Feathering as it pertains to propeller functions refers to aligning the propeller blades such that the difference in pressure between the camber face and the back face are almost equal and thus, creating minimal drag or air resistance (Shiosaki, 2017). This is incorporated when the engine is shut down and the propeller needs to create minimal thrust. Feathering is mostly done in Multi Engine Turboprop Aircrafts, where if any one of the engine fails, feathering of the propeller blades of that engine are done so that they create minimum drag, and also to prevent the engine from rotating without lubrication, which is dangerous. This is why it is important to be aware of this dynamic during an accident investigation.
"Turbine parts may have a memory” is an investigative expression which means, the mechanical works of the turbine system and the thermal damage that it undergoes, while it still keeps running regardless of the heat it is exposed to. Turbines play a major role in the investigation of an aviation accident. Whether the turbine failed before or after the accident can be determined during investigations. "Critical flows" needed by a turbine engine to operate properly means the conditions associated with the high and low pressure in the turbines. When air at a certain temperature and pressure flows through a constricted part or section with lower pressure, the turbine speed increases and thus, providing drag or thrust. There is a cause and effect relationship in regards to these flows where by, when the air and pressure flows through the nozzle with high pressure, the velocity of the turbines reduces providing no drag or thrust. These cause and effect relationships thus lead to the failure of the turbine engine to work properly, which in turn causes accidents involving turbine power plants.
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Reference
Shiosaki, D. T. (2017). U.S. Patent Application No. 14/966,493. https://patents.google.com/patent/US20170166302A1/en
