NTSB Safety Alert SA-029 - Engine Power Loss Due to Carburetor Icing

Engine Power Loss Due to Carburetor Icing

Recognizing weather conditions and applying simple

procedures can prevent avoidable accidents

The problem

 According to NTSB aircraft accident data, f rom 2000 to 2011 , carburetor icing was a

caus e or factor in about 250 accident s. On average , carburetor icing causes or

contributes to two fatal accidents per year.1

 Accident e vidence shows that some pilots :

 Do not recognize weathe r conditions favorable to carburetor icing and inaccurately

believe that carburetor icing is only a cold - or wet -weather problem.

 Have not used the carburetor heat according to the air craft’s approved procedures to

prevent carburetor ice formation .

 Do not recogniz e and prompt ly act upon the signs of carburetor icing.

Related accidents

 A pilot ditched a Varga Aircraft Corporation 2150A airplane into a lake following a loss of

engine power . The pilot sustain ed minor blunt force injuries but then became hypothermi c

and drowned . The throttle was found full open, the mixture control was found full rich, and

the carburetor heat was found in the cold position. During a postaccident test run of the

engine , it started and ran , and no preimpact abnor malitie s were found. The temperature

and dew point at the time of the accident were conducive to serious icing at cruise power

settings. Therefore, i t is likely that the pilot did not appl y carburetor heat during the

approach to the airport , and the airpla ne experienced a loss of engine power due to

carburetor ice . (NTSB accident number CEN12FA152 )

 A pilot was flying an American Champion 7GCBC airplane in the traffic pattern when the

airplane lost engine power . During the ensuing attempted forced landing, the pilot failed

to maintain a safe flying airspeed, which resulted in an inadvertent stall and crash and t he

pilot dying. Analysis of GPS and engine monitori ng system data revealed that, as the

airplane was rolling out on the downwind leg, the throttle was reduced , and t he airplane

then continued on the downwind leg for at least 14 seconds. As the airplane turned to the

base leg, t he first attempt to actuate the throttle occurred along with an increase in

manifold pressure, which continued to fluctuate as the airplane flew straight toward the

open field. An examination of the engine and airframe revealed no anomalies that would

1 The data are derived from the NTSB aviation accident database and represent accidents in which carburetor icing

was cited as a cause or factor in accidents involving aircraft equipped with a functional carburetor heat control.

Numerous other accidents inv olved a loss of engine power for undetermined reasons during a timeframe in which

conditions were favorable for the formation of carburetor icing; however, the investigation s did not conclude that

carburetor ic ing caused the power loss.

SA-029 December 2013 , revised December 2015 have precluded normal engine operation. A carburetor icing chart showed that the

weather conditions were conducive for moderate icing at cruise power or serious icing at

descent power. Therefore, data indicate that, as with the accident described above , it is

likely that the pilot did not apply carburetor heat during the flight , and the airplane

experienced a loss of engine power due to carburetor ice. (DFW08FA228 )

What can pilots do?

 Check the temperature and dew point for your flight to determine whether the conditions

are favorable for carburetor icing. Remember, serious carburetor icing can occur in

ambient temperatures as high as 90° F or in relative humidity conditions as low as

35 percent at glide power.

 Refer to your approved aircraft flight manual or operating handbook to ensure that you are

using carburetor heat according to the approved procedures and properly perform the

following actions:

 Check the func tionality of the carburetor heat before your flight .

 Use carburetor heat to prevent the formation of carburetor ice when operating in

conditions and at power settings in which carburetor icing is probable . Remember,

ground idling or taxiing time can allow carburetor ice to accumulate before takeoff.

 Immediately apply carburetor heat at the first sign of carburetor icing, which typically

includes a drop in rpm or manifold pressure (depending upon how your airplane is

equipped) . Engine roughness may follow.

 Consider installing a carburetor temperature gauge , if available .

 Remember that aircraft engines that run on automotive gas may be more susceptible to

carburetor icing than engine s that run on Avgas .

Interested in more information?

The reports for the accidents referenced in this safety alert are accessible by NTSB accident

number from the NTSB’s Aviation Accident Database & Synopses web page a t

www.ntsb.gov/aviati onquery/index.aspx. Each accident’s public docket is accessible from the

NTSB’s Docket Management System web page at http://dms.ntsb.gov/pubdms/.

Federal Aviation Administration (FAA) special airworthiness infor mation bulletin (SAIB)

CE-09-35, “ Carburetor Icing Prevention ,” contains a graph that shows t he probability of

carburetor icing for glide and cruise power settings at various temperature and relative humidity

conditions and can be accessed at www.faa.gov/aircraft/safety/alerts/saib/ . Also, see Advisory

Circular 20-113, “Pilot Precautions and Procedures to be Taken in Preventing Aircraft

Reciprocating Engine Induction System and Fuel System Icing Problems ,” which provides

information pertaining to aircraft engine induction system icing and the use of fuel additives to

reduce the hazards of aircraft operation that may result from the presence of water and ice in

aviation gasoline and aircraft fuel systems and can be accessed at

www.faa.gov/regulations_policies/advisory_circulars .

TP 10737, “ The Use of Automotive Gas (Mogas) in Aviation ,” Chapter 3.2 “Carburetor Icing,”

was published by Transport Canada and contains important guidance for pilots operating aircraft

with Mogas instead of Avgas.

This NTSB safety alert and others can be accessed from the NTSB’s Safety Alerts web page at

http://www.ntsb.gov/safety/safety -alerts/Pages/default.aspx .