Downrange
Downrange means the distance measured along a line whose direction is parallel to the projection of a vehicle's planned nominal velocity vector azimuth into a horizontal plane tangent to the ellipsoidal Earth model at the vehicle sub-vehicle point. The term downrange may also be used to indicate direction.
Source
14 CFR § 401.7
Scoping language
For the purposes of this chapter unless otherwise excepted, the following definitions apply: