Ask the A&Ps – Détails, épisodes et analyse

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 podcasts@aopa.org for a chance to get on the show. Join the world's largest aviation community at aopa.org/join 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. Email podcasts@aopa.org for a chance to be on the show. Join the world's largest aviation community at aopa.org/join

A light oil mist on his windscreen has one caller concerned he needs to split the case. Plus, Mike, Paul, and Colleen tackle cold cabins, tire changes, and horsepower calculations. Email podcasts@aopa.org for a chance to get on the show. Join the world's largest aviation community at aopa.org/join Full notes below: Grant has a Mooney M20F and he’s seeing a light mist of oil on the windscreen after flying. His mechanic thought it was coming from a case bolt, which he re-torqued. That didn’t solve the problem, and the mechanic said the proper way to fix it would be to split the case, which Grant doesn’t want to do. Paul said that’s not the problem anyway. He said misting oil on the windscreen is almost always the crankshaft seal or the prop o-ring, both which should be fixed together. The parts are cheap, and the job is relatively easy. Colleen just did this on her airplane and describes the process. Joe’s kids are freezing in the back seat of the family Cherokee. They’ve put tape around some gaps, and while it’s helped a little, it’s still very drafty. Paul mentions the spar carry-through gap between the cabin and the wing. There’s supposed to be a piece of foam in the gap, but often when the wings are removed the foam isn’t replaced. The floor is lifted up, and you can look in the gap with a flashlight and mirror to see if the foam is there. The rear spar also has a gap where there should be rubber discs glued onto the box where the flight controls pass through. Todd is curious how JPI derives the horsepower number. Mike said JPI keeps the math as a closely held secret. But he said there’s a right way to do it, and it's how Savvy does it. Power is regulated by air or fuel, whichever is in shortest supply. Rich of peak, you have more fuel than the engine can combust, so air is in short supply. Mass airflow is therefore the power determinate, which can be calculated with manifold pressure and rpm. MP is how much air goes into the cylinder, and rpm is how often that happens. Multiplying the two gives the mass airflow number. Power when lean of peak is a function of fuel flow. Fuel flow times a set number based on the compression ratio gives horsepower. He thinks the engine monitor doesn’t know whether it is rich or lean of peak, so it probably computes it both ways, and the lower number is the right one. Seth has some dry rot on his tires and he’s wondering if that means he needs to change thems. Desser says they need to be replaced when the cord is showing, and his mechanic says the dry rot means it should be changed. The hosts agree with the manufacturer that there’s no minimum tread depth, and to keep going.

A Vans customer wonders what to do next, and a 172 pilot asks if carb heat is really necessary all the way to the ground. Plus, the best spark plugs, and a vexing gear issue are on tap for Mike, Paul, and Collen this time. Email podcasts@aopa.org to be on the show. Join the world's largest aviation community at aopa.org/join Full notes below: Greg has a kit from Vans on order and he’s wondering what to do next. He can replace his quick build wing kit with the small cracks installed, but he wants to know if he should order replacements. Paul said when sheet metal work is done on certified aircraft in the field, a lot of cracks naturally come up. Greg said a customer has to agree to accept the modified terms of the new contract, and you have to either accept what they send you, or spend money on a second kit. Paul said to deburr as little as possible. The goal is clean, sharp corners, not a knife edge that can cut the rivet. Just barely touch the hole, he said. Travis has an unusual gear problem. He was tasked with ferrying a Wheeler Express RG, an unusual experimental. On the ground the gear works perfectly, but when flying it won’t reliably retract. The system is based on a Glasair 3, and Colleen said the Glasair racers have a similar experience with their airplanes at Reno. On a ferry flight the hydraulic fluid built pressure over a few hours, and Travis had to select the gear down lever in order to release the pressure. Paul said not to spend any more time on the system, and replace it with something from Cessna. Brian wants to get to the bottom of the fine wire and massive plug choice. His shop said he had to replace all 12 fine wire plugs at the last annual, all with around 800 hours on them. The shop recommended Temptest massives, which is what he did. He’s wondering if there’s really a difference in performance. Paul said fine wires tend to idle a little better and smoother. Corrosion was an issue on older Champion fine wires, which is what Brian had. And the ceramic is thicker on Tempest. Fine wires also last longer, usually long enough to cover the additional cost. Mike said they cost about four times as much, but last four times as long. He said some people also report smoother operation at very lean mixtures and small fuel economy improvements. Colleen has fine wire Tempests in her Cardinal but massives in her Skybolt. Her fine wires run a bit cleaner and don’t need to be gapped. Brian has seen a larger EGT differential when flying lean of peak with the massives. Dennis has a 172 and he wants to know if it’s really necessary to keep carb heat on all the way to the ground. Mike said a newer Lycoming Skyhawk is less susceptible to carb ice, but his Continental O-300 is much more likely to produce ice. He recommends installing a carb heat gauge if he really wants to avoid having the carb heat on longer than necessary.

