A 473-hour instrument-rated private pilot, alone in a fully fueled Cirrus SR22-G2, took off from Reno, Nevada, early on a Sunday evening in February 2005. The sun had set half an hour earlier; the moon, above a layer of clouds, was a mere sliver. He had filed an IFR flight plan via Truckee and Sacramento with a destination of Oakland, California, 155 nm to the southwest. The cruising altitude was to be 12,000 feet. Reno, where the field elevation is 4,415 feet, was reporting an overcast at 5,500 feet, light winds, and a surface temperature of 6º Celsius with a 7º temperature-dew point spread. The pilot's weather briefing, obtained from an FSS briefer an hour before the flight, put the freezing level at 6,000 feet and reported no precipitation in the area. No pilot reports were available for the route. When he filed his flight plan, the pilot told the briefer that he might request 14,000 once airborne.
The pilot contacted Oakland ARTCC as he climbed through 10,600 feet on the way to 14,000. A couple of minutes later he requested a clearance to climb to 16,000, in order to "see if I can get above these clouds."
After cruising for a few minutes at 16,000 feet, the pilot transmitted, "I guess this isn't going to work, I'm still in the clouds. Any chance of lower?" The Center controller told him to stand by. A minute or so later, the pilot told the controller that he could get above the clouds if he could climb another 200 or 300 feet. "Do you want to go up or down?" the controller asked. Up, the pilot responded, "so I could build up some airspeed, if that's okay." He received a block altitude between 16,000 and 17,000 - meaning that he was free to cruise anywhere in that range.
Radar showed the airplane climbing. It reached a maximum altitude of 16,700 feet before beginning a gradual descent.
"I'm coming down," the pilot reported. There was an unintelligible transmission, and then, "I'm icing up." The controller asked him to say it again. "I'm icing up. I'm coming down," the pilot said.
It was his final transmission. The last radar return, a few seconds earlier, reported an altitude of 15,700 feet.
The wreckage of the Cirrus was recovered from the base of a rocky face in the Donner Pass. The engine was heavily damaged, but there was no indication of mechanical failure prior to impact. The parachute recovery system had been deployed, but had separated from the airplane and come to earth 4,000 feet away from the main wreckage. According to the manufacturer of the system, the failures of the risers and suspension lines were consistent with deployment above the placarded maximum speed of 133 knots, which is also the maneuvering speed of the airplane.
The airplane was equipped with the "icing protection system" that oozes an antifreeze solution from the porous leading edges of the wings and horizontal tail and from a slinger at the propeller. The company's promotional materials paint an optimistic picture of the capabilities of the system, which it calls "an effective way to help you make an early retreat from unexpected encounters with airframe icing." The solution, it explains, "mixes with the supercooled water in the clouds, and the mixture flows off the aircraft without freezing." If "trace" amounts of ice have already formed, "the antifreeze solution will chemically loosen the bond between the ice and airframe, allowing the aerodynamic forces to carry the ice away."
Nevertheless, flying the SR22 into known icing conditions is prohibited, as the airplane's documentation repeatedly warns. The FAA-approved language of the Pilot Operating Handbook presents a somewhat less than optimistic view of the system's abilities, noting that "no determination has been made as to the capability of this system to remove or prevent ice accumulation ... . At the first indication of icing, the most expeditious and safest course of exiting the icing conditions should be taken."
Investigators concluded that the airplane had probably encountered icing from supercooled large water droplets near the cloud tops. In fact, a retrospective analysis of weather conditions, in light of the most recent research, showed a "clear likelihood" of severe icing conditions; but the aviation icing prediction algorithms used by the National Weather Service had determined that there was only a low probability of icing in the area, and so did not trigger an icing forecast.
Severe icing occurs when liquid water is carried upward through clouds at a fairly rapid rate - in this case, possibly lifted by a westerly flow against the rising foothills of the Sierra Nevada - but does not crystallize even though its temperature drops below the freezing point. Water in this condition is said to be "supercooled." When it strikes the surface of an airplane it freezes instantly, producing a rapid buildup. Areas of icing of this type are often small, with the result that one airplane does not experience icing while another, a little later or a short distance away, does. It is noteworthy-and this has been an article of flying lore since long before anyone had dreamed of supercooled large water droplets-that the heaviest icing often seems to occur near the tops of clouds.
