Eurocopter AS350 B3 N904CF

Summary

On 17 January 2010 at about 20:50 local time, a Eurocopter AS350 B3 registered N904CF, operated by Air Methods, was involved in an accident near Reno, Nevada, United States. 3 people were on board and nobody was injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

17 January 2010 at 20:50

Classification

Accident

Location

Reno, Nevada, United States

Nearest airport

Washoe Medical Center Heliport (NV57)

Coordinates

39.5261, -119.7961

Aircraft

Eurocopter AS350 B3

Registration

N904CF

Category

Helicopter

Engines

1

Operator

Air Methods

Operating rule

Part 91: General Aviation

Purpose of flight

Positioning

Phase of flight

Not recorded

Route

Reno → Winnemucca

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

WPR10FA112

Nobody was injured.

The improper installation of the engine-to-main gear box flex coupling, which resulted in the failure of the flex coupling and a loss of power to the rotor system during takeoff. Contributing to the accident was the mechanic who removed the engine's failure to follow the operator’s maintenance procedures. Also contributing was the Quality Assurance inspector's failure to follow the operator’s post-maintenance inspection requirements.

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

Read the full NTSB narrative

The pilot reported that he lifted the single-engine helicopter from the helicopter pad for the emergency medical service positioning flight to pick up a patient. The pilot maneuvered the helicopter into a 25-foot hover and, just as he was beginning the transition to forward flight, he heard a loud bang. The helicopter experienced a power loss and the pilot lowered the collective slightly, resulting in a hard landing on the pad. A surveillance camera that captured the accident sequence indicated that after the helicopter lifted into a hover over the pad, the nose abruptly rotated right 90 degrees and the helicopter descended vertically in a slight nose-down attitude, landing hard on the helipad. The postaccident airframe examination revealed that the nuts that attach the engine-to-main gear box flex coupling were not present on their respective bolts. The nuts and associated washers were located loose and clumped together just forward of the gimbal ring in the transmission input housing. An examination of the bolts and flex coupling by the Safety Board Materials Laboratory concluded that the nuts most likely had been hand tightened and that cotter pins had not been installed on the bolts. The improper installation lead to the failure of the flex coupling and resulted in a loss of power to the rotor system. Maintenance records showed that 59 flight hours before the accident the engine had been removed, the helicopter painted, and then the engine was reinstalled. The time between the engine removal and the reinstallation was 88 days. The mechanic who removed the engine stated that he removed the bolts to the engine-to-main gear box flex coupling, and then partially reassembled the flex coupling bolts. This action was not in accordance with the AS350 maintenance manual engine removal procedure. The mechanic who installed the engine 88 days later stated that he did not check the flex coupling bolts because the removal of those bolts is not specified in the maintenance manual as part of the engine removal or replacement procedure. The overall maintenance activity involved a 100-hour inspection, which included a visual inspection of the engine-to-main gear box flex coupling. Although a visual inspection of the engine-to-main gear box flex coupling is a required action, the Quality Assurance inspector signed off the maintenance without performing the visual inspection of the flex coupling.

Quoted verbatim from the NTSB record.