Bell 47D1 N9660

Summary

On 22 April 1994 at about 15:28 local time, a Bell 47D1 registered N9660 was involved in an accident near Marathon, Florida, United States. 3 people were on board and 2 died, one was seriously injured. The aircraft was destroyed. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

22 April 1994 at 15:28

Classification

Accident

Location

Marathon, Florida, United States

Coordinates

24.7097, -81.0805

Aircraft

Bell 47D1

Registration

N9660

Category

Helicopter

Engines

1

Operator

Not recorded

Operating rule

Part 91: General Aviation

Purpose of flight

Unknown

Phase of flight

Not recorded

Aircraft damage

Destroyed

Weather

VMC

Light

Day

NTSB number

MIA94FA125

2 people died.

SEPARATION OF THE TAIL ROTOR GEARBOX AND TAIL ROTOR BLADES FOR AN UNDETERMINED REASON. FACTORS RELATED TO THE ACCIDENT WERE: FAILURE OF MAINTENANCE PERSONNEL TO FOLLOW THE PROPER MAINTENANCE PROCEDURE AFTER A PREVIOUS TAIL ROTOR STRIKE, AND FAILURE TO CONDUCT A 100-HOUR INSPECTION WHEN DUE.

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

Read the full NTSB narrative

WITNESSES HEARD A LOUD NOISE AS THE HELICOPTER WAS FLYING AT 100' TO 150' AGL & SAW SOMETHING FALL FROM THE TAIL BOOM. THE HELICOPTER IMMEDIATELY NOSED DOWN & BEGAN SPINNING TO THE RIGHT. IT IMPACTED ON A ROCK ISLAND & CAME TO REST IN WATER NEXT TO THE ISLAND. THE TAIL ROTOR GEARBOX, TAIL ROTOR HUB & ONE TAIL ROTOR BLADE WERE NOT LOCATED AFTER THE ACCIDENT. ONE TAIL ROTOR BLADE WAS FOUND ALONG THE FLIGHTPATH IN 2 PIECES, ABOUT 150' FROM THE MAIN WRECKAGE. THE TAIL ROTOR GEARBOX HAD SEPARATED DUE TO OVERSTRESS; ALL FRACTURES OF THE RECOVERED TAIL ROTOR BLADE WERE TYPICAL OF OVER- STRESS. THE TAIL ROTOR BLADE HAD NO IMPACT MARKS ON THE LEADING EDGE OR TIP. NO PRECRASH FAILURE/MALFUNCTION OF THE REMAINING STRUCTURE, FLIGHT CONTROLS, MAIN ROTOR BLADES, TRANSMISSION OR ENGINE WAS FOUND. A TAIL ROTOR STRIKE OCCURRED 130 FLIGHT HRS BEFORE THE ACCIDENT; THE TAIL ROTOR BLADES WERE CHANGED, BUT THE HUB WAS NOT CHANGED AS REQUIRED BY THE MANUFACTURER'S INSTRUCTION. THOUGH OPERATING FOR HIRE, HELICOPTER HAD FLOWN 130 HRS SINCE THE LAST MAINTENANCE INSPECTION. CALCULATIONS SHOWED THAT DURING TAKEOFF, THE HELICOPTER'S CG WAS 3.4' FORWARD OF THE FORWARD LIMIT. WITH LOSS OF THE SEPARATED PARTS, THE CG WOULD HAVE MOVED ABOUT 2' FURTHER FORWARD.

Quoted verbatim from the NTSB record.