Can anyone think of an aircraft that has a internal static port used for instrumentation because I can not. Think he may be confusing this with the internal port for a cabin pressure controller or sensor for O2 mask deployment.
The likes of the Unpressurised Piper Pa 28 and the rest of the unpressurised range has one under the lip of the instrument panel, it is very similar to the fuel drain in design, on the likes of a Cessna 152 you break the glass on the VSI in an emergency.
Though as said there is some discrepancy between the outside port as the internal one so it is not as accurate.
The two I mention need an alternate source as they only have one external static port unlike most aircraft that have two.
Even on aircraft with two ports one on either side of the airframe, if one is blocked for whatever reason the system will lose accuracy because the ports on either side will normally compensate against each other for airflow etc over them.
Where an aircraft has two systems i.e pilot and co pilots and has 4 ports, two either side above and below each other, the system will be cross wired, i.e the upper port on the pilots system will cross connect to the lower on the other side and vice versa so both systems sense from an upper and lower port on either side so read equally between both systems, if that makes sense.
This shows describes the TBM system from its manual
http://www.smartcockpit.com/download...nstruments.pdf
Hope that helps.