Systems and methods are provided for real-time detection of the onset of stall in turbomachinery, such as compressor stall. The methods are capable of detecting and analyzing time of arrival of the chord of the blade at a sensor array to provide an indication of the onset of compressor stall. Systems for detecting the onset of compressor stall include: light sources; a plurality of linearly arranged optical fibers for transmitting light from the light sources and for receiving transmitted light reflected from a blade; a detector for measuring intensity of the reflected light; and a processor for analyzing the intensity of the reflected light to determine blade twist angle and from the blade twist angle identify onset of compressor stall. The invention can prevent the needless loss of life and assets caused by compressor stall that may lead to unexpected catastrophic failure of an engine.