CEN16FA276

The pilot's failure to maintain airplane control during an en route climb near convective activity, which resulted in an aerodynamic stall, an uncontrolled descent, and a subsequent in-flight breakup due to an exceedance of the airplane's design load limitations.

The commercial pilot departed on a cross-country flight in the multi-engine airplane and attempted to use visual flight rules flight following from air traffic control during the flight. The availability of this service is based on controller workload, and, as the flight neared an area of Class B airspace, the controller discontinued flight following services and instructed the pilot to remain clear of the Class B airspace. The airplane then climbed from its cruise altitude of 8,500 ft mean sea level (msl) to 10,300 ft msl while losing airspeed until reaching about 48 kts, well below its lowest published stall speed. The airplane subsequently entered a series of descending turns, reaching an airspeed of about 211 kts that exceeded the airplane's design maneuvering speed. The airplane experienced an in-flight breakup. Weather radar imagery identified reflectivity values consistent with convective activity immediately adjacent to the airplane's position just before the time of the accident. It is likely that the pilot initiated the climb in order to remain clear of the developing convective activity, and it is also likely that the airplane entered instrument meteorological conditions sometime between the initiation of the climb and the loss of control. The convective conditions present at the time of the accident were conducive to the development of updrafts, downdrafts, and turbulence; however, there were no recorded pilot reports for this area and the exact conditions encountered by the accident airplane could not be determined. Although maintenance records indicated that the airplane had undergone recent maintenance to the left wing and rivet holes in the left wing spar exhibited signs of anomalous installation, this likely did not contribute to the accident, since a performance study determined that the airplane exceeded its design maneuvering speed, which put the airplane at risk of exceeding its design load limitations and the subsequent structural failure. Toxicology findings indicated that the pilot was using two antidepressants, one of which, trazodone, is potentially impairing. While symptoms of depression often include cognitive deficits, it is impossible to know what, if any, medication side effects or cognitive symptoms the pilot may have been experiencing at the time of the accident. Therefore, whether his depression or its treatment contributed to the circumstances of the accident could not be determined from the available information.

