What threshold crossing height is used when computing landing distance?

The threshold crossing height used when computing landing distance is 50 feet. This height represents the altitude at which the aircraft is expected to cross over the runway threshold during landing. It is a crucial factor in determining the landing distance because it captures a realistic position relative to the runway environment during landing, where factors such as descent rate, configuration, and environmental conditions start to significantly affect aircraft performance.

Using 50 feet allows for a standardized reference point that aligns with both regulatory guidance and practical operational scenarios. Ensuring that pilots calculate landing distance from this height helps in maintaining safety margins, proper runway usage, and adherence to performance criteria under various landing conditions.

The other heights listed do not align with standard practices for threshold crossing calculations in aviation. For instance, using a lower or higher crossing height could provide misleading estimates in landing distance, potentially compromising safety or operational efficiency. Understanding this helps pilots ensure they adhere to safe landing practices during their operational duties.