An optical sensor could offer added security to pilots and passengers flying on commercial airliners. Developed by Physical Sciences Inc. in Andover, Mass., the sensor sends pulses from a diode laser upstream of the main part of the aircraft's engine. The device determines air density and velocity as it passes through the engine, assisting the pilot in determining the optimal amount of fuel necessary to fly an aircraft in given atmospheric conditions. It also acts as a safety feature able to detect changes in engine operating conditions preceding hazardous situations such as compressor stall. Engine manufacturer Pratt & Whitney has tested the device.