What to look for in a prebuy?

[mshac]

Originally Posted by ljmolina

 CABIN PRESSURE CHECK
-Take Plane upto 17,500 ft and ISOLATE each engine and check to see if
the cabin pressure can maintain max differential pressure (3.25psi)

You don't need to go to 17.5 to verify the pressurization system. You could do it at 8.5, just be sure the differential gauge on the pressurization control panel is at max.

That said, taking the plane to 17.5 will expose bootstrapping, weak mags, and weak wastegates/turbos. Its well worth it to fly that altitude during the prebuy if at all possible! If one engine can't hold manifold pressure or starts to miss up there, you know you have an issue.

These airplanes were designed to fly high. They are both faster and more efficient the higher they go. I find 17.5 to be a "sweet spot" on a lot of trips. You're VFR, but with flight following at that altitude, you get great service from controllers, almost as if you were an IFR flight. Also, there is very little traffic at that altitude. I'll go hours without ever seeing another aircraft sometimes. My father once complained that it was "boring" flying so high because he couldn't see anything, so I flew him from Nashville to Dallas at 2500 ft - he loved every minute of it! Kept me out of a strong headwind too