Trampers flown out of Tararua Range

Picture of the operation: https://www.facebook.com/LandSARNewZealand/photos/a.10151867569144600.1073741835.105882869599/10156320886669600/?type=3&theater

This is really odd, according to this article: "Due to the adverse weather, their general location was identified only, not an exact location." And they had a PLB. Is that even possible? http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=12034245

perhaps it just means it was one of the older non GPS models

what often happens is sar helicopters are fitted with aerials which switch to homing in directly on beacons when they get close to them, it just gives the direction the signal comes from only, but its not perfect, the signal can bounce around in valleys and basins and in bad visibility then its going to be hard to locate them

Possibly what @chriss said. 406MHz PLBs aren't guaranteed to have GPS receivers, although most modern ones do. Or maybe the weather was just interfering somehow with the GPS receiver of the PLB they had. If they don't transmit a derived position, the system attempts to triangulate their position from the satellites, but can take a few hours so it's much less instantaneous, and also less accurate. Because of this, PLBs will broadcast a 121.5MHz signal in parallel. As @waynowski said, that signal can be detected in parallel by equipped aircraft to locate the source more accurately when they're zooming around in circles. Up until a decade ago, all aircraft used to receive 121.5MHz, and the previous generation of PLBs relied on being detected by passing aircraft. Since 406MHz PLBs were standardised, the old system was switched off.

A number of things could get in the way of having an accurate and current position, even with a GPS equipped PLB. Perhaps they were in a location/ how the aerial was deployed meant the unit couldn't acquire sufficient GPS satellites to get an accurate fix. The unit would still send out the emergency notification without GPS position data, SAR would hopefully get an approximate (+- several km?) fix from doppler/triangulation of that signal. My thinking would be possibly they activated the beacon when on the tops and in trouble, it put out a correct and accurate position but then they (probably sensibly) kept moving, looking for some shelter from the wind, dropped off the ridge and took shelter at the base of a cliff/ under a big rock/ in a small gully or similar and from then on the signal wasn't getting out to satellites. SAR would have some positions, know they had kept moving but not have their exact current position when they went looking.

There's much more detail described here: https://times-age.co.nz/hours-from-death/ According to this, they were found by LandSAR teams in a tent, having triggered the PLB, somewhere just north of Pukemoremore. That's not far from Dundas Hut, and they were helped there for the helicopter to come and get them later once there was a break in the weather. They were located by LandSAR at 1.30am Tuesday morning, having triggered the PLB on Monday night. Does anyone know what they were attempting? My first thought had been a walk around the common loop via Roaring Stag, Herepai, East & West Peak to Dundas (Hut) and then to Cattle Ridge and back down to Roaring Stag. To me that doesn't seem to fully fit leaving on Saturday but being north of Dundas Hut on Monday night, though, and I wonder if they were navigating up from somewhere in the Mangahao Flats area. Here's the region, for anyone interested. http://www.topomap.co.nz/NZTopoMap?v=2&ll=-40.71007,175.482983&z=14

Speculation - but they were presumably aiming for Dundas that night (Sunday) and failed to make it. If I were aiming for Dundas for the night and crossing Pukemoremore then I'd be coming from either Burn or Herepai. Burn to Dundas is a 6-12 hour walk depending on fitness and how much the track has regrown since it was recut in 2013 (unless it's found a new keeper on the last 2 years). Herepai to Dundas is normally a half day walk, so seems less likely to end up late night on Pukemoremore unless there was an injury involved. The 'normal' route up from the upper Mangahao which I hear of people using / maintaining is the old track from Avalanche Flats up Triangle Spur which would bring them out on Mt Dundas, not Pukemoremore - the other side of Dundas Hut. There was an old route up from Harris Flat to West Peak but I've not heard of anyone using it in recent years. http://mapspast.org.nz/mapsheet/11/?zoom=13&x=1810233&y=5493217

depends on your local knowledge, theres a lot of unofficial routes around the tararuas. as madpom points out there are quite a few options that arent on the standard maps...