How long is window of survival?
LOST among the vast and unforgiving Australian bush.
The muffled chuff of a flying helicopter can be heard as search and rescue workers and volunteers comb through the land in the distance.
You scream for help and try to draw attention to yourself. But no one can see or hear you.
The scenario might be the makings of a nightmare but it's also one that plays out in real life almost every day across Australia.
Most missing bushwalkers are found alive, some are found dead, and others are never seen again.
But in the initial stages of becoming lost, and as the hours, and often days roll by, there's one question that haunts them all: "How long will it be until they give up looking for me?"
Senior Sergeant Michael Smith, operations co-ordinator for the NSW Police Rescue & Bomb Disposal unit, said the decision to "conclude a land search and rescue operation or to suspend a search" was not made lightly.
"The National Land Search Manual has criteria that must be met prior to suspension or conclusion of a search including, but not limited to, the reviewing of the search effort overall," he told news.com.au.
"A large number of factors are used to determine when and why a search would be suspended and can be based on the geographic and climatic conditions at the time the person went missing, prevailing weather, known medical conditions, survivability based on advice from medical experts from within this field and the lost person behaviour.
"Any suspension of a search would be made once all possible and probable identified search areas have been covered and the probability of detection has been covered and the likelihood of surviving has ceased."
Sergeant Smith said that relatives and next of kin were continually consulted throughout the search phases "with prior notice of at least 24 hours that the likelihood of survivability has been exhausted and the search will be suspended".
"Again, this can change from search to search," he said.
NEVER SEEN AGAIN
It was a beautiful spring day when avid hiker Bruce Fairfax, 66, and his wife Louise went on a walk with their dog Tessa at Duckhole Lake Track in Tasmania's south, on October 14 last year.
The couple became separated after Ms Fairfax walked ahead of her husband and Tessa. But as she waited for them at the couple's rendezvous point, only the dog showed up.
Mr Fairfax was never seen again despite an extensive search of Duckhole Lake by specialist divers which failed to find any trace of the former high school teacher.
Past students and Mr Fairfax's daughters flew from interstate to form a search crew of more than 60 people. Their efforts were also unsuccessful.
Police soon declared the window of survival had closed and formally suspended the search for Mr Fairfax on October 23, 2017.
It is believed Mr Fairfax, who required daily medication for Parkinson's disease, became disorientated on the walking track. He has not been found.
STARTING A SEARCH
A search is generally launched when general duties police contact the unit and inform them that a decision has been made to conduct a co-ordinated land search. The land co-ordinator then carries out a risk assessment and determines the search areas and resources required to assist. In some cases, particularly those involving young children or elderly people with medical conditions, an emergency response is activated immediately.
A search is then carried out by police and volunteers on foot but helicopters, light planes, kayaks and police divers can also be used.
"These resources will be allocated specific tasks based on their expertise (and) search areas based on their capability," Sergeant Smith said.
While not all of those reported missing are found, he said there was a "high success rate" when it comes to locating missing persons alive.
He said search and rescue operations for missing bushwalkers were carried out daily across the state with each lasting from a few hours to several days or longer.
"It's often dependant on geographical locations, the season and severity of someone who is injured," Sergeant Smith said.
"It can be a known location or suspected location of the person and requires only assistance, or others who are completely lost.
"Bushwalkers fit into a category of people that, if lost, will make attempts to 'self-help' or assist in their attempts to be found."
Two men who went missing in the NSW Barrington Tops National Park were found during a Search and Rescue operation earlier today.
The pair - aged 46 and 48 - were said to be canyoning and abseiling in the park when they activated an emergency beacon northwest of Dungog around 6.40pm on Sunday, according to police.
Heavy rain and a thunderstorms prevented an immediate search of the bushland, but a vehicle belonging to the men was found.
Police and paramedics set out early Monday morning to look for the men, aided by the Westpac Rescue Helicopter and Aviation Search and Rescue.
"Two males yesterday afternoon had planned a bushwalk, at around 8.30pm last night they activated the emergency location beacon as they were hit by torrential rain and storms," Westpac Rescue Helicopter spokesman Barry Walton said. He said both men were winched out of the location uninjured.
Sergeant Smith said it was important to prepare for the worst when going on a bushwalk or similar to increase chances of being found.
"Inform someone of their intentions when they are planning of heading off on a bushwalk, for example, where they are going, when they expect to return, a means of contact," he said.
"Take sufficient water and food for the duration of the walk, have a Personal Locator Beacon (PLB) with them and ensure it is registered and they know how to operate it.
"NSW Police and NSW National Parks have a joint venture called 'Think before you TREK' where PLBs are made available for loan through police stations in the Blue Mountains when bushwalking.
"This has been successful in locating bushwalkers where otherwise extensive resources would be needed to successfully search and locate the lost person."
Survival expert and instructor Bob Cooper told news.com.au it was "easy to get lost in the bush" but that the first few hours after becoming lost were the most crucial for survival.
"What you think governs your action and knowledge dispels fears," Mr Cooper, who is also the author of book Outback Survival, said.
"If you get emotional - and most people do - that will block off any common sense and then the person will start making decisions that aren't based on reality."