Altitude and speed differences on alternate static

[mshac]

If the normal static port has a restriction somewhere in the system, it will reduce airflow. This will cause a lower indicated airspeed, and a lower indicated altitude. VSI would show a lower rate of climb/decent.

[Mich3773]

This was a good question about something I had forgotten, even though it was posted literally right in front of me. See the picture! I tested it in low level cruise. Airspeed dropped by ~10 kts, altitude increased by 150 ft.