We heard the thump of chopper blades near midnight on Sunday before we saw it rise like a dark angel above the cliffs in the Magaliesberg. Pilots flew with night vision goggles, no lights, and torches lit up a rough landing zone. In Johannesburg the noise of helicopters conjures up cops chasing criminals and in movies, war. But to us - and to critically wounded patients in Gauteng and its neighbouring provinces - it meant a speedy rescue.An icy wind blew while the chopper circled, and the injured climber and rescue crews waited under a tree. If the Netcare 911 air ambulance hadn't been able to land, it would have taken us all night to evacuate the patient, a 72-year-old professor and expert climber, down the steep, forest trail after he had fallen dangerously. A rock had broken off in his hand eight hours before and he had briefly lost consciousness and dislocated his shoulder.The Mountain Club SA's Search and Rescue and the Off Road Rescue Unit responded first to the accident. Volunteers had hiked up with a stretcher and medical kit, stabilised him in the stretcher, given him a drip and safely taken him off the wall and up to the landing zone.After the helicopter touched down a paramedic checked the patient and we loaded him onto it. It took off for Netcare Milpark Hospital in Johannesburg and within half an hour he had been admitted to the trauma intensive care unit.Netcare 911 has the only helicopter emergency medical service (HEMS) in SA which flies around the clock with pilots using night vision goggles, inside two ICU-equipped choppers with diagnostic, ventilation and monitoring kit.Andrew Hoi, a fulltime road paramedic who does shifts for the emergency service and volunteers for the Joburg search and rescue team, helped out on Sunday. I first met him last month at the operations centre for Netcare 911's helicopter medical service at Rand Airport, along with specialised emergency care practitioner Marina Divov.The crew work in a green container, near the runway where one of the two Bell 222UTs stands. From March last year the helicopter medical service choppers have flown nearly 1000 hours.Divov is a livewire, who spends her free time training a Belgian Malinois dog to track - she doesn't like to sit still. But waiting is part of their 12-hour shift, starting at 5:30am.At 2.30pm the chopper was dispatched despite ominous weather. "They're isolated thunderstorms; we can duck in and out of them," said veteran pilot Craig Coleman.Hoi and Divov were ready to take off minutes later. Airborne, we turned towards Randfontein and landed at 3pm in a field close to a car accident.The patient had been stabilised in a stretcher by paramedics from an ambulance. Divov checked him to be airlifted. By 3.10pm he was on a drip and ready for take-off. The patient had a potential spinal cord injury.We soon landed at Milpark where the patient was classified as a "P1: a life-threatening emergency requiring immediate treatment" by the trauma doctor.Air ambulances get called for emergencies like serious road accidents, burns, gunshots and hiking accidents in remote areas.South Africa has other helicopter emergency medical services and Netcare 911 helicopter services has a long track record. The service celebrates its 11th anniversary next month...