Bell 47G-5 N1502L

Summary

On 30 May 1995 at about 19:10 local time, a Bell 47G-5 registered N1502L was involved in an accident near Falfurrias, Texas, United States. One person was 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

30 May 1995 at 19:10

Classification

Accident

Location

Falfurrias, Texas, United States

Coordinates

27.2192, -98.1403

Aircraft

Bell 47G-5

Registration

N1502L

Category

Helicopter

Engines

1

Operator

Not recorded

Operating rule

Part 91: General Aviation

Purpose of flight

Other Work Use

Phase of flight

Not recorded

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

FTW95LA239

Nobody was injured.

INADVERTENT INSTALLATION OF AN UNAPPROVED PART (TAIL ROTOR GEAR/DRIVE ASSEMBLY), THAT BECAME EXCESSIVELY WORN SINCE IT DID NOT CONFORM TO THE MANUFACTURER'S SPECIFICATION, RESULTING IN FAILURE OF THE ASSOCIATED TAIL ROTOR BEARING (ALSO AN UNAPPROVED PART), LOSS OF CONTINUITY (DISCONNECT) OF THE TAIL ROTOR DRIVE SYSTEM, AND A FORCED AUTOROTATION INTO AN AREA WITH TREES.

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

Read the full NTSB narrative

AS THE HELICOPTER WAS BEING MANEUVERED AT LOW ALTITUDE TO HERD CATTLE, THE TAILROTOR DRIVE LOST CONTINUITY. THE PILOT REPORTED THAT DIRECTIONAL CONTROL WAS LOST, AND THAT HE EXECUTED AN AUTOROTATION INTO A CONFINED AREA. DURING DESCENT/LANDING, THE MAIN ROTOR BLADE STRUCK A TREE, AND THE HELICOPTER ROLLED ONTO ITS RIGHT SIDE. AN INVESTIGATION REVEALED EXCESSIVE WEAR ON THE TAIL ROTOR GEAR/DRIVE ASSEMBLY (TRANSMISSION OUTPUT QUILL GEAR). A METALLURGICAL EXAMINATION OF THE ASSEMBLY REVEALED THAT THE GEAR'S SHAFT (WHICH CONSTITUTED THE INNER RACEWAY OF AN ASSOCIATED CYLINDRICAL BEARING) HAD NOT BEEN CARBURIZED AS REQUIRED BY THE DESIGN MANUFACTURER. ROTATION OF THE BEARING ROLLERS OVER THE RELATIVELY SOFT SURFACE OF THE SHAFT HAD WORN A GROOVE IN THE SHAFT. THE ASSOCIATED BEARING (TAIL ROTOR DRIVE ASSEMBLY BEARING) SUBSEQUENTLY FAILED. THE GEAR AND BEARING WERE UNAPPROVED PARTS AND DID NOT CONFORM TO THE MANUFACTURER'S DESIGN SPECIFICATIONS. THE SOURCE OF THE UNAPPROVED PARTS WAS NOT DETERMINED, ALTHOUGH PACKAGING OF THE PARTS WAS REPORTED TO RESEMBLE THAT OF THE MANUFACTURER. PART NUMBERS WERE FOUND ON THE GEAR AND BEARING, SIMILAR TO AUTHORIZED PARTS, ALTHOUGH A DIFFERENT METHOD OF MARKING (ETCHING) WAS USED TO MARK THE GEAR.

Quoted verbatim from the NTSB record.