When is the RNAV groundspeed readout most accurate?

• A. Always
• B. Only during flight at certain times
• C. Only near the destination
• D. Never

Answer: (A)

RNAV groundspeed readout comes from the GPS-derived velocity over the ground. It measures how fast your airplane is actually moving over the Earth's surface by tracking the change in position over time at the GPS update rate. Because this readout is based on satellite navigation rather than air data sensors, it directly reflects groundspeed (including the effect of winds) and updates in real time. In normal operation, with healthy GPS signals, this makes the RNAV groundspeed readout the most accurate indication of how fast you’re moving over the ground, regardless of phase of flight or where you are in the route. Only if the GPS signal is degraded or unavailable would its accuracy be compromised.