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Introduction
The lifespan of an aircraft ranges to thirty years enhancing the opportunities for their maintenance. In an aircraft maintenance of propellers is of utmost importance. Propellers manufacturers usually specify the time of propeller inspection. A regular daily inspection depends upon the type of the propeller. The inspection of the propellers varies a visual inspection to a more thorough checkup. The inspection must be meticulous and professional. The visual checks must include spinners, blades, weld and braze sections of the blade, dome shell and hubs of any evidence of failure. Oil level and lubrication must also be inspected. The propeller inspection and maintenance must always be carried out based upon the information provided by manufacturers. In general, there are different types of propellers, wood propeller, metal propeller, aluminum and composite propellers. For each and different types of propellers, the inspection and maintenance would vary (wijerathne, n.d.).
FAA Maintenance Regulations
FAA (Federal Aviation Administration) of the US department of transportation provides advisory circulars for the maintenance procedures of aircraft propellers. FAA recommends certain minimum requirements for propeller field maintenance. FAA also provides a thorough checklist for propeller annual inspections. FAA advisors recommend reading the manufacturer’s instruction for maintenance records, airworthiness directives and service bulletins that relate to the maintenance, care and inspection of propellers. The advisory circulars by FAA can be downloaded from the website of FAA. When maintained properly propellers operate safely for extended periods of time. However, despite the guidelines and regulations, failures do occur. FAA data on aircraft indicate that propeller failures occur across all the different varieties of propellers. The propeller maintenance information provided in advisory circulars offer the essential steps and techniques to reduce propellers failures and enhance it life (FAA.gov, 2005).
Types of damage
The damage type of a propeller would determine the failure or unairworthiness of the propeller. As defined by FAA there are six different types of damage namely, corrosion, twist, nick, erosion and dents and lightening strikes. Corrosion can be external corrosion on the metal plates known as surface corrosion or pitting. Pits are a more serious type of corrosion where cavities exist on the metal surface. Continued presence of moisture causes inter-granular corrosion resulting in loss of protective barriers, rolling of sheets and casting, and sometimes even cracks in the blade. Twist misalignment occurs when blades are bent or twisted leading to misalignment of propeller blade leading across of thrust and vibrations.
Nick is the displacement of the metal on the leading and trailing edge of the propeller. Due to erosion, a loss of metal from the blade surface occurs leading to failure of the blade. A lightning strike on a blade leaves a burn mark in the metal area which might or might not be visible but has serious implications for the functioning of the propeller. Two more damage types defined by FAA are caused by human errors like over speeding and object strike. According to FAA advisory, each of the different types of damage is a leading cause of making propeller’s airworthiness invalid.
Maintenance and Overhaul
FAA directives defined maintenance, repair and cleaning responsibilities for different types of propellers. Major repairs are specified in the manufacturer’s manual while minor repairs and cleaning must be carried out by the owner or the operator. FAA certified mechanics are also available with capabilities for carrying out maintenance and minor repairs. It is also required to maintain the records of aircraft maintenance. The maintenance records of propellers are a responsibility of owner/operator. Proper cleaning of the propeller is a critical aspect of the maintenance. Care should be taken while cleaning the propeller surface to avoid damage to the surface. Water causes corrosion on the blades, therefore cleaning followed by drying is important for the blades. Any acidic or alkaline solution must be avoided.
Propeller Inspection
There are five inspection methods for a proper propeller inspection. The five methods of inspection include visual, penetrant, ultrasonic, eddycurrent and magnetic particle inspection. The different types of inspection are inspection post-impact, tracking inspection, over speed and corrosion inspection. Similarly, for different types of propeller, each or all type of inspection must be carried out. There are different levels of inspection ranging from basic, general to detail. A basic and general inspection can be carried out on a daily basis or after any suspected impact. A detailed inspection is usually carried out after a hundred hours of flight or annually. The inspection interval depends on the time of latest inspection or the numbers of hours of flight.
Conclusion
Aircraft propeller maintenance and inspection is a critical aspect of increasing the safety and life of propellers. A proper inspection and maintenance avoid serious failures of aircraft and major accidents. Within the industry, there is a trend of outsourcing the maintenance and inspection activities. However, only FAA certified mechanics must be called for such activities. Repair work for propellers must be carried out at certified and proper repair stations. FAA specifies regular directives and steps for a proper inspection and maintenance of propellers. The FAA advisory circulars available on FAA website provide a detail of inspection methods, types and levels for different types of propellers. Maintenance procedures, methods are also available on FAA advisory circulars. FAA also provides damage conditions and factors that revoke a propeller’s airworthiness. FAA advises following manufacturer instructions and manufacturer manual for propeller maintenance and inspection activities.
Reference
FAA.gov,. (2005). Advisory Circular Aircraft Propeller Maintenance. Retrieved 24 February
2016, from http://www.faa.gov/documentLibrary/media
/Advisory_Circular/AC_20-37e.pdf
Quinlan, M., Hampson, I., & Gregson, S. (2013). Outsourcing and offshoring aircraft
maintenance in the US: Implications for safety. Safety science, 57, 283-292.
wijerathne, c. Aircraft systems: Propeller Inspection and Maintenance. Okigihan.blogspot.in.
Retrieved 24 February 2016, from http://okigihan.blogspot.in/p
/propellerinspection-and-maintenance.html
