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Omarama glider pilot Hugh Turner said Mr Marshall was competing in the South Island Gliding Championships in Omarama and was forced to make a "controlled but heavy landing" in a remote mountain river area.
The incident was witnessed by another gliding competitor and, initially, there were concerns for Mr Marshall when he did not exit his glider and attempts to contact him failed.
Rescue Co-ordination Centre New Zealand search and rescue officer Chris Wilson said the centre was notified of the incident about 4.30pm, when a beacon was activated.
A Southern Lakes Rescue Helicopter was sent from Te Anau to retrieve the pilot.
The search was supported by local light aircraft.
Mr Marshall was located about 6.15pm and flown to Queenstown Lakes Hospital with a broken ankle and other minor injuries.
Mr Wilson said the beacon had been "critical" in expediting the search effort.
"Correctly registered 406MHz beacons speed up the search and ultimately could save lives."
Mr Turner said the weather conditions at the time were "flyable", and the cause of the crash was not yet known.
The incident had been reported to the Civil Aviation Authority.