Gavin Grimmer
20 September 2016
Sorry, it's been a while since I have updated this site as I have been so busy lately.
So far this year I have been on several ground searches and a couple of aerial ones as well, so although I had found errors in my original calculations way back in January of this year, I have not had time to update this article. Seeing as the season was going into winter and likely ground searches were out of the question anyway, the importance did not seem of too much importance, but now it is Spring, this has all changed.
To compound the problem, I got absolutely sick of having MS Windows constantly crashing and what seemed like constantly updating itself, I decided to quit MS Windows and install Linux Mint 17. This of course meant a huge new learning curve - and to top it off the web site program I use does not work under Linux...so I have to jump back and forth between the two programs to do an update.... frustrating to say the least!
Anyway, there were certain aspects of my original calculations that did not fit the 'picture' as well as I would have liked - the main one being the downdraft area talked about on page 19 of this article. I always thought it was stretching things to expect a good area of downdraft there, but the calculations from the information I had at the time fitted it to that area.
On spending a lot of time thinking it over and identifying the areas that were subject to possible error, I decided to recheck the possibilities. Of course, the only problem is if the first 'known' radar ident position (36-40 nm north of Singleton) is out, then it throws the whole calculation out by the same factor.
The first observation by the Radar Operator was 40 n.miles north on that track and as you know, often the first observation ends up being the most accurate. MDX after all was a moving target, and so each time the operator looked, the target would have moved. On this basis I decided I would try my calculations from the 40 nm point rather than from the 36 nm claimed 'most likely' accepted position. I also eventually checked the calculations using 40 nm to 36 nm and found that 40 nm was bound to be the most accurate. To be able to check this, fortunately, in this case we have other factors such as known updraughts and downdraughts criteria to fulfill, so I was able to check these tracks against the terrain to see if these geographical positions fitted, and if it didn't it was obvious the start point was incorrect. I did this by by superimposing my original track from the "just west of the 36nm north, on the Mt Sandon / Singleton track" and moving it up to the 40 nm of where the Radar Controller first said he had observed it, and so forth for 37, 38 and 39 nm.
Using the 40 nm first ident position, and also taking into account another correction needed (I originally used a variation of 11 degrees from information that I had found on the Net but in one of Glenn Horrock's articles http://vhmdx.com.au/vh-mdx-background-information-magnetic-variation/ he said the most accurate figure for that area was 11.732°E and so this altered the calculations of "turn onto 150 by radar" (to West Maitland - page 15) by a further 0.732°. This doesn't sound like much, but it threw my calculation out by roughly 3/4 nm and as you know, this is a very long way in the bush.
With these two corrections combined, this places MDX flying parallel along a ridge (Caneens Gap Track) in an obvious updraught position at the time, and making the turn towards the Coast (Forster) just north of Stewarts Brook. Turning into a tailwind would have initially caused him to loose lift (remembering that he was only really being held up by the updraught due to the weight of ice on the plane) and also into an area of less updraught and so was in effect in a downdraught also at the correct time.... and then an updraught at the time of the call, "up and down like a yo-yo" as they traveled over the range above Carters Brush Track.
I haven't continued using my original track angle from the 09:34:30 turn onwards as it would have then of course had the track 4 nm north of Forster, so I readjusted that track direct to Forster.
MDX pg 28