During climbing flight using a turbocharged airplane, what happens to the manifold pressure as the critical altitude is approached?

As an airplane approaches its critical altitude during a climb in a turbocharged aircraft, the manifold pressure remains approximately constant. This is due to the nature of how turbocharging works; a turbocharger compresses the intake air, allowing the engine to maintain a higher level of performance at higher altitudes compared to normally aspirated engines.

As the aircraft climbs and air density decreases, a normally aspirated engine would experience a drop in manifold pressure due to the reduced atmospheric pressure. However, the turbocharger compensates for this by forcing more air into the engine, thereby maintaining consistent manifold pressure.

At the critical altitude, which is the altitude where the turbocharger can no longer maintain the desired manifold pressure, the engine will begin to experience a reduction in power. Hence, before reaching this altitude, the manifold pressure typically stays stable, allowing the pilot to achieve a more consistent and predictable climb performance. Once the critical altitude is exceeded, one would notice a decline in manifold pressure, which signifies that the turbocharger is no longer effective in compensating for the lower ambient air pressure.