Which part of the runway environment is considered necessary for safe landing?

The visual approach slope indicator (VASI) plays a crucial role in ensuring safe landings by providing pilots with important visual guidance during the approach phase. This system helps pilots maintain the correct glide slope to the runway, which is typically set at a three-degree incline. By indicating whether the aircraft is on the proper glide path, above, or below it, the VASI significantly decreases the risk of landing accidents due to improper descent rates.

While other factors, such as runway surface type, distance remaining signs, and weather conditions, can influence landing safety, the VASI directly provides pilots with the essential visual reference for achieving the correct approach angle, which is integral to a safe landing process.