Hazards of Wildfire Smoke

09.07.2017 - Added resources section
Visual conditions from forest fire smoke can be a deceptive form of IMC, luring the VFR pilot in with the promise of initial acceptable visibility, then degrading quickly and unpredictably.
09.07.2017 - Added resources section
Visual conditions from forest fire smoke can be a deceptive form of IMC, luring the VFR pilot in with the promise of initial acceptable visibility, then degrading quickly and unpredictably.

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The hazards of VFR flying in wildfire smoke

Now that we're in the midst of the summer fire season, it's a good time to talk about the dangerous phenomenon of smoke. 2017 seems to be one of the worst fire seasons for (my home) the Pacific Northwest in the last 30 years, with fires peppering the Cascade mountains from the California border all the way to Canada. And it doesn't stop there— British Columbia has been burning all summer too, with some of that smoke getting blown all the way down to Oregon. The smoke has been seemingly everpresent in the latter part of the summer, making flying and even just being outside an unpleasant experience.

While it may seem an obvious hazard to avoid for the VFR pilot, smokey air is often not a clear-cut go/no-go decision. Smoke varies in density, from a mild haze, to an utterly thick soup with zero visibility. It can lure you into entering what is effectively instrument meteorological conditions (IMC), however it's difficult to identify it as such because it often degrades too gradually to realize the danger until it's a serious low-visibility situation.

In this knowledge base article, we'll cover the reasons why smoke can sometimes be more challenging than IMC, and how to approach it in the following sections:

Smoke blankets much of the Northwest on Sept 6, 2017. Photo: NASA.gov

Controlled flight into terrain, or CFIT, is a term describing an error in pilot judgement where an airplane impacts terrain in an otherwise controlled state, due to loss of visual contact with the ground or terrain. We unfortunately see this mentioned too often in FAA and NTSB reports, but usually associate it with scud-running under low ceilings in cloudy weather, or night VFR gone wrong. Just as those conditions can result in sudden loss of horizon and visual cues, so can smoke. What amounts to "suddenly" is actually kind of sneaky, though. CFIT is a very real possibility when flying in smokey conditions in the mountains.

Retired US Fish and Wildlife (Alaska) pilot and CFI Mike Vivion wrote a similar article called PVFR and the Single Pilot on the dangers of low-contrast VFR flying, which he dubs PVFR, or "pretend VFR." It's a very related topic but not exactly the same as smoke; definitely worth a read.

Photo: Leonardo Correa LunaPhotographer and airline pilot Leonardo Correa Luna testing out the smokey conditions of northern California.

Boiling a frog

Smoke is a strange beast. Its effect on visual flight can range from mere haze to complete dense obscuration. It emanates from one source or many, and generate follows the path of winds and terrain. And it is no less dynamic in its development than any meteorological occurence, thus can be more dangerous than clouds as inadvertent IMC for VFR pilots because of one deceptive characteristic: during flight from clear air into smoke, visibility degrades so gradually that there's rarely an "uh oh" moment until it's really serious. It's like the old parable: if you put a frog in hot water, he'll jump right out, but if you put him in cool water and gradually turn up the temperature, he won't notice the danger and will be boiled alive.

Even at the low altitudes enjoyed by float flyers, definition of terrain features is very difficult to discern. Can you spot where the water meets land? Photo: Olivier Wery

Time for a short story... Years ago, coming home to Oregon from Idaho in my sparsely equipped Cessna 170B, I was about 100 miles out from my home base of Grants Pass when I could make out a massive wall of...something on the horizon. It appeared like a gigantic thunderhead with a very flat top, but it lacked the columnar appearance of a developing thunderstorm. As the miles ticked away, things seemed to get hazier and hazier. As it turned out, some forest fires to the southwest of Grants Pass in northern CA (well beyond my destination) were putting out a fair amount of smoke that was being blown into my home area by southwesterly winds.

