WPR22FA197

The right-seated pilot’s failure to correct the left-seated pilot’s mismanagement of the engine thrust, which resulted in undesired speed and thrust oscillations during the final approach and a subsequent descent into terrain.

The pilots were performing skydiving flights while the right-seated pilot was training the left-seated pilot on the operation. The pilots completed six flights without incident and completed the drop of the skydivers on the accident flight normally. The right-seated pilot could not completely recollect the minutes leading up to the accident due to his injuries. He did recall that airplane was descending as expected with the power at idle. The recorded ADS-B data revealed that after turning onto final approach, the airplane then completed a right 360° turn presumably because the altitude was too high. The right-seated pilot attempted to increase the power by slightly nudging the throttle forward and thought the engine power did not increase as expected. A performance study revealed that in the last 70 seconds of recorded data, the airplane underwent a series of speed and thrust oscillations consistent with a pilot increasing and then decreasing the power lever. The right seat pilot recalls aiming for an open dirt field and observing a berm in the immediate flight path. In an effort to avoid the berm, he maneuvered the airplane into a right turn. The airplane landed short of the runway, resulting in a collision with the berm. The engine was producing power at the time of impact. Postaccident examination of the airplane revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation. The right-seated pilot was in the process of training the left-seated pilot and stated that he took over the controls during the final approach. It is unknown when he took over the controls, so it is unknown which pilot was at the controls during the speed oscillations. The right-seated pilot likely took over the controls too late and the airplane impacted the terrain. The left-seated pilot’s ability to hear the changes in engine power might have been hindered because she was listening to music through her headset at an elevated decibel level. The airplane was modified by a Supplemental Type Certificate that replaces the original Pratt & Whitney PT-6 turbine engine with a Honeywell TPE331 turbine engine. The TPE331 engine’s characteristics are such that if the airplane is on final approach with the power near idle, the throttle sensitivity (change in thrust per unit of power lever movement) increases around the transition between the propeller-governing and underspeed-governing modes of the engine, which corresponds to a zero-thrust condition. Near this transition point, small movements of the power lever (about ¼ to ½ inch of deflection) can result in relatively large thrust changes that can surprise pilots inexperienced with this behavior and result in pilot-induced oscillations (PIO). Given the thrust oscillations observed shortly before the end of the ADS-B data, it is likely that the left-seated pilot was at the controls and experienced such a PIO on a short final approach to land.

