
Displaced threshold

A displaced threshold or DTHR is a runway threshold located at a point other than the physical beginning or end of the runway. 
The displaced portion of the runway may be used for takeoff but not for landing. After landing at the other end, the landing aircraft may use the displaced portion of the runway 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 as a noise mitigation measure for the communities overflown on approach, or 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 even if the reason for the displacement is lowered pavement resistance, because those aircraft are not impacting the runway with the force of a landing aircraft.
A "permanent" displaced portion of the runway has two markings:
Runway 29 at Indira Gandhi International Airport, in Delhi, India, has a displaced threshold 1,460 m (4,790 ft) from the physical beginning of the pavement. This produces a 1.5 km displaced portion of runway.
Runway 22R at John F. Kennedy International Airport has a displaced threshold due to noise abatement. This shortens the landing distance available to just 7,795 ft for the 12,079 ft runway.