improper use of carb heat in IMC?

[cointyro]

See the NTSB report below. My question is this: why is it improper use of carb heat to engage the heat while in cruise flight? I thought it was acceptable to push the heat on to check for carb ice. Should you not due this while IMC?

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NTSB Identification: BFO88LA013 . The docket is stored on NTSB microfiche number 35180.
14 CFR Part 91: General Aviation
Accident occurred Thursday, January 07, 1988 in ROCK CAMP, WV
Aircraft: PIPER PA-24-250, registration: N14BK
Injuries: 1 Minor.
DURING CRUISE FLIGHT IN IMC THE ENGINE STOPPED WHEN THE PLT TURNED THE CARB HEAT TO CHECK FOR CARB ICE. HE WAS UNABLE TO RESTART THE ENGINE. HE DESCENDED INTO VMC AND TRIED A FORCED LANDING IN AN OPEN FIELD. THE ACFT STRUCK A TREE SHORT OF THE FIELD. THE PLT LOST CONTROL OF THE ACFT AND IT LANDED HARD IN THE OPEN FIELD. EXAM OF THE ACFT DID NOT DISCLOSE EVIDENCE OF MALFUNCTION.


The National Transportation Safety Board determines the probable cause(s) of this accident as follows:

CARBURETOR HEAT..IMPROPER USE OF..PILOT IN COMMAND
FUEL SYSTEM,CARBURETOR..ICE



Contributing Factors

WEATHER CONDITION..CARBURETOR ICING CONDITIONS
OBJECT..TREE(S)

 

[avbug]

Evidently either the carb air mechanism failed and blocked the induction airflow, or this individual really had carb ice. Either way, the NTSB has stated it was pilot error because the pilot applied the heat...there was no other action taken which caused the event.

From the brief narrative, it appears that the pilot appropriately applied carb heat...the engine quit as the ice melted. Conversely, the pilot may have caused ice to form. Commonly disbelieved, it's a fact that inappropriate use of carburetor heat can cause carb ice to develop by raising the temperature in the carburetor to the ideal icing range. This can be true of full heat, and partial heat.

I had an engine failure in instrument conditions in a 182 once, just after applying carburetor heat. The engine began to run rough, I noted a decrease in RPM, and applied carb heat. The control came away in my hand, with the control wire having separated at the carb air box. I pulled it completely free of the panel and tossed it behind me. The engine failed, and I descended without power until breaking out, and then landed without power on a gravel strip below.

It appears the NTSB has made this statement, because there was nothing else to pin it on.

 

[cointyro]

Thanks avbug!

So the takeway lesson is:

(A) Be aware that leaving carb heat on during cruise may cause icing.

?? (B) Don't apply carb heat without indicated icing / engine roughness while in cruise / anywhere besides approach & landing ??

If the pilot appropriately applied heat, how is it considered pilot error? Does the FAA take the stance "it's pilot error if no other problem can be found"?

Thanks for any suggestions. I appreciate the advice on this board.

 

[Iceman21]

I believe the stance of the NTSB is correct in the use of "pilot error" because it has been established that the pilot caused the engine to quit BECAUSE he turned on the carb heat. It may not be known what made the pilot turn on the carb heat. There seems no reason to speculate and seems better to make a ruling based on what evidence there is, rather than speculate as to why he put the carb he on.

 

[cointyro]

Here's another case with carb heat. So let me get this straight... don't turn on carb heat in known icing conditions as the NTSB will call it pilot error?

I guess I'm still confused... when is it OK and proper to use carb heat? Only upon approach or dropping RPMs? Even then it looks as though the NTSB will call you out...

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NTSB Identification: FTW88LA056 . The docket is stored on NTSB microfiche number 35178.
14 CFR Part 91: General Aviation
Accident occurred Friday, January 29, 1988 in TOMBALL, TX
Aircraft: CESSNA 152, registration: N6614H
Injuries: 1 Minor.
THE AIRPLANE WAS DESCENDING TOWARD THE AIRPORT WHEN THE ENGINE LOST POWER. APPLICATION OF CARBURETOR HEAT RESTORED POWER UNTIL NEXT DESCENT. SECOND DESCENT WAS STARTED WITH FULL CARBURETOR HEAT APPLIED AND POWER WAS LOST AGAIN AND COULD NOT BE RESTORED. PILOT MADE OFF-AIRPORT, NIGHT, FORCED LANDING, HIT TREES AND THEN THE GROUND. NO MECHANICAL PROBLEMS FOUND. THERE WAS FUEL IN TANKS AT TIME OF POWER LOSS. WEATHER CONDITIONS WERE CONDUCIVE TO SEVERE CARBURETOR ICING.


The National Transportation Safety Board determines the probable cause(s) of this accident as follows:

WEATHER CONDITION..CARBURETOR ICING CONDITIONS
CARBURETOR HEAT..IMPROPER USE OF..PILOT IN COMMAND



Contributing Factors

LIGHT CONDITION..NIGHT
OBJECT..TREE(S)

 

[Singlecoil]

I think what they are saying is that if the carbretor heat was properly applied, then the ice wouldn't have formed so severly in the engine as to cause a failure. Don't wait until the engine fails to turn carb heat on, and then don't leave it on all the time as you are sucking unfiltered air.

 

[Iceman21]

After a brief skim of the second report. I believe the pilot error was getting into a situation where he could not control the amount of ice accumulation in the carb. It seems that the icing in the carb was so bad ice was able to form even though the carb heat was on. Not much he could do about that other than not be in the situation which is the pilot error.

As far as the first report, there is no indication that there was any carb icing there or any weather conditions conductive to carb icing. Raises the question why turn on the carb heat if you do not need it.

 

[BigFlyr]

As far as I know, carb heat should only be applied as power is reduced during approach and landing and/or prior to entering icing conditions. It should not be applied if ice is already suspected as it would melt and enter the engine. My 2 cents.

 

[A Squared]

As far as I know, carb heat should only be applied as power is reduced during approach and landing and/or prior to entering icing conditions. It should not be applied if ice is already suspected as it would melt and enter the engine. My 2 cents.

Hmmm, so if you're getting a little carb ice in cruise you're just going to sit there and let it build until the engine quits?

 

[BigFlyr]

Hmmm, so if you're getting a little carb ice in cruise you're just going to sit there and let it build until the engine quits?

No... You're going to get out of the icing conditions or take a chance at drowning the engine out with water if there's already a significant amount of ice built up. It's like everything else in aviation... If it works you did the right thing, if it doesn't you're screwed.