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The above shows the VHF (line of sight) radio reception area at 7800’(green areas) - just 300’ higher than shown on the previous image (previous page) and so you can see how precise it is to calculate what height Roy was likely to be at when he made contact with Hokitika. Go a little higher and there would have been no problem with reception. Go a little lower than 7500’, and no reception with Hokitika until clear of Mt Adams.

According to information I have, ZK-CSS was a Cessna 172K model (1969-1970 model) and it had a cruise speed of 114 knots at 9000’.

It is not known what the wind speed and direction was through the Godley Valley that day, although the observer inland of the Whataroa Bridge said there was no wind, and it was also reported that there was no significant wind at Tekapo at the time the Turners departed , so it appears Roy was ahead of the approaching front. It is then possible to calculate Roy’s ground speed reasonably accurately , but just to be sure, we will calculate a likely ground speed  using a range from 100 knots to 125 knots to allow for a possible head wind, or tailwind:

100 knots = 1.66 nm covered per min (14 knot headwind)

110 knots = 1.83 nm/min (4 knot headwind)

114 knots = 1.90 nm/min (advertised cruise speed)

125 knots = 2.08 nm/min (16 knot tailwind)

                                                         25 minutes @ 100 knots = 41.66 nm (25 x 1.66)

                                                                            @ 110 knots = 45.83 nm

                                                                            @ 114 knots = 47.50 nm

                                                                            @ 125 knots = 52.00 nm

If we then place these distances on his possible track, this is what we get:

You’ll note that the “still air” cruise speed (114 knots) fits the bill perfectly as it puts the position of ZK-CSS at 7500 feet just inside the first reception area which covers a distance of 1.34 miles and at 114 knots means it was in coverage for up to 42 seconds...long enough to get a call to Hokitika, get a call back, and get a off a request for the weather.

ZK-CSS 5
ZK-CSS 5
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