Just because a pitot-static system is on a certified aircraft doesn't necessarily imply that it is accurate. It simply implies that it is accurate against what is presented in the RFM. For example, the AW119 pitot-static system has massive errors (>10 kts) in certain flight regimes (mostly during low power descents, as well as during high power climbs at higher airspeeds). It's pressure ports are up above the windshield.