CEN18FA023

The flight instructor's and pilot's failure to recognize that a high descent rate had developed on short final, likely due to their distraction by an open engine cowling, and the unexpected strong pitch-down force during flap extension due to the installation in the airplane of a Short Takeoff and Landing system.

The private pilot had recently purchased the Bonanza airplane, which he and an experienced flight instructor were using to conduct his first training flight in a Bonanza. During a visual approach, the engine's left cowling opened. According to the pilot, who initially survived the accident, the flight instructor assumed control of the airplane. Based on video from home surveillance cameras, the descent rate for the approach increased to about 1,000 ft per minute about 100 ft above ground level. About 7 seconds later, the airplane impacted trees and a power line located 1/2 mile from the runway threshold. The airplane was one of three Bonanza airplanes modified with a Robertson Short Takeoff and Landing (STOL) system. The flight characteristics for this modification included a strong pitch-down force while extending the flap from 15° to 30° position, which is greater than in Bonanzas without this STOL system. The investigation could not determine if the pilot or flight instructor was aware of this unique flight characteristic, which was not described in the STOL certification information. The pilot had compiled a list of airplane discrepancies, which included "cowling latch - pilot's side rear spring." It is likely a latch for the left engine cowling opened in flight because it was not properly secured during the preflight. The flight instructor and pilot were likely distracted by the open engine cowling and did not expect the strong pitch-down force during flap extension, which resulted in a high descent rate on short final.

