Altitude measurement is a fundamental concept in aviation, essential for safe navigation and maintaining proper separation between aircraft. Pilots and controllers rely on various types of altitude measurements, each serving a specific purpose. Understanding these types and their applications ensures safe and efficient flight operations.

Types of Altitude Measurements

1. Indicated Altitude:
   • Definition: The altitude read directly from the altimeter in the cockpit, based on the local pressure setting.
   • Use: Used for most flight operations, including takeoff and landing, with the altimeter set to the current barometric pressure (QNH or QFE).
2. Pressure Altitude:
   • Definition: The altitude indicated when the altimeter is set to a standard pressure of 29.92 inHg (1013.25 hPa).
   • Use: Used above the transition altitude for maintaining standardized flight levels and ensuring separation in controlled airspace.
3. True Altitude:
   • Definition: The actual height of the aircraft above mean sea level (MSL).
   • Use: Critical for terrain clearance, especially in mountainous regions or during approach and landing.
4. Absolute Altitude:
   • Definition: The height of the aircraft above the ground or terrain directly below it (Above Ground Level - AGL).
   • Use: Important for low-level operations, such as takeoff, landing, and helicopter flights.
5. Density Altitude:
   • Definition: The pressure altitude corrected for non-standard temperature, representing the altitude at which the aircraft "feels" it is flying.
   • Use: Used for performance calculations, especially during takeoff and landing in high temperatures or at high altitudes.

How Altimeters Measure Altitude

Altimeters in aircraft measure altitude using barometric pressure. As the aircraft ascends, the atmospheric pressure decreases, and the altimeter translates this change into an altitude reading. Pilots adjust the altimeter setting to match the current atmospheric pressure reported by air traffic control or airport weather services.

Importance of Altitude Measurement

• Safety: Ensures proper terrain clearance and separation from other aircraft.
• Navigation: Helps maintain flight paths and comply with airspace regulations.
• Performance: Altitude affects aircraft performance, including fuel efficiency, engine output, and climb rate.

Transition Altitude and Flight Levels

The transition altitude is the point at which pilots switch from using local pressure settings (QNH) to the standard pressure setting (29.92 inHg or 1013.25 hPa). Above this altitude, aircraft operate at standardized flight levels, simplifying navigation and ensuring uniform separation.