When airplanes fly through the sky, the performance of the airplane is impacted by the density of the air. This is because the air flows over the body of the plane including the wings and the propeller.
As the plane climbs higher and the altitude increases, so does the density of the air.
It is important to keep track of the density altitude, also known as the pressure altitude, as it will help you to determine the performance of the airplane when it comes to taking off, landing, and everything in between.
However, an altimeter cannot be used to read the density altitude.
You need to calculate it using a chart or an E6B. today, we will show you how you can find the pressure altitude yourself, just keep reading to find out more.
Some Useful Terms
Before we look at how to calculate the pressure altitude, let’s go through some common terms that you need to know to understand altitude:
The true altitude is the height of the aircraft in the air, calculated from above sea level.
Pressure altitude is defined as the height above a standard datum plane. It can be used to determine the performance of the plane.
Density altitude is the same thing as pressure altitude, but it has been adjusted for non-standard temperature.
This is the term for the height of the aircraft above ground level rather than above sea level.
The indicated altitude is the altitude that is shown on the altimeter, with no adjustments made.
This is the altitude once it has been adjusted to correct any instrument errors.
Standard Datum Plane
These are the standardized atmospheric conditions of a ‘normal’ day at sea that can be used as a baseline to help pilots determine the performance of the aircraft.
Why Is It So Important To Know The Density Altitude And Pressure Altitude?
From a basic point of view, the pilot should always be aware of the altitude of their plane to make sure that they don’t crash into any obstacles or interrupt the flight path of any other plane.
The pilot must be aware of the density altitude to fly the aircraft safely.
The density altitude will help the pilot to determine how the plane is going to perform throughout the different stages of the flight.
The pressure altitude must be calculated first to figure out the density altitude.
The higher the density altitude, the lower the horsepower output of the engine of the aircraft and the less effective the propellers will be. This reduces how aerodynamic the plane is.
If the air density is high then the pilot will need to allow for a greater take-off distance and consider that the rate of climb will be reduced.
They may also want to account for a greater distance for their landing.
When a pilot is learning how to fly and how to operate an aircraft, the standard instructions are based on how the plane will perform in standard datum plane conditions.
One of the skills of being a good pilot is monitoring the actual conditions on the day of the flight and understanding how this will affect the plane’s performance, what adjustments they need to make to the landing and take-off distances, and how best to handle the plane.
By having a good understanding of the pressure altitude, a pilot will be able to calculate how much runway the plane will need to take off, how much it will need to land, and how quickly the aircraft will be able to climb and ascend.
This helps them to know what actions they need to take to avoid obstacles whilst in the air.
What Are The Most Dangerous Density Altitude Conditions?
There are certain conditions where the density altitude can be quite dangerous.
If the plane has a heavy load, the temperature of the air is high, there is high humidity in the air, and the airport is in an elevated position, then this can cause some difficulties for the pilot.
Even just one of these conditions would cause a diminished performance, so when they are all combined it can cause quite a lot of issues.
What Is An Altimeter?
Most aircraft have an altimeter onboard. It is a radio device that can measure how high the plane is flying above ground level by using air pressure.
It converts the air pressure reading into reading in feet and meters to show the altitude of the main.
How To Find The Pressure Altitude
The easiest way to find the pressure altitude is to use an altimeter.
Make sure you set the window in the altimeter to 29.92 first. If you don’t have an altimeter, then you can calculate the pressure altitude.
Take the standard pressure, take away your current pressure setting. Then multiply this by 1000 and add the field elevation. This will give you the pressure altitude.
How To Use A Density Altitude Chart
The easiest way to determine the density altitude is using an E6B flight computer. However, if you don’t have one of these then you can also use a density altitude chart.
Use the numbers down the right-hand side of the chart to make adjustments for the field elevation, and the numbers on the left-hand side for standard elevation.
The temperature is found at the bottom of the graph.
The table on the right can be used to adjust for the difference between standard pressure and whatever the pressure is at the airport.
Once you have found all of the relevant points on the chart, the point at which they intersect is the density altitude.
The pressure altitude is a very important number for the pilot to be aware of.
The pressure altitude will give the pilot an indication of how the plane will perform and is used to determine important things like how much runway will be needed to take off and land.
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