The 5 Types of Altitude in Aviation
Most people, particularly those who aren’t too familiar with aviation, perceive altitude in fairly straightforward terms – it’s simply how high an aircraft is from the ground. However, for pilots and those involved in aviation, understanding altitude isn’t as black-and-white. In fact, there are five different types of altitude that pilots need to consider during every flight. Let’s delve into these types and their significance.
1. Indicated Altitude
The first type of altitude is the indicated altitude. As the name suggests, this is the altitude displayed on the altimeter, the instrument used to measure the height of an aircraft above a fixed level. While the reading may be accurate, it also depends on the calibration of the instrument and the correct altimeter setting. Remember, when you see the term “indicated” in aviation, it suggests that there’s more to the situation than meets the eye!
2. Absolute Altitude
The second type is the absolute altitude, often abbreviated as AGL or “Above Ground Level.” This refers to the height of the aircraft above the terrain or any obstacles. While it’s crucial to know that you’re flying at a safe height to avoid any accidents, most of the pilot’s operations are done in terms of above sea level, not above the ground.
3. True Altitude
The true altitude is the height of the aircraft above mean sea level (MSL). Aviation altimeter settings are corrected to sea level, so if you input the current altimeter setting into your altimeter, the instrument should display the true altitude. However, this only works if you keep updating the altimeter setting as you fly.
Moreover, changes in air density, which your altimeter measures, are also influenced by temperature. Therefore, if it’s extremely hot or cold, your altimeter may not provide accurate readings. This is an essential consideration for instrument pilots, especially when flying approaches in cold conditions.
Altitude Performance Calculations
The next two types of altitude aren’t based on your instruments or even considered while you’re in the cockpit. Instead, they are theoretical figures used to calculate how well the aircraft will fly. Pilots usually calculate these during their pre-flight planning.
For the wings, propeller, and engine, it’s not about how high they are above sea level or the ground—it’s about the amount of air available. This boils down to pressure and temperature, the two factors that affect the density of the air. Having a good understanding of when there’s less air is critical because it means the aircraft has less performance.
Many crashes have resulted from pilots overestimating their aircraft’s performance and underestimating the effects of air pressure and temperature. This is most common at high elevations on very hot days.
4. Pressure Altitude
The fourth type is the pressure altitude, which is the height of the aircraft above (or below) the standard datum plane, represented as 29.92 inHg. So, instead of measuring the distance in feet above sea level or the ground, pressure altitude measures it from wherever the standard pressure (29.92 inHg) is on that day.
If it’s a standard day and sea level pressure is 29.92 inHg, then true altitude will equal pressure altitude. Also, if you set 29.92 into your altimeter, it will display the pressure altitude. The standard lapse rate for pressure is 1.00 inHg for every 1,000 feet. This is how altimeters are calibrated.
5. Density Altitude
Lastly, we have the density altitude. This is the altitude relative to the standard atmosphere conditions at which the air density would be equal to the indicated air density at the place of observation. In other words, it’s the altitude at which the aircraft “feels” its flying.
To wrap up, understanding these different types of altitude is essential for pilots to ensure safe and efficient flights. Whether you’re an aspiring pilot or a student at Melbourne Flight Training, these concepts are fundamental to your aviation education. By mastering these, you’re one step closer to becoming a competent and confident pilot.
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