CEN15FA040

The airplane's encounter with supercooled large droplet (SLD) icing, which resulted in a loss of lift and a subsequent uncontrolled descent into terrain. Also causal was the pilot's preflight and in-flight decision to fly in known icing conditions in an airplane that was not certified to do so.

Before departing on the instrument flight rules cross-country flight, the private pilot obtained a weather briefing that forecast moderate icing conditions along the intended route. The pilot, a commercial pilot-rated passenger, and a second passenger then departed on the flight in the high-performance, single engine airplane, which was not certified for flight into known icing conditions. Both the pilot and pilot-rated passenger were heard communicating with air traffic controllers during the flight and it could not be determined who was flying the airplane at the time of the accident. About 1 hour, 45 minutes into the flight, the pilot requested a higher altitude and stated to a controller that the airplane was "picking up a little ice." The pilot was granted a higher altitude, which was above the clouds, thus, reducing the potential for icing. About 20 minutes later, the flight began its descent toward the destination airport. Radar contact was lost about 8 minutes later when the airplane was at an altitude of 3,600 ft mean sea level. Based on an analysis of the weather conditions near the accident site at the time of the accident, the atmosphere was conducive to the formation of supercooled large droplet (SLD) icing. It is likely that, during the descent, the airplane encountered SLD icing, which rapidly accumulated on the airframe to the extent that the airplane could no longer sustain flight. The airplane then entered a steep, uncontrolled descent to ground contact. Due to the night conditions, it is possible that the pilots were not able to visually observe the amount of ice on the airframe or did not realize how quickly the ice was accreting. The airplane was equipped with a parachute system (CAPS) that could be deployed by the pilot in flight. The CAPS rocket motor was found expended; however, the parachute remained in its pack. The investigation could not determine whether the rocket was deployed before impact or as a result of impact forces. There were no observed airplane preimpact anomalies.

