To calculate Ground Speed, which four conditions must be met?

To calculate Ground Speed, which four conditions must be met?

• A. On radial of a NAVAID, in unaccelerated/cruising flight, outside of slant range, and have already set IAS for TAS
• B. In a descent, in a turn, inside slant range, and set Mach for TAS
• C. On a localizer approach, in a climb, within slant range, and not set IAS
• D. On a radial of a NAVAID, in a climb, outside slant range, and set IAS for TAS

Answer: (A)

Ground speed can be determined cleanly when you’re following a fixed ground track and your airspeed is steady, with the proper speed data ready. Using a VOR or other NAVAID radial gives you a defined path to ride along, so you must actually be on that radial and fly straight and level. This ensures the track you’re measuring is stable and corresponds to a single direction on the ground, not a changing course during turns or climbs/descents. Being outside the slant range to the VOR is important because close to the station the geometry becomes distorted and simple, straight-line calculations won’t match the actual ground distance traveled along the radial. Staying well outside that range keeps the relationship between your ground distance along the radial and your time on course reliable. Finally, converting indicated airspeed to true airspeed is essential because ground speed is based on the speed of the aircraft through the air (true airspeed) and the effect of wind along your path. If you haven’t set IAS to TAS, you’d be using the wrong speed in the calculation, leading to an incorrect ground speed estimate. In short, you’re on a VOR radial, in straight, level flight with constant airspeed, outside slant range, and with TAS correctly derived from IAS. These conditions yield a reliable ground-speed calculation; deviations like turning, climbing/descending, or being inside slant range would complicate or invalidate the method.

Ground speed can be determined cleanly when you’re following a fixed ground track and your airspeed is steady, with the proper speed data ready. Using a VOR or other NAVAID radial gives you a defined path to ride along, so you must actually be on that radial and fly straight and level. This ensures the track you’re measuring is stable and corresponds to a single direction on the ground, not a changing course during turns or climbs/descents.

Being outside the slant range to the VOR is important because close to the station the geometry becomes distorted and simple, straight-line calculations won’t match the actual ground distance traveled along the radial. Staying well outside that range keeps the relationship between your ground distance along the radial and your time on course reliable.

Finally, converting indicated airspeed to true airspeed is essential because ground speed is based on the speed of the aircraft through the air (true airspeed) and the effect of wind along your path. If you haven’t set IAS to TAS, you’d be using the wrong speed in the calculation, leading to an incorrect ground speed estimate.

In short, you’re on a VOR radial, in straight, level flight with constant airspeed, outside slant range, and with TAS correctly derived from IAS. These conditions yield a reliable ground-speed calculation; deviations like turning, climbing/descending, or being inside slant range would complicate or invalidate the method.