Winds Reported By Other Aircraft Flying At The Same Time
It quickly becomes apparent that the Barrington Tops and the lower lying ground to the SW of it was having an effect on the wind direction. The wind was 'funnelling' through this gap in the ranges and then spilling back in behind the Barrington Tops to make up with the short-fall of air deflected over the tops. This I would suspect would change the wind direction in the area where MDX was in as it travelled south (after the Ident position) to at least the 281°T direction reported by VH-CNW... maybe even as far as anything up to 300°T due to the air below being forced around the corner of the southern facing Barrington Top hills. Of course we will never really know the direction for sure, but the reason I had to check this possibility out was due to when the calculations based upon a wind of 240/56, they fell well short of the supposed radar identified position of 320°M at 46 nm (even 48) from Williamtown. All will be explained as you read on....
A lot of the problem is trying to understand what the radar operator was seeing on his screen as to what MDX was actually doing. The radar head was turning at a rate of once every 12 seconds, so what appeared to be the actual course taken by MDX may not have been so. Take into account also the lag times of the process time of the radar – although small – but it all adds up to increases in the error margin for the accurate pin-pointing of the actual position at a particular moment in time. The radar 'paint' position also covered an area of about one square mile on the screen, although I would take it that the actual spot the plane was in was in the centre of that 'paint' – presuming the radar was accurately calibrated. The radar operator himself said in the transcript (09:28:46) that it was not a very accurate way of determining an exact position: “Awh, not very accurate these things..he's probably about 36”.
The only real way of knowing the accuracy of the radar at that time was to get someone in constant radio contact with the radar operator to be guided on a flight to the same radar paint spot positions, but as this did not happen in the days just after the accident, this opportunity has been lost.
Every 12 seconds, at cruise speed MDX could have travelled anything from 0.35 nm to 0.7 nm - depending whether it was flying with a head-wind or tail-wind... a lot of distance!
Fortunately, there are ways of double checking at least some of these positions....
Mike was given a couple of clues as to his position – one being the obvious “36 miles north of Singleton and on the Mt Sandon – Singleton track.” He had 4400 hours as an Air Force navigator, so it would not have taken him very long to realise he had intersected this Mt Sandon – Singleton track pretty much as right angles (seeing as he had come from the direction of Taree) and then calculated a correction heading to get him back on track to Singleton. The only problem was he had been given a wind speed of 76 knots with which to work with. He would have immediately looked at his IFR Flight Chart to look up the magnetic heading to Singleton on the Mt Sandon – Singleton track but found it was........ not there!
MDX pg 13