FAA September 2012 Maintenance Alerts

Cessna: 680CE; Worn Brake Metering Valve Arms; ATA 5310

"Upon removal of the R/H floor panel," says this repair station mechanic, "it was observed there was some fretting material on the insulation bags and the surrounding area. Further investigation revealed the R/H and L/H arms (P/N's 6964000-16 and -17) that connect the brake metering valve to the brake cable clevises were severely worn. The bolts and clevises at the attach points are wearing into the brake metering valve arms. It looks like the bushings (spacer P/N NAS43DD4-16FC) were never installed. (I) recommend during a 3A Emergency Battery Service or inspection that this panel (162ET) is removed and the (valve) arms inspected for wear and spacer installation."

Bell: 206B; Failed Transmission Oil Sight Indicator; ATA 6320

"During a routine inspection," says this repair station submission, "(we) discovered the oil level indicated 'full' — after the main rotor transmission oil was drained. After removal, inspection of the indicator (P/N 206040093001) revealed the coating with the 'level markings' had separated from the metallic back plate. There is a ring of holes on the circumference of the indicator. These were not aligned with the holes in the 'level mark' coating on the back plate. This condition would not allow oil to drain from the sight glass — the only means to determine (correct) oil level in the main rotor transmission. Improper servicing of the transmission presents a potential for serious problems if left undetected."

Part Total Time: 4,143.0 hours

Lycoming: IO540AE1A5; Failed Intake Valve; ATA 8520

(The following description references a Robinson R44 Raven II helicopter.)

"Removal of the number one cylinder for visual inspection revealed a failure of the intake valve. Subsequent analysis from the data recorded by the JPI graphical engine monitor showed massive ingestion of engine oil into the remaining cylinders, causing loss of power — oil fouling the remaining (otherwise) unaffected spark plugs. Closer inspection of the effected cylinder showed catastrophic damage to the piston and combustion area from (piston/valve/head) multiple contacts. Fractured valve parts became wedged in the induction tube and in the common manifold area. When the intake rocker assembly was removed it was discovered the top portion of the valve stem above the 'keepers' was the area of separation/failure. A 30X power microscope was used for inspection. It is (our) opinion the failure of the intake valve may have been caused from a stress riser created during manufacturing at either the machining, heat treating process, or perhaps at the molecular level during creation of the raw material. It should be noted the aircraft was in compliance with Lycoming Service Bulletin SB388C exactly 85.8 hours earlier. No defect or abnormalities were noted at the time of the inspection."

Part Total Time: 381.0 hours

The FAA Aviation Maintenance Alerts provides the aviation community with an economical means to exchange service experiences and to assist the FAA in improving aeronautical product durability, reliability, and safety. To read more: http://www.faa.gov/aircraft/safety/alerts/aviation_maintenance/media/2012/2012_09_Alert.pdf.