Certified Flight Instructor - Flight Instructor Airplane Practice Exam

If both the ram-air input and drain hole of the pitot system are blocked, what airspeed indication should a pilot expect?

1. decrease of indicated airspeed during a climb

2. zero indicated airspeed until blockage is removed

3. no variation of indicated airspeed in level flight

4. increased indicated airspeed in descent

The correct answer is: no variation of indicated airspeed in level flight

When both the ram-air input and drain hole of the pitot system are blocked, the airspeed indicator will be fed from the static pressure only. In this scenario, the airspeed indicator operates as if it were an altimeter, relying on static pressure rather than dynamic pressure changes that typically inform it of airspeed. As a result, in level flight, where the atmospheric pressure remains relatively constant, the indicated airspeed will stay the same because there is no dynamic pressure to cause a change in that indication. This means that even if the aircraft is climbing or descending, the readings from the airspeed indicator will remain stable and not reflect any change in actual speed, effectively showing no variation in indicated airspeed. It’s critical to keep in mind that this condition can lead to misinterpretation of aircraft performance, as pilots may not receive accurate airspeed readings during flight, which can impact decision-making.