Aircraft Accident/Incident Report

Belmont, West Virginia 26134
Sunday, March 9, 2008 14:40 EDT

NTSB Narrative Summary Released at Completion of Accident

The helicopter was performing external load operations, and was removing a tower from the top of a 620-foot tall smoke stack. After lifting the load clear of the smoke stack, the pilot observed an "over torque" condition on the torque indicator. Several seconds later, the pilot felt a high frequency vibration through the helicopter, and shortly thereafter the tail rotor assembly separated from the helicopter. While the helicopter yawed through two 360-degree rotations, the pilot released the external load, reduced the collective pitch, and performed an autorotation. Postaccident examination of the separated tail rotor assembly revealed that one of the four blades had separated in-flight. Detailed examination of the separated blade revealed that its skins had cracked due to fatigue, and that the blade then separated due to overstress. The adjacent and overlaying doublers also cracked, likely due to fatigue, but no fatigue striations were found on those members. Some ductile dimples were also found in the damaged regions, indicating that at least part of the propagation was by unstable crack growth. The skin fatigue cracks were completely hidden by the overlying doublers, making detection impossible unless the doublers either cracked or were removed. Cracks in the doublers would have been visible on the inboard side of the blade, but not on the outboard side, where the inspection/repair tag covered most of the doubler. The bonds within the blade appeared to be in good condition, and no corrosion was found, suggesting that the blade failure was the result of a fatigue life issue. The helicopter’s maintenance manual specified that the tail rotor blades had no life limit, provided that certain flight restrictions were observed, but the investigation was unable to determine whether the helicopter ever exceeded any of the specified flight restrictions. None of the tail rotor blades were in compliance with an existing airworthiness directive, which required the installation of an abrasion strip along the entire length of the blade leading edge; however, it was not clear if this non-compliance affected the failure.

NTSB Probable Cause Narrative

The fatigue failure of a tail rotor blade during an external load lift.

Event Information

Type of Event Accident
Event Date 3/9/2008
Event Day of the Week Sunday
Time of Event 1440
Event Time Zone Eastern Daylight Time
Event City Belmont
Event State WEST VIRGINIA
Event Country --
Zipcode of the event site 26134
Event Date Year 2008
Event Date Month 3
MidAir Collision Indicator No
On Ground Collision occurred ? No
Event Location Latitude 392205N
Event Location Longitude 0811738W
Event Location Airport --
Event Location Nearest Airport ID --
Indicates whether the acc/inc occurred off or on an airport Off Airport/Airstrip
Distance from airport in statute miles --
Degrees magnetic from airport --
Airport Elevation --
Weather Briefing Completeness --
Investigator's weather source Weather Observation Facility
Time of the weather observation 1453 Eastern Daylight Time
Direction of event from weather observation facility (degrees) 270
Weather Observation Facility ID PKB
Elevation of weather observation facility 858
Distance of event from weather observation facility (units?) 7
Time Zone of the weather observation EDT
Lighting Conditions Day
Lowest Ceiling Height --
Lowest Non-Ceiling Height 3600
Sky/Lowest/Cloud Conditions Few
Sky Condition for Lowest Ceiling None
Visibility Runway Visual Range (Feet) --
Visibility Runway Visual Value (Statute Miles) --
Visibility (Statute Miles) 10
Air Temperature at event time (in degrees celsius) -1
Dew Point at event time (in degress fahrenheit) -7
Wind Direction (degrees magnetic) 200
Variable Wind Indicator Wind direction could be determined
Wind Speed (knots) 5
Wind Velocity Indicator --
Wind Gust Indicator Not Gusting
Wind Gust (knots) --
Altimeter Setting at event time (in. Hg) 30.38
Density Altitude (feet) --
Intensity of Precipitation --
METAR weather report --
Event Highest Injury Serious
On Ground, Fatal Injuries --
On Ground, Minor Injuries --
On Ground, Serious Injuries --
Injury Total Fatal --
Injury Total Minor --
Injury Total None --
Injury Total Serious 1
Injury Total All 1
Investigating Agency NTSB
NTSB Docket Number (internal use) 24750
NTSB Notification Source FAA Eastern ROC
NTSB Notification Date Mar 10 2008 12:00AM
NTSB Notification Time --
Fiche Number and/or location -used to find docket information --
Date of most recent change to record Dec 9 2008 1:56PM
User who most recently changed record grer
Basic weather conditions Visual Meteorological Cond
FAA District Office FAA/FSDO

Aircraft Involved

Aircraft #1

Aircraft Registration Number N1078T
NTSB Number NYC08LA129
Missing Aircraft Indicator --
Federal Aviation Reg. Part Part 133: Rotorcraft Ext. Load
Type of Flight Plan filed None
Flight plan Was Activated? No
Damage Substantial
Aircraft Fire None
Aircraft Explosion None
Aircraft Manufacturer's Full Name SIKORSKY
Aircraft Model S-58HT
Aircraft Series Identifier --
Aircraft Serial Number 58-1016
Certified Max Gross Weight 13000
Aircraft Category Helicopter
Aircraft Registration Class --
Aircraft is a homebuilt? No
Flight Crew Seats 2
Cabin Crew Seats --
Passenger Seats 2
Total number of seats on the aircraft 4
Number of Engines 2
Fixed gear or retractable gear Fixed
Aircraft, Type of Last Inspection Continuous Airworthiness
Date of Last Inspection Dec 20 2007 12:00AM
Airframe hours since last inspection --
Airframe Hours 18397
ELT Installed Yes
ELT Activated No
ELT Aided Location of Event Site No
ELT Type Unknown
Aircraft Owner Name St. Louis Helicopters LLC
Aircraft Owner Street Address --
Aircraft Owner City Sellersburg
Aircraft Owner State IN
Aircraft Owner Country USA
Aircraft Owner Zipcode 47172
Operator is an individual? No
Operator Name St. Louis Helicopters LLC
Operator Same as Owner? Yes
Operator Is Doing Business As --
Operator Address Same as Owner? Yes
Operator Street Address --
Operator City Sellersburg
Operator State IN
Operator Country USA
Operator Zip code 47172
Operator Code --
Owner has at least one certificate Yes - certificate holder
Other Operator of large aircraft? No
Certified for Part 133 or 137 Operation External Load
Operator Certificate Number --
Indicates whether an air carrier operation was scheduled or not --
Indicates Domestic or International Flight --
Operator carrying Pax/Cargo/Mail --
Type of Flying (Per_Bus / Primary) External Load
Second Pilot on Board No
Departure Point Same as Event No
Departure Airport Code PKB
Departure City Parkersburg
Departure State WV
Departure Country USA
Departure Time --
Departure Time Zone --
Destination Same as Local Flt dest & departure same, accident can occur anywhere
Destination Airport Code PKB
Destination City --
Destination State --
Destination Country USA
Specific Phase of Flight Maneuvering
Report sent to ICAO? --
Evacuation occurred --
Date of most recent change to record Dec 9 2008 10:52AM
User who most recently changed record grer
Since inspection or accident Time of Accident
Event Location Runway Number and Location N/A
Runway Length --
Runway Width --
Sight Seeing flight No
Air Medical Flight No
Medical Flight --