HISTORY OF FLIGHTOn 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 the right engine’s speed increased to 4,680 rpm. During the next 4 seconds, the left engine’s speed decreased to 2,450 rpm, the right engine’s speed decreased to 4,420 rpm, and the indicated airspeed decreased to 60 kts. From 1403:21 to 1403:37, the left engine’s speed remained between 2,570 rpm and 2,930 rpm, and right engine’s speed increased to a maximum of 5,370 rpm (which was about its maximum speed recorded during takeoff). The airplane’s left bank stopped, and it rolled into a right bank of no more than 8°. From 1403:38 to the end of recorded data at 1403:51, the left engine’s speed increased to a maximum of 3,360 rpm before ending at 3,310 rpm, the right engine’s speed decreased within 6 seconds to 3,200 rpm before ending at 3,220 rpm, and the indicated airspeed decreased, ending at 47 kts. Also between 1403:38 to the end of recorded data, the airplane remained in a right bank for the majority of the data points but then changed to a left bank, which increased in bank angle for the final 4 seconds, ending about 11°. At the end of the recorded data, the airplane was at 135 ft pressure altitude. AIRCRAFT INFORMATIONThe 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. AIRPORT INFORMATIONThe 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. WRECKAGE AND IMPACT INFORMATIONThe accident site was about 120 ft southeast from the last ADS-B target and about 0.7 nautical mile and 331° from the approach end of runway 12 at DED. Examination of the wreckage by an FAA airworthiness inspector revealed the left wing was extensively damaged. The left propeller actuator was found fully retracted, consistent with reverse position, which matched the left propeller’s blade angle. The right propeller actuator was found in an extended position, consistent with cruise position, which matched the right propeller’s blade angle. Examination of the cockpit revealed the left propeller regulator remained installed in the instrument panel. The Operating Mode Switch was in the “CONSTANT SPEED” position, and the rpm INC/DEC switch was broken. The right propeller regulator also remained installed in the instrument panel. The Operating Mode Switch was broken, its position was not determined, and the rpm INC/DEC switch was centered. The propeller control left and right red, guarded switches were found with both guards down. The left switch remained installed in the panel, and the right switch was found impact separated from the panel. Several wires of the left switch were fractured, either at the terminal fitting or in close proximity to it, and the bottom portion of the left switch was also impact damaged. The separated right switch exhibited impact damage. The two-channel “ON/OFF/ON” switches were not attached to the panel and not observed or located during the very brief examination of the wreckage. TESTS AND RESEARCHA review of FAA Advisory Circular (AC) 20-27G, "Certification and Operation of Amateur-Built Aircraft," issued September 30, 2009, and AC 90-89C, "Amateur-Built Aircraft and Ultralight Flight Testing Handbook," issued February 14, 2023, revealed no guidance for a builder of an experimental aircraft regarding reversible propellers. FAA Order 8130.2J, “Airworthiness Certification of Aircraft,” issued July 21, 2017 (and in effect at the time the accident airplane’s propellers were installed), provided policies and procedures for FAA aviation safety inspectors (and certain persons designated to act as representatives of the FAA) for issuing airworthiness certificates. Chapter 2 of FAA Order 8130.2J, which addressed policies and procedures for issuing a special airworthiness certificate, specified in paragraph 2-3(a)(1), that “a properly completed application [FAA Form 8130-6] is required to begin the process for issuing an airworthiness certificate.” Per paragraph 2-3(e)(4) of the Order, inspection of the aircraft included, in part, “verifying…[that] the propeller(s) and associated instruments operate per the manufacturer's instructions.”