Lancair ES N511ZZ accident near Fall Creek, Oregon

Probable cause

Total loss of engine power due to fatigue failure of the camshaft gear.

NTSB analysis

The pilot was conducting a personal cross-country flight when he descended from cruise flight in preparation for landing. Shortly thereafter, the engine lost power and started misfiring. The pilot attempted to restart the engine but was unsuccessful despite his actions. While over heavily wooded terrain, the pilot deployed the parachute system. During the descent through the heavily wooded terrain, the airplane collided with trees resulting in substantial damage. The airplane came to rest a few feet from the ground, still supported by the parachute, which remained stuck in the trees.

Postaccident examination of the engine revealed the camshaft gear failed due to fatigue-induced fracturing of multiple teeth. Fatigue cracks initiated at the fillet radii between the flanks and bottom lands of multiple gear teeth. The fillet radii exhibited more roughness and surface discontinuities, likely acting as stress concentration areas for crack initiation. Once the fatigue cracks had propagated through over half the material cross-section, the teeth fractured in overstress.

The exact cause of the crack initiation could not be concluded. There were no material defects, such as voids or inclusion, at the initiation sites. However, as previously stated, the fillet radii exhibited more pronounced surface features, which would lead to a higher chance of crack initiation. Once cracking started, propagation would be in high cycle with moderate loading modes, as evidenced by the depth of the fatigue cracks.

The gear was a nitrided alloy steel in the quenched and tempered condition. This should be a suitable material and manufacturing process for gear applications, not lending itself to any material incompatibility or excessive wear or corrosion concerns.

Text from the NTSB. Open the NTSB docket for WPR22LA019 for the full record.