History of Flight
On February 19, 2021, at approximately 1158 local time, a Piper PA-32-260 Cherokee Six, registration N57014, sustained substantial damage during an accident in Los Angeles, California. The pilot was fatally injured and a person on the ground received minor injuries. The flight was conducted under 14 CFR Part 91 as a personal flight.
According to ADS-B data provided by the FAA, the airplane departed Zamperini Field in Torrance at 1146 and proceeded south-southeast along the coastline while climbing to about 3,400 ft msl. The pilot was receiving VFR flight following from Southern California Terminal Radar Approach Control (SCT). At 1155:29, the pilot reported engine problems. When asked for details, at 1156:30 he stated, "I have an engine wobble; no rpm’s." About 20 seconds later, he said he would have to make an off-airport landing. His final transmission indicated he intended to land in Long Beach harbor, adding, "I am going to see if I can make it." ADS-B data showed the airplane proceeded toward Terminal Island and aligned for an emergency landing on a paved area.
Security camera footage revealed the airplane descended in a relatively flat pitch attitude. The left wing struck a semi-truck, then the airplane impacted a concrete barrier in a left-wing low attitude. The airplane cartwheeled and came to rest upright.
Aircraft Information
The airplane was powered by a Lycoming O-540-E4B5 engine, which had been overhauled in October 2010 (495 hours before the accident) and rebuilt in 2018 (about 35 hours before the accident). The last annual inspection was in August 2020, about 7 hours before the accident; all compressions were within limits. Invoices from the 2018 rebuild showed the mechanic purchased exhaust valve keepers, thrust buttons, and a seal and gasket set. The Safety Board could not interview the mechanic to determine why the keepers were purchased or on which cylinders they were installed.
Wreckage and Impact Information
The accident site was in a container shipping yard about 6.5 nautical miles southeast of Torrance. Wreckage was distributed over about 200 ft along a median magnetic bearing of 79°. The outboard left wing was the first debris found, resting in the truck cab. Paint transfers on the truck hood, about 6 ft above ground, were consistent with left-wing contact in a left-wing low attitude. Approximately 40 ft east of the truck, a 3-ft-high concrete barrier was displaced, with paint transfers. The fuselage came to rest upright, heavily damaged near the pilot seats. Control continuity was established.
The electric fuel pump was mounted in the cabin floor; its copper outlet line was pulled from the "B" nut. About one ounce of liquid resembling avgas remained in the pump, along with substantial sediment and water (indicated by water-detecting paste). The fuel screen was brittle and covered with sediment and rust. The copper fuel line from the electric pump to the firewall was fragmented and fractured at the firewall fitting. Hoses in the engine compartment had bright orange torque stripes indicative of recent installation. The engine-driven fuel pump was disassembled; diaphragms were pliable, with no anomalies. Fuel from the carburetor was clean and consistent with avgas, with no water detected.
Engine examination showed no crankcase holes; oil quantity was about 9 quarts. Continuity of throttle and mixture controls to the carburetor arms was established; controls were in the full forward position. The oil sump drain had penetrated the cabin air scat tube, which was draining oil to the carburetor airbox. The carburetor airbox filter had burn damage consistent with a carburetor fire; lower cowling had soot marks. The carburetor had intact plastic floats and liquid resembling avgas in the bowl.
Upper spark plugs were oily and dark; Nos. 1, 3, and 4 cylinder spark plugs had no electrode gap. No. 3 spark plugs were undamaged. Bottom spark plugs: Nos. 3, 4, and 6 cylinders were damaged. Magneto timing was within Lycoming recommendations; spark was visible when the propeller was rotated.
Removal of rocker box covers revealed the exhaust rotator cap on No. 2 cylinder was loose inside. No. 6 cylinder exhaust valve springs were displaced, with the rocker arm contacting the upper spring seat and the exhaust pushrod bent. No. 2 cylinder removal showed numerous metal pieces in the crankcase. No. 4 cylinder piston face had gouges from metal consumption. Pieces of worn metal were found in intake and exhaust pipes.
No. 6 cylinder: the upper portion of the piston was trapped in the barrel, dislodged from the wrist pin. The piston was fractured into multiple pieces; impact marks on the crown and cylinder head interior. The exhaust valve guide had extruded outward; cam follower on the No. 6 exhaust tappet body was worn. The No. 6 exhaust valve was fractured through the stem; the valve seat face had a shiny metallic appearance. Spring seats had wear and fracture features; the upper spring seat flange had fractured along an approximately 225° arc segment, with striated features consistent with fatigue crack progression.
Separation of crankcase halves revealed numerous broken lifter heads; large pieces were found in the crankcase. Camshaft lobes and heels showed normal wear.
No. 5 and No. 6 cylinders and components were sent to an engine overhaul facility. Intake and exhaust guides on both cylinders were over the new tolerance but within service limits. Intake valve stem wear was within limits. No. 5 exhaust valve stem wear was within service limit. Inner and outer exhaust springs on both cylinders failed compression tests. Magnaflux inspection of No. 6 cylinder intake valve spring seats revealed cracks in both upper and lower seats. No. 5 cylinder lower exhaust valve spring seat had cracks.
Further analysis at the Safety Board Materials Laboratory found that a fatigue crack had formed in the exhaust valve upper spring seat of No. 6 cylinder assembly, consistent with eventual release of the exhaust valve. The crack originated at the base of the cup housing the valve stem keys. Examination findings were consistent with No. 6 exhaust valve floating, which likely would have decoupled the motion of the valve and spring seat, removing compressive load on the keys and allowing them to move and rub against the support flange and sidewall of the spring seat cup. The No. 6 exhaust valve springs also failed compression test, suggesting a floating valve was possible. The No. 5 exhaust valve springs also failed, but wear features around the key cup were not observed. Because the keys and valve stem were not found (likely destroyed during operation), they could not be examined to determine if there was any issue with either component.
Additional Information
According to the Lycoming Overhaul manual, at each 400-hour inspection, the following valve inspection must be completed: Remove rocker box covers and check for freedom of valve rockers when valves are closed. Look for evidence of abnormal wear or broken parts in the area of the valve tips, valve keeper, springs and spring seats. If any indications are found, the cylinder and all its components should be removed and inspected for further damage. Replace any parts that do not conform with limits shown in the latest revision of Special Service Publication No. SSP-1776.