Above Aerodrome Elevation (CA), abbreviated as AAE, is a critical parameter used in aviation to determine an aircraft’s height relative to the elevation of the aerodrome or airport terrain. It is an essential reference point for pilots during approach, landing, and takeoff procedures. Understanding Above Aerodrome Elevation (CA) helps ensure safe altitude margins and accurate altitude reporting throughout the phases of flight near the airport environment.
Given that aerodrome elevations can vary widely—from coastal airports at sea level to mountainous airports above several thousand feet—Above Aerodrome Elevation (CA) offers a standardized way to express altitude relative to the specific aerodrome reference point. This measure is particularly important for decision-making during critical flight phases where clear altitude awareness is necessary to avoid obstacles and maintain safe vertical separation.
Above Aerodrome Elevation (CA) in Aviation
In aviation, Above Aerodrome Elevation (CA) designates the height of an aircraft above the elevation of the airport’s highest point on the landing area. This is sometimes referred to as Height Above Aerodrome (HAA) or Height Above Airport, but AAE is the more precise aviation term. The aerodrome elevation itself is the elevation above mean sea level (MSL) of the highest point on an airport’s usable landing surface.
For example, if an airport has an elevation of 1,500 feet MSL and a pilot reports being 500 feet Above Aerodrome Elevation (CA), the aircraft’s true altitude is approximately 2,000 feet above mean sea level (1,500 + 500 feet). This calculation is vital for instrument approach procedures where minimum descent altitudes (MDAs) or decision altitudes (DAs) must be strictly observed to ensure obstacle clearance and safe landing.
The Role of Above Aerodrome Elevation (CA) in Instrument Approaches
Above Aerodrome Elevation (CA) plays a pivotal role in various instrument approach procedures (IAPs). These approaches rely heavily on altitude references relative to the aerodrome to maintain safe flight paths, especially in low visibility conditions. Minimum altitudes listed in approach charts are frequently expressed as height above aerodrome elevation, enabling pilots to understand exactly how high above the airport they must be at specific approach segments.
For instance, during a non-precision approach like Localizer (LOC) or VOR approaches, pilots use Above Aerodrome Elevation (CA) to determine when visual contact is necessary before descending further. These values are critical in preventing Controlled Flight Into Terrain (CFIT) accidents by ensuring clearance is maintained above surrounding terrain or man-made obstacles.
Calculating and Converting Above Aerodrome Elevation (CA) Values
In practice, calculating Above Aerodrome Elevation (CA) involves subtracting the aerodrome elevation from the aircraft’s altitude above mean sea level (MSL). Pilots must be aware of the airport elevation published in aerodrome charts or the Airport/Facility Directory (A/FD). These elevations are normally given in feet unless operating under the metric system, where meters are used.
For example, if the aircraft’s indicated altitude is 3,250 feet MSL and the airport elevation is 1,200 feet MSL, the Above Aerodrome Elevation (CA) is calculated as 3,250 – 1,200 = 2,050 feet. This conversion is essential for altitude awareness during airport operations. Further technical information can be reviewed through official FAA publications or ICAO documentation for instrument flight procedures (FAA Instrument Procedures).
Understanding how to convert between Above Aerodrome Elevation (CA) and other altitude metrics such as Above Ground Level (AGL) or Mean Sea Level (MSL) is crucial. While AGL is referenced to the actual ground immediately below the aircraft, CA is specifically tied to the airport’s highest point, which can differ from surrounding terrain elevations.