Which atmospheric factor is NOT mentioned as affecting engine thrust?

The factor that is not mentioned as affecting engine thrust in the context of gas turbine engines is humidity. While the other options—pressure, density, and temperature—are fundamental atmospheric factors that significantly influence engine performance, particularly thrust, humidity does not have a direct and well-documented impact on how engines produce thrust.

Pressure affects thrust because it directly influences the amount of air entering the engine; lower pressure at high altitudes means less air for combustion. Density is crucial as it determines how much air mass is available for combustion, impacting thrust generation—denser air provides more oxygen for fuel combustion. Temperature influences the efficiency of air entering the engine; hotter air is less dense, which can reduce thrust.

Humidity, while it affects the air’s density, does not have the same level of influence on thrust as the other parameters because it typically accounts for a smaller variation in mass flow compared to variations caused by changes in pressure or temperature. Humidity can indirectly affect overall engine efficiency and operational characteristics by altering the air's density, but it is not a primary consideration when calculating thrust compared to the other factors listed.