The pilot was flying a Cessna 175B near Wellsville, Utah, when during a climb to cruise flight, the engine rpm suddenly reduced. He applied carburetor heat, which momentarily increased engine rpm, then it decreased again.
He began troubleshooting the engine and performed the emergency landing checklist. He turned the ignition switch off and back on and the engine backfired once; however, the engine rpm remained at 1,000. He made a forced landing to an open, snow-covered field. During the landing roll, the plane nosed over.
During the post-accident examination the carburetor was disassembled and examined. The carburetor float bowl contained water.
Investigators determined that at the time of the accident the temperature was 25° Fahrenheit with a dew point at 19°. The reported weather conditions were conducive to carburetor icing at glide and cruise power.
Given the sudden loss of engine rpm before and the rise in engine rpm following the application of carburetor heat, investigators determined it was likely that carburetor ice was the reason for the loss of engine power and subsequent off-airport landing.
NTSB Identification: WPR13LA108
This February 2013 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
At 25f is almost the carb icing range,water could have been from fuel tanks if they weren’t drained before flight. I’ve been fly’in my 182 in Utah 4 yrs in winter,never had to use carb ice.
A 6 degree dewpoint spread at an OAT well below freezing is not conducive to carb ice. Water in the float bowl did not come from carb heat deicing of carb. Water in the bowl came from the fuel tank and was most likely cause of uncommanded engine decel as that water would have caused formation of carb ice as it was drawn into carb venturi throat at the high power setting for climb.
I understand that icing of the carburetor occurs in and around the carburetor venturi and on the throttle butterfly valve under given conditions of temperature moisture in the air and throttle settings.
I don’t understand how water made its way into the carburetor bowl. I did not know that water created by de-icing could be drawn into the bowl. I would appreciate a response from a learned person on the subject to explain to me how an icing carburetor being de-iced with carburetor heat contributed to water in the carburetor bowl. I would like to know what I am missing.
The OAT reads 25F; carb heat should be on the checklist, don’t you think?
Actually, because there is a drop in temperature as the airflow speeds up in the carb throat, 25 degrees OAT can be far safer than 50 degrees. Colder air holds far less moisture in suspension.
Confused?! keeping WOT + carb heat have prevented the need for off-airport landing?