By the time MDX would have completed the turn, the calculations place MDX at 09:34:30 within 3 nm of the 320/46 nm radar position that was plotted at the same time by S1.
According to Glenn in his radar article, these radar positions have an accuracy of 2 nm and the radial bearing of -2°/+4° which means the actual position could be anywhere within a few nm radius of this radar spot. This also means that the first radar identification spot of MDX could have been two miles different to what we have, which if applied, would correct this possible error, but this calculation so far seems to be reasonably accurate to the two actual positions plotted by S1 that we have used.
Williamtown had a positive SSR radar identification 90 seconds later on the same radial but it was recorded on the audio as 45 nm, but later recorded and initialed on the handwritten transcript as 48, and on the 13th August 1981 (4 days later) the Controller stated in an interview that it was more likely 48 than 45. Glenn explains the reasoning behind this confusion in his Presentation.
The 09:36:00 position is within the limits and I wonder if WLM actually took a real close look at the position. Judging by the confusion over the 45 to 48 nm, I would guess not, as the position I have it is only a further 2° anyway... probably not noticeable on the radar screen especially when you consider that the WLM Controller was on his own in the Tower, and had to leave his station to walk over to the radar screen to check. (refer to Glenn's excellent Presentation).
Using the wind of what VH-CNW observed in this area 270°M/50 knots, the ground speed of MDX would have increased to 209 knots on this track out towards the coast. The calculations show that he had not slowed the plane down up to this point and so I don't see why he would have slowed it down now.
09:36:42 “we’re up and down like a yo-yo.” Lets have a look at the ground profile that he was over at that time:
Looking at this profile it now becomes very obvious that he was not bouncing up and down as the words suggest, but simply at that point the 1000 ft/min downdraught had turned back into an updraught... possibly up at the same rate. You can tell by the tone in his voice that this Mike Hutchins was a bit of a character!
09:36:24 “We’re having a little bit of a problem in that our standby compass is swinging like – like blazes.” For the sake of those that don't know, the standby compass simply means the magnetic compass. The distance covered in the downdraught would equate to anything up to 1000 ft if the 1000'/min rate continued, so if he started off at 8500 ft, then they would have got down to 7500 ft and possibly gained 300 ft in the next updraught, which would place them at something like 7800 ft. The yellow line is the line that the profile is based on. In the 24 seconds from the 09:36:00 position, they would be 1.39 nm further along the track and in the lee of the mountain shown in the above profile. This mountain profile is the end of a ridge making the position they flew over it more like a mountain peak. The strong wind would have been swirling all around it making conditions downwind of it very turbulent.
MDX pg 20