Which of the following is NOT required instrument flight equipment?

The weather radar is not considered a required instrument flight equipment for flying under instrument flight rules (IFR). The primary focus of required instruments is to ensure basic navigation and control during flight in instrument meteorological conditions, where pilots rely heavily on instruments due to limited visibility.

In the context of required IFR equipment, the airspeed indicator, vertical speed indicator, and attitude indicator are essential instruments that provide critical information regarding the aircraft's speed, rate of climb or descent, and orientation relative to the horizon. These instruments help pilots maintain control of the aircraft and navigate safely when visibility is poor.

In contrast, while weather radar can be a valuable tool for avoiding severe weather and enhancing situational awareness, it is not mandatory for IFR flight operations. This distinction emphasizes that certain instruments are indispensable for flight safety, while others, like weather radar, enhance operational capability but are not strictly necessary for compliance with IFR regulations.