This episode Mike, Paul, and Colleen help an owner with an engine that randomly dies after 2100 rpm. Plus, the role of avgas as a lubricant, prop governor issues, and getting back into maintenance. Email your question to podcasts@aopa.org for a chance to be on the show. Join the world's largest aviation community at aopa.org/join Full notes below: Dennis has a Cardinal RG with a prop governor issue. When it’s warm, the prop underspeeds just a little. He’s done a bunch of troubleshooting, and he is at a loss. The manufacturer said to send his prop in, but he is reluctant to do that given how often prop shops deem them unfit for continued service. Dennis is an A&P and he asks if he is allowed to open up the governor and work on it. Mike said he doesn’t advise it because he both can’t do it legally and doesn’t have the right tools. Both Paul and Colleen said their props do the same thing, and they recommend he crank up the rpm just a little since a small amount of overspeed is allowed under the type design. Luis is looking to get back into aviation maintenance after earning an A&P many years ago. The hosts debate the FAR, which says that a mechanic is current if the Administrator deems he or she so, or if the mechanic has served as a technician for the past six months. The hosts think Luis should use the preventative maintenance provisions to do the work without supervision. Jeff built an airplane with a PZL Franklin 235 and the engine won’t make full power. The static rpm is 2800, and anything beyond 2100 kills the engine. He thinks either his homemade exhaust is causing too much back pressure, or there was a manufacturing issue. He wonders if there’s a way to isolate the problem. The ignition timing is set to 32 degrees, which is the manufacturer spec. Mike and Paul recommend backing off the timing first to see what happens. Paul suggests he could also remove part of the exhaust to see what happens. Josh wonders if we are too eager to get off avgas, specifically because of its proprieties as a lubricant. He’s always heard that it lubricates valves, but Mike thinks it’s probably not a concern. It’s true that before valve seats were hardened, there was some microwelding, which led to valve seat recession. Lycoming switched to hardened valve seats in the 90s, and Continental switched in the early 2000s. There is a possibility that some of the older Continental cylinders could have problems with valve recession, but it's too early to tell. He details the work that AOPA is doing with the dual-fuel Baron, which is seeking to understand some of these issues.

Mike, Paul, and Colleen help an owner raise his oil temperatures, explain the rules around ELT battery replacements, debate the merits of a tuned exhaust, and help an owner whose airplane won't quit. Email podcasts@aopa.org for your chance to get on the show. Join the world's largest aviation community at www.aopa.org/join Full notes below: Chris has a Super Decathlon with CHTs as low as 270 degrees and oil temperature around 150. Even with the oil cooler covered during winter, it still doesn’t get hot enough. Mike said they like to see oil temperature up to 200 degrees if possible. Chris can check the vernitherm by putting it in boiling water to see when it actuates. Mike said the oil temperature gauge is typically reading at the coolest part of the process, and the oil may climb 40 degrees higher. Curtis just wanted to change his ELT battery. His mechanic sent it away to a service center. He received an invoice with three options, none of which included replacing the battery. His standby current apparently tested high. Unfortunately Curtis was in an unusual situation with a foreign-produced part. There are two answers, Mike said. There’s the answer where you feel like you have to follow the manual, and one if you follow the regulations. The manual says the battery must be replaced by a Part 145 shop, but the regs allow the owner to do it under preventative maintenance. Mike contends that since the battery replacement section of the manual is not an airworthiness limitation, Curtis can just brush it off. Pierre-Louis and his club in Switzerland have a tuned exhaust system on their airplane and while he is seeing some benefits in terms of fuel burn and climb rate, he is most interested in the smoothness of the engine. He said it feels like having a 6-cylinder engine and he’s wondering if tuned exhaust systems offer better engine longevity. Colleen thinks it’s possible the engine is actually working harder (more horsepower), so she guesses that the engine longevity would be reduced. Mike said he disagrees because the engine isn't producing more power, its power is being used more efficiently. Paul suggests that less vibration is ultimately better for the engine. Frank has a Rockwell Commander 112 and when he shuts it down it sometimes diesels, or won’t entirely quit. Typically it only happens in the summer after a flight when it’s warm. Mike and Paul said the only way that happens is if the mixture doesn’t fully shut off the fuel supply. Mike said the mixture cable to the carb is the first place to check. Colleen suggests that it could be a leaking primer as well. Mike recommends fault isolating it by disconnecting the primer to see if it resolves. 

