Carburetor heat
Does it need to be cold outside?
By Ferdi Mack
Q: I’m training in a carbureted Cessna Skyhawk. My instructor insists that carburetor heat should be applied as per the checklist, regardless of how hot it is outside. Should I only worry about carburetor ice when it is cold out?
A: Your instructor is correct. You should use carburetor heat as the checklist instructs, with limited exception such as when engine performance suffers on days when carb ice potential is negligible. Also, many pilots forget to remove carb heat during a go-around, so don’t forget to follow the checklist when it says to turn it off as well.
The FAA Pilot’s Handbook of Aeronautical Knowledge covers this in section 7 on aircraft systems. High carb ice potential exists when the outside air temperature (OAT) is between 20 degrees Fahrenheit and 70 degrees F, and with relative humidity of 80 percent or greater. Some carb icing is possible at an OAT of as high as 100 degrees F and with relative humidity as low as 50 percent.
High OAT doesn’t preclude carb icing. Lower air pressure in the carburetor throat results in colder induction air. Carb ice can occur at outside air temps well above freezing.
I have experienced carb icing in some rather surprising scenarios. The first was crossing the mountains west of Rock Springs, Wyoming, in August, and the second over Maryland’s Chesapeake Bay in July. In both cases, the surface temperatures were typical for summertime heat. The OAT at altitude was lower than the surface but still well above freezing.
The first indication of a problem in the Cessna 182RG was that the indicated airspeed fell off by 10 knots, then 20, without any pilot-induced power reduction. I was perplexed, since the common training tip is to look for a drop in rpm as an indication of carb ice. The constant-speed propeller masked the power loss by allowing the propeller to move toward coarse pitch in an effort to maintain rpm, so no rpm drop occurred. The carb ice was only indicated by the airspeed loss.
For more information, contact AOPA’s Pilot Information Center at 800-872-2672 or [email protected].
Ferdi Mack is senior manager of the AOPA Pilot Information Center.
TIPS from PPS
Diagnosis of depression
Mental health as an aviation medical consideration
By Gary Crump
Pilots are passionate about flying, no surprise. Sometimes that passion gets in the way of sound decision making, and loss of a medical certificate is often the first thing pilots think about when they receive news that could affect that certificate. The important thing with any medical condition is to realize that we have a problem, then seek treatment. And a diagnosis of depression is by no means the end of one’s flying. In fact, there are relatively few circumstances involving a diagnosis of depression that would result in permanent denial of medical certification. That said, if you are diagnosed with depression, you shouldn’t fly at least until you have a good understanding of the issues. Discuss your flying with the treating physician or psychologist and heed his or her advice as to the proper time to attempt to resume flying. There is an established protocol that allows the FAA to favorably review applicants for special issuance consideration, but each case is reviewed with respect to the specific individual case history.
Gary Crump is senior director of the medical division of the AOPA Pilot Information Center.
