How does pressure altitude affect true airspeed (TAS)?

True airspeed (TAS) is defined as the actual speed of an aircraft through the air, corrected for non-standard temperature and pressure conditions. The relationship between pressure altitude and true airspeed is predominantly influenced by the density of the air.

When the air density is lower than the standard atmospheric conditions (ISA), which typically occurs at higher altitudes or warmer temperatures, the TAS will increase. This is because an aircraft needs to move faster through less dense air to maintain the same performance characteristics as it would at a lower altitude where the air is denser. Essentially, for the same amount of thrust, an airplane will produce more lift at higher TAS due to the reduced air density.

Therefore, as pressure altitude increases and if density falls below standard levels, the true airspeed will increase, making the correct choice pertain to this understanding of the atmospheric conditions affecting performance.