Hiller UH-12E N9293Z

Summary

On 3 February 1995 at about 19:15 local time, a Hiller UH-12E registered N9293Z, operated by Stephen R. Streeter, was involved in an accident near Chowchilla, California, United States. One person was on board and nobody was injured. The aircraft was destroyed. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

3 February 1995 at 19:15

Classification

Accident

Location

Chowchilla, California, United States

Coordinates

37.0691, -120.2708

Aircraft

Hiller UH-12E

Registration

N9293Z

Category

Helicopter

Engines

1

Operator

Stephen R. Streeter

Operating rule

Part 137: Agricultural

Purpose of flight

Aerial Application

Phase of flight

Not recorded

Aircraft damage

Destroyed

Weather

VMC

Light

Not Reported

NTSB number

LAX95LA096

Nobody was injured.

the in-flight failure and separation of the main rotor hub due to a fatigue crack.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

THE PILOT WAS APPLYING CHEMICALS TO A FIELD AT A SLOW AIRSPEED ABOUT 10 FEET OFF THE GROUND. A SEVERE VIBRATION STARTED THROUGH THE AIRFRAME, AND THE PILOT DECIDED TO LAND IMMEDIATELY. THE PILOT WAS TURNING TO A LANDING AREA WHEN THE VIBRATION SUDDENLY CEASED, THE HELICOPTER FELL TO THE GROUND ON ITS NOSE, AND ROLLED OVER ONTO ITS TOP. ONE MAIN ROTOR BLADE AND HALF THE HUB WERE FOUND MORE THAN 100 YARDS FROM THE HELICOPTER. THE SECOND BLADE WAS FOUND ATTACHED TO THE REMAINDER OF THE HUB, ABOUT 150 FEET FROM THE WRECKAGE. THE TWO PIECES OF THE FRACTURED AND SEPARATED MAIN ROTOR HUB WERE RECOVERED AND METALLURGICALLY EXAMINED. THE HUB SEPARATED DUE TO A FRACTURE THROUGH ITS CENTER. THE EXAMINATIONS DISCLOSED THAT THE FRACTURE THROUGH THE HUB CENTER STEMMED FROM FATIGUE CRACKS WHICH INITIATED FROM THE TENSION-TORSION PIN HOLE ON THE LEADING EDGE SIDE OF ONE HUB ARM. THE ORIGIN POINT OF THE FATIGUE CRACK WAS DETERMINED TO BE INSIDE THE TT PIN HOLE AND EXHIBITED CORROSION DEPOSITS TYPICALLY SEEN IN ALUMINUM ALLOYS. THE CRACK WOULD NOT HAVE BEEN VISIBLE DURING AN EXTERNAL INSPECTION. THE FATIGUE CRACK AND FRACTURE ARE IN AREAS NOT COVERED BY THE RECURRING INSPECTION REQUIREMENTS OF AD 73-20-03.

Quoted verbatim from the NTSB record.