"but as far as I am aware, only one ignition is required when anti-ice is switched on, and only. .remains on for a short while, if there is only little turbulence.". .. .G'day, FD. .Are you referring to the sort of Anti-ice system which fires up the ignitors automatically for about 60 seconds to prevent a flameout due to Anti-Ice melted ice (i.e. ice which may have formed previously in your engine inlet)? . .. .Perhaps Blacksheep is more concerned about preventative or long term use of the Anti-Ice System, i.e. to stop the ice build up in the first place and keep the engines ice free. I believe that ice, if left to accumulate in an engine intake over a long period in the absence of anti-ice may snuff out the engine irrespective of whether the ice was melting or not (due to disrupted airflow in the inlet).. .. .In your situation, if the engine should flame out, due to the build up of ice or the melting of ice, you only have half the capacity to relight the engine. If there is no ice build up in the first place (say because you predicted that there would be ice ahead and switched on the Anti-Ice system beforehand manually), the engine would be less likely to flame out under icing conditions (and you wouldn't need to restart the engine with a single ignitor).. .. .Hope this makes sense.. .. .Rgds.. .Q.