Final answer:
The emergency application of air brakes on a train when it passes a red signal is caused by the use of an air brake system invented by George Westinghouse in 1869.
Step-by-step explanation:
The emergency application of the air brakes on a train when it passes a fixed signal indicating red is caused by the use of an air brake system.
This system was invented by George Westinghouse in 1869 and works by sending compressed air through a line to enable the train's engineer to apply brakes from the locomotive.
The air brake system allows for safer and more efficient stopping of trains, preventing accidents and ensuring the adherence to signal indications.