In icing conditions, what is the general effect on pitot-static instrument readings?

• A. Ice can block ports, causing unreliable readings or failures
• B. They become more accurate
• C. They operate normally
• D. Only the air data computer is affected

Answer: (A)

In icing conditions, moisture can freeze on the pitot tube and static ports, blocking those openings. The pitot tube supplies the dynamic pressure signal that drives the airspeed indicator, while the static ports provide the ambient pressure signals for the altimeter, vertical speed indicator, and the airspeed indicator’s reference. If ice blocks these ports, the air data system can no longer sense correct pressures, so readings become unreliable or fail altogether. That’s why you may see erratic airspeed readings, an altimeter that sticks or jumps, and erroneous vertical speed indications. It’s not that the system becomes more accurate or that only the computer is affected—the blockage feeds bad pressures into the entire air data system, leading to multiple instruments behaving improperly.