How can compressor stalls be initially recognized?

The correct answer identifies the early signs of compressor stalls, which include abnormal engine noise, an increase in Interstage Turbine Temperature (ITT), and a simultaneous decrease in N1 (fan speed) and torque. Recognizing these indicators is crucial for pilot awareness and safety.

When a compressor stall occurs, the airflow through the engine becomes disrupted, leading to a loss of efficient combustion and a resulting increase in engine temperature. The associated abnormal engine noise can manifest as a sudden change in sound, often described as a 'backfire' or rumble, indicating that airflow is no longer stable across the compressor section.

In tandem with these auditory cues, an increasing ITT suggests that the engine is overheating due to incomplete combustion, while the decreasing N1 indicates that the engine is not producing the necessary thrust and is struggling to maintain power. This combination of symptoms makes option B the most comprehensive and accurate for recognizing compressor stalls early on.

The other options either suggest a stable engine performance or fail to highlight specific symptoms associated with instability, which are essential for recognizing the onset of a stall.