Instrument Blockages

Question 1

Pitot tube & drain hole blocked

Answer 1

ASI will freeze in level flight, and will show faster-than-normal airspeed as you climb and slower-than-normal as you descend

Question 2

Static port + drain blocked

Answer 2

• Airspeed: low in climb, high on descent
• ALT/VSI: Frozen

Question 3

Static port blocked and drain open:

Answer 3

• Airspeed: low in climb, high on descent
• ALT: Frozen
• VSI: VSI will go to 0 due to the calibrated leak

Question 4

How do the instruments respond with the alternate static source?

Answer 4

• ASI: Reads high
• ALT: Reads high
• VSI: reverses