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I now know, Mike had not turned onto the ‘Mt Sandon/Craven waypoint’ radial as I previously thought, as that was not the radial he had used previously. He would have turned that way simply because he was now out of cloud and could see the lights of Newcastle.

From my understanding, Williamtown had TACAN rather than VOR and as that uses a different frequency exclusive to military aircraft, MDX was unable to tune into it... but they did have an NDB that could be tuned to with an ADF.  It is very possible he tuned to the Williamtown NDB at that point, although in the turbulence they would have been experiencing there, I believe that would be rather difficult... but not impossible.  The outcome would be the same however... they would drift towards the east away from the direct line to WLM... given the strong SW wind.
 

With the final descent down to the 5000 ft point - and further, they would have experienced very strong turbulence and in fact were probably in rotors, so to avoid ripping the wings off and also in an attempt to slow the descent rate, Mike would have had the motor on full power and slowed the plane down to around 90 knots (Best rate of climb speed). There’s two reasons for this… one is to arrest the rate of sink by increasing the angle of attack of the wing to maximum climb rate (and going to full power), and the other to ride out the turbulence. The slower the speed… the smoother the ride, and the easier on the airframe and the passengers.

Once he had pulled out of the dive, he would not have increased the speed very much so as to ride out the turbulence… maybe 100 knots (maybe slower) - up to the maximum rough air speed of 119 knots.

To calculate this drift towards the East, you would need the forward speed (100 to 119 knots) and the “sideways” speed (40 to 60 knots?).

Based on a heading needed to make Newcastle, and an estimate of the possible wind speed and direction which would have been at that point - almost right angles to the flight direction….  Forward speed: (100 kts = 1.66 nm per minute) to (119 kts = 1.98 nm/min)…. Crosswind: (40 kts = 0.66 nm/min) to (60 kts = 1.0 nm/min)…. In other words – a lot of drift!

Here it is ‘drawn’ on Google Earth:

Needless to say, where this person saw it ‘go in’ is in is within this fan, so it makes this sighting very valid!

For the benefit of those readers that don’t know what an ADF is, it is an instrument that if the needle of the instrument is kept in the middle after tuning into a particular NDB frequency, it will keep the nose of the aeroplane pointing towards the NDB Station tuned to, if flying towards the NDB. The aircraft will always point at the destination, but is still at the mercy of any crosswind component, and if there is a crosswind, (and there is no compensating turns allowed for) the aircraft will fly what is known as a parabolic curve.
I say “compensating turns” as if the wind speed and direction is known prior to the flight, it is easy to calculate the extra turns required into wind to allow a relatively direct course to be flown, but in this case Mike did not have that luxury, as his work load would have been far too high… He would have just been trying to make the best of a very bad situation!

MDX pg 37