notes below:
Steve’s primer in his Saratoga sat for a long time and was pumping air when he came back to fly it. He had to track a fitting to get it to pump fuel again. Paul thought that since the pump is lower than the level of the fuel tank, then it should have probably been ok with the long break from flying. He suggested that air had gotten in the system somewhere other than the pump. Although the problem hasn’t re-occurred, he wants to be sure there aren’t underlying problems. The hosts think since there aren’t any stains from leaking fuel that he probably doesn’t have an issue.

Dennis is looking to buy an airplane and he’s trying to establish the maintenance costs difference between having a hangar and being on a tie-down. They recommended a cabin cover to try and keep the water and UV out of the interior. Dennis is worried about the freeze-thaw cycle during his cold winters, but the hosts aren’t concerned. Paul said not to worry about all the snow that sits on airplanes during the winter either. Dennis asks about glass versus steam, and they suggest that maybe glass would fare better in cold weather.

Mark wants to install an air conditioner as a minor alteration in an Aerostar. He and the hosts talk in detail about the challenging issue of minor versus major alterations and what’s involved in that decision. Mark’s concern is that the air conditioner should have a few operating recommendations about usage, recharge, and so on, and he is worried about pushing into the major category. Adding limitations and a flight manual supplement would do that, but the hosts think he could legally offer operating suggestions that don’t cross into limitations.

Andrew works at a flight school with some airplanes have that airspeed in knots and some in miles per hour, and he is looking for a way to make life easier for his students. They discuss the issues involved with glass displays that are incorrectly labeled, and what that does to the legality of the airplane. Mike thinks so long as the original backup instrument is still legal that is probably ok. 

Is there a limit to how much oil consumption is too much? This episode, Mike, Paul, and Colleen answer this important question. Email podcasts@aopa.org for a chance to get on the show.
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Full notes below:
Jim has a Cardinal with 3,000 hours on the engine. Everything looks good, except that the oil consumption has increased substantially. They tried the ring flush procedure, and saw the fluid coming out of the carb intake and exhaust manifold. The second cylinder took an immense amount of effort to pull the prop through. They took that cylinder off, and found that the oil control ring had a lot of crud. Mike said he wouldn’t get too invasive in order to solve the problem. It’s not a safety of flight issue. They suggest replacing the cylinders only if the oil consumption bothers Jim and his partner. Jim’s partner suggested also overhauling the bottom end with cylinder changes. They advise against it, instead looking at the cam when the cylinders are off. Mike wonders if the ring flush was done wrong. None of the fluid should come out of the exhaust or carb. He and Paul said they’ve never seen fluid come out of the valves. They recommend trying again.
Nicolas and his partner disagree on how often they should change the oil on their Grumman Tiger. His partner wants to change the oil before the winter, when they usually only fly a few hours, and then again in the spring, when they fly around 30 hours. Mike said the oil change intervals are inexact. As the airplane is flown, the oil gets increasingly corrosive. He suggests not letting the airplane sit with old oil throughout the winter. So that’s when he would change it. He’s wondering if he can avoid changing the oil in the spring after only flying for seven hours over the winter. The hosts agree that it’s probably fine not to change the oil at that point. They recommend also getting a dehydrator to keep the inside of the engine dry.
John has a twin Cessna with one engine that quits when it’s cold. Mike said the fuel pressure at low rpm isn’t high enough. Or the idle mixture isn’t rich enough, or there’s something wrong with the flow divider. The easiest and cheapest thing to do is to adjust the fuel pressure or the idle mixture on the fuel control unit. Paul said his Cirrus does the same thing in winter. He thinks it’s the fuel divider.
Cheryl has a Skycatcher with a window tint and she is concerned about its legality, and whether it should be noted in the airframe logbook. So long as it doesn’t inhibit the view, the hosts think it’s fine.