Mike Rhodes wrote:

Patterson's note of the chart referenced from altitude, as opposed to
manifold pressure, causes me to scratch my head, too.

There's another chart in the manual that relates combinations of manifold pressure
and rpm to horsepower (but not to altitude). It has a similar limit band, but this
one makes sense to me. It basically says that you should never exceed a manifold
pressure of 25.3 HG at 2200 rpm (for example). I don't know why that limit band is on
the altitude/hp chart. I'm hoping that it's something that only applies to CS props.
In that case, perhaps the chart simply means that it is impossible to exceed a
manifold pressure of 25.3 HG at 2200 rpm above 6,000' ASL but below that the pilot
needs to be careful?

George Patterson
If a man gets into a fight 3,000 miles away from home, he *had* to have
been looking for it.