US Patent 10436060 Shaft event detection in gas turbine engines

There is described herein methods and systems for detecting a shaft event in a gas turbine engine comprising a power turbine having a first shaft extending in a first direction and a second shaft extending in a second direction opposite from the first direction. A first speed measurement is obtained at a first location along the first shaft and a second speed measurement is obtained at a second location along the second shaft. A speed ratio is determined between the first speed measurement and the second speed measurement, and is compared to a detection threshold. The shaft event is detected when the speed ratio is beyond the detection threshold.