This episode Mike, Paul, and Colleen debunk myths, describe valves that are eligible for lapping, and cover the basics of the red box and leaning. Email podcasts@aopa.org for a chance to get on the show. Join the world's largest aviation community at aopa.org/join Full notes below: Maciej is a new private pilot who is questioning some operational procedures he was taught. He was taught not to put fuel back into the tanks after sumping it, and he thinks if you sample it and it’s clean, why not put it back? The hosts agree that if the sample is clean, put it back. He also wonders about oversquare on the impact on the propeller. A ground school he took says that it is too hard on the propeller to run it at low rpm and high power. Mike questions the validity of this, and Paul said to go ask the source because it doesn't seem right to him either. George has an airplane with some valve issues. Five of his cylinders have varying levels of green on them. He was told that four could probably be lapped, but the fifth has to be pulled. He’s wondering if green on a valve, which is later lapped clean, weakens or otherwise compromises the valve. Most of the green you see is green deposits, according to Mike. In early days of borescoping cylinders, the colors on the face of the valve were all we had to go on. Now, when we can position the camera between the valve and the seat, and can see if there’s erosion. If there isn’t erosion, it’s a good candidate for lapping. Mike said as long as the valve isn’t a train wreck that it’s worth lapping. Most people don’t do it aggressively enough. Doug is an instructor who was flying a Cessna 182 with a client and the owner didn’t want him to lean, even though they were flying higher than 8,000 feet. Finally he convinced the owner that it was ok to lean a little to smooth out the engine. Apparently the owner was worried about the red box. Since the goal is to stay below 400 degrees on the cylinder head temperatures, Mike thinks it’s hard to get 182 cylinders that hot at altitude, and below 400 degrees there is no red box. Paul makes the point that because power output at 8,000 feet is below 65 percent, you can’t hurt the engine by leaning.

With everything going electronic in the cockpit, will owner-produced parts become a thing of the past? Plus, Mike, Paul, and Colleen talk about their least favorite magnetos, deferring maintenance, and more. Email podcasts@aopa.org for a chance to be on the show. Join the world's largest community of aviators at aopa.org/join Full notes below: Justin owns a Columbia 400 and he’s wondering if he can make owners-produced parts for some of his electronics. The hosts agree that this is a problem with aircraft maintenance. Because it’s difficult to show original design criteria for electronics, it’s hard to prove the part meets the original standards. There are a lot of things you can’t easily duplicate, Paul says. Ben is a new aircraft owner and a lot of the previous squawks were deferred. He wants to know what he can do to help keep the airplane in top form before the next annual. Most of what Ben mentions is preventative maintenance and relatively minor. Paul said to focus on corrosion issues, including at the forward and aft wing attachments. Those are steel attached to aluminum. If you catch it early you can avoid future maintenance issues. Paul recommends using FAR Part 43 Appendix D as a guide for the what Ben should watch for. Colleen said to focus on things that would be expensive later. There’s a lubrication chart in the service manual, and Paul said to use that and go over the entire airplane. David had a scary experience in his Lance. He was approaching an airport and lost power. He ran through a checklist and nothing helped. At about 400 or 500 feet, descending toward a beach, he got a stall warning. The stall warning caused him to pitch forward abruptly, and the engine restarted. He was able to come in and land normally. After some extensive testing they found that a spring had broken in a mag. David thinks that maybe the spring was wedged in the wall of the case, and dislodged when he pitched forward. The hosts don't see how that's possible, but without further information, can't make a better diagnosis. Ray has a P210 and used an in-flight mag check to diagnose a problem. He was flying back to the States from Canada and he noticed the engine was running a bit rough. He checked the mags and found one wasn’t operating properly. He later decided to stay on one magneto. He’s gone through three magnetos in the past few years. He wonders if continuing the flight on one mag was a good idea, and what he should do now. They all agree that he did exactly the right thing by continuing and flying on one mag. Mike said he hates pressurized magnetos, and he would swap them out for electronic mags ASAP. 

