SESKStuff Everyone Should Know
SESK: Stuff Everyone Should Know · sesk.info/ifr-static-blocked-asi-climb

Static ports block at 4,000 feet. You then climb well above that. How does the airspeed indicator read?

Lower than actual airspeed.

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  1. Higher than actual airspeed
  2. Lower than actual airspeed ✔
  3. Exactly right

Why: The trapped static pressure is higher than normal for the new altitude. That makes the ASI read less than the actual airspeed. Descending below the blockage altitude gives the opposite error: a reading that is too high.

Huh, didn't know that: Errors in the airspeed indicator and VSI almost always point to a blocked pitot tube, static ports, or both.

The dad joke
I asked my airspeed indicator to be honest. It said it was under a lot of pressure.
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References

Answer: Lower than actual airspeed. The trapped static pressure is higher than normal for the new altitude. That makes the ASI read less than the actual airspeed. Descending below the blockage altitude gives the opposite error: a reading that is too high.

  1. FAA Instrument Flying Handbook (FAA-H-8083-15B) www.faa.gov/sites/faa.gov/files/pilots/FAA-H-8083-15B.pdf
    the airspeed indicates lower than the actual airspeed
    Checked 2026-10-11.

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Test yourself in the game

FlyingIce blocks a pitot tube's ram opening and its drain hole. What does the airspeed indicator do in a climb?FlyingYour static system is blocked. What does the vertical speed indicator show while you climb?FlyingStatic ports ice over at 5,000 feet and you climb to 7,000. What does the altimeter show?

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