Landing distances are determined on the basis of a threshold crossing height of fifty feet. Given a three to six degree glide path, the latter being more appropriate for light training aircraft, touch-down will occur somewhere near five hundred feet in from the threshold.
Down here in OZ the fifty feet threshold crossing height is required to clear dead trees, single strand telephone wires, ant hills, barbed wire fences and all the other paraphernalia associated with an 'outback' airstrip. Some of the city runways are equally as challenging with delivery vans and the like crossing on roads in the undershoot.
Why teach a student to land on the threshold if you must ultimately re-train him/her to land properly in a later sequence. If the runway is not long enough to touch-and-go without planting on the threshold one must question the wisdom and the legality of conducting a touch-and-go.
Sure, the runway behind is of no further use, but the runway ahead would look mighty good if you were hanging from a strand of wire 100 metres short of the threshold!
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dragchute
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