The Office of the Chief Medical Examiner, Oklahoma City, Oklahoma, performed an autopsy on the flight instructor and attributed his death to "smoke inhalation and thermal burns." The FAA's Bioaeronautical Research Sciences Laboratory Oklahoma City, Oklahoma, performed toxicology tests on the flight instructor. The results were negative for all tests conducted. The Office of the Chief Medical Examiner, Oklahoma City, Oklahoma, performed an autopsy on the pilot and attributed his death to thermal injuries. The FAA's Bioaeronautical Research Sciences Laboratory performed toxicology tests on the pilot. Therapeutic levels of morphine, which is commonly prescribed in an emergency medical setting, were detected. Flight Instructor The flight instructor, age 61, held commercial pilot and flight instructor certificates with airplane single- and multiengine land and instrument ratings. On his most recent Federal Aviation Administration (FAA) airman medical application, dated May 15, 2017, the flight instructor reported 2,529 hours of civil flight experience with 110 hours in the previous 6 months. On an insurance application dated May 1, 2017, the flight instructor reported 11,456 hours of total flight experience, which included his military flight experience. The flight instructor owned a Beech Bonanza airplane and frequently trained in them. Pilot The pilot, age 39, held a private pilot certificate with an airplane single-engine land rating. The pilot was issued a third-class medical certificate with no limitations on September 10, 2014. A logbook review revealed that the pilot had accumulated 231 flight hours as of June 1, 2017. The pilot had recently purchased the airplane and chose to receive training from the flight instructor based on the instructor's strong teaching reputation with Bonanza airplanes. The accident occurred during the pilot's first training flight and second flight overall in the accident airplane. Evidence indicates that the airplane impacted a tree, followed by a power line, before coming to rest inverted in a shallow wash adjacent to a steep hill. Most of the fuselage and the right wing were consumed by fire, and several trees near the accident site were burned. Examination revealed that the flight control cables were continuous from end to end. The cables had separated from the cockpit controls and empennage flight surfaces due to melting of the structure at the cable ends. The aileron bellcranks were intact with the control cables attached. The elevator trim actuator was not located in the wreckage. The left-wing flap was found extended 30°, and the landing gear were extended. Two control yokes were found in the wreckage. The engine was lying on its left side with the main wreckage. All six cylinders remained attached to the crankcase, and the magnetos remained attached to their respective mounting positions. The magneto housings and internal components were thermally damaged. The top spark plugs were removed and exhibited normal wear when compared to the Champion Check-A-Plug chart. The fuel pump exhibited thermal and impact damage. The drive coupling was fractured, and the fuel pump would not turn by hand. The fuel pump was disassembled, and the internal components were thermally damaged. The fuel manifold valve had separated from its mount and exhibited severe thermal damage. The fuel nozzles were removed and were free of debris. The cylinder combustion chambers were examined with a lighted borescope with no anomalies noted. As the crankshaft was manually rotated, thumb compression was obtained on all six cylinders, and continuity was established to the accessory gears. The muffler did not exhibit any breaches or signs of external sooting. The propeller governor was removed, and the control arm rotated freely by hand from stop to stop. The propeller governor drive rotated freely, and oil was discharged when rotated by hand. The propeller remained attached to the crankshaft propeller flange and exhibited thermal damage. One blade was relatively straight, the second blade was bent aft near the blade hub, and a third blade exhibited "S" bending. Examination of the engine and flight control system revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation. Three of the four engine cowling latches and three of the four bayonet fittings were recovered from the wreckage. Both left cowling latches were partially melted by postcrash fire. The right forward cowling latch remained attached to the structure and exhibited minimal fire damage. The rear half of the right cowling access doorframe was consumed by postcrash fire. None of the three cowling latches recovered were engaged by a bayonet fitting. Two of the recovered bayonet fittings had their mounting brackets attached, but they were not attached to a cowling access door. Based on the design of the brackets, these two bayonet fittings were determined to be the forward bayonet fittings. The third bayonet fitting, an aft fitting, was found attached to a portion of a melted cowling access door. It could not be determined if the third bayonet fitting was from the left or right side of the engine. The exterior handles on both sides of the engine cowlings were found in the latched position. The airplane, serial number D-9544, was issued a standard airworthiness certificate on October 17, 1973. The airplane was equipped with a Continental IO-520-BA10 engine, serial number 241368-R, and a three-bladed McCauley propeller. The airplane's last annual inspection occurred on May 1, 2017, at a total airframe time of 1,927.7 hours. A second control yoke was installed before the accident flight. In 1979, a Robertson Short Takeoff and Landing (STOL) system was installed in accordance with Supplemental Type Certificate (STC) SA503NW. The modification included removal of the ailerons; installation of full-span, single-slotted flaps; and installation of a spoiler roll control system. Flap positions for the STC modification were 0°, 15°, and 30°. The airplane was one of only three Bonanza airplanes modified by the STC. A handwritten list of airplane discrepancies, with penmanship matching entries in the pilot's logbook, was found in the pilot's hangar. One of the listed discrepancies was "cowling latch - pilot's side rear spring." A review of cowling latch part information indicated that each latch had two springs. One spring returned the latch jaws to the closed position when the bayonet fittings were pushed into the latch, and one spring exerted tension on the latch mechanism. The airplane flight manual contained the following information concerning the engine cowlings: The Bonanza is equipped with Hartwell latch mechanisms on the right and left upper engine cowling for quick and easy access to the engine compartments without the aid of tools. Each cowl latch (two per cowl) is locked and released by a single recessed handle located in the lower cowling panel on each side of the engine. To close the cowling, lower the cowling to the closed position with the handle in the prelatch position. The handle has three positions: flush with the fuselage is latched; held fully forward is unlatched; approximately 90° to the fuselage is prelatch (ready to close cowl). An audible click denotes the bayonet fittings, located forward and aft on the upper cowl, sliding into the latch safety catch. The cowl is locked by moving the latch handle to the full recessed position. The security of the forward latches can be checked by pulling out on the check tab attached to the lower forward edge of the upper cowling. If the cowling can be moved after latching, open the cowling, check the latch alignment and re-latch. A video of an exemplar engine cowling being shut and photographs of an exemplar engine cowling, latches, and bayonet fittings, are included in the docket for this investigation. In 1995, Beechcraft released