Bell 205A-1 N90230

Summary

On 23 March 1998 at about 15:40 local time, a Bell 205A-1 registered N90230, operated by Los Angeles City Fire Dept., was involved in an accident near Los Angeles, California, United States. 6 people were on board and 4 died, 2 were seriously injured. The aircraft was destroyed. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

23 March 1998 at 15:40

Classification

Accident

Location

Los Angeles, California, United States

Coordinates

34.0994, -118.3190

Aircraft

Bell 205A-1

Registration

N90230

Category

Helicopter

Engines

1

Operator

Los Angeles City Fire Dept.

Operating rule

Part 91: General Aviation

Purpose of flight

Public Use

Phase of flight

Not recorded

Route

Los Angeles → Los Angeles

Aircraft damage

Destroyed

Weather

VMC

Light

Day

NTSB number

LAX98GA127

4 people died.

An excessive bending load applied to the tail rotor blade assembly of an undetermined origin which produced a fatigue crack, the separation of the assembly, and a forced landing. Factors were the lack of suitable terrain to perform a forced landing, the manufacturer's unclear maintenance bulletin instruction and procedures which facilitated the operator's inadequate inspection for the yoke's straightness, and the inadequacy of restraint systems and protective equipment.

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

Read the full NTSB narrative

During an air ambulance flight in the public-use helicopter, the tail rotor and gearbox separated from the helicopter. The pilot autorotated to a forced landing. During the descent over mountainous terrain, the helicopter collided with trees and impacted hard terrain on its left side which crushed inward. The operator's policy required all crewmembers to wear helmets during flight. Helmets were not provided for the two paramedics. During the crash sequence, the passenger seat stanchions and tubing buckled, which resulted in multiple lap belt anchor point separations and the catapulting of crewmembers into the overhead cockpit panel. Safety Board survival factors documentation in conjunction with helmet crashworthiness analysis revealed helicopter impact forces were within human tolerance. The lack of and/or inadequate strength helmets and the lap belt anchor point failures allowed crewmembers' excursions resulting in head trauma. The tail rotor component separations in flight resulted from a fatigue crack originating in the surface of the yoke onto which the tail rotor blades had been attached. In 1996, Bell issued an Alert Service Bulletin (ASB) number 205-96-68, which was designed to measure yoke deformation resulting from adverse in-flight or ground handling operations which imposed excessive bending loads. The test protocol was found problematic in its accuracy due to technical errors in the bulletin and a lack of clarity. City mechanics failed to adhere to all of the ASB's requirements. The bent yoke fractured at a total time in service of approximately 4,113 hours, about 117 hours after its inspection for evidence of deformation. The yoke's stainless steel composition and requisite metallurgical properties were confirmed by the Safety Board. An x-ray diffraction examination of the yoke revealed reduced compressive residual stress in the fracture origin region which allowed operational loads to initiate and propagate the fatigue crack. This significant reduction of the residual stress was likely due to excessive flexure (bending) of the yoke. The initiating event which overstressed and bent the yoke was not identified.

Quoted verbatim from the NTSB record.