Incident Overview
On October 14, 2021, at approximately 1815 Pacific daylight time, a Lancair ES experimental airplane (registration N511ZZ) sustained substantial damage during a forced landing near Fall Creek, Oregon. The pilot, who was the sole occupant, reported no injuries. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a personal flight.
Sequence of Events
The pilot stated that during cruise flight, he descended to 4,500 ft mean sea level in preparation to land at Mahlon Sweet Field Airport (EUG) in Eugene, Oregon. Shortly after disconnecting the autopilot and turning north, he felt the engine decelerate suddenly and begin misfiring. Realizing he was too far from the airport to reach the runway, the pilot scanned for a forced landing site but saw only forest. He attempted to restart the engine but was unsuccessful.
As smoke entered the cockpit and altitude continued to decrease, at about 1,000 ft above ground level, the pilot checked his airspeed and pulled the ballistic recovery system handle. The parachute deployed, and during the descent through dense trees, the airplane collided with foliage, resulting in substantial damage to the left wing and separation of the empennage. The aircraft came to rest a few feet from the ground, suspended by the parachute, which remained caught in the trees. The pilot exited and walked to a nearby road.
Postaccident Examination
Examination of the wreckage showed no external damage to the engine. The oil dipstick indicated about 7 quarts of oil. Lower spark plugs were removed, and borescope inspection of the cylinders revealed normal combustion deposits and valve head signatures. All six piston heads had impact marks from the valves.
Manual rotation of the crankshaft via the propeller assembly resulted in cylinder thumb compression on only four cylinders. Rocker covers were removed, revealing undamaged overhead components covered in oil residue. Further rotation of the crankshaft showed no movement of the overhead components.
The engine was removed and disassembled. The oil sump contained metal fragments. Crankcase halves were separated; mating surfaces were undamaged, but small metal fragments were found throughout the engine interior. Valve lifters in both crankcase halves were intact. The camshaft drive gear (part number 631845) exhibited missing teeth and material deformation, with approximately two-thirds of its teeth damaged. Camshaft lobes showed normal lifter contact wear, with mechanical damage on several edges. Crankshaft main bearings were undamaged and showed normal wear.
Laboratory Analysis
The camshaft drive gear, along with five separated teeth and fragments, was sent to the NTSB Materials Laboratory. Examination revealed that 36 gear teeth had fractured and separated. Three fracture surfaces showed sloping, angled orientations consistent with post-fracture smearing. Another tooth exhibited a fatigue crack that propagated about halfway through before overstress fracture, with an initiation site along the fillet radius showing concentric features. A second initiation site near a flat edge had radial lines consistent with crack propagation. A final tooth showed similar fatigue crack propagation with a single initiation site at the fillet radius, collocated with a gouge or machine mark.
Composition analysis using energy dispersive x-ray spectroscopy (EDS) and x-ray fluorescence (XRF) indicated the gear was made of nitrided alloy steel. A surface layer containing nitrogen was consistent with a nitride treatment. Microindentation hardness testing per ASTM E384.2 showed base alloy hardness of 41 HRC (401 HV500), consistent with a quench and tempered condition.
Maintenance History
Aircraft records showed the engine was overhauled on July 30, 2015, during which a serviceable camshaft gear (part number 631845) was installed. At that time, Service Bulletin (SB) 97-6B was in effect. The engine had accumulated about 351 hours of operation at the time of the accident.
On August 9, 2005, the engine manufacturer issued SB05-8, later superseded by SB05-8A in August 2009, introducing an improved camshaft gear nominally 0.060 inches wider. The manufacturer recommended replacement of the camshaft gear during the next overhaul or as required. In November 2009, revised SB97-6B identified the camshaft gear (part number 631845) as a mandatory replacement item at overhaul. In August 2018, Critical Service Bulletin CSB05-8D was issued to eliminate the possibility of camshaft gear tooth fracture, leading to power loss or in-flight shutdown, and required inspection and removal of multiple camshaft gears, including part number 631845.