Extrapolation of graphs

[JeroenC]

Hi all,

i am working on the flightplanning for my USA trip. The plane will be a PA-28-140 160 HP Cherokee.
Now, in some places i will encouter a density altitude >>>> 7000 ft.

The POH graphs don't go above 7000ft and state "extrapolation of chart above 7000 ft is invalid".

Of course the service ceiling is also way above 7000 ft, so what does this mean? How can I make a flightplanning in this way?

The strange thing is, that some graphs do go up to 14,000 ft., e.g.: Climb performance, engine performance, cruise performance, glide performance.

It basically is only the take-off and landing which goes up to 7000 ft.

Thanks in advance.