Before beginning any flight under IFR, what information must the pilot in command become familiar with?

The information that a pilot in command must become familiar with before beginning any flight under IFR includes critical details that affect the safety and feasibility of the flight. One of the most critical aspects is understanding runway lengths and the aircraft's takeoff and landing data. This information is essential for determining whether the aircraft can safely operate at the intended airports given the current aircraft weight, environmental conditions, and runway conditions.

Runway length is particularly important because it directly influences the aircraft's performance during takeoff and landing. If the runway is too short for the aircraft's performance capabilities under the current conditions, it could result in an unsuccessful takeoff or landing, leading to potentially hazardous situations.

While other choices encompass important factors (such as approaches and weather conditions), they do not carry as immediate an impact on the aircraft's ability to operate safely within the confines of the physical limitations posed by runway lengths and performance data. Understanding runway lengths along with aircraft performance ensures that the pilot can make informed decisions that prioritize safety in IFR operations.