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Threshold crossing height (TCH)

Threshold crossing height (TCH). The theoretical height above the runway threshold at which the aircraft’s glideslope antenna would be if the aircraft maintained the trajectory established by the mean ILS glideslope or MLS glidepath.

Comments

  1. Sunny Daniels says:

    Dear Mr Scott,
    I have seen non precision VOR DME jeppesen approach plates which indicate TCH of 50′.
    How does that explain the above definition which relates TCH only to ILS/MLS?
    Request your comments please?
    Thanks
    Sunny

    • K Morley says:

      This is not an official explanation & may not be fully accurate, yet hope it helps. TCH more generally applied term than just for precision/IFR approaches. VASI/PAPI systems typically sited for TCH approapriate to the runway and types of aircraft that use it, for example. Sited to be “co-incident” with the ILS Glide Slope signal if ILS exists & to account for Hight-Group of largest aircraft to use runway. Otherwise, typically sited for nominal 3-degree approach path and for appropriate minimum TCH for the conditions and to safely provide minimum buffer of altitude clearance above obstacles out to a given distance downwind of the threshold.

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