Why you shouldn't jam the throttle forward launches this episode. Also, Mike, Paul, and Colleen help an owner with high oil temperature, advise a builder on engine modifications, help ease the mind of an owner with water in his tanks, and discuss how best to use a borescope. Email podcasts@aopa.org for a chance to get on the show. Join the world's largest aviation community at aopa.org/join Full notes below: Juan has a turbocharged 210 and he's having trouble going full power on takeoff. He flies out of a high elevation in Colorado, and when he rapidly goes full throttle the engine will quit. It's a bad idea to jam the throttle forward quickly, Mike said. That's especially true with turbocharged engines. Mike said he throttles slowly enough that he's about at full power at rotation speed. Paul points out that even if your oil is at 130 degrees on the gauge, that's not the temperature in the entire system. Everywhere outside in the hoses, etc, is colder. Advancing the throttle quickly can choke the system. Also, in the turbo 210, you can't just slam things forward. You must modulate the manifold pressure because overboosting can flood the engine.  Andrew has a 310 with high cylinder head temps and oil temps on his right side. Some new plugs and new baffling has helped his CHTs come into control. His oil temp is still high. He's replaced the vernitherm, sent out the oil cooler for overhaul, and done some other troubleshooting. The hosts suspect airflow because it happens under reduced power on descent. There's a baffle that separates the cylinder and oil cooler that Mike thinks could be an issue. Paul suggests flying with a GoPro or a borescope camera in the cowling to see what happens in flight.  Dan is building an RV10 with an IO-540 that he's going to overhaul before he installs it in the airplane. He's considering going to 10:1 pistons and porting and polishing and he's wondering about performance and reliability. Mike throws a little cold water on Dan's plans. He thinks it's not worth the risk. Colleen made a pro/con list and she said they are forged, which makes them stronger. They are more energy efficient, but that means they burn more fuel. There's a different magneto timing. They run at a higher pressure, and that probably means they'll need to replaced sooner.  Dennis gets water in the left tank of his Piper M600. His mechanic checked the cap, didn't find an issue, and swapped caps. Now both tanks have water. Paul said it could be that there's no new water, but leftover water from long ago. The water that collects sticks to the sides of the tanks and then rolls around as little balls until it finally makes it to the drain port. In other words, he suspects it's all old water that is just working its way out.  John has a borescope and he's wondering how to best put it to use. Mike mentioned Savvy's new borescope image collection efforts, and he refers to the intro, where they discuss the standard set of images. 

Mike, Paul, and Colleen help an owner with a bad lifter that shows itself after oil changes, guide an owner through a change his maintenance schedule, discuss what constitutes damage history, and take a guess at why POH numbers change over model years. Send your questions to podcasts@aopa.org for a chance to be on the show. Join the world's largest aviation community at aopa.org/join Full notes below: Steve has a 1975 Taylorcraft with an O-200. After oil changes one of his cylinders has some valve clatter. It tends to go away sometime later, only to come back after the next change. The oil filters are always clean and the oil analysis is good. Paul said there’s not much he can do about it, and Colleen said it’s also not a big safety of flight issue. Mike suggests they measure the dry tappet clearance to see if it’s wide enough to accommodate a larger pushrod to help eliminate the problem. Colleen said she read about a technique to fly it full power for an hour to see if resolves. They call it an Italian tune-up. Jim is on board with condition-based maintenance, and wants to alter the rubber hose component change schedule in his Rotax. Mike suggests that Jim can extend the change interval to maybe 10 years because he lives in the Midwest, and keeps his airplane hangered. The hosts discuss their method for inspecting hoses, how to manufacture them, and the various materials and considerations. Ken is considering a Cessna 180 with damage history. It was repaired and has flown 200 hours since repair. The damage history in question wasn’t so much damage as an improperly installed part that was replaced. Metal was found in the filter, a top overhaul was completed, and the owner is confident the airplane is running well now. Mike said the two things he needs to consider are whether the cylinders were reworked appropriately, and whether they were installed correctly. Considering it was a reputable overhaul company, the hosts are confident everything is ok to move forward. Scott wonders why on the same airframe, the performance speeds change over time. Paul guesses that early performance numbers were a combination of optimism, marketing, and guessing. And newer numbers are spot-on and well tested. Mike guesses that aircraft generally get heavier over time and maximum gross weights increase, necessitating speed increases.