Two hang-gliders had to be rescued by helicopter from a rock at the bottom of a cliff after they were injured during a tandem flight at Stanwell Park.The delicate rescue operation occurred under a darkening sky after an unexpected change of wind forced the emergency landing about 4.30pm yesterday.Hang-glider operator Tony Armstrong, 55, of the Stanwell Park Hang-gliding and Paragliding School, was initially knocked unconscious while landing on the rock.He was later taken by helicopter to St George Hospital with head injuries and is in a stable condition.The other man, an Irishman in his 30s visiting Australia on a working holiday visa, received cuts to his leg and was driven by ambulance to Wollongong Hospital.Mark Mitsos, secretary of the school, told the Mercury northern suburbs man Mr Armstrong had more than 25 years' hang-gliding experience and had spent thousands of hours in the air off Bald Hill."There was a very sudden change in wind direction and he effectively had to make an emergency landing down at the bottom - and there's not too many options down there," Mr Mitsos said.Local hang-glider Matt Radzyner said sudden wind changes at Bald Hill were almost impossible to predict. He praised Mr Armstrong."He would have been in control the whole time and he obviously put his passenger first because his passenger had much lesser injuries."He took the brunt of the crash."The injured Irishman used his mobile phone to call five friends waiting on Bald Hill, who walked 40 minutes down a steep track to the men's aid.Ambulance officers began the trek just after 5pm, but the rescue helicopter reached the injured men first and winched them back to the top of the cliff.The friends were transported to a nearby beach.The most high-profile hang-gliding accident in recent times at Bald Hill occurred in September 2000 and left two dead.Police officer Sergeant Glenn Connor, of Otford, was flying tandem with an Albion Park Rail woman when their gilder became tangled in the lines of a paraglider being flown by Hurstville man Vitali Kouznetsov. The woman survived.