To what altitude will a turbocharged engine maintain sea level pressure?

A turbocharged engine is designed to maintain a constant manifold pressure, which can be equivalent to sea level pressure, at higher altitudes. This capability is primarily limited by what is known as the critical altitude. The critical altitude is the maximum altitude at which the turbocharger can maintain its rated boost pressure, ensuring that the engine continues to receive enough air for optimal performance.

When the aircraft climbs above this critical altitude, the turbocharger may not be able to compensate for the decrease in ambient air pressure, resulting in a drop in manifold pressure. Therefore, the critical altitude is the specific altitude at which the turbocharged engine can sustain sea level pressure, making it the correct answer in this context.

In contrast, service ceiling refers to the maximum altitude at which an aircraft can maintain a specified rate of climb, but it does not specifically indicate sustained sea level pressure. Pressure altitude is a reference used in aviation that corresponds to the altitude in the Standard Atmosphere when measured using a barometer set to 29.92 inHg but does not define the performance characteristics of a turbocharged engine in relation to maintaining sea level pressure.