HILLER UH12E near Becker, MN — 2022-07-06

Final reportCEN22LA318

Date: 2022-07-06
Location: Becker, MN, USA
Aircraft: HILLER UH12E
Registration: N64272
Category: Helicopter
Highest injury: Serious
Fatalities: 0
Phase of flight: Maneuvering

Probable cause

The in-flight failure of the main rotor mast hub due to several undetected fatigue fractures.

NTSB narrative

While the pilot was conducting an aerial application flight, he felt a small jolt, the main rotor mast failed, and the helicopter collided with terrain. Four days before the accident, a mechanic performed a dye penetrant inspection on the rotor mast; the helicopter had only flown 9 hours since the inspection. Attempts to retrieve the rotor mast parts from the operator were unsuccessful and when contact was reestablished with the owner, he had already disposed of the parts. Photos of the broken rotor hub were reviewed by the National Transportation Safety Board (NTSB) Materials Laboratory, which determined that several preexisting, progressive cracks were present.