Propeller Basics
Part 2
Operators and maintainers of uncertified or experimental aircraft should apply a great level of vigilance in the maintenance and inspection of the propeller. Experimental installations often use propeller-engine combinations that have not been tested and approved. In these cases, the stress on the propeller and, therefore, its safety margin is unknown. Failure could be as severe as loss of propeller or propeller blades and cause loss of propeller control and/or loss of aircraft control.
Experimental aircraft may operate with unapproved engines or propellers or engine modifications to increase horsepower, such as unapproved crankshaft damper configurations or high compression pistons. These issues affect the vibration output of the engine and the stress levels on the propeller. Significant propeller life reduction and failure are real possibilities.
Frequent inspections are strongly recommended if operating with a non-certificated installation; however, these inspections may not guarantee propeller reliability, as a failing device may be hidden from the view of the inspector. Propeller overhaul is strongly recommended to accomplish periodic internal inspection.
Visually inspect metal blades for cracks. Inspect hubs, with particular emphasis on each blade arm for cracks. Eddy current equipment is recommended for hub inspection, since cracks are usually not apparent. Identified damage must always be evaluated and repaired by an authorized source. Otherwise, you may induce unexpected safety concerns.
For more information, refer to the propeller manufacturer’s maintenance information and to the following FAA Special Airworthiness Information Bulletin’s (SAIB):
- NE-06-13 Using Propellers with Four or More Blades
- NE-08-18 Engine Dampers
- NE-08-19 Propeller Installation on Experimental Aircraft
- NE-08-20 Propeller Maintenance
- NE-08-21 RPM Restrictions & Placards
- NE-08-22 Search Inspection
You can find the specific SAIB at this address: http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgSAIB.nsf/MainFrame?OpenFrameSet by entering the SAIB number in the search box.
This month’s Maintenance Safety Tip was sponsored by Hartzell Propeller; Piqua, Ohio.
