Bell 407 N509MT

Summary

On 14 April 2012 at about 07:55 local time, a Bell 407 registered N509MT, operated by Med-Trans Corp, was involved in an accident near Aberdeen, South Dakota, United States. One person was on board and one had minor injuries. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

14 April 2012 at 07:55

Classification

Accident

Location

Aberdeen, South Dakota, United States

Coordinates

45.4667, -98.4764

Aircraft

Bell 407

Registration

N509MT

Category

Helicopter

Engines

1

Operator

Med-Trans Corp

Operating rule

Part 91: General Aviation

Purpose of flight

Positioning

Phase of flight

Not recorded

Route

Aberdeen → Aberdeen

Aircraft damage

Substantial

Weather

VMC

Light

Night

NTSB number

CEN12LA242

1 person had minor injuries.

The fatigue failure of two turbine engine blades due to vibration.

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

Read the full NTSB narrative

The pilot reported that, shortly after departure, the helicopter yawed left and that he heard a "loud howling/grinding sound" emanating from the upper area of the helicopter. He subsequently reduced power and performed a minimum power descent to an open area. During the landing, the helicopter touched down hard. A postimpact examination of the engine found that two third-stage turbine wheel blades had cracked and separated due to high-cycle fatigue at the trailing edge during operation of one or more natural frequencies of the wheel. Four additional blades displayed fatigue cracks. Metallurgy examinations revealed that the blades had no evidence of material anomalies and met the material hardness and composition specifications. The observed high-cycle fatigue initiation and propagation characteristics were consistent with operating in a condition conducive to vibration. The engine manufacturer plans to release design changes that will increase the operating speed natural frequency margin and improve the vibration margin.

Quoted verbatim from the NTSB record.