Why Reset your Altimeter on IFR Center Command
What does this phrase mean? In Instrument flight you are in contact with a person from air traffic control, like Atlanta Center, that starts with the current altimeter setting expressed in inches of mercury. For example, 29.92 inches of Hg is the normal atmospheric pressure on a aircraft altimeter at sea level.
When you are aloft the atmospheric pressure decreases as you gain altitude. Center will give you the latest pressure reading in inches of Hg as you fly towards your destination.
Your altimeter must be set to the latest altimeter setting received from Center. Why? If you don't set your altimeter to the latest value provided by Center the phrase "Flying from High to Low Look out Below" takes on meaning.
Each inch of Hg (Mercury) represents approximately 1,000 feet of altitude. If your current altitude is 6,000 feet and your altimeter setting is 29.92 inches of Hg and you forget to reset the altimeter to, for example, 28.92 inches of Hg Center just provided (a deepening Low Pressure area ahead) your aircraft is actually flying 1,000 feet lower than you think. (Read his article several paragraphs down for a detailed diagram that illustrates how the error occurs)
This is a serious mistake. Instrument rated pilots must repeat back to Center the altimeter setting he just read to you over your planes radio. He is reminding you to set the altimeter setting NOW.
If the base of the clouds is only 300 feet above ground level the pilot will crash the plane while thinking he has plenty of altitude while on a instrument approach to the airport runway.
The opposite occurs if your flying from a Low Pressure area to a High Pressure area if you don't reset the altimeter setting to the value transmitted to you by Center. You are flying a 1,000 feet higher than you think.
Remember the idea of the FAA Centers is to provide separation between planes at the same level and/or keep a vertical distance of 1,000 feet between flight levels of two or more planes.
You can purchase a Encoding Altimeter that transmits information to Center that allows him/her to see what you actual altitude is. It is embarrassing when Center tellls you of your altitude error.
Why Reset your Altimeter on IFR Center Command
What does this phrase mean? In Instrument flight you are in contact with a person from air traffic control, like Atlanta Center, that starts with the current altimeter setting expressed in inches of mercury. For example, 29.92 inches of Hg is the normal atmospheric pressure on a aircraft altimeter at sea level.
Each inch of Hg (Mercury) represents approximately 1,000 feet of altitude. If your current altitude is 6,000 feet and your altimeter setting is 29.92 inches of Hg and you forget to reset the altimeter to, for example, 28.92 inches of Hg Center just provided (a deepening Low Pressure area ahead) your aircraft is actually flying 1,000 feet lower than you think. (Read his article several paragraphs down for a detailed diagram that illustrates how the error occurs)
This is a serious mistake. Instrument rated pilots must repeat back to Center the altimeter setting he just read to you over your planes radio. He is reminding you to set the altimeter setting NOW.
If the base of the clouds is only 300 feet above ground level the pilot will crash the plane while thinking he has plenty of altitude while on a instrument approach to the airport runway.
The opposite occurs if your flying from a Low Pressure area to a High Pressure area if you don't reset the altimeter setting to the value transmitted to you by Center. You are flying a 1,000 feet higher than you think.
Remember the idea of the FAA Centers is to provide separation between planes at the same level and/or keep a vertical distance of 1,000 feet between flight levels of two or more planes.
You can purchase a Encoding Altimeter that transmits information to Center that allows him/her to see what you actual altitude is. It is embarrassing when Center tellls you of your altitude error.
