What does the knob on an altimeter do?

On a sensitive altimeter, the sea-level reference pressure can be adjusted with a setting knob. The reference pressure, in inches of mercury in Canada and the United States, and hectopascals (previously millibars) elsewhere, is displayed in the small Kollsman window, on the face of the aircraft altimeter.

Why do pilots change altimeter?

Before going flying, you have to set the altimeter. Since your airport has an automated weather report broadcast, you tune it in and hear that the altimeter setting is 29.42. You turn the adjusting knob until 29.42 Atmospheric pressure decreases at a regular rate as altitude increases.

Why do we need to adjust the altimeter pressure?

As you fly from high-pressure weather systems to low-pressure systems (or vice versa), you need to adjust your altimeter to get an accurate Mean Sea Level (MSL) altitude reading on your altimeter.

What does the Kollsman window on the altimeter allow a pilot to do?

The Kollsman window on the front of the instrument allows the pilot to set the altimeter to the current local pressure. Without an adjustment, the altimeter would be subjected to pressure changes as a result of weather, and not just a change in altitude (see “Weather: It’s Not That Simple,” p. 50).

What kind of pressure does the altimeter measure?

An altimeter is a device that measures altitude—a location’s distance above sea level. Most altimeters are barometric, meaning they measure altitude by calculating the location’s air pressure. Air pressure decreases as altitude increases.

What happens when you change altimeter setting?

When you adjust the altimeter setting to a higher barometric pressure (29.92 to 30.02, for instance), your altimeter indication moves upwards (from, say, 5000 feet to 5100 feet). On the altimeter, increase in setting (pressure) means an increase in altitude.

What is Kollsman window?

The Kollsman window is located at the 3 o’clock position on the altimeter dial. This window allows access to read a sub-dial, which contains the barometric readings. Altimeters report altitude as a function of atmospheric pressure. Typically pilots will obtain a local barometric reading from the nearest airport.

Why is it called Kollsman window?

In 1928, a German-American inventor named Paul Kollsman changed the world of aviation with the invention of the world’s first accurate barometric altimeter, which was also called the “Kollsman Window.” His altimeter converted barometric pressure into the distance above sea level in feet.