1. should heat be checked randomly and often or only if the engine becomes rough ? You want to use it whenever icing is "likely" i.e. whenever you're operating below about 50% power and there's moisture in the air, which is whenever the OAT is around or above freezing. At higher power levels there isn't sufficient vacuum in the carb throat to drop the temperature enough to freeze, below freezing there isn't sufficient moisture to form ice. Carb heat is first and foremost a preventive measure. If you're pulling it on because the engine is running rough, you waited too long. 2. only during cooler weather ? See above. Carb ice can form at pretty high OAT's. I've seen charts that show the temperature/humidity combinations that are dangerous, but couldn't point you to one. Anyone? It's a surprisingly broad range of conditions. (I'll have to dig around and find it, one of these days) 3. During approach, should one just pull to check on downwind or base, or heat be left on during the entire landing sequence? Pull it out and leave it out. If you're approach is extended, give the engine a little throttle now and then to help clear out any congestion from the over-rich condition and confirm that it's still ready for the go-around. 4. Is the application of a little heat better or worse than none at all ? Common lore says that it's either on or off. If you need it, put it on. If not, leave it off. Now some of you may think the questions (at least some of them) are silly, and perhaps they are. But you'd be surprised at the varied opinions you get when the subject comes up in "hangar talk". Yup. Here's some more. These small Continentals are KNOWN for carb ice. If you're complacent about it it WILL get you one of these days. Regardless of the temperature or humidity. I was crusing along once, on a sever clear day, OAT in the 50s. Low humidity. I pulled back to about 2000 RPM and set up for the downwind. About 30 seconds later I pulled on the Carb heat. The engine just about quit. It was so violent, I pushed it back in. Then myself said to me "NO! Wrong! Pull it back out!" I did and 5 seconds later everything was back to normal. I was flying with several other planes and I was the straggler. They were all on the ground and all had their hearts jump into their throats, along with mine. The moral: Put it on while your power level is still in the "green". That way, no surprises. One example: Some think heat should be left on through the entire landing sequence, and frankly I think they are right. The downside argument is that if you need to "go around" your power is reduced . Push it in to go around. Full power is immediately available as long as it's not all loaded up (see above). If it's iced and you push the throttle in for the go-around, you're gonna have your hands (and pants) full! I had both experiences as a student many years ago. I 've had an engine quit on final because I forgot to pull heat ( in late fall) and landing in the tree tops in north west Penna. is no fun. I don't know, If I was going to do it, I think Northwest PA is probably the place to do it.... For years I had a Beech Musketeer with Lyc. O360 A4K. It had a funky side draft carb that was immune to carb icing, for the most part. Carb heat was not on the approach checklist. Good way to get into a bad habit... And I've suffered loss of power while doing a touch 'n' go because I forgot to get rid of the heat. Should run fine, just a few horses short, maybe 250 RPM or so. Try pulling it out when climbing at a safe altitude. Better than nothing! With a Stromberg carb, and no accelerator pump, it doesn't take too much ice to kill it if you suddenly go to full power. The mixture goes super lean and you might as well have shut the switches off. But----, I think I'd rather suffer a loss of full power, than a dead engine on final. So!------what think you,---list? Violent agreement. John
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