Landing Distance Available (LDA)

What is Landing Distance Available (LDA)?

LDA is the portion of a runway declared by the aerodrome authority as available and suitable for landing. It begins at the threshold and extends to the end of the runway, excluding any stopways or clearways. This value is critical for pilots and dispatchers when determining if an aircraft can safely land and stop within the available runway length.

LDA vs. Landing Distance Required

The landing distance required (LDR) is the actual distance an aircraft needs to land and come to a full stop from a standard screen height (typically 50 ft). However, regulations require that the LDR must not exceed a certain percentage of the LDA to ensure a safety margin. For jets (Class A), the LDR must not exceed 60% of the LDA; for turboprops (Class B), it must not exceed 70%.

Factoring for Runway Conditions

When calculating if the LDA is sufficient, you must apply correction factors for runway slope, surface type, and condition. For example:

• Add 5% to the required landing distance for each 1% of downslope.
• For wet runways, multiply the required distance by 1.15.
• Combine these with the regulatory safety factor (1.67 for jets, 1.43 for turboprops) to determine the minimum LDA needed.

LDA in Landing Performance Planning

The LDA sets the absolute limit for landing performance calculations. Pilots must ensure that, after applying all required correction and safety factors, the calculated landing distance does not exceed the published LDA for the intended runway. This is essential for both dispatch planning and in-flight decision-making, especially if conditions change.

Demonstrated Landing Distance

The 'demonstrated' landing distance is determined during aircraft certification, representing the actual ground run from 50 ft to a full stop under test conditions. For operational use, this value is increased by regulatory factors to provide a safety margin before comparing with the LDA.