Sorry but I have to take issue with the comments made by 411A... I'm sure he has considerable experience but in this respect he's off centre. Point 1... they are not simply ice-vanes... think of them by the correct term "Inertial seperators"... Point 2....they do a superb job at keeping any gravel / FOD etc out of the engines and it's recommended by Raytheon/Beech and FlightSafety Int. that they're used for start and taxi... though the checklist may say optional. Having operated KingAirs from unmade strips in Africa and Afghanistan under extremely hot conditions when WAT limited due to runway length and trees my preferred method of operation was to have them on on the take-off roll until 40 knts (above which speed it's unlikely that you'll suck up grunge into the intakes) and then knock them off so as to achieve max Torque and Min ITT for the climb out.... That's just my system but whatever, don't underestimate the benefits of keeping grit out of the engines.