I hope this may be of some help to you all on this subject because it makes me go cold when i think about it !.
first the tech details.....aircraft Robin DR400-180..engine Lycoming 0-360-A3A
The met situation.......FL90 temp +1 cloudbase 3000ft tops well above FL100 moderate rain.
I had been using carb heat about 60% of the time at FL100 and was having no trouble clearing the ice ,at top of drop about 27 NM south of the isle of man i was cleared to FL70 i selected carb heat and reduced the power about 250 RPM for a cruse descent after about 500ft it was clear that the ROD was much higher than normal for that power setting so i pushed the throttle all the way up and very little happend the EGT was indicating that the engine was making some power as the temp was well above the bottom stop ,the next thing i tried was setting the mixture full rich ....RPM and EGT droped instantly so that came back to the highest EGT setting that i could get this gave the lowest ROD.
It was now becoming clear that i could not maintain FL70 so a call to ATC got me clear to descend as far as i needed to with the other trafic getting moved clear i was all ready on a HDG that was going to get me ditching as near to land as i could get.
AS we passed about FL50 the engine started to pick up and by 4000Ft was running normaly,engineering investigation found no problems but i changed the carb as the butterfly valve shaft was showing evidence of wear.
The lessons from this ?
1 dont give up on trying to start the engine.
2 stay with the carb heat even if it seems to be having no efect.
3 Full rich on the mixture may be too rich at altitude with most of the carb blocked with ice.
4 Have the proper safety equipment for the flight , if i had ditched i had all the kit to give me the best chance of being alive and found IE life jackets ,liferaft,ELT,dye markers,pyros and the training to use them.
[ 23 August 2001: Message edited by: A and C ]