Allensworth BABY BELLE N9094P

Summary

On 28 August 2005 at about 14:15 local time, a Allensworth BABY BELLE registered N9094P was involved in an accident near El Dara, Illinois, United States. One person was on board and one died. The aircraft was destroyed. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

28 August 2005 at 14:15

Classification

Accident

Location

El Dara, Illinois, United States

Coordinates

39.6389, -90.7786

Aircraft

Allensworth BABY BELLE

Registration

N9094P

Category

Helicopter

Engines

1

Operator

Not recorded

Operating rule

Part 91: General Aviation

Purpose of flight

Personal

Phase of flight

Not recorded

Route

New Canton → New Canton

Aircraft damage

Destroyed

Weather

VMC

Light

Day

NTSB number

CHI05LA243

1 person died.

The manufacturer failed to specify a relief radius on the tail rotor spindle drawings, which resulted in the spindle being manufactured with an inadequate relief radius at the point of fatigue failure.

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

Read the full NTSB narrative

The experimental amatueur-built helicopter collided with trees and terrain following an in-flight separation of a tail rotor blade. Witnesses reported seeing the helicopter spinning prior to it contacting the terrain. The helicopter was involved in a hard landing in 2004 after which the main rotor blades and tail rotor assembly including the spindle and blades were replaced. According to the pilot's friend, they balanced the new tail rotor blades after they were installed, but the blades continued to run "rough." The pilot voiced these concerns to the manufacturer and the manufacturer sent replacement tail rotor blades to the pilot. According to the manufacturer and the pilot's friend, the helicopter was running fine after the replacement blades were installed. Examination of the wreckage revealed all major components of the helicopter were located at the main wreckage site except for one of the tail rotor blades and the respective outboard 2 inches of the tail rotor spindle which were not located. The tail rotor spindle contained two integral rods, which extended out in opposite directions. The length of each rod was manufactured with sections of consecutively reduced diameter. A metallurgical examination of the spindle revealed a fatigue failure was present, which initiated at the fillet radius between the sections where the rod steps down from 0.812-inch diameter to 0.750-inch diameter. The relief radius in this area was rough and irregular. The manufacturer provided the engineering drawings for the tail rotor spindle. Drawing #15 did not specify a relief radius for the transition area between the .812-inch and .750-inch diameter sections. On September 14, 2005, Canadian Home Rotors (CHR), provided a revised drawing #15 requiring a 0.0156-inch relief radius between the 0.812-inch and 0.750-inch diameter sections. The relief radius measured at the failure was approximately 0.0073-inch.

Quoted verbatim from the NTSB record.