Bell 205 N205WW

Summary

On 4 September 2011 at about 22:00 local time, a Bell 205 registered N205WW, operated by Kern County, was involved in an accident near Tehachapi, California, 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

4 September 2011 at 22:00

Classification

Accident

Location

Tehachapi, California, United States

Coordinates

35.0644, -118.4236

Aircraft

Bell 205

Registration

N205WW

Category

Helicopter

Engines

1

Operator

Kern County

Operating rule

Part 133: Rotorcraft Ext. Load

Phase of flight

Not recorded

Route

Tehachapi → Tehachapi

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

WPR11GA431

1 person had minor injuries.

The pilot's inability to adequately execute an emergency autorotation due to the flight's low altitude during external load operations, which resulted in a hard landing. Contributing to the accident was a torsionally overstressed tachometer shaft, which sent erroneous engine rpm readings to the cockpit.

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

Read the full NTSB narrative

During an external load operation to drop water on a fire, the helicopter was about 100 feet above ground level at 10 knots when the engine rpm light illuminated and the low rotor rpm horn sounded. The emergency procedures section of the flight manual states that in the event of an engine failure or low rpm, a red light will illuminate and an audio signal will sound when the audio switch is in the AUDIO position. The flight manual instructs the pilot to immediately execute an autorotative descent. The pilot released the water, and made a left-pedal turn to exit the canyon and move away from the fire. He checked his engine rotor rpm gauge and saw that the needles had split: the rotor needle was at the 4-5 o'clock position, and the engine needle was at the 6-o'clock position, which he stated indicated maximum rpm. He maneuvered to establish an autorotation into a landing zone. The helicopter sustained substantial damage to the airframe and tail boom as the result of a hard landing, which collapsed the landing skid. Postaccident examination discovered that the N2 tachometer drive shaft was sheered as a result of torsional overstress. The N2 tachometer drive delivers engine rpm readings to the cockpit engine tachometer; failure of the N2 tachometer drive would send erroneous engine rpm readings to the cockpit. Accordingly, the pilot's instruments indicated that there was an engine overspeed, but the warning lights and audio were indicating a low power condition. The pilot elected to perform an autorotative landing in accordance with the flight manual instructions for a low rotor rpm.

Quoted verbatim from the NTSB record.