Respect your Limitations!
We operated a nightly round trip from central Europe to Yerevan, Armenia (EVN/UDYZ) in fall 2005. SATs were around -70°C to -71°C (at FL350 if memory serves me right).
Due to fuel shortage we departed home base with a full load of fuel (19,3 to) on a lightly loaded A319. Shortly prior to TOD we got the Advisory Condition that the left outer tank was at -41°C. So we descended just a couple of minutes earlier.
During tournaround we uplifted only about 3,500 kgs so trouble came back about an hour after reaching cruising altitude. Lower levels were all blocked an Rostov ATC was not really cooperative (probably not understandig WHY we wanted to descend).
So we contacted our trouble-shooters (engineering dept) via acars and asked if there were any objections against opening the fuel x-fer valves to mix the 2x 700 kgs outer tank fuel with the significantly warmer inner tank fuel. They gave us the go-ahead which saved the poor controller a mayday-call and an unapproved descend, which we would have done at -44°C in any tank, as our book gives a Limitation to keep fuel temp 3 degs above freezing point.
Good Thing about the Wing A/I, never thougt about it. Maybe switching on some ovens in the galleys might work as well.
Regards, MAX