Pitot Static Blockages

Question 1

What happens when the Ram Air and the Drain Hole are blocked?

Answer 1

• Airspeed indicator acts like an altimeter

• Climb: airspeed increases

• Descent: airspeed decreases

• Why: pitot pressure is trapped while static pressure changes

Question 2

What happens if the Ram Air is Blocked and the Drain Hole is open?

Answer 2

Airspeed displays “0”

Question 3

What happens when the Static Source is blocked?

Answer 3

Altimeter:
• Freezes at the altitude where blockage occurred

VSI:
• Drops to zero and remains there

Airspeed Indicator:
• Climb: indicates lower than actual
• Descent: indicates higher than actual

Why:
• Static pressure is trapped
• Only pitot pressure changes

Question 4

What happens to the Altimeter if the static port is blocked?

Answer 4

• Altimeter freezes at the altitude where the blockage occurred

• Does not change with climbs or descents

• Why: static pressure is trapped, so the aneroid wafers no longer sense pressure changes

Question 5

What happens to the VSI if the static port is blocked?

Answer 5

• Indicates zero and remains there

• Why: no change in static pressure over time

Question 6

What happens to the Airspeed if using the Alternate Static Source?

Answer 6

• Reads higher than actual

• Why: cabin static pressure is lower, increasing the pitot–static pressure differential

Question 7

What happens to the Altimeter if using the Alternate Static Source?

Answer 7

When using the alternate static source, the altimeter will indicate higher than actual because the cabin pressure is lower than outside static pressure.

Why this happens:

• The alternate static source is usually inside the cabin.

• Cabin air pressure is typically lower than outside static pressure because of:
• Venturi effect
• Airflow around the fuselage
• Slight suction inside the cabin

Lower sensed pressure → altimeter thinks you’re higher.

Question 8

What happenes to the VSI if using the Alternate Static Port?

Answer 8

It momentarily shows a climb.

The VSI momentarily indicates a climb when using the alternate static source because the sudden drop in static pressure creates a temporary pressure differential across the diaphragm, which the instrument interprets as a rate of climb.