What speed should be indicated in the flight plan box marked SPEED for the entire cruise?

The correct response highlights the importance of indicating true airspeed (TAS) in the flight plan box marked SPEED for the entire cruise. True airspeed is defined as the speed of an aircraft relative to the surrounding air mass. It accounts for variations in temperature and pressure, which affect how air density influences the performance of the aircraft.

When planning a flight, pilots use true airspeed as a standard to ensure that their calculations for fuel consumption, distance, and time are accurate. It provides a consistent reference regardless of altitude or atmospheric conditions. This metric is especially critical when considering the aircraft's performance and navigating efficiently, as it correlates directly with the aircraft's actual motion through the air.

In contrast, other speed metrics like estimated ground speed, equivalent airspeed, or indicated airspeed serve different purposes in flight operations and planning. Estimated ground speed relates to how fast the aircraft travels over the ground but can fluctuate based on wind conditions. Equivalent airspeed adjusts for compressibility effects at higher speeds but may not reflect the actual speed through the air in various flight conditions. Indicated airspeed, while crucial for determining aerodynamic characteristics and ensuring safe operation within the aircraft's limits, does not provide a reliable representation of the aircraft's velocity in terms of navigation and fuel