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Altimeter density error

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Aircraft Systems, Commercial Pilot, Flight Instructor, Instrument Rating, Private Pilot, Student Pilot

I understand that the Altimeter operates with the static system with the relative changes of pressure that inflates a wafer that turns the linkages of the needle. High to Low look out below.. Low pressure usually is cold air and is more dense with less kinetic energy.

My question...  Is it because there are more air molecules going in the static port that inflates the wafers more which indicates a higher indicated altitude?

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1 Answers



  1. Brent on Jun 02, 2015

    I think you have the relationship between the wafer and the pressure backwards. As pressure increases, the wafer deflates. Decreasing pressure means the wafer inflates. Think of the wafer as an inflated balloon trapped in a jar. In this analogy, the air in the jar represents the pressure inside the instrument let in from the static port. The size of the balloon is the balancing point between the force of the pressure inside the balloon pointing out versus the pressure in the jar pointed inward on the balloon. If you increase the pressure in the jar (more air molecules) then the force inward on the balloon increases and the balloon gets smaller. Letting air out of the jar has the opposite effect on the balloon.

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