The AWOS at my home field (actually located on a nearby mountain at about 2,600 AGL) was reporting IFR (1.7 mi viz) according to the XM Weather on my Garmin 496, but it didn't seem that bad where I was; hazy and diminished viz for sure but I could still see ahead fairly well so I kept flying on, expecting the observation to be inaccurate, trusting more in my own eyes on the flight path ahead; 25 miles out.

Only when I caught myself flying by constantly looking down at the ground through the side window for reference rather than straight ahead did I realize that I was in a hairy situation. I was in IMC and it had taken a long time to realize it.

The thing that really made me turn 180° out (on instruments) to the better visibility I knew was behind me was the sudden realization that any other traffic that might be converging on my destination in these same conditions would have just as poor visibility; we would never see each other. I probably would have flown on because I knew the terrain and the area, but traffic would have been impossible to spot. Looking back I realized it was no better than any other types of IMC and I was the fool, being slowly boiled alive. Luckily, mostly commonly, the exit is directly behind you, and unlike actual IMC from clouds and moisture-saturated air, it rarely closes in behind unless the wind shifts dramatically.

Many pilots who've chimed in on this topic in our forum recently seem to have their own "live to tell" story of a hairy situation in smoke. In fact, the chain of events always sounds very similar to my story above.

Photo: Travis WisbergShould you cross those hills VFR? Will the viz remain constant or begin to degrade on the other side?

Dynamics of smoke

As mentioned, smoke is a strange beast. Unlike condensing water vapor, which materializes in place as the air reaches the dew point, smoke consists of combustion byproducts like carbon monoxide and water vapor, and wood particulate of various sizes, carried upward into the atmosphere by rising hot air. The particulate can range from microscopic, that seems to be homogenous with the air, to small pieces of ash that can rain down to the surface as the outlying air cools and descends.

Photo: Brad ThornbergOften smokey conditions are reliable enough for local flights, but continued flight into worsening conditions should be approached with caution.

In addition to being a breathing hazard for mammals of all sizes, and possibly unhealthy for engines using carburetor heat (unfiltered air), smoke behaves just a little differently than storm air. While it does consist mainly of water vapor, its density/opacity is seemingly less-affected by warming. It rises from the fire, carried as high as the hot rising air will take it, and descends and settles with the same air mass as it cools. It can remain suspended like some neutrally buoyant helium balloon and move laterally as the air mass expands. It will settle into valleys and canyons and remain there, possibly even increasing in density as it mixes with continually descending air. It can blanket vast regions of flat farmland.

Smoke can appear to stratify where layers of the atmosphere differing in temperature prevent it from convecting any higher, sometimes creating a very clear layer that can be flown with great visibility. But it's something that is hardly reliable.

Why is this important? Isn't it just enough to avoid smoke altogether, making knowledge of its dynamics an non-issue?

Photo: CFOT

The point is that smoke is not reliable. Visibility and "ceiling" can appear better on the ground because contrast appears to be improved, but moments after takeoff you can climb out of visual range of the ground and horizon. We often find ourselves looking straight down at the ground because that's the shortest line of sight; the least obscured. Looking toward the horizon requires us to look at a diagonal, a much longer distance through that particulate/gases/water vapor. And light source direction plays a large role too. Is the smoke in your field of view back-lit, front-lit, or side-lit?

Smoke can be extremely deceptive because, unlike a big white cloud or fog or ceiling, it's thinner at the outskirts and more dense the closer you get to the source, so the diminishing viz can lure you in with hopes that it's not getting any worse than it currently is. You get used to it quickly but subconsciously start tuning into other visual references besides the horizon.

Sometimes, however, smokey conditions can be reliable enough for local flying. It's the continued flight from clearer air into worsening conditions that requires caution and awareness. But how easily can you remain in those thinner, hazy regions of the smoke?

Photo: Olivier WeryReally the only item of reference in this photo is the wing.

