What aircraft was involved and where did it happen?

The accident on 1999-01-24 involved a Hiller UH-12E, registration N67064, at Lemoore, CA.

What was the probable cause of the accident?

The inadequate nature of the operator's maintenance, which failed to detect the primer and magneto discrepancies. An overly lean fuel mixture and/or magneto cross firing resulted in detonation, an ensuing connecting rod failure, and a total loss of engine power. Contributing factors were the helicopter's low altitude…

Helicopter Engine Seizure and Rollover During Aerial Application Flight (N67064)

On January 24, 1999, a Hiller UH-12E (registration N67064) was involved in an aviation accident near Lemoore, CA. Investigators recorded the probable cause as: The inadequate nature of the operator's maintenance, which failed to detect the primer and magneto discrepancies. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.

While maneuvering 15 feet above an alfalfa field, a helicopter's engine seized. The pilot performed a forced landing on soft terrain, resulting in a rollover. Examination revealed a broken connecting rod and evidence of detonation.

Accident Details

During an aerial application flight, the pilot was maneuvering at approximately 15 feet above an alfalfa field when a noise emanated from the engine, followed by engine seizure. The pilot executed a forced landing in the underlying soft field. Upon touchdown, the helicopter rolled over due to the uneven terrain.

Maintenance History

A review of maintenance records indicated that the engine had operated about 482 hours since its last overhaul.

Engine Examination

Post-accident examination of the engine revealed that the number two connecting rod was broken at its crankshaft end. Inspection of the associated cylinder and piston showed evidence of detonation. Similar excessive heat exposure signatures were observed on the other five piston heads. Additionally, a small hole was found chaffed into the fuel primer line. Carbon deposits and burned rotor fingers were present in both magnetos.

Findings

The investigation documented the mechanical failures and conditions found, but no probable cause was stated in the source.

1999-01-24: Hiller UH-12E (N67064) — Lemoore, CA