CEN18FA144 · Cirrus Design Corp SR22 G1

The private pilot was conducting a personal, cross-country flight with one passenger onboard. According to air traffic control (ATC) communications and radar data, while en route to the destination airport about 5,425 ft mean sea level, the pilot reported to ATC that the airplane was accumulating ice, and he requested to divert to the nearest airport. However, due to the overcast cloud layer at 200 ft above ground level (agl) at the nearest airport, the pilot chose to attempt an instrument landing system (ILS) approach into another airport with a slightly higher overcast cloud layer of 500 ft agl. During the descent to intercept the localizer for the ILS approach, the pilot flew through the localizer path, and he did not realize it until the controller notified him that he had done so. The pilot subsequently requested additional vectors to attempt to intercept the localizer again, and the controller instructed the pilot to turn left. The airplane subsequently turned left toward the north. About 39 seconds into the turn, the airplane began to descend, and the airspeed increased. About 10 seconds later, the left turn tightened, and the airplane began to spiral until the radar data ended. The airplane subsequently impacted the ground in a steep, nose-low, wings-level attitude.

A review of weather information current at the time of the flight revealed that the airplane likely encountered instrument meteorological conditions (IMC) about 500 ft agl on the initial climbout from the departure airport and remained in IMC and conditions favorable to icing for the rest of the flight. The airplane likely encountered some turbulence along the flight route in the cloud cover and would have had to climb above 10,400 ft msl to escape the IMC and icing conditions. Super-cooled liquid droplets (SLD) and icing conditions were likely present along the flight route throughout the flight.

Before the flight, a forecast icing potential (FIP) indicated that light-to-moderate intensity icing existed near the accident site, and a current icing potential product indicated that SLD existed near the accident site; this information would have been available to the pilot before the accident flight departed.

The pilot received a weather briefing via the ForeFlight application on his mobile device about 10 hours before the accident flight. At that time, the forecast showed cloud cover, snow showers, and instrument flight rules conditions. Since the AIRMET received in the weather briefing expired at 0500 the pilot should have requested an updated briefing with the valid AIRMET. In the time between the weather briefing and the accident, an AIRMET was issued for moderate icing, IFR/mountain obscuration, and low-level turbulence, and was valid until 1100. An updated AIRMET advisory was recorded via the flight plan identification number less than 2 hours before departure. No records were found indicating whether the pilot retrieved any other weather information before or during the flight. Therefore, although the pilot had sufficient weather forecast information available to him before departure to have known about the existing icing conditions along the flight route, the investigation could not determine whether he received all of the pertinent information before the flight.

Although the pilot reported that the airplane had accumulated ice, the investigation could not determine if the airplane was significantly affected by structural icing during the approach. The airplane was not equipped with an anti-icing or deicing system, which prohibited the pilot from flying into known icing conditions per Title 14 Code of Federal Regulations Section 91.527, "Operating in Icing Conditions."

Although postaccident examination of the wreckage was limited due to postimpact fire damage, the examinations of the airframe and engine did not reveal evidence of any preaccident mechanical malfunctions or anomalies that would have precluded normal operation. The examination revealed that the Cirrus Airframe Parachute System (CAPS) handle remained in its holder, and that its safety pin, which was supposed to be removed before flight, remained installed. The CAPS was found deployed, and the CAPS solid rocket propellant was expended. All evidence revealed that the CAPS was not activated in flight but rather that it deployed due to impact forces and thermal exposure.

The autopsy of the pilot revealed that he had heart disease; however, this would not have affected his decision-making, his ability to identify and respond to icing on the plane, or his ability to fly the airplane in IMC; therefore, his heart disease did not contribute to the accident. Although toxicology testing detected ethanol in the pilot's liver tissue, no ethanol was found in his muscle tissue. Given that, after absorption, ethanol is uniformly distributed throughout all tissue and body fluids, it is likely that the ethanol detected in the liver occurred postmortem and did not contribute to the accident. The toxicology testing also detected two impairing psychoactive substances, diphenhydramine and clonazepam, in tissue specimens. These drugs alone or in combination could have affected the pilot's decision-making and/or slowed his detection of potential hazards and his reaction to them. However, antemortem levels of these two drugs could have been low enough to not have affected him, but, because antemortem levels cannot be calculated from tissue levels, it could not be determined whether effects from the pilot's use of diphenhydramine and clonazepam contributed to the accident.

The radar data showed that the airplane was flying a relatively smooth and consistent flightpath with altitude and heading changes that were indicative of the pilot using the autopilot for a majority of the flight, until the final turn after flying through the localizer course. The pilot's failure to recognize that he had not intercepted the localizer is consistent with his failure to appropriately configure the avionics for the approach or with his attention being diverted from navigational tasks due to his workload while trying to conduct the approach. Conditions conducive to the development of spatial disorientation, including restricted visibility and IMC while maneuvering, existed. Further, the accident circumstances, including the spiraling radar track data and the subsequent high-velocity impact were consistent with the known effects of spatial disorientation. Therefore, the airplane's entry into a descending left turn while the pilot was being vectored back toward the localizer course, which subsequently tightened, was likely due to the pilot experiencing the effects of spatial disorientation due to a vestibular illusion referred to as a "graveyard spiral," which can occur when an airplane returns to level flight following a prolonged bank turn. The spatial disorientation resulted in the pilot's loss of airplane control and a high-velocity impact with terrain.

Verbatim NTSB analysis and probable cause from the NTSB dataset