Wreckage that came to rest away from the main wreckage did not exhibit any thermal deformation or discoloration. The area around the main wreckage exhibited damage consistent with a ground fire. Recording of communications from the Chicago Terminal Radar Approach Control facility were reviewed along with their transcripts. The transcripts are appended to the docket material associated with this investigation. Communication from one sector in the facility, in part, stated: PILOT: Private approach, twin Comanche 7409 Yankee. Would you maintain 8,500? CONTROLLER: Whoever's calling, ident. PILOT: Twin Comanche 7409 Yankee with you, maintaining 8,500. CONTROLLER: Contact Chicago departure, 126.62. Maintain VFR outside the Bravo. PILOT: 126.62? CONTROLLER: Yes. PILOT: Roger. Communication from another sector in the facility, in part, stated: PILOT: (Unintelligible) 7409 Yankee. We're just checking in at 8,500. CONTROLLER: All right. Who, what, say your location the VFR (phonetic) craft checking in. PILOT: I'm just outside of the class, the airspace here, by Lewiston University. CONTROLLER: Okay. Have I already talked to you? PILOT: Negative. They told me to call you up. I'm just passing by to the west. CONTROLLER: Okay. Did they assign you a code? PILOT: 1647. CONTROLLER: Okay. Well, they haven't told me anything about you. Just maintain (unintelligible) class Bravo. I'll get back to you. PILOT: Roger. That was the last recorded communication with the accident airplane. Metallurgical Examination Two pieces from the forward end of the left engine crankshaft along with the crankshaft's forward split main bearing shells were sent to the NTSB Materials Laboratory for detailed examination. An NTSB Senior Materials Engineer examined the components and produced a Materials Laboratory Factual Report, which is appended to the docket material associated with this investigation. The materials report, in part, stated that the first examined piece was the crankshaft piece from the propeller flange to a fracture through the oil tube hole in the first main bearing journal. The other piece was the crankshaft piece from the fracture to a cut through the second connecting rod journal. The propeller flange on the crankshaft exhibited bending deformation, with one region bent forward and the opposite region, 180° around the shaft bent aft. A portion of the oil flinger flange was fractured leaving an approximate 120° region intact. The crankshaft was fractured in the circumferential direction at the oil tube hole in the first (forward) main bearing journal. The fracture surfaces had a comparatively rough appearance and were inclined about 45° to the bearing surface. The exhibited features were consistent with a bending overstress fracture. The split bearing shells were deformed; however, they exhibited no otherwise notable features. Aircraft Performance Examination An NTSB Air Traffic Control Specialist requested radar data from the FAA in reference to the accident flight. The radar data was provided to an NTSB Performance Specialist who produced a Performance Study, which is appended to the docket material associated with this investigation. The study, in part, stated that the radar data provided began about 1044. Until about 1108, the airplane was travelling along a path oriented at approximately 320° (true), at an altitude of 8,500 ft, and a groundspeed of about 150 kts. About 1108:23 the airplane began to gain altitude while losing speed until 1111:10 when it reached an altitude of 10,300 ft. The airplane held 10,300 ft until 1111:23 when it began to descend and gain speed. About 1111:28 the airplane reached its lowest calculated equivalent airspeed of 48 kts. The final radar point was at 1112:37.78 when the altitude was recorded at 2,200 ft and the calculated equivalent airspeed was 211 kts. The recorded rate of climb for the accident airplane from 8,500 ft to 10,300 ft was about 600 ft/min. The POH reported the multi-engine full throttle rates of climb, given a calculated density altitude, were between 800 ft/min at 3,600 lbs and 1,200 ft/min at 2,800 lbs. This recorded rate of climb at this altitude was within the capability of the airplane. The calculated pitch and angle of attack for the final climb was calculated using a simplified aerodynamic model. The model showed that while the airplane gained altitude, it lost airspeed, and its angle of attack increased to nearly 20°. A high angle of attack and low airspeed can put an airplane at risk of an aerodynamic stall. The POH reported the gear and flaps up stall speed to be between 76 mph (66 kts) at 3,600 lbs gross weight and 67 mph (58 kts) at 2,600 lbs. Radar data showed that the airplane lost altitude and began a series of turns, the first to the left, after the equivalent airspeed dropped below 60 kts. The data indicated the airplane was at 10,300 ft. The airplane then picked up speed after it began descending and rolled left, reaching a maximum calculated equivalent airspeed of over 200 kts before the radar data ended. The flight manual reported the never exceed speed to be 230 mph (200 kts). The maneuvering speed was reported as being between 135 mph (117 kts) at 2,450 lbs gross weight and 162 mph (140 kts) at 3,600 lbs. The airplane exceeded the POH airspeed restrictions while rolling left and right during its descent. Structures Examination A NTSB Aircraft Structures National Resource Specialist examined the recovered wreckage and identified sections to be further examined in detail. The identified sections were subsequently examined by the structural specialist and an airplane manufacturer's engineer. The specialist produced a Structures Group Chairman's Factual Report, which is appended to the docket material associated with this investigation. About 83 inches of the separated left outboard wing exhibited leading edge skin separations. The outboard approximate 68 inches of the left aileron remained attached to the separated section of wing with the aileron balance weight still secured to the aileron. The inboard section of the left aileron was separated from the remainder of the structure and was recovered. No evidence of fire or fire damage was noted to the separated section of wing or aileron. The left tip tank was separated from the outboard section of the wing and found breeched from impact damage to the leading edge. The remainder of the left wing remained attached to the fuselage; fire damage was noted to the inboard area of the left wing. The left flap was found separated from its mounts at the main wreckage site and exhibited impact and fire damage along the entire span of the flap. The left engine and nacelle structure were separated from the left wing. The left aileron bell crank assembly remained attached and the bell crank fitting was recovered at the main wreckage site. The aileron control cable attach points to the bell crank were found fragmented from the bell crank assembly. Left aileron control continuity was established except where impact separations were noted. The left aileron control cables were found twisted around themselves and the aft wing spar exhibited "saw" marks along the top edge of the spar. The upper main spar and lower spar chord fractured and both exhibited evidence of upward and aft bending. An examination of the shear lips on the horizontal legs of the spar chord at each of the fracture locations confirmed the upward bending along with the fractured ends of the horizontal legs of the spar chords deforming in an upward direction. The left wing's spar chords also exhibited evidence of trailing edge up twisting deformation consistent with the outboard wing rotating counter clockwise about the main the spar when looking inboard. The left wing's main spar web was missing sections in the area of the aileron bell crank assembly. The rear spar was missing in the area of the rear spar aileron hinge fitting. Neit