The Limbach engine is an ice maker. There are almost no weather conditions in UK when it doesn't ice up. Taxy can be on cold but extensive running at 2000 rpm is needed during pre take-off checks to clear the ice. During cruise hot air is needed every 10 mins, and it is routine to pull the hot air control every 5 mins and watch the rpm. No drop or a rise in rpm is a sure indication of icing. I once assumed that cold air was OK with an OAT of minus 1 and flt level of 7,500 ft over the sea between Cornwall and Wales. The sudden onset of coughing and banging plus the possibility of a ditching sure changed my mind.
