I wrote this several years ago. I came across it on my computer this morning and thought it was relevant given that we're at that point in the summer where smoke from fires is forcing decisions.
----------------
I don't have that many "never again" or "live to tell" stories, as I tend to be pretty conservative with my flying. This one though is something I'll never forget, and I often tell this story around the campfire when stupid pilot tricks are being discussed. Now that the summer fire season is upon us, I thought I'd share this phenomenon for the greener pilots.
Smoke can be more dangerous than clouds as inadvertent IMC for VFR pilots because it's deceptive, and visibility degrades so gradually that there's rarely an "oh shit" moment until it's really serious.
Years ago, coming home to Oregon from Idaho in my sparsely equipped 60 year old Cessna, I was about 100 miles out from my destination when I could make out a massive wall of...something on the horizon. As the miles ticked away, things seemed to get hazier and hazier. Turns out, some forest fires to the SW (well beyond my destination) were putting out a fair amount of smoke that was being blown into my home area by winds.
The ASOS at my home field (actually located on a nearby mountain) was reporting IFR (1.7 mi viz) according to the XM Wx 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 my flight path ahead.
Only when I found myself flying by looking down at the ground for reference rather than ahead did I realize that I was in a situation. I was in IMC and it had taken a long time to determine it. That's why smoke can be so deceptive: 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. 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 and will be boiled alive.
The thing that really made me 180 out (on instruments) to the better viz 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 being the fool. Luckily, the exit is right behind you, and unlike actual IMC from clouds, it rarely closes in behind unless the wind shifts dramatically.
TL;DR Smoke can lure you into entering what is effectively IMC but it's difficult to identify it as such because it degrades too gradually to realize the danger until it's a serious low-visibility situation.












IMHO.