Answer :
A displaced threshold marks the portion of the runway that cannot be safely used for landing or takeoff, typically due to temporary obstructions or conditions requiring this section to be avoided.
A displaced threshold is a runway threshold that is located at a point down the runway other than the designated beginning of the runway. It marks the portion of the runway that cannot be used for takeoff or landing, often due to construction, repairs, or other hazards that make that section of runway unusable for safe aircraft operations.
In aviation regulations, such as FAR 23 and FAR 25, the landing field length is an important consideration, and includes distances needed for various phases of the approach and landing, including clearing a 50-foot obstacle, the approach glidepath, and the flare distance. The threshold location must be considered when calculating these distances since it would impact the available landing distance.
