ERA24LA208

The uncommanded movement of the left propeller into reverse during approach for undetermined reasons, resulting in an in-flight loss of control of the airplane at low altitude during approach.

The pilot proceeded toward the destination airport in the experimental, amateur-built, twin-engine airplane that was equipped with a customized propeller pitch control system consisting of a standard electronically controlled propeller pitch device, plus various selectors and other limit switches, enabling the propellers to provide reverse thrust capability. After reducing power while on a base leg of the airport traffic pattern with both engines operating within about 30 rpm of each other, the pilot believed the propeller for the right engine went uncommanded into reverse. He said that he had not moved the propeller control guarded switches (which would have been one of several steps required to command the propeller to reverse) and that he did not see any propeller mode light illuminate on the instrument panel. Within 1 to 3 seconds, the airplane was uncontrollable and entered a spin, which, according to a witness, was to the left, and the airplane quickly lost altitude and impacted the ground. Based on recorded data for various airplane parameters, about the time and location where the pilot likely reduced power, the left engine’s speed increased within 1 second from 4,630 rpm to about 5,330 rpm, consistent with propeller blade angle decreasing toward fine or low pitch, while the right engine’s speed remained about 4,660 rpm to 4,680 rpm. During the next 21 seconds, the left engine’s speed decreased and remained below 3,360 rpm, while the right engine’s speed increased to a maximum of 5,370 rpm, consistent with the maximum value recorded at takeoff. During that time, the airplane rolled left briefly before rolling to and remaining in a right roll, the maximum extent of which was about 8°. During the next 13 seconds (to the end of the recorded data), the airplane’s indicated airspeed decreased to the lowest value of 47 kts, the left engine rpm values increased slightly while the right engine rpm decreased then stabilized, with both engines ending within 90 rpm of each other. The airplane’s bank angle values and directions changed, continuing in a left bank that increased during the last 4 seconds of the recorded data. Postaccident examination of the wreckage revealed that the left propeller actuator was retracted, consistent with the propeller being in reverse, which matched the position of the left propeller blades, and the right propeller actuator was extended, consistent with the propeller being in cruise, which matched the position of the right propeller blades. Both propeller control guarded switches were found closed, consistent with the pilot’s statement. Thus, based on the engine data parameters and the wreckage evidence, when the pilot reduced the throttles in preparation for landing, the variable-pitch left propeller moved uncommanded to, and likely past, the fine or low pitch position into reverse range. The reason for the uncommanded pitch change was not determined. Although the pilot mistakenly perceived that the issue was with the right propeller and responded by applying left rudder (which would have exacerbated a spin to the left), given the airplane’s low altitude, the pilot had little time to assess and address the condition and likely could not have successfully regained control of the airplane before the airplane impacted the ground.

