As at 16th May 2010, I have information that ZK-CSS may well have flown a course
    from  Tekapo, up the Godley River, over the Sealy Pass, Scone Creek, Perth River,
    Whataroa River, Gunn River, Darnley Creek, just north of  Lake Mapourika, and then
    out towards the coast in the area of Three Mile Beach.
An aeroplane was heard at the time coming out of the Perth River and headed up the
    Whataroa above cloud. It was next heard again above cloud north of Lake Mapourika
    and was last heard at Okarito where a crash noise was heard soon after. The crash
    noise was heard in the direction of Three Mile Beach.
Using this scenario, and by using a ground speed of 105 knots, it calculates out
    precisely for Roy Turner’s position to be such as to be able to have VHF radio contact
    with Hokitika 25 minutes into the flight and then loose this contact due to the signal
    being obscured by Mt.Adams (as Hokitika received no acknowledgement after giving
    a weather report).
The final radio call at 32 minutes into the flight (where he asked for the weather
    at Hokitika and Fox Glacier - but none was available for Fox Glacier) would put him
    precisely just north of Lake Mapourika where the observer heard an aeroplane above
    cloud flying back and forth (trying to make up his mind which way to go, or circling
    up [or down] through a hole in the cloud?).
From that position, it is thought that he may have flown out to the coast to attempt
    to descend through the cloud, and when he entered cloud, he became disoriented, lost
    control, and crashed into the forest.
It was reported, that at the time, there was an unusual event of a front coming through
    under the higher layer of cloud and this may have caught him unawares.
Although much of the forest was searched at the time, there was a lot not searched.