Which statement best describes the four Ground Speed criteria?

Which statement best describes the four Ground Speed criteria?

• A. On radial of a NAVAID, in unaccelerated/cruising flight, outside of slant range, and have already set IAS for TAS
• B. On a radial of a NAVAID, in a descent, inside slant range, and have not set IAS for TAS
• C. In a climbing turn, with Mach, outside of slant range, and have IAS not for TAS
• D. On a course made good, in a level flight, inside slant range, and not set IAS for TAS

Answer: (A)

Ground speed readings along a NAVAID radial are most reliable when you’re flying a steady, straight course defined by the VOR, with no change in speed or altitude. Being on a radial gives you a fixed track relative to the station, so the path over the ground follows a known line. In unaccelerated cruising flight, your true airspeed stays constant, so there’s no ongoing change in the speed through the air that would mess with a ground-speed calculation. Being outside the slant range means you’re far enough from the VOR that the geometry of sight distance doesn’t distort measurements or the perceived relationship to the radial. And having IAS set for TAS ensures the indicated airspeed matches your true airspeed, so wind corrections and ground speed derived from TAS are accurate. Descent, climbing turns, or being inside slant range introduce speed changes, maneuvering, or geometric distortions that disrupt the steady relationship needed for a reliable ground speed criterion. Using Mach instead of a stabilized IAS/TAS relationship adds variables that complicate the calculation.

Ground speed readings along a NAVAID radial are most reliable when you’re flying a steady, straight course defined by the VOR, with no change in speed or altitude. Being on a radial gives you a fixed track relative to the station, so the path over the ground follows a known line. In unaccelerated cruising flight, your true airspeed stays constant, so there’s no ongoing change in the speed through the air that would mess with a ground-speed calculation. Being outside the slant range means you’re far enough from the VOR that the geometry of sight distance doesn’t distort measurements or the perceived relationship to the radial. And having IAS set for TAS ensures the indicated airspeed matches your true airspeed, so wind corrections and ground speed derived from TAS are accurate.

Descent, climbing turns, or being inside slant range introduce speed changes, maneuvering, or geometric distortions that disrupt the steady relationship needed for a reliable ground speed criterion. Using Mach instead of a stabilized IAS/TAS relationship adds variables that complicate the calculation.