The main wreckage exhibited charring, deformation, and discoloration consistent with a ground fire. Separated airframe components in the debris field exhibited localized discoloration and charring consistent with a post-impact ground fire. A witness reported the sound of an explosion consistent with a ground impact explosion. An NTSB senior air traffic specialist obtained radar data from the FAA. He produced a table of the data and graphical images of the airplane's radar returns. The data was given to the weather group chairman and vehicle performance group chairman for use in their reports. The radar data and graphics are appended to the docket material associated with this case. An NTSB senior aerospace engineer, who was the vehicle performance group chairman, used the radar data to produce a three dimensional graphic. The graphic does not depict the airplane's airspeed or descent rates. However, the graphic visually shows the slope of the accident airplane's descent near the accident site. The vehicle performance graphic is appended to the docket material associated with this case. The vehicle performance group chairman produced a performance study that, in part, found that the accident flight encountered clouds and ice while in cruise at 9,000 feet just south of Tippecanoe, Indiana. A climb to 10,000 feet took the flight out of the clouds. However, when the airplane began its descent to the destination airport about 20 minutes later over Woodburn, Indiana, it again encountered clouds. During the descent, at an altitude of about 6,000 feet, the airplane pitched down over 70 degrees and entered a steep right turn. During the final 20 seconds of radar data, the airplane's bank angle exceeded 60 degrees as it descended at a rate of about 9,000 feet per minute. Impact occurred about seven and a half minutes after the start of the descent. The published aerodynamic stall speed for the Cirrus SR22 is 70 knots, and estimates from radar data indicated that the airspeed was around 150 knots before the airplane pitched down abruptly. However, both bank angle and ice accretion would increase the stall speed. The vehicle performance study is appended to the docket material associated with this case. The accident airplane's CAPS activation handle, activation handle holder, activation handle safety pin, and the rudder's upper and lower sections were shipped to the NTSB Materials Laboratory. An NTSB chemist indicated that the submitted rudder from this accident was sent to the NTSB Materials Laboratory to determine if rocket fuel residue from the parachute system was present on the exterior surface of the rudder skin. The entire surface was swabbed and the individual swabs were analyzed using a Fourier transform infrared spectrometer with a diamond attenuated total reflectance accessory in accordance to ASTM E1252-98 (American Society for Testing Materials E1252-98: Standard Practice for General Techniques for Obtaining Infrared Spectra for Qualitative Analysis). The spectra from all the samples were compared to a known spectra for the rocket fuel components. No spectral signatures matching the rocket fuel components were found in any of the swab samples. An NTSB senior materials engineer also examined the airplane components and produced Materials Laboratory Factual Report No. 16-026. The report, in part, indicated that the plunger portion of the handle exhibited marks along the outer edge of the plunger end face and along the edge of an inner pass-through hole for its cable. The edge exhibited an arc-shaped segment where the red anodization layer had been removed and circumferential wear marks were observed, consistent with a sliding contact. On either end of the sliding contact region and at a few locations within, the edge exhibited linear impression marks consistent with the width of wires that makes up the cable. A deformed flat was observed on the side of the plunger next to the edge and additional linear impression marks were observed further up the plunger. The marks along the edge of the inner hole also exhibited linear features and the hole was deformed. The marks along the edge of the inner hole subtended a similar arc angle as the marks along the outer edge. Visual examination of the cable revealed one of its wires was bent at a right angle at a location consistent with it having been bent over the outer edge of the plunger end face. A second wire was found fractured at the same location as the bend. Examination of the cable at the pass-through hole revealed three broken wires, wear, and material transfer on the outside of the cable. The handle holder exhibited linear impression marks, similar to those observed on the plunger. The marks were concentrated along the edges of the chamfer where the barrel meets the end face of the holder. The width of one of the deeper impression marks was consistent with the width of wires that comprise the cable. The handle holder mounting bracket was bent forming a U-shape. Relative to its as-installed orientation, the bend was consistent with the bracket bending down, aft, and to the right side of the airplane. The safety pin was visually examined and no notable features were observed. Examination of the rudder revealed it was fractured through the middle third separating it into a lower piece and an upper piece. The lower piece exhibited features consistent with exposure to elevated temperatures including soot on the skin, organic constituents volatilized from the paint, and incipient melting of the skin at the upper end. The upper piece was crushed and bent and it exhibited features consistent with scraping of the paint off of the right side. At the forward end and bottom edge of the upper piece there was a riveted L-shaped bracket with a horizontal arm that was deformed downward and the rivets had pulled out of the bracket. The rudder skin fractures along the right and left sides of the rudder respectively, exhibited features consistent with tensile overstress fractures. At the aft end of the rudder, the skin exhibited a bend and tear in the skin. Together, the features were consistent with a tensile/bending overstress fracture starting at the forward end of the rudder and terminating at the aft end of the rudder. The skin at the upper end of the lower piece exhibited sagging, surface oxide cracking, and waviness of the skin, consistent with incipient melting. The region of incipient melting was confined to the upper portion of the skin and the transition occurred along an approximately linear boundary. Toward the forward end on the left side, there was a split in the skin that had opened into two approximately parabolic shapes. The skin on the left hand side of the rudder was resting on the skin on the right hand side of the rudder at either end of the parabolic region and the left side skin was sagging in between. The materials laboratory report is appended to the docket material associated with this case. Both the pilot and pilot-rated passenger were heard communicating on the air traffic control frequency during the flight. Additionally, the investigation could not determine which pilot-rated occupant was flying the airplane or where each pilot-rated occupant was seated due to the fragmentation of the airplane. According to NTSB accident report CEN13FA096, on December 10, 2012, about 2016 central standard time, a Messerschmitt Bolkow-Blohm model BK 117-A3 helicopter, N911BK, impacted the ground near Compton, Illinois. The pilot, flight nurse, and flight paramedic were fatally injured, and the helicopter sustained substantial damage from impact forces. The emergency medical services (EMS) equipped helicopter was registered to Rockford Memorial Hospital, and operated by Air Methods Corporation under the provisions of 14 Code of Federal Regulations Part 135 as an on-demand air-taxi flight. Night visual meteorological conditions prevailed for the flight, which operated on