A displaced threshold is a runway threshold located at a point other than the physical beginning or end of the runway. The portion of the runway so displaced may be used for takeoff but not for landing. Landing aircraft may use the displaced area on the opposite end for roll out.
Most often the offset threshold is in place to give arriving aircraft clearance over an obstruction while still allowing departing aircraft the maximum amount of runway available. A displaced threshold may also be introduced if a beginning section of the runway is no longer able to sustain the continuous impact from landing aircraft. Aircraft are expected to land beyond the displaced threshold. Departing aircraft are permitted to use the displaced section of the runway for takeoffs or landing rollouts because those aircraft are not impacting the runway with the force of a landing aircraft.
Displaced thresholds have arrows as the center line of the runway. A thick white line with usually four arrows pointing in the direction of the runway denotes the end of the threshold and the beginning of the runway.
Thresholds are counted as part of the runway, and are included in the runway size. When viewing a runway's size with displaced thresholds, one must find out how long the displaced thresholds are in order to calculate the available landing distance.
- Aircraft Information Manual 2013, Chapter 2-3-3 h (2) Section 3. Airport Marking Aids and Signs
- 3.3 Displaced Runway Threshold
- 5.2.4 Threshold Markings
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