In turbine engine investigations, which option indicates a Low RPM - Low Angle impact in the compressor?

• A. Blades not bent or uneven
• B. Blade imprint on case
• C. Disk rub
• D. Little FOD ingestion (Correct)

Answer: (B)

When a compressor experiences a low-energy impact from debris at low RPM and a shallow angle, you often see a blade imprint on the inner compressor case. The energy is not enough to bend, nick, or eject the blade, so the blade edge or tip leaves a mark where it pressed into the casing. That imprint directly reflects the contact geometry and low energy of the event, making it the most telling sign of a Low RPM - Low Angle impact.

Other signs don’t align as neatly with this scenario. If blades look undamaged, that argues against a significant contact. Disk rub points to rotor-stator contact that typically involves different energy or timing conditions and isn’t specific to a low-speed, shallow-angle hit. And while little FOD ingestion tells you the debris load was small, it doesn’t by itself indicate the impact’s energy or angle.