A deafening roar fills the sky over this tiny village and a fierce gust of wind lashes across the landscape. Half a dozen local children gaze on from the undergrowth, transfixed, as a Black Hawk helicopter descends towards them and a dozen figures in military fatigues leap out and speed away. For this isolated Amazon settlement it can only mean one thing: Brazil's national airmail service has arrived.

The airmail service, or Correio Aereo Nacional, does not deliver postcards or Christmas gifts. It is a group of air force medics who risk life and limb to bring healthcare to the remotest corners of the world's largest rainforest.

Created in 1941, CAN's first pilots were known as the "flag bearers of the skies". Their mission was to help to integrate remote Amazon outposts with the rest of the country, building runways in the jungle and transporting residents of isolated riverside communities to the city. Until the early 1990s, when budget cuts forced the airmail service into extinction, dozens of its planes flew above the Amazon.

Then in 2004, during the first term of the leftwing president Luiz Inacio da Silva the service was resuscitated as a means of bringing medical care to areas so isolated that without aircraft they could only be reached by boat or weeks trekking through the jungle. The flying doctors became known as the Angels of the Amazon.

Caramambatai, an indigenous settlement home to around 190 members of the Ingariko tribe and the scene of the latest airmail mission, is about as remote as they come.

Hidden away on Brazil's tri-border with Venezuela and Guyana, the area is said to have been the inspiration for Arthur Conan Doyle's 1912 novel The Lost World.

The book charts the adventures of an eccentric British scientist called Professor Challenger who claims to have found dinosaurs living on a mysterious Amazonian plateau. The plateau in question was Mount Roraima, a colossal tabletop mountain that surges through the thick layers of mist hanging over Caramambatai.

Life as an airmail medic in Brazil's lost world is not for the light-hearted. Using 10-seater Cessna Caravans, Black Hawk helicopters and a Canadian Buffalo cargo plane built in 1968, CAN doctors and nurses from the air force hospital in Manaus are shuttled between terrifyingly short runways - often mud strips first carved into the dense jungle by illegal gold miners.

During a recent visit to Xitei, a Yanomami Indian community in Roraima state, the Caravan plane in which the Guardian was traveling with the airmail team spun off the narrow, waterlogged airstrip and into the undergrowth.

When the doctors emerged from the plane they found the burnt out carcass of a helicopter that had smashed into a nearby river and exploded a few years earlier. The helicopter's charred remains - and presumably its occupants - had long since been engulfed by the surrounding forest.

But for Flying Officer Karine Tiemy, a 27-year-old dermatologist from Sao Paulo who took part in a recent six-day CAN mission during which nearly 700 patients were treated, the risks are worth taking.

Officer Tiemy says her most challenging mission to date involved being flown into a jungle clearing onboard the Black Hawk to rescue a gold-miner who accidentally shot himself in the leg while setting a hunting trap.

"One more day and he probably would have died," says Tiemy, an angelic-looking Phil Collins fan, recalling how she used 10 liters of fluid to clean the gaping wound. After four days in the forest it had become infested with larvae, she says.

"The smell was terrible. We had to open the helicopter's doors to get rid of it."
Fidel Anderson Ingariko, 31, a Caramambatai resident who was recently bitten by a poisonous Surucucu snake and airlifted to hospital as he slipped into a coma, is another who owes his life to the Angels of the Amazon.

"I was real bad," says Anderson, a Guyana-born Brazilian who speaks English with a strong Caribbean accent. "If the doctor's hadn't got me I probably would have died like the others."

The humanitarian value of such work is impossible to deny. But airmail missions are not just about airlifts and portable ultra-sound machines. The Brazilian military also uses the trips to gather intelligence on the remote areas around Brazil's border with Colombia, Venezuela and Guyana and to crack down on illegal gold mining and cocaine trafficking.

"We can't leave empty spaces," says Colonel Jose Hugo Volkmer, a 50-year-old fighter pilot from the south of Brazil who worked as a UN military observer in Sarajevo during the 1990s and is now responsible for CAN missions in the western Amazon.

"Empty spaces get occupied. If we don't occupy them, then our neighbour will."
Colonel Volkmer says one major concern is the reported presence of the Revolutionary Armed Forces of Colombia (Farc) in Venezuelan territory.

He claims the Joint Inter-Agency Task Force South, a US backed anti-drug trafficking agency, has recently detected Farc members operating there, not far from the border with Brazil.

"This makes us open our eyes to this area ... We need to be there to know that these runways are being used to bring healthcare not as a logistic point to transport drugs."

After recent intelligence suggested that Ingrid Betancourt was being held captive in the Brazilian Amazon, Colonel Volkmer says he personally flew over the area, triggering a Special Forces raid on a Farc camp in which fifteen arrests were made. The hostage was not found.

"We have to be permanently present and flying in this region is our way of doing this."
Colonel Volkmer laughed off the dangers involved in landing on miniscule, mud-clogged airstrips deep in the jungle. It was the perfect way to train young air force pilots, he said.

"The moment we stop taking risks is ... when it is time to get into the coffin and wave a little goodbye to everybody," he says at an improvised clinic in the Manalai indigenous village, to which Indians from Venezuela and Guyana also flock in search of medical treatment. Minutes later Winifred Thomas, a 48-year-old indigenous woman from a remote settlement in Guyana, limps into the field hospital.

"I couldn't get any help there so I came here," said Thomas, who recently underwent a hip-replacement operation in the Brazilian city of Boa Vista and had trekked several days through the jungle to find the CAN medics.

Thomas had only one complaint - that the airmail doctors couldn't give her a lift home in their Black Hawk.
"I want to go back in the helicopter," she grins. "It's only fifteen minutes to my home. On foot it'll take me two weeks."