What is the primary reason to check runway length before takeoff?

Checking runway length before takeoff is primarily crucial to assess takeoff and stopping distance. This is because the length of the runway directly impacts the aircraft's ability to achieve the necessary speed for takeoff and, in case of an abort, to safely stop before the end of the runway. Each aircraft has specific performance parameters that dictate how much runway is needed based on factors like weight, weather conditions, and altitude.

Understanding the available runway length ensures that the pilot can make informed decisions about whether conditions are safe for takeoff. If the runway is too short for the conditions or the aircraft's performance requirements, it could lead to inadequate acceleration or dangerous situations during the takeoff roll or abortion scenarios.

While factors like fuel efficiency, compliance with regulations, and passenger load capacity are indeed important for overall flight planning and safety management, they are not the immediate concerns tied directly to the specific lengths required for safe takeoff and stopping. Thus, assessing takeoff and stopping distance remains the primary reason to check runway length beforehand.