How does the pitot-static system provide air data, and what happens if a pitot tube is blocked?

• A. It uses pitot and static pressures to feed the airspeed indicator, altimeter, and vertical speed indicator; blockage can cause erroneous readings and an alternate source must be used.
• B. It relies on outside air temperature alone to determine airspeed and altitude, so a blocked pitot tube only affects the airspeed indicator.
• C. It uses a single static source to power all instruments, and a blockage affects only the vertical speed indicator.
• D. It self-corrects when blocked, requiring no pilot action or alternate source.

Answer: (A)

The important idea is that air data comes from two pressure signals: dynamic pressure from the pitot tube and ambient static pressure from the static ports. The airspeed indicator uses the difference between those two pressures (dynamic minus static) to show how fast the airplane is moving through the air. The altimeter relies on static pressure to determine altitude, and the vertical speed indicator uses the rate of change of static pressure to show climb or descent.

If the pitot tube is blocked, the dynamic pressure can’t reach the airspeed indicator, so the airspeed reading becomes unreliable. The static system, which feeds the altimeter and VSI, can continue to operate, but the airspeed indication may become erratic or stuck. To restore accurate air data, pilots switch to an alternate static source (and, if available, use alternate pitot pressure) so the airspeed indicator can receive a usable pressure signal. That’s why this option correctly captures how the pitot-static system feeds the instruments and what happens when the pitot tube is blocked.