What is the role of the pitot drain hole?

• A. It allows collected water to drain so that pressure readings remain accurate.
• B. It vents cabin air during flight.
• C. It measures outside air temperature.
• D. It seals the pitot tube to prevent contamination.

Answer: (A)

The pitot drain hole keeps the dynamic-pressure sensing path clear of collected water so that airspeed readings stay accurate. The pitot tube measures dynamic pressure to determine indicated airspeed, and water from rain, condensation, or humidity can accumulate inside the tube or at the sensing port. If that water isn’t allowed to escape, it can distort the pressure signal and cause erroneous airspeed indications. The drain hole provides a small, unobstructed outlet for that water, helping prevent blockage and maintaining reliable readings. It isn’t meant for venting cabin air, measuring outside air temperature, or sealing the tube—those functions would interfere with the system rather than protect accuracy.