This is our tenth weather-accident article in a series we started in 2015. Our intent is to examine some of the ways that seasoned pilots manage to get into deadly predicaments. Safety procedures are well-covered in training materials, your aircraft manual, and FAA publications, so we prefer to teach the aviation meteorology of these situations. Our goal is to give you a rich background to help you to make good decisions when things go wrong.
The Deadly Climb
Our example takes us to Susanville, California, a town nestled in the lee of the northern Sierra Nevada range about 70 miles northwest of Reno. Our pilot was a 61-year old attorney who led an accomplished career in municipal law and medical malpractice before moving to Susanville. His logbook showed 1200 hours of flight time, with single-engine and instrument ratings.
Shortly before noon on a blustery, threatening November day, the pilot arrived at Susanville Municipal Airport, a small nontowered airfield with a 4000-foot runway. Winds were gusting past 30 knots, as the pilot headed into the FBO. An ominous overcast filled the sky, and a light showery rain was reaching the ground.
The pilot wanted to fly to Lodi, about 160 miles south. He was to meet his girlfriend and her sons, then spend an evening out that included dinner and a movie. In an earlier phone call with her he remarked the weather was “going to turn to crap soon” and it was noted that he sounded “a bit distracted.”
But once at the airfield he called her again and said he was going to hurry his flight preparations because of deteriorating weather. The wind was weakening but it was getting colder. Ceilings were rapidly lowering, and the wind-driven showers became persistent wet snowfall.
The Weather Briefing
The pilot called for a telephone weather briefing. He said he wanted to depart as soon as possible. The briefer noted his flight details, and with little hesitation started in: “As far as the adverse conditions, we’ve got airmets for turbulence, icing, and mountain obscuration this afternoon, all associated with a cold front coming through central California this afternoon.”
The briefer went on in detail: moderate turbulence below 18,000 feet, freezing level up to 20,000 feet, mountains obscured by clouds, precipitation, and mist. But with that came the admission, “Let’s see. I’m not getting a report out of Susanville, I’ve got, uh, light snow at Blue Canyon showing up, 3500 overcast with a mile and a quarter visibility in light snow, they’ve got gusty winds also a really nasty day, 200 at 26 gusting to 40.”
This conversation suggested the briefer wasn’t getting the full picture. The freezing level was already far below 20,000 feet, and though Susanville was not transmitting an observation, the lowering 900-foot ceiling would have been obvious to the pilot.
The briefer sorted through PIREPs: “Minus 2 degrees at 17,500 surprisingly enough seems a bit high, there must be an inversion there or something, or a second freezing level about 7000 feet, the freezing level in the area right now.” There was no further discussion of icing or freezing levels.
Clearly, the briefer was confused by the conflicting details of freezing levels and icing, and did not pass on a clear picture to the pilot. There were no inversions. In fact, it was the opposite—steep lapse rates due to the cold advection aloft. And the atmospheric column was changing rapidly. Many flight weather services primarily rely on centralized charts showing generalized freezing levels, but these are not suited to fast-breaking weather situations.
The lesson here is that flight weather services don’t always have the answers. Don’t blame the briefers; they have the difficult job of covering a broad area with widely varying conditions. This multiplies the complexity of building a mental weather picture, which every forecaster must do. The briefers also are unable to see what you’re seeing. Your gut feeling about local flying conditions while standing on the ramp is often more accurate than the picture they have. Briefers must also refer to certified products that satisfy safety and liability requirements. They can’t jump on the Internet and use new and interesting products to improve their view.
Ultimately it’s up to you to sort out what’s happening. This is why Wx Smarts exists: to help you work through confusion in the weather picture by using tools and products available to you. It’s also designed to help you get the most out of your routine weather briefings.
Ready To Go
After the briefer wrapped up the arrival forecast, the pilot gave the briefer his flight plan, saying he was ready to “get out of here.” Shortly after that he picked up his IFR clearance.
It was then snowing. Winds were 6 knots gusting to 15 with a 200-foot ceiling and -mile visibility. He started his Cessna 182K, warmed the engine, and taxied out to the runway. Just 20 minutes after the initial weather briefing, the pilot was airborne.
The airplane began a slow ascending turn, circling gradually to the filed cruise altitude of 14,000 feet. This was contrary to the departure that was filed, which proceeds 20 miles east over flat terrain to allow a gradual climb. However this circling turn was an established habit of the pilot. The idea was to clear the 8000-foot mountains six miles south of the airport. By spiraling up, the pilot could take a more direct route south. On previous occasions he assured friends that his GPS would keep him clear of terrain, and that no airplanes were likely to be over the airport.
Witnesses said the plane was not visible in the low overcast, but they could hear about three to five passes overhead. Shortly after this came the sound of changing power settings. The engine got louder, reaching full power, then there was a powerful “whump” that shook windows near the crash site. The Cessna impacted the ground vertically at high speed, crashing on the bank of an irrigation ditch in a muddy field. Investigators reported that the fuselage was crushed like an accordion, and no ground scars or debris was found outside the impact point. It was clear this was a high-speed dive.
It was expected the pilot would call ATC after takeoff. The FAA reported that no contact was made.
