As general aviation pilots, we often associate icing with winter’s chill—frozen runways, frosty wings, and the need for de-icing equipment. But what if I told you that one of the most insidious forms of icing can strike on a balmy summer day, when the sun is shining and temperatures are soaring? Carburetor icing, often dismissed as a cold-weather problem, is actually a year-round threat, and it’s particularly sneaky during the warmer months. In this blog post, we’ll dive deep into the concerns surrounding carburetor icing, drawing directly from a insightful one-pager chart produced by the FAASTeam (Federal Aviation Administration Safety Team). This chart, titled “Carburetor Icing: A Summertime Threat!”, serves as a vital tool for pilots to assess and mitigate risks. By understanding how to use it, you can stay ahead of this potentially engine-killing phenomenon and ensure safer flights.
Understanding Carburetor Icing: The Science Behind the Freeze
To appreciate the dangers, let’s start with the basics. Carburetor icing occurs in piston-engine aircraft equipped with carburetors, where fuel is mixed with air before entering the engine. The process involves the Venturi effect: as air flows through the narrow throat of the carburetor, its speed increases, causing a drop in pressure and temperature. This cooling can be dramatic—up to 70°F below ambient temperatures in some cases. When moist air is present, water vapor condenses and freezes on the carburetor’s internal surfaces, like the throttle valve or venturi walls.
The result? Restricted airflow, an overly rich fuel mixture, and a gradual or sudden loss of engine power. In mild cases, you might notice rough running or a slight RPM drop. In severe scenarios, it can lead to complete engine failure, forcing an emergency landing. According to FAA data, carburetor icing has been implicated in numerous accidents, often because pilots don’t recognize the signs early enough. It’s not just a nuisance; it’s a safety hazard that can turn a routine flight into a life-threatening situation.
What makes it especially concerning for general aviation (GA) pilots is its unpredictability. Unlike structural icing, which requires visible moisture like clouds, carburetor icing can form in clear air. It’s most common in aircraft without fuel injection systems, such as many Cessna 172s, Piper Cherokees, or older trainers. GA pilots, who often fly at lower altitudes and in varying weather, are particularly vulnerable. And here’s the kicker: while we think of icing in sub-freezing conditions, the FAASTeam chart highlights that it can happen even when outside air temperatures (OAT) reach 100°F, as long as humidity is present.
Why Summer Poses a Unique Risk
Summer flying evokes images of blue skies and smooth air, but the season’s high humidity levels create prime conditions for carburetor icing. The chart provides specific averages for summer in Ohio: temperatures ranging from 65°F to 95°F (averaging 75°F), dew points from 60°F to 78°F, and relative humidity (RH) often hitting 80% to 100%. These conditions align perfectly with icing probabilities.
The chart explains that carburetor ice is most likely below 70°F OAT and above 80% RH, but due to the carburetor’s internal cooling, it can occur at higher temperatures and lower humidities—down to 50% RH at 100°F. In humid summer environments, like those in the Midwest or Southeast U.S., pilots might encounter icing during takeoff, climb, or descent, especially at reduced power settings like glide or cruise. Imagine cruising at 75°F with 90% RH: the air feels muggy, but your engine could be silently accumulating ice.
For GA pilots, this is alarming because summer flights often involve recreational outings, cross-countries, or training in variable weather. A power loss at low altitude, say during approach, leaves little room for recovery. Historical incidents, such as a 2018 NTSB report on a Cessna 150 that experienced carb icing on a warm, humid day leading to a forced landing, underscore the risk. Without vigilance, what starts as a minor RPM fluctuation can escalate quickly.
Decoding the FAASTeam Chart: Your Visual Guide to Icing Risks
Now, let’s turn to the heart of this post: the FAASTeam chart itself. This one-pager is a graphical representation designed for quick reference, making it an essential pre-flight tool. The chart plots ambient temperature (°F) on the x-axis (from 0°F to 110°F) against dew point (°F) on the y-axis (from 0°F to 100°F), but it’s effectively a proxy for relative humidity, as dew point correlates closely with moisture content.
Color-coded zones indicate icing severity:
- Blue Zone: Moderate icing at glide and cruise power. This is the broadest area, showing where ice can form under normal operations.
