What is ALT3 in Aviation? (Altitude)

Altitude is a crucial term in the field of aviation. It refers to the vertical distance between an aircraft and a specific reference point, typically measured in feet or meters. Altitude plays a vital role in aviation as it determines the aircraft’s position and separation from the ground or other airborne objects. Pilots are trained to constantly monitor and maintain a safe altitude during flight to ensure the safety of the aircraft and its passengers.

In aviation, altitude is denoted by the abbreviation “ALT” or “ALT3” (as used in this article), making it easier for pilots and air traffic controllers to communicate and understand the altitude information. Throughout this article, we will explore the significance of altitude in aviation, its types, and how it is measured.

Understanding Altitude

Altitude is a crucial aspect of flight operations as it aids in maintaining proper separation between aircraft and obstacles, such as terrain, buildings, and other aircraft. It also ensures proper vertical spacing between multiple aircraft flying in the same airspace, preventing potential collisions. Understanding altitude is essential for pilots to navigate and communicate effectively while in the air.

Types of Altitude

There are several types of altitude that pilots need to be aware of during their flights. Let’s take a look at some of the most important types:

1. Indicated Altitude (ALT)

Indicated Altitude (ALT) refers to the altitude displayed on the aircraft’s altimeter, which is a specialized instrument used by pilots to measure altitude. The altimeter takes into account atmospheric pressure to provide an accurate reading. The altitude indicated on the altimeter is based on the aircraft’s position relative to a defined pressure level, typically set to 29.92 inches of mercury (inHg) or 1013.25 hectopascals (hPa). Pilots must adjust their altimeters based on the local atmospheric pressure to obtain the correct indicated altitude.

It is important to note that the indicated altitude may not always correspond directly to the aircraft’s true altitude above mean sea level (MSL). Factors such as non-standard atmospheric pressure and altimeter errors can cause discrepancies between the indicated and true altitude readings.

2. True Altitude

True Altitude represents the actual height of an aircraft above mean sea level (MSL). It is the most accurate measure of altitude as it is not affected by atmospheric conditions or altimeter errors. True altitude is crucial for navigation, flight planning, and maintaining adequate obstacle clearance during flights.

To determine true altitude, pilots need to consider the atmospheric pressure at their current location and adjust it for any variations from standard atmospheric conditions. This adjustment ensures that the altitude measurement accurately reflects the aircraft’s position above mean sea level.

3. Pressure Altitude

Pressure Altitude is the altitude above the standard datum plane, which is a theoretical plane where atmospheric pressure equals 29.92 inches of mercury (inHg) or 1013.25 hectopascals (hPa). It serves as a reference point for measuring altitude, especially for aircraft flying at higher altitudes where the atmospheric pressure significantly varies from standard conditions.

Pressure altitude is crucial for flight planning, performance calculations, and determining aircraft performance limitations. It allows pilots and engineers to assess the aircraft’s engine performance, aerodynamic characteristics, and provides important data for flight instrument calibration.

Measuring Altitude

Altitude is measured using various instruments and systems on board an aircraft. Let’s explore some of the common methods used to measure altitude:

1. Altimeter

The altimeter is the primary instrument used by pilots to measure altitude. It relies on the principle that atmospheric pressure decreases with increasing altitude. The altimeter uses an aneroid barometer, a sealed case with an evacuated and flexible cell, to sense changes in pressure. As an aircraft climbs or descends, the altimeter adjusts accordingly, providing real-time altitude indications. However, it’s important to note that the altimeter measures pressure altitude, which needs to be adjusted for non-standard atmospheric conditions to obtain the true altitude above mean sea level (MSL).

2. GPS (Global Positioning System)

The Global Positioning System (GPS) is a satellite-based navigation system that provides precise position, velocity, and altitude information to aircraft. GPS receivers on airplanes use signals from multiple satellites to triangulate the aircraft’s position and altitude. GPS altitude measurements are typically very accurate, providing pilots with reliable information for navigation and flight planning.

It is important to cross-reference GPS altitude with other altitude sources, such as the altimeter, to ensure accuracy and maintain safety during flight.

3. Airborne Radar Altimeter

Radar altimeters are commonly used in aviation to measure the aircraft’s height above the ground or other objects. This type of altimeter emits microwave signals towards the ground and measures the time it takes for the signals to bounce back. By calculating the time difference, the radar altimeter accurately determines the aircraft’s altitude above the terrain directly beneath it.

Radar altimeters are particularly useful during the approach and landing phases of flight, providing pilots with critical altitude information to ensure a safe touchdown.

The Importance of Altitude in Aviation

Altitude plays a crucial role in aviation safety and efficiency. Here are some key reasons why altitude is of utmost importance:

1. Collision Avoidance

Altitude provides vertical separation between aircraft, reducing the risk of mid-air collisions. Air traffic control systems and regulations ensure that aircraft flying at different altitudes maintain a safe distance from each other. Proper altitude management and adherence to air traffic control instructions are essential for collision avoidance in busy airspace.

2. Obstacle Clearance

Altitude is critical for maintaining obstacle clearance during flight, especially during takeoff, landing, and low-altitude operations. Pilots need to maintain a certain minimum altitude to avoid hitting terrain, buildings, or other obstacles.

Proper understanding and adherence to altitude restrictions and procedures help ensure a safe and obstacle-free flight path.

3. Performance and efficiency

Altitude affects aircraft performance, fuel efficiency, and range. As an aircraft climbs to higher altitudes, the air becomes thinner, resulting in reduced aerodynamic drag. This allows the aircraft to achieve higher speeds while consuming less fuel.

Pilots often optimize cruising altitudes based on factors such as aircraft weight, weather conditions, and ATC instructions to maximize fuel efficiency and range. Operating at the correct altitude improves the overall performance of the aircraft.

Altitude is a fundamental concept in aviation that impacts all aspects of flight. Whether it’s maintaining separation between aircraft, achieving obstacle clearance, or optimizing performance, understanding and managing altitude is vital for safe and efficient flight operations.


Altitude is a critical element in aviation that determines an aircraft’s vertical position and separation from the ground and other airborne objects. Pilots rely on various instruments and systems to measure altitude, including altimeters, GPS, and radar altimeters. Understanding the different types of altitude, such as indicated altitude, true altitude, and pressure altitude, is essential for safe and accurate navigation during flight.

Altitude plays a crucial role in collision avoidance, obstacle clearance, and overall aircraft performance. Pilots must continually monitor and adjust their altitude to maintain a safe flight path and comply with air traffic control instructions. By effectively managing altitude, pilots can ensure the safety and efficiency of their flights, providing a smooth and enjoyable travel experience for passengers.

For More: What is EUROCAE in Aviation? (European Organisation For Civil Aviation Equipment)