The Pitot-Static Instruments and Their Failures

The pitot-static system feeds the airspeed indicator, the altimeter, and the vertical speed indicator. The pitot tube captures ram air pressure and feeds only the airspeed indicator, while the static port senses ambient pressure and feeds all three instruments. The airspeed indicator compares ram and static pressure and displays speed on color arcs: white for the flap range, green for normal operation, yellow as a caution range for smooth air, and a red line at the never-exceed speed. Blockages are predictable. If the pitot ram inlet clogs but the drain stays open, airspeed falls toward zero; if both the inlet and drain block, the airspeed indicator acts like an altimeter, rising with altitude. A blocked static port makes airspeed inaccurate, freezes the altimeter, and disables the VSI — the reason an alternate static source exists. The altimeter measures static pressure and needs the current setting in its Kollsman window, remembering that flying from high to low pressure without resetting means "look out below." The VSI shows the rate of climb or descent with a slight lag because it senses how fast static pressure is changing.