# NTSB NYC92GA089: Mcdonnell Douglas 500E, N97BR, Mount Zion, KY, April 30, 1992

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Final report
- Date: April 30, 1992, 13:25 local (17:25 UTC)
- Place: Mount Zion, KY
- Coordinates: 38.779434, -84.599685 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=38.7794&lon=-84.5997&mi=10
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 3 uninjured
- Status: Completed, report May 26, 1993
- Report: Approved by Office Director
- NTSB case key (mKey): 37075
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=NYC92GA089
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/37075/pdf
- Page: https://openairdocs.org/ntsb/NYC92GA089

## Probable cause

AN IN-FLIGHT SEPARATION OF THE TAIL ROTOR ASSEMBLY AS THE RESULT OF THE LOSS OF AN ABRASION STRIP FROM THE LEADING EDGE OF ONE OF THE TAIL ROTOR BLADES, WHICH INDUCED VIBRATIONAL STRESSES HIGH ENOUGH TO INITIATE FATIGUE FAILURE IN THE TAIL ROTOR GEAR BOX MOUNTING STUDS.

## Sequence of events

In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf).

- Airframe/component/system failure/malfunction, cruise - normal
  - rotor system,tail rotor blade abrasion strip - disconnected (cause)
  - material inadequate, company maintenance personnel (contributing factor)
  - rotor drive system,tail rotor gearbox(90 deg) - separation (cause)
  - aircraft control - not possible, pilot in command
- Forced landing, descent - emergency
- In flight collision with terrain/water, descent - uncontrolled
  - terrain condition - ground

## Analysis

WHILE FLYING IN A CRUISE CONFIGURATION AT 1500 FEET MEAN SEA LEVEL, AND ABOUT 10 MINUTES INTO THE FLIGHT THE HELICOPTER STARTED TO VIBRATE.  THE PILOT ELECTED TO MAKE A FORCED LANDING IN THE MOST SUITABLE AREA AVAILABLE.  DURING THE DESCENT THE VIBRATION CONTINUED TO WORSEN.  AT ABOUT 5 FEET ABOVE THE SELECTED LANDING SITE THE PILOT HEARD A LOUD BANG, THE HELICOPTER YAWED TO THE RIGHT AND PITCHED NOSE DOWN.  THE PILOT LOWERED THE COLLECTIVE AND PUT THE HELICOPTER ON THE GROUND. METALLURGICAL EXAMINATION DETERMINED THAT THE LOSS OF THE ABRASION STRIP FROM THE LEADING EDGE OF TAIL ROTOR BLADE S/N 5086 INDUCED VIBRATIONAL STRESSES THAT WERE HIGH ENOUGH TO INITIATE FATIGUE FAILURE IN THE TAIL ROTOR GEAR BOX MOUNTING STUDS WHICH RESULTED IN THE SEPARATION OF THE GEAR BOX ASSEMBLY FROM THE HELICOPTER.

## Aircraft

- Registration: N97BR (not matched to a registry record)
- Reported make and model: MCDONNELL DOUGLAS 500E
- Category: Helicopter
- Serial number: 145E
- Airframe hours: 1350
- Engines: ALLISON 250-C-20D 420 horsepower turbo shaft
- Damage: Substantial damage
- Flight: Public aircraft, Part 91
- Operator: US Customs Service
- Registered owner: US Customs Service
- Airworthiness certificate: Standard, Normal
- Last inspection: 100 hour, January 2, 2000, 59 hours before
- Departed: CVG, CINCINNATI, OH
- Destination: CVG
- Flight plan: Company VFR

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 37; flight instructor, airline transport, commercial; airplane ratings: single-engine sea, multi-engine sea, single-engine land, multi-engine land; instrument ratings: helicopter, airplane; medical: class 1, valid medical--no waivers/lim.; seat: right; flight hours: 5,750 total, 500 in this make and model, 4,700 as pilot in command, 150 in the last 90 days, 50 in the last 30 days, 6 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: calm
- Visibility: 25 statute miles
- Lowest ceiling: none
- Temperature: 75 °F
- Altimeter: 30.00 inHg

From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model.

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