# What is the critical altitude?

What is the definition of critical altitude and why is important to know in Vmc graph? Also, is there any critical altitude in the Piper PA-44 Seminole?

• Do you have a copy of this Vmc graph? It may help get a more definite answer. – GdD Feb 20 '19 at 11:33

## 1 Answer

Critical altitude is the maximum altitude where the engine turbochargers (or turbonormalizers) can maintain sea level standard pressure to the engines. Above the critical altitude the engines will produce less power, although still delivering more power than an normally aspirated engine at the same air density.