Low visibility flying

If you've ever flown at or near the actual ceiling and visibility minimums for Visual Flight Rules (VFR), then you know that it's downright scary. 3 miles visibility is very short. It does not leave much time to make quick decisions when some variable like ceiling or terrain change. We're always told to stay a few steps ahead of the airplane, but 3 miles challenges that concept strongly.

Many of us operate light aircraft that aren't equipped for flying by reference to other than the horizon. I frequently fly Cubs that do not have an attitude or heading indicator other than the GPS display. Flirting on the edge of IMC would be an extremely dangerous proposition; one slip into actual instrument conditions and there's a fair chance I'd exit it in some unusual attitude.

It is completely possible to have VMC and have no discernable horizon, making orientation difficult and vertigo a serious concern. 8 mile visibility and instrument conditions? Very possible in smoke. Imagine the ground blending into the sky with barely a discernable horizon.

Pilots who fly single-pilot IFR are usually committed to the idea and prepared with the necessary charts, plates, and aircraft. They're mentally committed to flying on instruments. But trying to operate in the in-between zone of VFR and IFR is a delicate existence. I've read stories recently of hardened IFR flyers who struggled to stay on instruments when tempted by the erratic visual references experienced in smokey conditions.

Night VFR in smokey conditions? Even less advisable than daytime. Without sunlight and/or the lights of a metropolis, it's impossible to avoid obscuration.

Photo: Brad Thornberg

Photo: Justin Jacobson

It is highly recommended to employ some sort of traffic alert and avoidance tool when flying even in just hazy conditions, and more so in bad smoke viz. These include good old flight following with your radar facility of choice, ADS-B, and finally just some good anti-collision lighting.

The frog continued to simmer as I descended along the ridge on the right side of the canyon. Visibility steadily diminished. It was also nearly sunset, and I could hear Coyote's advice chiming in with the little voice in my head, "Watch out when the sun goes over the horizon. It will go from bad to worse. In that case you don't really have 30 minutes more of daylight VFR. It becomes instant IFR".

It turns out that I did not have to wait for my decision point to bail out. As I followed the side of the ridge down not only did my forward visibility disappear, but my downward visibility began to disappear also leaving me only the side of the canyon I was hugging as a visual reference, but I had set myself up so that I was in a good position to turn around. I started my 180 just as Center called to cut me loose. "Center, I got smoked out and we are turning around.. would like to remain with you," I said as I wondered how the other airplanes I had heard were managing to proceed through this stuff. No sooner had I gotten myself back to some better visibility and given Center a brief report on the conditions, did I hear the other planes in the area follow suit.

-Forum user "CFOT"

Thinking about escaping the smoke by climbing on top? That too is a gamble. The vertical extent of the smoke is very difficult to ascertain. Many pilots have said that they have attempted to climb to get on top, as the blue sky above seemed to be quite close. But after climbing to at or near their aircraft's service ceiling, they were still in the smoke, it had been but a tempting illusion. And by that time, any ground visual contact is likely lost. Once again, you're in IMC, and quite high. Got oxygen?

A final word on low-viz flying: Slow down! If you've found yourself in a pickle where visibility is low and everything seems to be happening too fast to make a good decision, slow the aircraft down. Things happen much faster at 120mph in 3 mile visibility than they do at 75-80mph. Granted, we're usually in XC mode and trying to make a destination at cruise speeds, but if the situation degrades to a cautionary status, slowing down will give you more time to process inputs and make a good decision.

Photo: Olivier Brad ThornbergThe red disc of the sun is a common sight for Earthlings this time of year.

Trapped on the ground

Ever been camped out in the backcountry, cut off from communications, only to wake up to find a mass of smokey air has moved in, making departure a difficult decision? Do you take off immediately, hoping to beat worsening conditions? Will that put you in minimum VFR or IMC? Or do you wait it out hoping for a shift in the wind to clear it out? What if the fire is actually moving your way?

It's a tricky question, and as a lower time backcountry pilot, I'm not sure what I would do. I'd probably opt for the former if it looked flyable, but remain prepared to return and hunker down. The danger of chasing one door out is letting the other close behind you.