Toxicology testing performed by the Federal Aviation Administration Forensic Sciences Laboratory detected ketamine in the left-seated pilot’s cavity blood and in her liver tissue consistent with it being administered post-accident for resuscitation purposes. Body camera video footage and first responder’s reports indicate that when arriving on scene, both pilots were unresponsive. The right-seated pilot was found partway through the left window, supported by the window frame and the left side of the instrument panel. The left-seated pilot was found under the right-seated pilot. The police officer who extricated the right-seated pilot stated that the pilot did not appear to be wearing a seatbelt and that the officer did not have to unbuckle anything to remove him from the wreckage. He noted that the right-seated pilot’s shoulder harness was not used and he observed the right seat belts hanging behind the seat; he could not recall if the lap belt was secured. The airplane was modified in 2012 by the Supervan Systems, Ltd. (Texas Turbines) with a TPE331 engine and 4-blade aluminum propeller installation via Supplemental Type Certificate (STC) SA10841SC. The airplane’s engine is managed by the pilot through the power lever and speed lever located in the cockpit center console. The engine power lever (black) connects to the propeller pitch control and the manual fuel valve. The engine speed lever (blue) connects to the propeller governor and to the underspeed fuel governor (USFG). The right-seated pilot was employed by Desert Sand Aircraft Leasing Co. Inc., the airplane owner, and had been a pilot for the company for over 20 years. He was training the left-seated pilot how to fly the airplane and learn the operations. He stated she started about two weeks before the flight and estimated she would have needed about two more weeks before she would have been proficient to the company standards. He stated that she was doing very well and that he was comfortable with her piloting abilities. The left-seated pilot was undergoing training; she had six days of experience flying a modified Cessna 208, equating to 25.8 hours. All the pilot’s known flight time in a Cessna 208B was accumulated in a 208B equipped with a TPE331 engine. This was her third day in the left seat. All her training in the airplane was conducted by the right-seated pilot. She had numerous photos of the airplane systems (including the throttle quadrant) on her phone and notes about the operation of the airplane. According to the pilot’s iPhone application, she was listening to music in her Bose A20 Aviation headset at about 79 decibels during the accident flight. The headset is designed such that the primary source of audio is from the airplane’s intercom and the secondary source of audio is the device connected (in this case, the iPhone). Only one source can be heard at a time and the audio from the secondary source will never override intercom communications. On June 03, 2022, about 1347 Pacific daylight time, a Cessna 208B, modified as a Supervan Systems. LLC 900 airplane, N7581F, was substantially damaged when it was involved in an accident near Bob Maxwell Memorial Airfield, Oceanside, California. The left-seated pilot was fatally injured and the right-seated pilot was seriously injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 skydiving flight.   On the day of the accident, the pilots were performing skydiving flights while the right-seated pilot was training the left-seated pilot on the operation. A flight consisted of two pilots taking a group of approximately 17 skydivers to an altitude of about 11,500 feet mean sea level (msl) to jump out and then returning to the airport. The flights started about 1015 and were airborne for an average of 17 minutes, with about 15 minutes on the ground between flights, during which the airplane’s engine was kept operating while a new load of skydivers boarded the airplane. The pilots completed six flights without incident and departed on the accident flight at 1331.    The right-seated pilot stated that he could not recall many of the details leading up to the accident. He remembered that, on the accident flight, everything was normal with the departure and the unloading of the skydivers. The airplane was descending as expected with the power at idle. As the airplane turned onto final approach, about 2-3 miles from the approach end of runway 25, the left-seated pilot either had her hand on the throttle or began to reach up to the throttle. The right-seated pilot thought the airplane was low and attempted to increase the power by taking the controls and slightly nudging the throttle forward. He noticed that the engine power did not appear to change in response to the movement of the lever and he moved the throttle lever further forward. The lever was still unresponsive, and he estimated the airplane was about 400 ft above ground level (agl). He aimed for an open dirt field and observed a berm in the immediate flight path. In an effort to avoid the berm, the pilot maneuvered the airplane into a right turn.   Investigators reviewed the automatic dependent surveillance – broadcast (ADS-B) flight track data covering the area of the accident during the time surrounding the accident. After departing from runway 25, the airplane made a gradual climb to 11,575 ft msl as it circled to the right, back to the airport. The airspeed was reduced to about 80 KCAS (presumably to unload the skydivers) and then the airplane made a steep, turning descent reaching 130 KTAS (110 KCAS) when transitioning to the downwind leg of the traffic pattern. The airplane was at an altitude of about 2,400 ft msl and 2.5 nautical miles (nm) from the approach end of runway 25 when it turned onto final approach. When the airplane was about 2 nm from the runway, it made a 360° right-turn which was about 0.5 nm in diameter (see Figure 1 below). Figure 1: Accident Flight Path At 1346:10, about 1,025 ft msl, the airplane rolled out of the 360° turn and continued west toward the runway. For the remainder of the flight (one minute), the airplane was roughly following Highway 76 making a gradual descent toward the runway (see Figure 2 below). Figure 2: Flight Path on Final Approach The last recorded ADS-B point was at 1347:10 about 975 feet east of the accident site. At that time, the data indicated that the airplane was at 230 msl (190 feet above ground level) at a ground speed of 68 kts (76 KCAS). Witnesses stated that they observed the airplane flying at a very low altitude (see Figure 3). The airplane then pitched down in a nose-low attitude and banked to the right. The airplane impacted terrain and collided with the side of a berm. A security camera captured the airplane seconds before impact (see Figure 3 below). Figure 3: Video Footage Showing the Airplane Before Impact The accident site was located about 1,615 feet east of the approach end of runway 25 on flat terrain composed of soft, dry dirt. The wreckage was found distributed over an approximate 125-foot distance with the nose pointed on a heading of about 335°. The right wing was partially separated from the fuselage root and had folded forward and over upon itself, coming to rest inverted. The first identified piece of debris was a fragment of the right wingtip light lens, consistent with the right wingtip contacting the ground at the beginning of the accident sequence. All flight control surfaces were at the main wreckage and attached at their respective fittings. The left flap was found in the retracted position, and damage at the inboard end of the right flap was consistent with it being retracted at the time of impact. Investigators established flight control continuity during the postaccident examinations. The left side of the center pedestal was crushed and a majority of the fuselage deformation was near the left