Height, Altitude, Elevation and Aviation Units

The datum changes the meaning

Height is vertical distance above a specified datum, usually the ground directly below the aircraft. Altitude is measured above mean sea level. Elevation is the height of a fixed point, such as an aerodrome or hill, above mean sea level.

A drone display often shows height relative to the launch point. A crewed aircraft altimeter normally references mean sea level when set to QNH. That difference can create a dangerous misunderstanding near aerodromes or terrain.

Think in both AGL and AMSL

If a drone is 400 ft above a site that is 1500 ft AMSL, the aircraft is about 1900 ft AMSL. A crewed aircraft reporting 2000 ft near the same site may be much closer than a new remote pilot expects.

The remote pilot should know the elevation of the operating site and understand whether the aircraft display is showing relative height, terrain-following height or another estimate.

Use the right unit for the context

Australian aviation commonly uses nautical miles for navigation distance, feet for altitude and elevation, knots for wind and aircraft speed, metres or kilometres for visibility, Celsius for temperature, hectopascals for pressure and kilograms for weight.

RPA manuals may also use metres per second, kilometres per hour, pounds or Fahrenheit. Conversions are not academic; they are part of checking limits before flight.

• 1 nautical mile is 1.852 km.
• 1 knot is 1 nautical mile per hour.
• Kilograms to pounds is approximately kg x 2.2.
• Standard sea level pressure is 1013.2 hPa.

Practice Questions