The following information is derived from the FAAs Service Difficulty Reports and Aviation Maintenance Alerts. Beech A36 Fretting Engine Mount Bolts During an annual inspection, the IA found black fretting corrosion below the center two, l/h aft engine mount bolts. The bolts were loose in the mount even though their nuts were tight. Investigation revealed the bolts are a little too long and the nuts were running out of threads. The solution was to add another washer below the nuts, then re-torque back to specifications. Part Total Time: 1672.1 hours. ECI Cylinder Improper Machining A cylinder-base oil leak was discovered during the engines initial run-up. The technician determined the cylinder (p/n EC 636122ST) base lacked a machined area for the O-ring seal to seat. Part Total Time: 0.0 hours. Beech B24R Blown Electrical Capacitor Before takeoff, the airplane proved hard to start, drawing down the battery. During the takeoff, the pilot reported hearing a “pop,” then seeing smoke in the cabin. The takeoff was aborted and an emergency gear-up landing was made, resulting in substantial damage. 288
Fretting And Chafing
During an annual inspection, the IA found black fretting corrosion below the center two, l/h aft engine mount bolts. The bolts were loose in the mount even though their nuts were tight. Investigation revealed the bolts are a little too long and the nuts were running out of threads. The solution was to add another washer below the nuts, then re-torque back to specifications.
Key Takeaways:
- Manufacturing defects, such as an improperly machined cylinder or incorrect engine mount bolt length, can lead to immediate or long-term operational issues.
- Wear and tear, often exacerbated by inadequate protective measures (e.g., chafing fuel line sleeves, moisture-trapping insulation), frequently causes critical system failures in older aircraft.
- Electrical system failures, exemplified by a blown capacitor leading to an emergency landing, pose significant safety risks and can result in substantial damage.
- These Service Difficulty Reports underscore the critical role of thorough maintenance inspections in identifying and addressing potential hazards like fretting corrosion and chafing before they escalate.
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