Carb ice.

[Mooneymite]

There seems to be a perception that carbureted Mooneys are immune to carburetor ice.  This was in today's "Flying Lessons", an excellent weekly newsletter even if it is written by a Bonanza guy:

"   Debrief
Readers write about past FLYING LESSONS

Reader/instructor Sam Dawson writes about last week’s LESSONS on the use of carburetor heat: 

Another great issue. I have one thing to add about carb ice. There is a myth that certain airframes and engines are not susceptible to carb ice. This could not be farther from the truth and the NTSB files are full of Piper accidents, often fatal, where carb ice is the suspected cause.

NASA did a study in the 1970s and concluded, "As no practical or statistical significance exists between the major manufacturers of either airframes or engines, no distinction between makes was carried through the subsequent analysis. These results contradict informal reports that specific manufacturers produced designs more or less prone to carburetor ice difficulties." (NASA CR-143835, "A Study of Carburetor/Induction System Icing in General Aviation Accidents").

The NTSB came to the same conclusion and, in a Safety Recommendation dated January 8, 1990, recommended that the FAA mandate that aircraft flight manuals and pilot operating handbooks of carbureted equipped airplanes be amended to require the use of full carb heat in the descent and before landing checklists.

This was not done, probably due to liability issues, so the Piper manuals still state that "Carburetor heat should not be applied unless there is an indication of carburetor icing..." The problem with this, as pointed out by NASA and the NTSB, is that on approach most pilots will not recognize the build up of carb ice until it is too late- when they apply power due to being low or during a go around. At this point it is usually too late to apply carb heat and the outcome is a forgone conclusion. Again, one need only Google "Piper carb ice accidents" and a number of them come up.

This is one of those cases where blindly following the POH/AFM can be deadly. Unless a pilot has checked the Carb Ice Probability Chart and knows for sure that there is no chance of carb ice, I would highly recommend using carb heat at low power settings, no matter the make and model of the airframe and engine.

I would add that my one carb ice encounter was in a big bore Continental, in the summer, in New Mexico. After a long descent the engine ran rough as I applied power. I immediately went through the partial engine failure flow (air, fuel, spark), and carb heat, after initial roughness, cleared it up.

Thank you, Sam. A more recent NTSB Safety Alert adds:

According to NTSB aircraft accident data, from 2000 to 2011, carburetor icing was a cause or factor in about 250 accidents. On average, carburetor icing causes or contributes to two fatal accidents per year. Accident evidence shows that some pilots: 

• Do not recognize weather 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 aircraft’s approved procedures to prevent carburetor ice formation. 
• Do not recognize and promptly act upon the signs of carburetor icing. 

The FAA chimes in with Advisory Circular 20-113, “Pilot Precautions and Procedures to be Taken in Preventing Aircraft Reciprocating Engine Induction System and Fuel System Icing Problems,” which notes:

• “…regularly use [carburetor] heat under conditions known to be conducive to [carb] icing….”
• “When the relative humidity is above 50 percent and the temperature is below 70°F [21°C], apply carburetor heat briefly immediately before takeoff, particularly with float-type carburetors, to remove any ice that may have accumulated during taxi and runup.”
• “Conduct takeoff without carburetor heat, unless extreme intake icing conditions are present.”
• “With instrumentation such as carburetor or mixture temperature gauges, partial heat should be used to keep the intake temperature in a safe range. Without such instrumentation, full heat should be used intermittently as considered necessary.”
• “If induction system ice is suspected of causing a power loss, apply full heat or alternate air. Do not disturb the throttle until improvement is noted. Expect a further power loss momentarily and then a rise in power as the ice is melted.”
• “If the ice persists after a period with full heat, gradually advance the throttle to full power and climb at the maximum rate available to produce as much heat as possible. Leaning with the mixture control will generally increase the heat but should be used with caution as it may kill the engine under circumstances in which a restart is impossible.”

"

 

https://mastery-flight-training.com/

[midlifeflyer]

Good post. I also had a massive carb ice incident . Mine was in a Lycoming 0-540 Piper Comanche on a June day. when the OAT aloft was in the 70's.

On susceptibility, many point to the difference between Cessna's recommendation to use as a preventive and Piper's recommendation to use only as needed. But there's some evidence that the difference isn't about susceptibility as much as it is about the location of the carb heat control. 

[Candy man]

Great post!

 

I was also taught that Mooney’s aren’t susceptible to carb ice.

 

Well… I was at 11,000 feet in imc over Pennsylvania, autopilot was on, and I was monitoring everything as usual. I notice that my airspeed had come way down into the white arc. It was the autopilot trying to maintain altitude (and willing to kill me in the process) I immediately disengaged the autopilot and started descending to increase the airspeed. It took me a good minute or 2 to come up with carb ice. Once your told its not a problem it seems to go further down on the mental things to check.
 

I trained in a Cessna and always used carb heat in low power settings. Anyway I added carb heat got a k-chunk k-chunk and a vroom. The other thing that I don’t like is in my 1970 c with vernier controls the carb heat is totally out of sight, and it’s kind of out of mind. I really wish there was a way to show pilots while trying what carb ice is really like. I’ve never had the problem again and have since added the jpi 900 with carb temp, but I know it can really happen in a mooney.

Lawrence

[Hank]

I really like my carb temp gage, even though it's in ºC and my OAT is in ºF--that's why the gage has an orange stripe.

Just another reason to watch closely when IMC [or just above / just below] the OAT and Carb Temp, and why I pull the Pitot Heat whenever going IMC.

With power-on descents, they can be as long as needed with no need to pull carb heat, I work the throttle and mixture to maintain cruise EGT values all the way to pattern altitude, with an eye on carb temp if IMC or close to it.

[midlifeflyer]

46 minutes ago, Hank said:

I really like my carb temp gage, even though it's in ºC and my OAT is in ºF--that's why the gage has an orange stripe.

Just another reason to watch closely when IMC [or just above / just below] the OAT and Carb Temp, and why I pull the Pitot Heat whenever going IMC.

With power-on descents, they can be as long as needed with no need to pull carb heat, I work the throttle and mixture to maintain cruise EGT values all the way to pattern altitude, with an eye on carb temp if IMC or close to it.

I think those are really useful gauges.

When I had my carb ice incident (in the clouds over the Rockies), I got interested in the topic and started looking at NASA ASRS reports. Most of the ones I looked at had a common theme - flying airplanes where it was used "as needed" and forgetting it., especially when the pilot flew multiple types, some carbureted, some not.  There was also an earlier NTSB study, ending with a 1990 recommendation that carb heat always be used as a preventive. The recommendation was ignored.

At least with a carb temp gauge, with a decent scan of engine health, there is a bit less likelihood of out of sight, out of mind. 

[GeeBee]

Agree 100% with carb temp gauge. Had one on my SuperCub and I will never be without it again.

[Mooneymite]

3 hours ago, Candy man said:

Great post!

I was also taught that Mooney’s aren’t susceptible to carb ice.

Any Mooney pilot who claims, "I've never had carb ice in my Mooney" should always add the word, "yet".

[AIREMATT]

On 5/18/2023 at 1:04 PM, Mooneymite said:

Any Mooney pilot who claims, "I've never had carb ice in my Mooney" should always add the word, "yet".

Or “as far as I know.”