Altimeter

Question 1

How does and altimeter work?

Answer 1

In an an Altimeter, aneroid wafers expand and contract as atmospheric pressure changes, and through a shaft and gear linkage, rotate pointers on the dial of the instrument.

Question 2

What are the limitations that pressure altimeter is subject to ?

Answer 2

1 - Temperature variation expand or contract the atmophere and raise or lower pressure levels that the altmeter senses.

• On a warm day* - the pressure level is higher than on a standard day. The altimeter indicates lower than actual altitude.
• On a cold day* - The pressure level is lower than on a standard day. The altimeter indicates higher than actual altitude.

2 - Changes in surface pressure also affect pressure levels at altitude.

• Higher than standard pressure* - The pressure level is higher than on a standard day. The alitmenter indicates lower than actual altitude.
• Lower than standard pressure* - The pressure level is lower than on a standard day. The altimeter indicates higher than actual altitude.

REMEMBER - High to low or Hot to cold look out below!!!

Question 3

For IFR flights, What is the maximum allowable error for an altimeter?

Answer 3

If the altimeter is off field elevation by more than 75 feet, with the correct pressure set in the Kollsman window, it is considered to be unreliable.