- Green Zone: Serious icing at glide power. Glide phases, like descents, especially during pattern work, are riskier due to lower engine heat.
- Orange Zone: Serious icing at cruise power. Cruise settings can still allow rapid buildup.
- Red Zone: Icing specific to pressure-type carburetors, which are less common but still relevant for certain aircraft.
A yellow arrow points to the “Icing (glide and cruise power)” label, emphasizing common scenarios. There’s also a star marker highlighting typical summer conditions in Ohio, right in the heart of the high-risk zones.
Below the graph, explanatory text reinforces key points: “Carburetor ice is most likely to occur when temperatures are below 70°F and the relative humidity is above 80%.” It notes the cooling effect and stresses immediate action upon power loss—apply full carburetor heat, even if it causes temporary roughness.
This chart isn’t just pretty colors; it’s a predictive tool. By cross-referencing current weather data (OAT and dew point or RH), pilots can gauge risk levels before takeoff. Try doing this with METAR reports at your local airport during varied temperatures and dewpoints.
How to Use the Chart to Avoid Carburetor Icing
The real power of this chart lies in its practical application for GA pilots. Here’s a step-by-step guide to integrating it into your flying routine:
- Pre-Flight Weather Check: Before every flight, obtain METARs, TAFs, or forecasts from sources like Aviation Weather Center (AWC). Note the OAT, dew point, and calculate RH if needed (using online calculators or apps). Plot these on the chart mentally or physically. For example, if OAT is 80°F and dew point is 70°F (roughly 70% RH), you’re edging into the blue zone—moderate risk.
- Assess Flight Phases: The chart differentiates by power settings. During glide (e.g., landing approach), risks spike in the green zone due to cooler engine temps. At cruise, watch the orange areas. Adjust your plan: If conditions fall in high-risk zones, consider delaying takeoff or routing to drier areas.
- In-Flight Monitoring: Carry a printed copy or digital version in your flight bag. Monitor engine instruments for signs like unexplained RPM drops, manifold pressure changes, or rough running. If you’re in the chart’s risk areas, apply partial carb heat prophylactically during descent or in humid air.
- Mitigation Strategies: The chart advises: Upon noticing power loss, apply full carb heat immediately. This bypasses the carburetor with warmer air from the exhaust, melting ice. Resist turning it off prematurely, even if the engine runs rough initially—it needs time to clear. The text warns: “The pilot must resist the temptation to decrease the carburetor heat usage. Carburetor heat must remain in the full-hot position until normal power returns.”
- Examples from Real Scenarios: Take the Ohio summer averages on the chart (75°F OAT, 60-78°F dew point, 80-100% RH). Plotting this puts you squarely in the serious icing zones for glide power. A pilot departing Columbus on a humid morning might experience icing during initial climb. By consulting the chart, they could apply carb heat early, avoiding trouble. Contrast this with a dry desert flight at 100°F and 20% RH—low risk, per the chart.
Incorporate this into your personal minimums. For student pilots, review it during ground school; for experienced flyers, use it for recurrent training. CFIs, use it with your students to improve their understanding of the risks..
Train for recognition.
Wrapping Up: Stay Vigilant, Fly Safe
Carburetor icing isn’t just a winter woe—it’s a summertime saboteur that demands respect from every GA pilot. This recent FAASTeam chart demystifies the threat, offering a clear, visual way to predict and prevent it. By referencing OAT, dew point, and RH against its zones, you empower yourself to make informed decisions, potentially averting disaster.
Click Here for a downloadable PDF of this
graphic you can post and share at your local airport!
As you prepare for your practical test, remember that the Designated Pilot Examiner (DPE) isn’t just evaluating your flying skills—they’re assessing your aeronautical decision-making (ADM), with weather at the forefront. On checkride day, the responsibility for determining if conditions are suitable falls squarely on you, the applicant. The DPE will expect you to independently analyze the weather and decide if it’s go or no-go for completing all required maneuvers. This isn’t a shared call; it’s your judgment under scrutiny, aligning with FAA standards that emphasize pilot-in-command (PIC) authority from the outset.