The amphibious, experimental, amateur-built pusher airplane was powered by two Rotax 912 ULS2-01 engines and originally equipped with fixed-pitch, Warp Drive, three-bladed propellers. The application for airworthiness was approved on November 15, 2023. According to the airplane’s maintenance records, on February 7, 2024, at an airplane time of 25.6 hours, the Warp Drive propellers were removed, and electrically controlled, four-bladed, DUC Flash-2 PVRG variable pitch propellers were installed by the pilot. As part of the Conditions and Limitations associated with the Special Airworthiness Certificate, any major change, and, specifically, a change from a fixed-pitch to variable-pitch propeller, required the owner to fill out FAA form 8130-6, Application for U.S. Airworthiness Certificate with the airplane remaining in flight test after the change for a minimum of 5 hours. There was no record of FAA Form 8130-6 having been submitted for the propeller change. Representatives of the variable-pitch propeller manufacturer stated that, after the pilot installed the propellers, they assisted him with adjustments to propeller pitch and the electrical actuators in February 2024. The pilot stated that, because the range of the microswitches for the propeller actuator pitch were not initially set right from the propeller factory, the propeller actuators were disassembled and the microswitch range was set. No record of this work was documented in the airplane’s maintenance records. A maintenance record entry by the pilot on February 26, 2024, at an airplane time of 31.2 hours, documented that the FAA-prescribed flight test was completed and that the airplane was controllable throughout its normal range of speeds and throughout all maneuvers to be executed, had no hazardous characteristics or design features, and was safe for operation. A flight instructor who flew with the accident pilot in the accident airplane on April 30, 2024 (2 days before the accident), reported that, while performing taxi operations on the water, at one point, after takeoff power was applied, the airplane was “static” and did not move. The pilot then reduced the power on both engines to idle and cycled the propellers through full reverse and then forward. Subsequently, when the pilot increased the power on both engines, the airplane began moving forward normally. The pilot then performed a normal takeoff and returned to the departure airport uneventfully. During the postflight debriefing, the pilot informed the flight instructor that he was still “working out the kinks in the system” and that he would have the propeller control issue addressed. There was no entry in the maintenance records that any subsequent work or inspection of the propeller control system was performed. The airplane was equipped with two standard Flybox Avionics PR1-P Propeller Regulators (one for each propeller) installed on the pilot’s instrument panel to control propeller blade pitch. Each propeller regulator was wired to a potentiometer installed on an actuator near the respective propeller. The PR1-P propeller regulators were not capable of providing reverse thrust capabilities as delivered by the manufacturer. Each propeller regulator featured a small rectangular display screen and an “Operating Mode Switch,” which was required to be pulled out and then placed in either the “CONSTANT SPEED” or “MANUAL” positions. Manual mode was to be used only when testing the system or in the event of failure or emergency. Each propeller regulator also had an rpm switch labeled “INC” (increase) and “DEC” (decrease), and a knob that could be rotated to increase or decrease rpm or pressed like a pushbutton to enter a menu for various settings. To accomplish propeller blade pitch control of each propeller below the low-pitch setting into Beta and reverse, a left and right three-channel “ON/ON” red, guarded switch on the pilot’s side rail, one for each propeller, must be placed into the “on” position, which disconnects the Flybox PR1P from the actuator, and then a second two-channel “ON/OFF/ON” switch for each propeller also installed on the pilot’s side rail aft of the three-channel red guarded switches must be used to manually control the propeller pitch. By design and for redundancy, both microswitches of the fine or low pitch stop must engage, the left and right three-channel “ON/ON” red, guarded switches must activate, and the second, two-channel “ON/OFF/ON” switch must activate to allow for increase or decrease of propeller blade angle between the reverse pitch stop and the coarse pitch stop positions. (There was no design feature to prevent the propeller from going below the fine or low pitch stop in flight, such as in the event of failure of both microswitches, incorrect position of the microswitches, false electrical contact of the microswitches, or intentional pilot action.) The airplane was equipped with “LH BETA PROP” and “RH BETA PROP” annunciation lights installed on the center and top portion of the instrument panel. The pilot reported that each light was designed to illuminate when the red, guarded switch for the respective propeller was in the “on” position for reverse. A representative of the propeller manufacturer reported that the accident airplane was the only airplane in the United States or worldwide flying with DUC propellers installed that were capable of producing reverse thrust. On May 2, 2024, about 1404 eastern daylight time, an experimental, amateur-built amphibious AirCam airplane, N848HP, was substantially damaged when it was involved in an accident near DeLand, Florida. The airline transport pilot was seriously injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. Based on a review of FAA ADS-B data and information from the pilot, the flight departed about 11 minutes earlier from Spruce Creek Airport, Daytona Beach, Florida, and proceeded west toward the destination, DeLand Municipal Airport-Sidney H Taylor Field (DED), DeLand, Florida. The data showed that accident flight flew north of DED about 600 ft barometric altitude and entered the airport traffic pattern on a left base leg for runway 12. According to the pilot, while flying the base leg, he reduced power on both engines and set final flaps for landing. He stated that, upon reducing engine power, the “RH [right] engine propeller went uncommanded and not expected into full pitch reverse.” The pilot stated that he did not touch the propeller switches, the guarded switch covers were closed, and no instrument panel propeller mode lights illuminated. Within 1 to 3 seconds, the airplane was uncontrollable and entered a spin. He recalled applying full left rudder to try to correct the spin, having no time to shut down the affected engine, and seeing the ground rushing toward him before the impact. He reported that there was no preimpact issue with the engines or the flight controls. A pilot who was flying nearby observed the accident airplane “rotate around the vertical axis to the left,” quickly losing altitude and impacting the ground. The airplane was equipped with a Garmin GDU 460 unit capable of recording a variety of airplane parameters over time, including location, pressure altitude, indicated airspeed, roll angle, engine 1 (left) and engine 2 (right) rpm, and other engine performance parameters. The unit was not equipped to record propeller blade angle. A review of data downloaded from the unit revealed that, at 1403:15, the flight was flying north of DED about 600 ft pressure altitude, 71 kts indicated airspeed, in a slight left bank, with the left and right engines operating at 4,630 rpm and 4,660 rpm, respectively. During the next second, the left engine’s speed increased to 5,330 rpm (which was consistent with its maximum speed recorded during takeoff), while