Preventing FOD using the Inertial Separator is much simpler than one might think. The function of the Inertial Separator is to help prevent foreign object damage (FOD) to the engine. It is recommended to use it by energizing the separator when the aircraft is on the ground and during the landing approach, as this will prevent FOD particles from entering the compressor section. It is also fairly common in instances to see the ITT increase by about 6 to 8 degrees Celsius due to air inlet entry restriction. Its also good practice to deploy the initial separator during takeoff and once wheels are up remove the bypass and set it back to Normal condition. This in turn will also help prevent FOD from the runway entering the compressor.
The deployment of the inertial separator to the bypass (icing) position forces air in the nacelle to execute a sharp turn before entering the engine. Foreign objects (e.g.: stones, ice, sand, snow, rain) tend to maintain their original high velocity path because of their inertia and weight being heavier than air are discharged overboard through the separator bypass duct.
Note: The inertial separator is an airframe supplied item. Not using the inertial separator in icing conditions can result in costly damage to the compressor blades. Always ensure the separator operates freely. Erratic movement of the separator vane may cause engine ITT increase.
Always refer to the AMM
Using the Inertial Separator is a great way to help preventing FOD in your engines. We see more damage in FOD related scrap then any other single cause at overhaul. As important as cost from FOD, is poor compressor performance due to heavy blending. Optimal compressor care at overhaul is important. BG Aerospace has a compressor profiling process that not only profiles single blades, but also matched the profile of each set to the next, optimizing the flow of air through the compressor. Ask us for more information so that you can count on the heart of your engine to maximize the performance of your turbine.