"Check it, log it, and then relax"

Ask the A&Ps

Can you have a prop strike without a prop? This is one of the more unusual questions the hosts have faced. They also track down a carbon monoxide leak, advise on Continental rpm settings, and help an owner who likely had a pre-ignition event.

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Full notes below:

Robert is an A&P who is trying to help a flight school track down a carbon monoxide leak in a Cherokee. An instructor had a carbon monoxide event, took up a monitor, and found that it was reading at least 300 ppm. The exhaust and heater shroud were replaced, but the cabin was still getting more than 10 ppm. He’s wondering if there is a maximum level allowed in aircraft. Mike said Car 3 didn’t have a maximum, but that Part 23 says 50 ppm is the allowed maximum under current regulations. Hypoxia and carbon monoxide are cumulative, and he said his current comfort is below 20 ppm. He also said leaning impacts CO levels. Peak or lean of peak EGT lowers CO. How it gets in is a bit of a mystery sometimes. He said there was a case where Mooneys with air conditioning were drawing in air from the intake on the side of the airplane. Paul said in a Cherokee it comes in via the forward wing attach point. There is supposed to be insulation to stop it from coming into this area, but over time they are taken out or lost. It’s often not from the engine compartment. It’s through the belly or downstream from the exhaust pipe.

John wonders if you can have a prop strike without a prop on the engine. He bought an RV9 with the engine on, but no propeller. He loaded it into the back of a box truck. Stopping partway to check on it, he found the tie-down straps had slipped and the airplane had be banging around in the truck. He’s wondering if he should be concerned, and what he should be checking for. Paul said to put a dial indicator on it and check to make sure it’s less than .005. Some of the bolts on the Van’s prop simulator were lose, and one was hard to screw back in. Paul said he would be surprised if there was any damage.

Jesse has a 310 with Continental engines and he’s wondering about the service bulletin that recommends maintaining 2300 RPM in cruise. Previously the hosts said it’s probably good advice when rich of peak, but you could ignore it lean of peak. He wonders if he should go lean of peak first, and then pull the prop back, or is going to a lower rpm first ok? Mike thinks it’s sufficiently brief that it won’t make a difference.

Rick had an infant mortality issue with his Mooney. His A&P found valve wear, oil though the rings, and corrosion on the engine, which only had a few hundred hours. He did a top overhaul, flew for 27 hours with the propre break-in procedure. About 30 hours later he got a high CHT indication on a descent, followed by dropping oil pressure. The belly was coated with oil and only 2.5 quarts were left. They found broken rings on 3 of the cylinders. They took off the electronic ignition, but are looking for ideas as to what may have happened. Mike found Rick’s data, which showed the CHT event was in cylinder #1, and the temperature rose at around .7 degrees per second. That approaches Savvy’s rule of thumb that anything at a rate of a degree per second or higher is a pre-ignition event. The hosts think it's possible the electronic ignition was the culprit. He thinks the broken rings may be an unrelated event. Colleen said improper ring installation could have caused the new ones to break She also suggests checking to make sure he doesn’t have a cracked plug.