Bell 47G-4A N7NB

Summary

On 3 April 2004 at about 15:45 local time, a Bell 47G-4A registered N7NB was involved in an accident near Bakersfield, California, United States. One person was on board and one was seriously injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

3 April 2004 at 15:45

Classification

Accident

Location

Bakersfield, California, United States

Coordinates

35.3500, -119.0000

Aircraft

Bell 47G-4A

Registration

N7NB

Category

Helicopter

Engines

1

Operator

Not recorded

Operating rule

Part 137: Agricultural

Purpose of flight

Aerial Application

Phase of flight

Not recorded

Route

Shafter → Unknown

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

LAX04LA176

1 person was seriously injured.

a loss of tail rotor drive due to a disconnection of the drive shaft's splined coupling at the tail rotor gear box. The splined coupling to tail rotor gear box disconnection occurred as a result of tail boom flexing due to the combined effects of an uninstalled structural support tube and a crack in left side frame tubes. Inadequate maintenance inspection was a factor.

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

Read the full NTSB narrative

The helicopter experienced a loss of tail rotor control and collided with terrain. During an aerial application flight, the pilot heard a rattling noise from the aft end of the helicopter. He then lost tail rotor authority and entered a flat spin. The pilot attempted to make a run-on landing, but the helicopter continued to spin until it impacted terrain. A Federal Aviation Administration inspector examined the helicopter after the accident. He noted that the cross-over support tube near the aft end of the tail boom was missing. A crack was found on the tail boom left side frame tubes. Deposits of rust in the area suggests that the crack was a pre-existing crack. The inspector thought that this would have added excessive stress to the structure during turning maneuvers and caused the last spline coupling shaft to disconnect from the tail rotor gear box as the tail boom flexed. A 50-hour maintenance inspection was completed the day before the accident.

Quoted verbatim from the NTSB record.