checkbord - posted blocked static - increase alt = ias decreases
Actually checkbord - posted blocked static - increase alt = ias
increases.
Pitot tube has Dynamic Pressure (airspeed information) AND static pressure in it. The Air Data Unit (ADU) subtracts the sensed static pressure (from the static port) from the pitot total pressure to determine the dynamic pressure alone, and thus calculate the airspeed.
If the pitot becomes blocked, the dynamic pressure & static pressure
at the time of the blockage remains the same. As the aircraft climbs, the sensed static pressure reduces (with the reducing altitude) so the ADU subtracts a
smaller static pressure from the pitot total pressure, and thus comes up with an increasing airspeed. The airspeed guage is now working something like an altimeter.
... Now that's the theory - it actually depends on the nature of the blockage and the leakage within the "blocked" pitot system.