For operation into and out of high altitude airports, consult your Handbook. Use of Carburetor Heat Carburetor heat should be used whenever atmospheric conditions indicate icing is a possibility and the engine is being operated at 75 percent power and below. When using Carburetor heat, always use full heat. Comply with all engine and airframe manufacturers service bulletins, letters, etc. Use your checklist.
Direct drive means that the propeller is bolted to, and turns at the same speed as, the crankshaft.
No reduction gearing is used. Normally aspirated means that the engine has no supercharger or turbocharger to maintain sea level atmospheric pressure at higher altitudes and, therefore, its maximum available power decreases with altitude. Fuel flow through either a carbureted or fuel injected induction system must be adjusted manually, in almost all instances, to provide for the most efficient fuel to air ratio for efficient combustion within the cylinders. Given certain fuel to air mixtures, it's possible to have a situation where the engine will run rough or will not run at all. Since air density varies with temperature and altitude, it's important to understand when and how to adjust the mixture control to obtain the best performance, fuel economy and maximum life from your engine.