Airframe icing is one characteristic of flying I’ve learned to respect. Over the years, I picked up my share of it, once carrying at least a quarter-inch of the clear kind for another 500 nm or so before it melted on descent for my destination. In the winter, I pay particular attention to Airmets Zulu, along with temperature aloft and cloud forecasts. There have been many occasions when I simply cancelled or rescheduled a trip on learning the freezing level was at the surface or below my desired cruising altitude and visible moisture was about.
That discipline didn’t come easy. Although my airplane isn’t flight-in-known-icing (FIKI) approved, I flew it by the old saying, “Ice is where you find it.” As long as I had an out—warmer air below and/or clear air above—I motored through it to better conditions more or less routinely on many flights.
I got something of a “religion” on ice, though, once crisp spring day over Arizona. I was headed for a planned fuel stop at Winslow and, just before letting down from 13,000 feet, happened upon some white puffies. They exhibited little vertical development and there was plenty of above-freezing air beneath me, so I didn’t bother to twist the autopilot’s heading bug to go around them.
I punched through a couple before starting my descent and noted a splattering of ice on the windscreen. Checking the wings, there was the merest trace of ice, which I knew from experience wouldn’t be an aerodynamic problem. I landed at Winslow, as planned, and taxied to the self-serve pumps.
Upon shutting down and climbing out, I heard a faint hissing sound. At first I thought a tire was leaking air. Then I spied the fuel puddle under the wing. I loosened that wing’s fuel cap and was greeted with a whoosh of air as pressure inside the tank equalized. What happened?
The tank’s vent became plugged with ice from that very short encounter with the puffies. By the time I finished fueling, the ice had melted and all was well. But I couldn’t help wondering what would have happened on some dark and stormy night if I needed the fuel being vented overboard. That episode taught me about FIKI-approved airplanes—and how mine wasn’t.
It can take that kind of wake-up call for the average pilot to understand icing’s effects on an airframe. Until then, here’s a pilot who learned this lesson the hard way.
On November 20, 2009, at 1246 Pacific time, a Cessna 182K crashed about 1.5 miles east of the Susanville (Calif.) Municipal Airport, shortly after takeoff. The solo pilot was killed; the airplane was substantially damaged and consumed by a post-impact fire. Instrument conditions prevailed, and an IFR flight plan to Lodi, Calif., had been filed. The flight originated at about 1245.
A witness working in his shop ¼-mile from the crash site said it was snowing heavily with limited visibility. He heard an airplane circling his shop, making about five passes. He heard the plane making power changes before finally coming on with full power that was followed by a “whump,” which shook the windows of his shop. He looked outside, saw a fire, and knew the airplane had crashed.
The airplane wreckage was located 1.5 miles northeast of the Susanville Municipal Airport in a flat grass pasture. When emergency responders arrived, the airplane had been mostly consumed by fire. A sheriff’s deputy reported he “was unable to locate any evidence to indicate that the plane had impacted the ground elsewhere and slid to the location where it was resting. It appeared that the plane had impacted the ground vertically or nearly so.”
The airplane sustained severe thermal and crush damage. Examination of the airplane’s wings showed leading-edge crushing along the entire length of both wings, and wing skin was crushed accordion-style longitudinally. Pieces from all sections of the airplane’s flight control system and structural components were identified. All three propeller blades exhibited leading-edge polishing and chordwise scratches. The blade tips were bent slightly forward.
The 1200-hour pilot was based at Susanville and was very familiar with the local airspace. The pilot’s girlfriend stated he would always make a left turn after takeoff no matter what runway he used and circle over the airport to gain altitude. Another pilot stated the accident pilot regularly used his own departure procedure of circling over the airport until he reached his desired altitude, instead of the published procedure. The accident pilot used this self-developed departure procedure in both good and poor weather.
At 1225, the pilot received a weather briefing and filed an IFR flight plan. The briefing included information on Airmets for turbulence, icing and mountain obscuration associated with a cold front coming through central California that afternoon. Moderate turbulence was forecast below 18,000 feet, freezing level up to 20,000 feet, mountain obscuration by clouds, precipitation and mist all along the route of flight.
At 1245, the Susanville Airport AWOS recorded the following automatic weather observation: wind from 140 degrees, at six knots, gusting to 15; ½-mile visibility; temperature 1 deg. C; sky conditions overcast at 200 feet.
The National Transportation Safety Board determined the probable cause(s) of this accident to include: “The pilot’s decision to take off 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.” Since no anomalies with the airframe or engine could be found, the NTSB settled on icing as the probable cause.
There’s no way to know if ice had, in fact, accumulated on the airframe, but with an observed surface temperature of one degree C, it’s pretty much a no-brainer. Basic ground school teaches us the standard lapse rate is two degrees C for each thousand feet, so this airplane could easily have been icing up almost immediately after entering IMC. At the same time, we don’t know the extent to which snow built up on the airframe before takeoff.
What’s instructive here is that it took roughly only 10 minutes for this pilot to ice up a presumably clean, lightly loaded airplane and crash. That’s how long it takes to make the five turns the witness working in his shop heard at standard rate. Your mileage may vary.