Even with access to real time weather products, predicting smoke the next day can be difficult.

Smoke is maddening because it's harder to predict where and when things will be bad based on the usual tools for prediction (pressure, winds, temp/dew point etc.) We arrived one day last week in central Idaho in pretty heavy smoke. The next couple of days weren't too bad, but the morning of our departure was 3 miles with broken clouds 4,000' AGL, and it didn't improve much for 6 hours. Of course, there was nothing in the forecasts about this. There are just too many variables and, with the exception of the Firesmoke.ca, the weather models don't seem to be tuned for smoke or haze.

-Forum user "CAVU"

Traffic and TFRs

Firefighting TFRs pepper the Cascades from border to border in Oregon.

One serious hazard presented by low-visibility flying is the reduced time to spot traffic. As mentioned above in the "Boiling a Frog" story, I only reversed course when it occurred to me that other converging traffic was impossible to see, radio calls or not.

Modern tools like tablet apps and satellite wx/data put TFRs on our screens pretty readily, but they can often pop up faster than the data can be updated (especially if cellular signal is unavailable at altitude.) The TFRs are meant to separate firefighting traffic like helicopters, spotter aircraft, and heavy attack vehicles, all of which are coordinated by their own agency, from coming into contact with private aircraft. If you are that close to the active fire, conditions are probably unflyable anyway, but the fact remains that if you're ignorant of the TFR, you can easily encroach on the boundaries of one without knowing.

Photo: Leonardo Correa LunaHow would you like to come face-to-face with this CalFire OV-10 Bronco in the smoke?

Health effects

We've all sat around a campfire trying to avoid huffing too much doug fir or madrone smoke, but it's usually pretty short lived, and walking away to fresh air is an option. It even smells kind of good. Sustained periods of breathing not just wood smoke, but smoke from anything that has burned on the ground (ever breathed poison oak smoke?) as a result of wildfire, can lower oxygen intake. Combined with altitude, this can be a recipe for hypoxia, irritated airways, and longer term effects on the lungs.

Clear thinking and decision making are one of the first things to go in a hypoxia or carbon monoxide poisoning situation. The more dense the smoke you're flying in, the greater the chance these conditions could occur. Compromised faculties are the last thing you want to experience when determining whether to turn around, press on, or pop up IFR.

Photo: SkiermanmikeIt won't be long before the smoke from that field burn will be dispersed and at altitude, causing zero visibility.


There are some good tools available for planning purposes, which simply means avoiding smoke or not being trapped by it.


Airfire.org from USFS has some great visualization products on where fires are burning and where their smoke is headed. Up to 72 hr forecasts available.


Firesmoke Canada is a great tool for visualizing and forecasting smoke location and density. The forecast maps featured animated smoke coverage similar to radar imagery.


NASA has some amazing medium resolution satellite imagery of smoke coverage. As far as I can tell, it's not real time, so not a great forecasting tool, but a good visualization.

Alaska Interagency Coordination Center - Air Quality

This is a great collection of public tools for air quality and visibility information, mostly focused on Alaska but many have CONUS coverage.

I'll add more resources if they are submitted.


For most of us, it's an easy decision to look at the smokey conditions and decide to not fly. For others, maybe not such an easy decision if flying is commercial in nature, or you're just plain addicted. And trying to get back home from a remote destination when visibility is hampered by smoke can be the hardest decision of all. Continued VFR flight into smokey conditions should be performed with the utmost vigilance, as visibility can worsen almost undetectably until it is at or below VFR minimums. Consider that smokey areas, when entered from clear air, will be hazy at the outskirts and gradually worsen at an unknown rate, and often at an unknown directional vector. Wildfires are just that— wild. They can ignite, develop, and cause serious problems for pilots before they're ever reported. Have an escape plan ready!

Photo: Ravi FryNear Hamilton, MT. September 2017.