The Weather Picture
The Susanville airport sensors showed that when the pilot got to the airport, the temperature was 43 degrees F with a dry 30-percent relative humidity. Winds were 20 gusting to 40 knots, and a light shower was falling. One hour later as the pilot started up his airplane, the temperature had plunged to 34 with near-100 percent relative humidity. Winds had died to 6 knots gusting to 15, with snow falling.
Note that this sounds vaguely like the changes from a thunderstorm bearing down on a desert airport like Phoenix or Las Vegas. Indeed there are similarities. But here, downdrafts are working the air mass over a wide area from the strong mid-level cold advection. As this cold layer is filled with moisture from the Pacific, it causes an effect called “wet bulbing.” The layers of cold, humid Pacific air invade eastward, spreading over warmer, drier air. This produces a potent cold-over-warm situation—classic thermal instability. Plus, the cold layers turn into a precipitation and downdraft factory due to upper level lift, dumping it all into the layers below.
From the ground, we see this as broken to overcast cumuliform layers with lots of virga and gusty winds caused by falling precipitation evaporating into the dry air, cooling the layers below and causing intense downdrafts. The direction of this surge tends to follow the mid-level winds. Not only do strong gusty winds reach the surface, but moderate to severe turbulence is likely as this process continues. It gradually works downward and only ends once the lower levels are chilled and saturated, and the warm air is mixed out.
This process affected much of the Sierra Nevada region, including Reno-Tahoe International Airport. There, winds were as high as 31 gusting to 62 knots, causing flight cancellations and two diversions.
By the time our pilot took off, the mixing had subsided, but the wet bulbing brought cold, humid air much closer to the surface. We don’t have the benefit of a radiosonde sample near Susanville, but Reno’s balloon launch data in standard sounding format. For a review of how to read these diagrams see the October issue of IFR.
This shows a very similar occurrence to what happened at Susanville. The day started out dry in the low levels (blue) but six hours later cooled dramatically (red). This lowered the freezing level from 10,000 feet to 6000 feet. This change probably took place in just a few hours. Don’t read too much into the dewpoint lines on the left—it’s difficult to get a good moisture profile in poorly mixed convective weather. However because of the power of this system and the extensive overcast, we can safely assume that many of the cooler layers are saturated, with a good chance a slight icing layer from 10,000 to 14,000 feet rapidly developed into a moderate to severe icing layer between 6,000 to 12,000 feet.
With Susanville at 4100 feet, we conclude the pilot entered icing moments after takeoff. Convective situations with widespread cumuliform clouds, instability, and dynamic lift like the one in this example are excellent producers of large supercooled droplets. Clear icing likely accumulated rapidly on the airframe, created a stall, and at that point the control surfaces were no longer effective. There’s no record of exactly how these events unfolded, but the 1994 American Eagle flight in Roselawn, Indiana yields some sense of the final moments.
The National Transportation Safety Board concluded that the crash was due to “the pilot’s decision to takeoff into weather conditions conducive to ice accumulation, which resulted in an inadvertent stall/spin while maneuvering in the initial climb. Contributing to the accident was the likely accumulation of snow and ice on the airborne airplane.”
It appears that the pilot thought the icing hazards were routine and confined to higher levels. It’s not clear whose fault this was, but the briefer’s available charts were probably not sufficient to cope with this highly dynamic weather. We know three important things: (1) the takeoff temperature was near freezing, (2) there was a low overcast with precipitation, indicating abundant moisture, and (3) inversions are usually not associated with strong Pacific cold fronts. In fact temperature decreases sharply with height. Thus, you can assume heavy icing is just above the surface.
But the ultimate complication was classic “get-there-itis” caused by the weather closing in. The pilot could have simply waited until the weather was more manageable. However one friend who gave a witness statement to investigators explained that the pilot “tended to take risks other pilots would shy away from,” and was confident in being able to operate contrary to normal protocols and procedures. Whether true or not, don’t let this be your own epitaph.
We’ve also seen the difficulties for weather briefers with rapidly evolving weather. There’s no way for them to be fully engaged with the weather that will affect you during every phase of your flight, so you need to also develop your own conceptual understanding of the weather picture. Most of the time you and the briefer will agree, but if something doesn’t add up, that’s when you should ask questions or dig around in the briefing products you have available. The atmosphere is more predictable than it might seem at times, and it’s rare that weather defies rational explanation.
So make time to get a closer look at the weather. Review TAFs and METARs at surrounding airports. This seems redundant when the conditions matched your expectations. Look for the anomalies that will create trouble: an unusual wind direction at a nearby airport, or the unexpected appearance of precipitation on one of the METAR reports. That’s a sign you need to take a better look.
As you get familiar with these products, take a look at radar, satellite, and even model data, or soundings as we’ve done here. Soundings paint a fantastic picture of the atmosphere. There are great tools out there. The idea isn’t data overload that confuses you, but to help you build a solid mental picture of what’s happening, so that when you hear a PIREP on the radio you’ll know exactly how it fits in. Use whatever works for you. Every little bit helps you build that picture, gain experience, and develop intuition.
I hope this article gives you some material to reflect on and encourages you to be more proactive about getting a complete weather picture. To learn more, look back through Wx Smarts in IFR, or study some meteorology books—especially (shameless plug) mine.