Squawk Box

Cessna Model 172S Skyhawk SPArcing Avionics MasterPilot reported burning smell and failure of avionics #2 buss during run-up. Troubleshooting revealed the right side of the avionics master switch (#2 buss) had been arcing internally. Replaced switch; ops check okay.

Beechcraft Model F33A Bonanza/IO-520Cracked Magneto Impulse CouplingDuring a 500-hour magneto inspection, the impulse coupling was discovered to have cracks in its flyweight base plate. The cracks were detected using magnetic particle inspection and appear to have originated from the sharp-cornered feature of the base plate that forms the full advance stop. Slick p/n M3050.Part total time: 565.0 hours

Landing light switch was stuck in the on position. Suspect internal arcing and welding of contacts. The overheating caused by the arc- ing can cause the switch body to melt, but did not in this case. No signs of heat damage of external switch surface were found.

We own and fly a Diamondstar DA40 from our home in Michigan to destinations all over the country. Generally my wife and I plan a two-week trip each fall and spring, often to the coasts. However, the word plan is figurative as we expect weather deviations and our routing may change at any time. We literally wake up in the morning, look at the current weather and decide our destination for the day. Typically, we will fly no more than 500 miles and land at a suitable GA airport. While I button down the airplane, my wife books a hotel, rents a car and finds out what to see and do in town from the always-friendly and helpful FBO staff.

While in cruise flight, pilot noticed smoke coming out from under instrument panel. Pilot aborted flight but noticed landing gear extension much slower than normal. Aircraft was placed on jacks and gear retracted. Pump motor (p/n 98811281) could be heard grinding and working very slowly. Pump motor was too hot to be touched. Battery was disconnected, aborting retraction. New pump and motor were installed.

The tailwheel could not be steered during an annual inspection. The tailwheel had been painted; its grease fitting had been completely covered. The owner stated a technician told him not to grease the tailwheel and to tighten the nut on the bottom of the steering pivot bolt as tight as possible. Disassembly revealed all parts inside the tailwheel unit were extremely worn.

The number 3 cylinder exhaust pushrod broke, due to a valve stuck in the closed position. The valve was not stuck at the time of the investigation. No marks were seen on the top of the piston as viewed through a borescope. The lifter came apart as a result of the broken push rod but appears to have been operating properly prior to the event.

Aircraft had been inactive and hangared for approximately six months. While trying to troubleshoot a fuel quantity indication problem, a fuel sample revealed contamination, which was sent for analysis. While awaiting results, tanks were drained and an anti-bacterial fuel additive was added before they were refilled.

Inspection after aircraft received from paint shop found left elevator actuating rod nut unpinned and backed off almost completely, with its bolt backing out. Left aileron outboard hinge was not attached. Hinge plate pinched between skin. Aileron binding. This aircraft was flown in this condition.

The pilot could not pull the right engines condition lever into the fuel cutoff position; the firewall shutoff was used to shut down the engine. Inspection revealed the linkage between the power lever and the condition lever on the fuel control unit was corroded and the linkage jammed with residue. The linkage was cleaned and lubricated, and the aircraft returned to service.