I had a look at Vigi FRCs and the advice on carb heat seems a bit 'wooly' to me - or maybe I'm just a grumpy old man? There seems to be some 'Carb Heat As Required', and also the following line, that is less than clear:
CARBURETTOR ICING If carburettor icing is suspected, use full carburettor hot air for 30 seconds. For optimum de-icing use a high power setting with the cabin heating at cold, An initial further decrease in RPM and an increase in rough running is usual during any ice melting process. It is recommended that carburettor air is selected to hot prior to any prolonged period of flight with low power setting, including within the circuit. Carburettor air should not be selected to cold before commencing the final turn but should at some point, be selected to cold before applying full power for a roller landing and, time permitting, before selecting power for an overshoot.
So maybe the increase in rough running on Vigis compared to G109Bs is due to the somewhat less than clear advice on the use of carb heat?
LJ
