If the pitot tube ram air inlet and drain hole both freeze, only the airspeed indicator will be affected—it will act like an altimeter, reading higher as the aircraft climbs and lower as the aircraft descends. It will also read lower than actual speed in level flight. If the static port freezes, all of the instruments connected to the Pitot-Static System will be affected. The AIRSPEED INDICATOR will remains accurate at the altitude frozen as long as the static pressure in the indicator and the system equals outside pressure. If the aircraft descends, the airspeed indicator will read high because the outside static pressure will be greater than that of the air trapped in the system. If the aircraft climbs, the AIRSPEED INDICATOR will read low because the outside static pressure will be lower than that of the air trapped in the system. The ALTIMETER will indicate the altitude at which the system became blocked. The VSI will indicate level flight. When using an alternate static source vented from inside the airplane, the static pressure will be lower. Therefore, the ALTIMETER will read higher than the actual altitude, the AIRSPEED INDICATOR will show a greater than actual airspeed, and VSI will show a climb while in level flight.