This is a living article in the Knowledge Base. If you have feedback on the accuracy or legitimacy of this entry, or would like to add more information, join the discussion below or email knowledge@backcountrypilot.org to volunteer your input. Suggestions and changes will be incorporated readily.

  • Text and select photos by Zane Jacobson
  • Some information culled from forum topic "Boiling a Frog"
  • Select photos by Olivier Wery
  • Select photos by Thomas "Paco" Gilman
  • Select photos by Brad Thornberg
  • Select photos by Travis Wisberg
  • Select photos by Skiermanmike

09.07.2017 - Added resources section 08.16.2017 - Format article - Z. Jacobson

Overall Rating (1)

5 out of 5 stars
  • Rated 5 out of 5 stars

    Well written (as always <g>;) Z. Thank you for taking the time to put this together.

  • Good thoughts Zane, and right on time for what is happening now.

  • Hi ZZZ,

    I like the article, and think it's worth synthesizing the comments. Pierre's new post really describes what it's like and having to go on the gauges to keep things right. One other piece of advice to consider adding is to slow down when things get dicey. Not stall slow, but a comfortable maneuvering speed with half flaps rather than boring along at full cruise speed. The slower speed allows more time to check ground references and delays the arrival of something really bad up ahead that you can't see (e.g., an embedded thunderstorm).

    It seems like every trip I've done from the 1st of July right through last weekend has involved flying at VFR minimums with the threat of worse. I'm going to change the oil and clean the plugs on the 206 this weekend. I think that spending hours and hours in smoke has dirtied things up more than usual. Thanks for taking the time to write this up.


    Comment last edited on about 6 months ago by Zzz
  • Very nice article Zane. Thanks.

    A couple of points I'd add:

    The time of day we fly in PVFR really (REALLY) affects visibility. Sun angle is a big deal in the mountains. Some folks suggest "fly early or late". Well, we might have better DA early in the morning or as the afternoon heat abates, but the sun angle creates shows that become black holes when mixed with even moderate amounts of smoke (by "black holes" I mean areas we can't see into to understand what the terrain looks like). When we're IN the shadow, where the sun is behind a mountain, we can see pretty well in moderate and light smoke. The sun's light is diffuse and not bouncing off of the smoke particles. The problem here is we have to be fairly low (close to the ground) to fly IN the shadows. If we encounter thicker smoke... a strong possibility when fires are burning all over the place we could get trapped below high terrain we can't out climb. I know of some really big fires (3-5K acres and larger) in the back country of Washington, Oregon, Idaho without a TFR to flag the fire's position.

    Speaking of TFRs, we need to remember that while rotor wing aircraft USUALLY (but not always) fly fairly low the fixed wing air tankers, jump ships, Lead planes, and aerial supervision modules that may operate within a TFR have to go to a runway someplace for fuel, more retardant, and to give pilots/crew some break time. These fire fighting aircraft may fly between the runway and the fire frequently at 2-3k above the highest terrain or higher. On some fires we might encounter air tankers that are multi-engine jets. Not all fires get a TFR. Many do not. But they still may have air tankers and other fixed wing or rotor wing aircraft operating over them. We should think about where the tanker bases are located in relation to fires. Draw a straight line between a likely base and the fire and be very aware we might encounter conflicting traffic along that line. Ditto for a fire where no TFR exists. For example, this summer several single engine air tankers (converted AT 802 fixed wing AG planes) flew over a fire near Orfino, ID. They made multiple drops, then were ordered to "load and return" from a nearby tanker base. Flight visibility was PVFR at 5-7 miles. A trick I use is to monitor the CTAF for non-towered airports and the tower frequency of the big Blue airports where tanker bases exist. For example, in north Idaho and eastern WA the Coeur d'Alene, Idaho tanker base provides a lot of large tanker support, and may also support single engine tanker ops. When tankers are aloft they announce their departure direction of flight, and upon return call in several miles out announcing their direction of flight and preferred runway. That's a good clue to where they are working.

Airframes Alaska

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