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SESK: Stuff Everyone Should Know · sesk.info/pilot-glass-backup-shared-pitot

In many light airplanes with glass displays, why could a blocked pitot tube fool the backup instruments too?

They often share the same pitot-static inputs as the main display.

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  1. They often share the same pitot-static inputs ✔
  2. Backup instruments run on the same battery only
  3. Backup instruments use GPS for airspeed

Why: The FAA notes that many glass-panel light airplanes feed the backup instruments from the same pitot tube and static ports. If those are blocked, both the main and backup displays can be wrong.

Huh, didn't know that: Some systems combine the air data computer and the attitude system, so a blockage can even affect the attitude display.

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My glass cockpit and its backup always agree. Even when they are both wrong.
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References

Answer: They often share the same pitot-static inputs. The FAA notes that many glass-panel light airplanes feed the backup instruments from the same pitot tube and static ports. If those are blocked, both the main and backup displays can be wrong.

  1. Airplane Flying Handbook FAA-H-8083-3C, Chapter 18 www.faa.gov/sites/faa.gov/files/regulations_policies/handbooks_manuals/aviation/airplane_handbook/19_afh_ch18.pdf
    many of the light aircraft equipped with glass displays typically share the same pitot-static inputs for the backup instrumentation.
    Checked 2026-10-09.

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