[Kharon]

Out loud thinks...Gundaroo Cirrus..

Item 1: -BoM Graphic Area Forecast – Freezing levels :-

Area 'C' into 'A'. Fzl 5000' – 6000' – 8000' – 10,000'.


Item 2: -BoM Graphic Area Forecast – Cloud:-CU/SC -

Without getting too technical; a quick study of the forecast suggests a high probability  of in-flight icing. Lots of CU, lots of 'mixing' indicated by the wide range of freezing levels prescribed. To me, this indicates possibility of icing from just after departure to landing, along with turbulence and some areas of reduced forward visibility. In short, not a pleasant sort of day – routine enough for those running turbines or pistons with ice protection; but would I have taken off and set out for a 'look-see' in a single with little more protection than a heated pitot? Probably yes; provided the back door was wide open and the welcome mat out. The key factor would be performance margin available if I get iced up. How much ice can I manage, can I lose it, and if the build up continues (on descent), where can I go?

Much to consider; IFR without ice protection – route selection and 'what-if' options  would/should be a prime consideration. From the data we can see, seems the aircraft had a steady climb to altitude, seems reasonable to speculate that this was achieved without a significant ice build up; 02:36 to 02:45 (ish) nine minutes to TOC (1885' to 9,000+/- = 7000' gained : 9 minutes)– from the ADS-B data, routine stuff.

But; the 'speed' line begs some consideration, as does the mean freezing level. Hard to arrive at any conclusion from the crude 'graph' – HERE - . But, it tells a part of the story worth a thought or two..




At 02: 36 (ish) climb speed <100.
At 02: 37 (ish) climb speed <110.
At 02: 38 (ish) climb speed <125.
At 02: 39 (ish) climb speed =100.
At 02: 40 (ish) climb speed <120.
At 02: 41 (ish) 8,000 speed >130.
At 02: 42 (ish) 8,000 speed <100.
At 02: 43 (ish) >8,000 speed <100.
At 02: 44(ish) 8,500  speed <100.

Yes;yes,  really rough numbers, scientifically indefensible I realise; but, it seems a brick wall was hit at about the 8000' level; cloud up to 10,000, the concentration of potential 'airframe ice' would be at that height; as the vertical component of the CU (lapse rates) would be easing off as stability (balance) was reached. Probably a mix of super cooled and ice particles; perfect for the real stuff on the ice cold airframe.

What occurred between 02:45 and 02:47 is well  beyond my remit or knowledge; and speculation beyond that point would be foolhardy and best left to the investigator (IMO). But, without much doubt, the wheels came off at 8,000 and airframe ice involvement is a racing certainty.

I shall now retire back to knitting and await the report – (and wait and wait).. ATSB IIC ain't got a lot to work with on this one; apart from the obvious eliminations. 'Nuff said, probably too much.

Toot – toot.