is a term usually used in aviation
. It refers to the distance between an aircraft and an external reference point, usually on the ground. This distance is directly
- as in, the absolute distance of a line drawn between the two; if the reference point
is on the ground, the line would be between the point on the ground and the aircraft at altitude
, hence, it would be slanted
. This, then, would be longer
than if the line was drawn between the reference point and the point on the ground directly beneath
the aircraft's current location.
The reason this term is used is because when one is performing theoretical navigation, such as with maps and using dead reckoning, it is typical to use distances that do not take into account the altitude of the aircraft. However, when one is using navigation systems that measure the actual position of the aircraft or measure actual distances, such as GPS, DME, or TACAN, the distances reported are typically the actual distance between the aircraft's current location and the reference point - which includes the altitude difference. This is the slant range.
It is also used by military pilots and air defense types, as the difference between slant range and ground distance can be critical when determining ranges to target for air defense or air-to-ground weapons.