N601YP

On June 3, 2023, at 1320 central daylight time, an experimental, amateur-built Zenith 601XL, N601YP, was substantially damaged when it was involved in an accident near Albertville, Alabama. The commercial pilot was fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 flight.

A friend of the pilot, who was a mechanic and familiar with the build project of the accident airplane, had observed several test flights. He reported that he was assisting the accident pilot with troubleshooting several systems, notably the oil pressure and airspeed, and their respective interface with the Electronic Flight Instrumentation System and Engine Monitoring System. After fixing the airspeed issue and working with the pilot to reset the oil pressure triggers per the engine manufacturer, the pilot began another test flight. According to the mechanic, he informed the pilot to stay over the airport per the regulations and for safety reasons.

The pilot departed the Albertville Regional Airport-Thomas J Brumlik Field (8A0)

Albertville, Alabama, and data recovered from the airplane’s electronic instruments showed that the airplane flew to the southwest. Over the next 30 minutes, the airplane made several heading changes and a climbed to 4,000 ft msl before descending and leveling off at 2,050 ft msl. Several witnesses near the accident site reported that the airplane appeared to be flying slow and at low power when, suddenly, it “went full throttle” and nosed over. One witness reported that it pitched up and down several times and rolled left and right before descending.

The airplane impacted trees and terrain and came to rest inverted on the side of a stream bed about 3 1/2 miles northwest of 8A0 at an elevation of 1,007 ft. All major components of the airplane were located at the accident site. The wreckage path was oriented on a heading of 057° magnetic and was about 50 ft long. The fuselage, empennage, wings, and all flight controls were discovered in the immediate vicinity of the primary impact site. The engine was separated and located in a creek bed about 40 ft north of the primary impact site.

Shattered tree branches, several of which exhibited features consistent with having been cut by a propeller, were located around the impact site. Both wings were displaced aft but remained partially attached to the wing spar that was torsionally twisted. The two internal fuel tanks were severed from their internal mounts and were in the debris field. The fuel tanks were compromised and there was a smell of automotive gasoline in the area along with vegetative fuel blight on the grass and surrounding leaves and bushes.

Examination of the airframe revealed that the electrically-actuated elevator trim was in the full up position (nose down trim) and the flaps were retracted. The empennage separated during impact but remained in the immediate vicinity of the main wreckage. Rudder continuity was established from the rudder pedals through breaks in the cables, consistent with overload. Aileron and elevator flight control continuity was established on all surfaces by manual manipulation of control cables and tracing the cables through breaks. The breaks in the cables displayed fracture features consistent with overload separation with a “broom straw” appearance. There were several cuts in the cables made by emergency personal recovery attempts.

Examination of the engine and propeller assembly revealed that the propeller hub remained attached to the flange. Two propeller blades were fractured and severed about 3 inches outward from the hub and one blade was fractured about 9 inches outward from the hub; all the blade fractures were bent in the opposite direction of rotation. Several pieces of delaminated propeller blades were distributed throughout the accident site in multiple directions.

Engine crankshaft continuity was confirmed and there was smooth action of all rockers, valves, and springs when the crankshaft was rotated 720°. Compression and suction was attained on all cylinders and all the spark plugs displayed normal coloration with normal electrodes as compared to the Champion Aerospace AV-27 Check-A-Plug chart.

The cockpit was destroyed by impact forces. The forward-lift clamshell canopy frame was deformed by impact forces and only remnants of plexiglass remained in in the frame. The hydraulic lift assist was in the extended position. No secondary canopy latch was discovered in the wreckage and no witnesses reported seeing the canopy in the open position during descent.

The elevator trim actuator was sent to the manufacturer for examination and bench testing under supervision of an National Transportation Safety Board investigator. The actuator was connected to a test fixture, and power applied. The actuator arm was observed to move progressively in both directions, with appropriate indications on the test stand position indicator. The unit turned off as it reached its limit in both directions, and the geartrain sound and speed appeared normal when compared to an exemplar unit. The supplied electrical wires did not show any evidence of chafing or exposed conductors and the LED position indicator was found to be operational. There were no anomalous irregularities with the trim unit.

The airplane was equipped with a cockpit multi-function display, which was a panel-mounted combination Electronic Flight Instrumentation System (EFIS) and Engine Monitoring System (EMS) that stored data in non-volatile memory. The unit was recovered from the accident site and sent to the NTSB Recorders Laboratory, Washington, DC, for data download, which captured the entire flight through the descent and impact. Data including, but not limited to, oil pressure, temperature, fuel flow, fuel remaining, and engine rpm revealed no indications of an interruption of engine power. Airplane performance data consisting of pitch, yaw, speeds (both groundspeed and indicated airspeed), altitude, heading, and vertical speeds were also recorded. The data depicted that after the airplane departed, it performed basic maneuvers including turns, descents, and straight and level flight.

About 30 minutes into the flight, while the airplane was at 2,050 ft msl on a GPS ground track of about 055°, the data showed that it entered a left roll as the pitch decreased. About 20 seconds before the data ended, the engine power increased from the previously established 4,500 rpm to 5,500 rpm and the airplane’s speeds began to increase. During the final 12 seconds of the recorded data, the airplane reached a maximum roll near 35 degrees left, with a downward pitch near -20 degrees. The airplane descended at a rate of about -900 feet per minute while its magnetic heading and GPS ground track remained relatively constant. The engine rpm decreased slightly to about 4,900 rpm during the final 5 seconds of the recorded data.

The Alabama Department of Forensic Sciences (ADFS) performed the pilot’s autopsy. According to the pilot’s autopsy report, his cause of death was blunt force injuries, and the manner of death was accident. Examination of the heart was limited by injury, and the coronary arteries could not be examined. Within the limitations of the autopsy, it did not identify significant natural disease.

Accompanying narrative information from death investigator records documented that the pilot had a medical history including prediabetes and vascular issues; the source of this information was not specifically documented.

ADFS postmortem toxicological testing did not detect any tested-for substances. The Federal Aviation Administration Forensic Sciences Laboratory also performed toxicological testing of postmortem specimens from the pilot, detecting metformin and glipizide in liver and muscle tissue. Glucose was not detected in vitreous. No blood was available for testing.