Pressure Altitude

Pressure Altitude Vs Density Altitude: What’s the Difference

Pressure and altitude are two factors to consider when above ground. If you are a pilot, passenger, or even flight attendant, this information proves useful. This article is valuable, allowing anyone, including yourself to have a full-on idea of factors associated with flying. The content helps you to understand the difference between pressure and density altitude. It portrays the relationship between pressure, altitude, and density and their effect on an aircraft, giving insight on factors to consider upon escalation.

Why keep this information to yourself? Share it with family and friends so they can have some understanding of what occurs on a flight. After completing this article, you should have a good understanding of pressure altitude and density altitude.

What is Pressure Altitude?

An in-depth look at pressure shows where pressure altitude is corrected for the nonstandard difference in temperature. The pressure altitude is also defined as the height above the “standard” datum plane.

Additionally, an altimeter is designed to make readings on pressure altitude as well. The device detects the pressure altitude as the reading approaches 29.92 in air pressure value. Knowledge of the values can help to decide the performance of the aircraft. If the value is read correctly then you should be able to decide how optimal the engine, lift, and aerodynamics should be.

What is Altitude?

Altitude is defined most simply as the height that an object occupies above the sea, or in some cases, ground level. It has a relationship with air pressure. As altitude increases, the amount of air pressure that you are exposed to falls. Therefore, altitude and pressure are regarded as being inversely proportional.

It can be present in several types and contribute to several factors. The types of altitude are:

  • Indicated altitude – This is the altitude reading found on the altimeter. It is used to measure aircraft performance, which is especially useful in a high-altitude flight.
  • Pressure altitude – This is regarded as the height that a body exists above the standard datum.
  • Density altitude – The density altitude is defined as the altitude that is pressure corrected or relative to the measurement of temperature. It allows for the measurement of nonstandard temperature variations.
  • True altitude – True altitude determines the actual elevation of the aircraft above mean sea level (MSL).
  • Absolute altitude – The absolute altitude is the distance that an aircraft travels above terrain or structure. Note the distance must be vertical and is measured in meters.
  • Pressure – Pressure is the force that is exerted against the surface area of an object. This means that the more force that is exerted and the smaller the area which the force makes contact with, the larger the pressure. Force and area are related to pressure through inverse proportionality. In simpler terms, if the volume of the surface area should decrease then the pressure should decrease.

In most cases emphasis is placed on the surface area rather than the force. This says that the force can remain constant but the surface area changes in each situation to determine the pressure.

How Does an Altimeter Help to Understand Them?

Before understanding how an altimeter helps to understand both pressure and altitude we must understand what an altimeter does. An altimeter is a tool used within an aircraft of any kind to determine atmospheric pressure also termed static pressure. Its role is to create a relationship between atmospheric pressure and altitude. How? By converting built-up surrounding atmospheric pressure into altitude for measurements. If you are a pilot, then this should help you to understand just how high you are above ground or sea level (altitude). It gives you an exact measurement.

The altimeter’s unique properties make it different from any other device within an aircraft’s “six-pack”. While most of the other instruments can measure altitude they are incapable of sensing the changes in air pressure when compared to the altimeter. Additionally, they can read this at high levels.

What Are the Kollsman Window and Barber Pole Readings?

The altimeter instrument is constructed with several parts different identified parts. These parts contribute to the different capabilities of the altimeter. One such part is the Kollsman Window and Barber Pole Readings. These are two different parts that serve different purposes.

The Kollsman Window is designed specifically for accumulating and producing measurements to give an overall value for air pressure within the aircraft. It is somewhat similar to that of a barometer. It is located to the right side of the altimeter. In most aircrafts the Kollsman Window records in units of Hg. This is the standard unit for air pressure and it represents “inches of mercury.”

On the other hand, the Barber Pole Readings determine the height of the aircraft. If the aircraft flies above a certain level, ideally 10,000 feet in altitude, then the barber pole appears. It simply serves to provide an alert and disappears when the point is deescalated.

The barber pole is located in the lower half of the altimeter. It is so-called as a result of its design inclusive of white and black stripes that interchange. Its design is of a half-crescent shape, and it accommodates a pilot’s sight by making readings more visible as soon as focus is placed on it.

Why Does Density and Pressure Altitude Matter?

If you are a pilot, whether newly trained or professional, then you should be aware that pressure and altitude encounter many difficulties. These can affect your aircraft in many different ways, especially if it is not equipped to withstand them. Initially, this affects your safety as you are in the aircraft, and without the proper PPE or protective gear, it can cause danger to your health. To understand why it plays a vital role we need to understand the factors it affects and how it affects them. These can be seen below:

  • Altitude – Density and pressure altitude have a direct effect on the performance of the aircraft. It affects the aircraft’s engine as it requires a certain capacity of atmospheric pressure, approximately 14.7 psi to perform optimally. As the aircraft goes up, atmospheric pressure decreases, and less oxygen is available. Initially, the engine fails as it has less to support fuel burning and can cause a crash. Additionally, this can also make it difficult to breathe.
  • Temperature – This makes it equally as difficult as altitude for the engine to perform. A rise in temperature produces hot air. Hot air, in turn, produces less dense air. In other words, deoxygenated air and decreasing fuel burning.

Density and Pressure Altitude Charts and Calculating

The density altitude and pressure altitude charts demonstrate the relationship between altitude and both density and pressure. Each chart should contain variable values of pressure, altitude, density, or a variable such as a temperature that relates to them. Initially, the chart should establish a relationship between all altitudes against the other variable, ultimately placing corresponding values and giving proportionalities. In short, this means that as a factor increases, the other should increase or decrease accordingly.

The charts show respectively the change in air density concerning the change in altitude and the pressure altitude against ambient pressure.

  • Density altitude – The Density Altitude Graph displays the altitude and pressure in units of Hg. An analysis shows that as altitude increases the pressure drops. With each drop in pressure of approximately 0.1, an altitude of 100 is gained. As mentioned graph should have a relationship with temperature. This relationship shows how density is derived in terms of pressure altitude with respect to temperature.
  • Pressure altitude – The Pressure Altitude Graph shows the relation between the Ambient Pressure according to the International Standard Atmosphere. An inverse proportionality is established whereas the Ambient Pressure falls each time the Pressure Altitude increases.

Tips for Flying in High-Density Altitude Areas

When an aircraft is exposed to highly dense areas due to the altitude then both you and the aircraft come are exposed to several factors. These factors range from having decreased atmospheric pressure and less oxygenated air. As discussed, it can cause several dangers. Therefore, there a list of tips you can consider to further prevent this. Some tips to be considered are:

  • Scheduling and conducting flights in when the temperature is cooler allowing for denser oxygenated air.
  • Ensure that the aircraft weighs with only a 10 percent fraction of the gross weight.
  • Make extra stops and fly for less extended time and distances.
  • Make contact with advisors about density altitude concerning the airport of destination.
  • Ensure that you are aware of the performance of the aircraft to have an insight into the climbing rate. This should instruct you on how optimal drag or lift can be produced.


In brief, the information presented throughout this article helps you to understand how both factors affect the typical aircraft. You should be able to now understand some of the complications and precautions that are taken upon aircraft usage. An understanding between the likes of pressure, density, and altitude should also be established. Ultimately this enables you to understand the factors interrelated to density and pressure upon flight.

Additionally, it should also allow you to place the clear difference between both topics. Ensure that you share such valuable knowledge with those close to you, family, and friends that they can become aware of how these factors on a simple flight could affect their travel.

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