Definition
A condition in which the pitot tube, the static port, or both become obstructed — typically by ice, water, insects, or debris — preventing the pitot-static system from sensing ram air pressure, ambient static pressure, or both. Because the airspeed indicator, altimeter, and vertical speed indicator all rely on these pressure inputs, a blockage produces erroneous or frozen readings on one or more of these instruments, with the specific error pattern depending on which port is blocked.
Plain English
Something is plugging the small openings on the aircraft that the speed and altitude instruments use to sense the air. When that happens, those instruments stop showing the correct numbers and can be misleading.
Context Anchor
Encountered during preflight inspection, instrument flying, and troubleshooting when the airspeed indicator, altimeter, or vertical speed indicator does not behave as expected.
Derivation
“Pitot” comes from Henri Pitot, who developed a tube for measuring moving-fluid pressure. “Static” means still or not moving; in this system it refers to the surrounding air pressure. The term helps remind you that the system depends on two pressure sources: moving-air pressure and outside-air pressure.
Why Pilots Care
Unrecognized blockage leads to false airspeed and altitude indications that can cause loss of control or flight into terrain.
Analogy
It is like trying to judge water flow through a straw when part of the straw is plugged. The gauge may still show something, but it is no longer showing the real flow or pressure.
Grounding Statement
If a small pressure opening on the airplane is blocked by ice, water, insects, or a cover, the connected instruments may no longer show what the airplane is actually doing.
Intuition Check
Do not assume a blockage always makes an instrument go to zero. A blocked pitot-static line can trap pressure, so an instrument may freeze or give a believable but wrong indication.
Example Sentence 1
After climbing into icing conditions, the pilot suspected a blockage of the pitot-static system when the airspeed indicator began behaving like an altimeter, rising as the aircraft climbed.
Example Sentence 2
In icing conditions the pilot activated the pitot heat to avoid blockage of the pitot-static system.