”We don’t check the accuracy of your fuel gauges”

You may think an annual inspection includes a verification of the accuracy of your fuel gauges, but you'd be wrong. Nor does the IA check the accuracy of your tach or any other number of instruments. This information comes to a pilot undergoing a first annual. Mike, Paul, and Colleen also tackle oil loss and temperature issues, why we stop our engines with the mixture, and the difference between a major and minor alteration. Submit your questions to podcasts@aopa.org for a chance to be on the show.

Full notes below:

Chuck flies a 1941 Interstate Cadet with a Continental 85-8F engine. He had a prop strike four years ago, was inspected and got some new rings, gaskets, and a few other parts. He’s noticed he goes through a quart every four or five hours, compared to 15 hours prior to the overhaul. Mike suggests there may have been a problem when honing the cylinders, and Colleen suggests borescoping to see what the honing looks like now. Paul said a normal honing crosshatch is about 30 degrees, but that on a teardown they use a ball hone that doesn’t make a regular pattern. If it’s at all shiny it means they’re glazed. But ultimately they all agree it doesn’t matter and that it’s an acceptable amount of oil loss.

Tom is a new mechanic who is looking for advice. A friend asked him to install a new stall warning horn to augment the stall warning light in his Cherokee. Paul suggests looking at a newer version of the airplane with a horn and a light, and submitting that information as approved data to the FAA. FAR 1.1 defines a major versus minor alteration. Advisory Circular 43-2B is acceptable methods for aircraft alterations, which Collen calls the bible of alterations. Mike makes the point that it’s a mechanic’s decision as to whether an alteration is major or minor. A major requires someone else’s signature, such as a field approval or FAA sign-off, while minor is only the mechanic’s signature.

Jay flies a Mooney with M20F with an IO-360 with a JPI engine monitor. The oil temp probe is located near the first cylinder. On climb it hits 230F and trips the over-temp alarm. In cruise it stabilizes at 195F. The analog probe shows 30 degrees cooler. The hosts aren’t at all surprised that the probes are different. Colleen mentioned that when she changed engine monitors they moved the probe and her oil temps have gone down. Mike said our goal is to usually measure the oil temp at the coolest location.

Peter has a Cardinal and is going through his first annual. He is wondering where the accountability is for previous mechanic oversights. His IA has found things like airworthiness directives that haven’t been complied with, a bucking bar left in the airplane, and so on. Mike makes the point that there is a difference between airworthiness discrepancies and things that are more discretional in nature. And all three hosts caution that each annual and pre-buy inspection are unique, and that it’s impossible to snag every discrepancy.

Walter asks why we don’t just turn off the key when stopping a traditional piston airplane engine. The hosts agree that it is solely a safety consideration, and meant to get gas out of the system. That way an ungrounded mag can’t refire the engine and create a safety issue with the propeller.

Rolf has a TB-20 with an IO-540 engine that’s never been overhauled and is trouble-free. Last year he noticed on the engine monitor traces that the number 1 and number 2 EGTs were very low at low fuel flow. His shop measured the dry tappet clearance and found the intake valves were well in excess of the limit. They were able to bring them within limits, but the EGTs are still bottoming out. Mike makes the point that the valve clearance limit is only to ensure that the amount of play in the system so that the hydraulic lifter can “take it up.” The hosts agree his engine is in fine shape, and not a safety issue. They do recommend he prepare for an overhaul in the future based on the symptoms.